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Noise and hearing loss in farming Winters, Meghan 2008

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          NOISE AND HEARING LOSS IN FARMING   August, 2005      Prepared for: Farm and Ranch Safety and Health Association, #311, 9440 - 202 Street, Langley, BC V1M 4A6  Prepared By: Meghan Winters, Elaina MacIntyre, Cheryl Peters, Jadine Thom, Kay Teschke, Hugh Davies* School of Occupational & Environmental Hygiene University of British Columbia 2206 East Mall, Vancouver, BC, V6T 1Z3  *corresponding author Noise and Hearing Loss in Farming  page 2 of 69   2 Executive Summary This literature review was produced at the request of FARSHA, the Farm And Ranch Safety and Health Association of Langley, BC.  Farming in British Columbia has come under the Jurisdiction of the BC Workers’ Compensation Board relatively recently, and noise exposure on farms, and its effects on hearing are topics that have not received a great deal of attention in the past.  This literature review was commissioned to provide FARSHA and its clients an up to date overview of the current knowledge regarding the risks of noise exposure to those working on farms, and methods of controlling exposure to reduce that risk. We conducted a systematic and comprehensive review of the peer-reviewed scientific literature with respect to hearing loss among farmers and their exposure to noise, and the determinants of noise exposure, and methods for controlling those exposures on farms.  We found that studies have shown farmers are at increased risk of noise-induced hearing loss, with as many as 92% of farmers in one study having significant hearing loss; noise has been pronounced a major priority in agricultural health.  A very large number of farmers are likely exposed to noise. A National Institute for Occupational Safety and Health study from the early 1980’s estimated that 84% of workers in agricultural services were exposed to noise at levels higher than 85 dBA, the level at which we know prolonged exposure causes hearing loss.  Many factors make noise exposure and noise-induced hearing loss a more difficult problem on farms than in other occupational settings. Exposure, for example, may begin at a very young age because of children’s involvement in the family farm. Farmers work very long hours often with short breaks, and we know that risk of hearing loss increases proportionally with increased duration of exposure, and reduced “rest” periods where normally the ear can recover from over-exposure earlier in the day.  Average noise levels are often well above the level permitted by the BC WCB (85 dBA), and have been reported to reach up to 90 dBA among vineyard workers, and 95 dBA for operators of medium-powered tractors and cereal farmers.  Farmers have been encouraged to implement so-called hearing conservation programs that lay out a series of steps to reduce exposure and risk of noise-induced hearing loss. Key among those steps is the reduction of noise at the source, which can be achieved by ensuring all manufacturer-fitted controls (like mufflers) are in place and equipment is well maintained and serviced. Some noisy equipment – such as tractors – can be retrofitted with noise- reduction devices such as sound-proofed cabs. Noise level should be taken in to account when purchasing new equipment as many manufacturers now provide such information for new products.  Hearing protection devices (earmuffs and plugs) should only be used as a last resort, and must be fitted properly and worn consistently. Young farm workers are more likely than older workers to wear hearing protection, but even so it is difficult to achieve the level of Noise and Hearing Loss in Farming  page 3 of 69   3 protection claimed by the manufacturer when hearing protection devices are adopted in the “real world”.  We identified several “knowledge” gaps that could be the focus of future research. These include noise exposures in animal confinement facilities and greenhouses, and confirmation of earlier studies – that were mostly done in other countries – in Canada. Additional work needs to be done to understand what strategies for reducing the risk of NIHL are likely to be most successful in the BC farming community.      Noise and Hearing Loss in Farming  page 4 of 69   4 Table of Contents   Executive Summary _____________________________________________________ 2 Table of Contents _______________________________________________________ 4 Why are we writing this report?_______________________________________________ 6 Introduction _______________________________________________________________ 6 Hearing loss in farmers - Is there a problem?____________________________________ 6 How well do farmers hear? _________________________________________________________ 7 What about children on farms? ______________________________________________________ 8 Noise on farms – Where does it come from? _____________________________________ 9 How do we define noise?___________________________________________________________ 9 How loud are farms? _____________________________________________________________ 10 Does noise on farms exceed regulations? _____________________________________________ 12 What factors can increase the risk of noise-induced hearing loss? __________________________ 13 What can you do to reduce the risk? __________________________________________ 13 Hearing Conservation Programs ____________________________________________________ 13 Reducing Noise Exposure _________________________________________________________ 15 Engineered Noise Controls ________________________________________________________ 15 Hearing Protection Devices ________________________________________________________ 16 Conclusions __________________________________________________________ 17 Recommendations for research___________________________________________ 17 Possible solutions in the future ___________________________________________ 17 Active Noise Controls_______________________________________________________ 17 Pharmaceutical Treatments _________________________________________________ 18 Acknowledgements_____________________________________________________ 19 References ___________________________________________________________ 20 Appendix 1: Literature Review Methodology ________________________________ 24 Appendix 2: Health Studies ______________________________________________ 25 Appendix 3: Noise Source and Exposure Studies Table _______________________ 35 Appendix 4:  Noise Control Studies Table __________________________________ 40 ACTIVE NOISE CONTROL COMMUNICATION HEADSETS FOR THE ENTERTAINMENT INDUSTRY _________________________________________ 46 Executive Summary ____________________________________________________ 47 Table of Contents ______________________________________________________ 48 Introduction ______________________________________________________________ 49 What is active noise control?_________________________________________________ 49 Noise and Hearing Loss in Farming  page 5 of 69   5 Active noise control headsets_________________________________________________ 51 How might active noise control communication headsets be useful in the entertainment industry? _________________________________________________________________ 53 Is your unwanted noise external background noise? _____________________________________ 53 Is your unwanted noise emitted by the headset? ________________________________________ 56 Summary_________________________________________________________________ 56 Acknowledgements_____________________________________________________ 57 Appendix 1: Literature Search Strategy ____________________________________ 60 Appendix 2: Summary of articles that assessed noise exposure from headsets _____ 61 Appendix 3: Summary of ANC headset articles ______________________________ 64 Noise and Hearing Loss in Farming  page 6 of 69   6 Why are we writing this report?  In early 2005 the School of Occupational and Environmental Hygiene was approached by the Farming and Ranch Safety and Health Association (FARSHA) to conduct a literature review on noise exposure and hearing loss in farming. This report summarizes the findings of a comprehensive review of the scientific literature on noise and hearing loss in the agricultural setting; more detailed results are reported in the appendices. The first appendix, appendix A, describes how the information was identified.  Introduction  The Canadian farming industry is vital to our nation’s economic and social well being. While this is one of our most established industries, it is sadly also one of our most dangerous (May 1990; May 1993; Pickett, Hartling et al. 1999; Perry 2003). Farmers and farm workers incur numerous exposures, including pesticides, organic dusts, gasoline fumes, excessive sun exposure, mechanical injury, injury from livestock, noise and vibration (Cordes and Rea 1991; Perry 2003). In British Columbia, the farming sector was brought under the jurisdiction of the Workers’ Compensation Board of British Columbia in 1998.  This review will focus on noise exposure in the farming environment, its effects on farm workers and possible methods to reduce noise exposure and prevent noise-induced hearing loss in farmers. Hearing loss in farmers - Is there a problem?  It has been well documented that as we age there is a progressive loss in hearing ability, a process called presbycusis. Research into presbycusis allows us to make predictions of hearing ability for healthy adults at different ages or stages in life. Through this we are able to compare an individual’s actual hearing ability with what we would expect for a healthy individual of the same age.  In studies of rural and farming populations, hearing ability has repeatedly been lower than what would be expected for healthy adults (Townsend, Bess et al. 1975; Thelin, Joseph et al. 1983; Karlovich, Wiley et al. 1988; Cordes and Rea 1991; Merchant, Stromquist et al. 2002; Rautiainen and Reynolds 2002). Additionally, when comparisons of rural non-farming versus rural farming populations are made, greater hearing loss has been found in farmers (Marvel, Pratt et al. 1991). As a result, hearing loss has been identified as a major priority in the field of agricultural health (McDuffie, Dosman et al. 1994; Solecki 1999). However, the distribution and severity of hearing loss is more difficult to study among farm populations than in concentrated occupational settings such as factories (Crutchfield and Sparks 1991), making this a challenging population to study.  A recent review by McCullagh synthesizes progress in the area of the preservation of hearing in farm workers over the past five decades (McCullagh 2002).  Noise and Hearing Loss in Farming  page 7 of 69   7 An explanation of the clinical pathway by which our environments can permanently damage hearing ability is beyond the scope of this review. However in short, the most common reason for hearing loss (other than age) is noise exposure, resulting in permanent, irreversible damage to the cochlea, or “inner-ear”. There are two types of noise-induced hearing loss (NIHL); (1) temporary, known as TTS (temporary threshold shift) and (2) permanent, known as PTS (permanent threshold shift) (Marvel 1992). TTS occurs immediately after being in close proximity to noise (rock concert, metal grinding, chain sawing, etc.) and results in a short time period (up  to several hours) where hearing ability is diminished but eventually returns to normal. Most of us have experienced TTS. PTS occurs when the hearing loss is permanent; it is irreversible and thus can have significant health consequences. Repeated episodes of TTS may eventually lead to PTS.  Farms are increasingly adopting mechanical technologies that, while helping to increase production, have the drawback of often producing excessive noise (Solecki 1995). In Japan, it was estimated that 2 million workers were at risk for noise-induced hearing loss due to their jobs, and more than 1/6 of these workers were employed in farming (Miyakita and Ueda 1997).  Noise-induced hearing loss is not the only risk associated with noise exposure.  Noise exposure can increase stress levels (Marvel 1992) and farmers are at greater risk for being injured when exposed to noise (Rautiainen, Lange et al. 2004). The ability to hear is critical for participating in farm work and chores. Farmers and farm workers must be able to hear their co-workers over the sounds of animals and machinery to ensure safe working environments. Also, noise is not the only occupational cause of  hearing loss; exposure to certain chemicals such as insecticides may worsen the effect of noise on hearing ability (Teixeira, Augusto et al. 2003). How well do farmers hear?  Numerous studies have investigated NIHL in many different populations. The studies mentioned here focused solely on either farming or rural populations. In these types of studies, people are usually removed from the study if they have recently been exposed to excessive noise levels, thus only permanent (PTS) hearing loss is studied.  In this section we will summarize the finding of these studies. Please see Appendix 2: ‘Health Studies’ for more detailed information on the studies below.  Based on present research, farmers appear to be at risk for noise-induced hearing loss from noise exposure received from farming tasks and activities (Troester and Seidel 1970; Plakke and Dare 1992; Solecki 1995; Solecki 1998; Merchant, Stromquist et Hearing loss is often measured by audiometry which determines how loud a sound must be for the subject to hear it. Those with normal hearing will have zero decibels of hearing loss. If a sound must be increased by 10 dB to be heard by a subject then he or she is said to have 10 dB of hearing loss, or a “hearing threshold level of 10dB”.  According to the World Health Organization, a hearing threshold level between 26 and 40 dB is considered slight; between 41 and 60, moderate; between 61 and 80; more than 80, profound hearing loss. Noise and Hearing Loss in Farming  page 8 of 69   8 al. 2002; Solecki 2002; Stewart, Scherer et al. 2003; Miyakita, Ueda et al. 2004).  For example, 92% of 182 dairy farmers were found to have functionally significant hearing loss (Beckett, Chamberlain et al. 2000). A study in Saskatchewan found 31% of 1,418 farmers to have early signs of hearing loss1 and an additional 39% to have hearing loss (Lupescu, Angelstad et al. 1999).  Some studies measured both noise exposure and hearing ability. One such study found that, when considering hours per year exposed to noise, farmers in the both mid and high exposure groups suffered from hearing loss (Anttonen, Virokannas et al. 1994). More information about noise exposure will follow in a later section.  In typical hearing tests, hearing is tested at different pitches (also called frequencies). As is common with noise-induced hearing loss, farmers often appear to have greater hearing loss at high frequencies. For example, in three separate studies, 37-45% of farmers tested were found to have had mid-frequency hearing loss and 65-78% to have high-frequency hearing loss (Marvel, Pratt et al. 1991; Beckett, Chamberlain et al. 2000; Solecki 2002). A fourth study found between 16-78% of farmers to have hearing loss, depending which frequency level was tested (Kerr, McCullagh et al. 2003).  Farmers may not realize the extent of their hearing damage. In one study, 22% of farmers self-reported hearing loss (Hwang, Gomez et al. 2001) but it has been shown that self- reported hearing loss underestimates actual hearing loss (Kerr, McCullagh et al. 2003).  Throughout many of these studies, farmers tended to have greater hearing loss in the left versus right ear (May, Marvel et al. 1990; Marvel, Pratt et al. 1991; Solecki 1995). This is likely a result of constantly looking over the right shoulder to monitor farming implements behind the tractor, which exposes the left ear to noise generated by the motor.  What about children on farms?  Traditionally, farm settings have been both a place of work and a home. Thus, children who live on or visit farms are exposed to many of the same dangers as adult farmers (Perry 2003). While young children may be exposed to farm environments through play, older children are often exposed while participating in farm work. A study of high school children found that 71-74% of those involved in farming had hearing loss2 versus only 36-46% of those who did not farm (Broste, Hansen et al. 1989). Hearing loss has been found in young farmers who are exposed to excessive levels of noise (Broste, Hansen et al. 1989; Anttonen, Virokannas et  1 Early signs if hearing loss were defined as a loss of at least 15 dB at 3, 4 and/or 6 kHz. 2 For this study, hearing threshold values of greater than 10 dB were considered abnormal. Frequency is commonly referred to as ‘pitch’.  A high frequency makes a high pitched, shrill noise, whereas a low frequency may sound like a deep, bass hum. We can hear sound produced between 20-20,000 Hertz.  Sound below 1,000 Hertz is considered low frequency and sound above 1,000 is considered high frequency (Industrial Accident Prevention Association. 1985). Noise and Hearing Loss in Farming  page 9 of 69   9  “A-weighting” (dBA) filters out low-pitched sounds, therefore, exposures reported in dB are generally higher than identical exposures measured in dBA, especially where there is a great deal of low-pitched sound. This is done because hearing loss occurs mainly at higher frequencies. al. 1994). It has been speculated that hearing loss observed in adult farmers may actually have begun in childhood (Thelin, Joseph et al. 1983; Broste, Hansen et al. 1989). Noise on farms – Where does it come from? How do we define noise?  Noise is often defined as ‘undesirable sound’.  Air movements are produced by noise sources and we experience the resulting air pressure as sound. Sound has both pitch (frequency; which we quantify in units called Hertz) and loudness (amplitude; which we quantify as air pressure and summarize in units called decibels, abbreviated dB) (Crutchfield and Sparks 1991). Throughout this review, the loudness component of sound will be expressed in either decibels (dB) or A-weighted decibels (dBA), depending on how it was reported in the study referenced.  Below is a table illustrating noise levels produced by common sources. (Adapted from : “The Canadian Hearing Society” at http://www.chs.ca/info/noise/levels.html).  Table 1: Common Sounds and Noise Levels COMMON SOUNDS NOISE LEVELS (dB) EFFECT Very near a plane taking off  140 Shotgun firing 130 Threshold of pain Thunderclap from nearby lightening heard outdoors 120 Threshold of sensation Power saw Pneumatic drill Chainsaw 110 Regular exposure of more than 1 min. risks permanent hearing loss Near a shouting voice 90 Manual machining 80 Level at which hearing damage begins Need to shout to be heard by a person one meter away Normal Conversation 65 Quiet office with mechanical ventilation 50 Comfortable Whisper 30 Very quiet Normal breathing 10 Just audible  Noise and Hearing Loss in Farming  page 10 of 69   10 How loud are farms?  The Workers’ Compensation Board of British Columbia (WCB) has set guidelines for the maximum sound level permitted in occupational settings.  Under the WCB regulations the maximum permitted noise level for a typical 8-hour shift is 85 dBA, which is in concordance with recommendations in other jurisdictions. However it is widely accepted that the risk of hearing loss is not zero for those exposed below 85 dBA, and that a maximum level of 75dB should be maintained to ensure hearing safety.  Farms are inherently noisy environments; noise levels depend on the type of farming, the machinery used and the work practices.  The focus of the following section is to explore specific noise sources which farm workers are exposed to that could be damaging to human health.  Please see Appendix 3: ‘Noise Source & Exposure Studies’ for more detailed information on the studies below.  A common source of farm noise is tractors.  Studies have found that tractors produce noise at hazardous levels under a range of operational conditions (Matthews 1968; Deshayes and Jr 1969; Walker 1970; Mumgaard, Leviticus et al. 1977; Sullivan, Schnieder et al. 1980; Meyer, Schwab et al. 1993; Pessina and Guerretti 2000). This is true for diesel and gasoline-run tractors (Deshayes and Simpson 1969), although at most frequencies diesel engines are noisier than gasoline engines (Mumgaard, Leviticus et al. 1977).  Noise levels vary according to tractor type, engine speed and farming task (Matthews 1968).  Noise measurements are most often taken at the ear of the tractor operator (Matthews 1968; Sullivan, Schnieder et al. 1980) to estimate the operator’s exposure. On average, the exposure levels have been found to be around 90 dBA (Dennis and May 1995; Beckett, Chamberlain et al. 2000), but may range from 78-103 dB (Troester and Seidel 1970; Holt, Broste et al. 1993).  In one study, 75% of tractors without a cab and 18% of tractors with a cab (with windows closed) were found to result in noise levels above 90 dB (Holt, Broste et al. 1993).  Noise exposures from tractors may also be measured at the position of a bystander (Mumgaard, Leviticus et al. 1977) or the worker (Meyer, Schwab et al. 1993). Routine testing of tractors in the US has shown an increase in the proportion of tractors producing safe noise levels for tractor operators over 1970-1993, but no improvement for exposure for a bystander 25 ft from the tractor (Meyer, Schwab et al. 1993).  For one tractor tested, the bystander exposure ranged from 60-83 dBA depending on operation and surface conditions (Meyer, Schwab et al. 1993).  Since bystanders are often children, this illustrates the importance of taking measures to reduce their exposure to noise.  Furthermore, the exposure of bean-bar riders (those who work on equipment off the back of tractors) is on “Equal Energy Rule”. The equal energy rule shows us that the same amount of damage will occur to any ear that is exposed to the same amount of acoustic energy – whether the energy is delivered at a low level for a long time, or a high level for a shorter period. This rule can be formalized by noting that sound energy DOUBLES with every 3 dB increase in level. Thus, 8 hours exposure at 85 dBA is equal to 4 hours exposure at 88 dBA, or 16 hours at 82 dBA. Using this rule, one can see that the “safe level” – 8 hours at 85 dBA – can be reached in a mere 15 minutes if one is exposed to 101 dBA! Noise and Hearing Loss in Farming  page 11 of 69   11 average 10 dBA higher than that of bystanders, and likely exceeds safe levels (Meyer, Schwab et al. 1993).  Many other practices may cause farm workers to be exposed to noise at levels that exceed 85 dBA (Crutchfield and Sparks 1991). Several studies have looked at noise exposure from hand-operated power tillers. Noise exposure for operators of tillers with a battery-operated walking tractor was 89-91 dBA, whereas the exposure from the gas-powered walking tractor was 77-79 dBA. Another study compared battery-run power tillers with kerosene and diesel engine power tillers and found the operator’s noise exposure to be 80 dBA, 115 dBA and 121 dBA, respectively (Bodria and Fiala 1995; Murugesan and Tajuddin 2001). Small hand- held tillers resulted in noise exposure for the operator of less than 85 dBA (Ragni, Vassalini et al. 1999).  Other studied sources of noise on farms are livestock ventilation units (Guul-Simonsen and Madsen 2000), barn machinery (Matthews 1968; Gressel and Venable 1992), power cleaning tools (Christensen, Vinzents et al. 1992), chainsaws (Anttonen, Virokannas et al. 1994; Dennis and May 1995) and power tools (Matthews 1968; Gressel and Venable 1992).  A study of chicken dressing plants demonstrated excessive noise exposure in 5 out of 9 picking rooms (over 85 dB) and in the lung removal stations (90 dB on average) (Oser and Jones 1967).  In dairy farms the milking area, milk house, vacuum pump and milk cooling compressor were found to produce noise exposure of between 74 dBA to well over 85 dBA (Dennis and May 1995; Beckett, Chamberlain et al. 2000). All of  these exposures have the potential to cause hearing damage (May 1993).  Chainsaws and circular saws are particularly concerning even if their use is sporadic, as noise levels can exceed 100 dBA (Solecki 2000).  During the process of this review, it became apparent that there was little information regarding noise levels produced by livestock (Humann, Donham et al. 2005). While most would agree that machinery is the main source of noise on farms, the recent increase in animal confinement buildings has drawn attention to noise exposure from livestock. A case report which measured noise produced by pigs in swine confinement buildings found levels to reach 110 dB during periods of heavy squealing and an overall minimum of 90 dB during feeding periods (Kristensen and Gimsing 1988). Another study found that ear marking and tattooing of swine produced on average 92 dBA of noise (Christensen, Vinzents et al. 1992). Finally, a recent study found that out of 10 work-related tasks commonly done in swine confinement buildings, 2 produced noise levels above 90 dBA (Humann, Donham et al. 2005). The same study recommended that future research evaluate mechanical noise sources in confinement buildings such as fans, automatic feed delivery systems, and rattling of steel grates.  Other sources of noise exposure which are important for farming populations arise from recreational or non-occupational activities (Townsend, Bess et al. 1975; Broste, Hansen et al. 1989; Beckett, Chamberlain et al. 2000). Snowmobiles produce noise in the range of 93-104 dBA (Anttonen, Virokannas et al. 1994) and are heavily used during the winter months in many rural areas. Listening to music during work has also been found to increase personal noise exposure by at least 3.1 dB  (Oser and Jones 1967; Holt, Broste et al. 1993) as high volume levels are required in order to cover background noise. Finally, hunting has been cited as a source of noise exposure in numerous studies (Wilkins, Engelhardt et al. 1998; Beckett, Chamberlain et al. 2000). Noise and Hearing Loss in Farming  page 12 of 69   12 Does noise on farms exceed regulations? As noted above, the regulatory limit for noise exposure in BC is 85 dBA. This is equivalent to an 8 hour work day over which the average noise level is 85 dBA. If either the total length of noise exposure or the average level of noise exposure increases, the other must decrease to prevent permanent hearing loss.  Exposure to noise for greater than 8 hours results in less time for the ears to recover from excessive noise exposure.  As such, if the average level of noise exposure is not adjusted for the increased duration of exposure then permanent hearing loss or NIHL may occur.  The table below lists the maximum daily exposure times for different average noise levels. (Adapted from: “The Canadian Hearing Society” at http://www.chs.ca/info/noise/levels.html). A 3 dB increase means that sound energy is doubled (Industrial Accident Prevention Association. 1985).  Table 2. Maximum Allowable Exposure Times for Various Noise Exposures Decibels (dB) Maximum Exposure Time 82 dB 16 hours 85 dB 8 hours 88 dB 4 hours 91 dB 2 hours 94 dB 1 hour 97 dB 30 minutes   Please see Appendix 3: ‘Noise Source & Exposure Studies’ for more information on the studies below.  A National Institute for Occupational Safety and Health (NIOSH) study from 1981-1983 estimated that 84% of workers in agricultural services are exposed to noise at levels higher than 85 dBA.  This may depend on the farming environment; one study found that farmers of field crops were exposed to excessive noise 30% of the time versus only 1% for farmers of nurseries (Nieuwenhuijsen, Schenker et al. 1996).  Though the 8-hour shift is standard in many workplaces, farmers are known to work long hours. Depending on the type of farm and time of year farmers can work up to 11-15 hours per day (Dennis and May 1995; Solecki 2000).  Because of the unique work schedule held by farmers, some studies have calculated noise exposure based on a yearly average (Franzinelli, Maiorano et al. 1988; Anttonen, Virokannas et al. 1994). In a Polish study measurements were taken over one full year on large multi-production farms. Daily exposures were highest in August, July and September (Solecki 1995), with a mean annual noise dose of 95 dBA for operators of medium-power tractors and a mean annual noise dose of 90 dBA for high- power tractors.  A second study looked at different types of farms for a full year and found that farmers in cereal growing were exposed, on average, to 95 dBA per year, while in wine growing the annual exposure was 90 dBA (Franzinelli, Maiorano et al. 1988).  A measurement technique called “dosimetry” is used to measure personal noise exposure. A monitor is placed on an individual and measurements are continually taken over their entire Noise and Hearing Loss in Farming  page 13 of 69   13 work shift. Dosimetry is preferred to area measurements, as it generally provides a more accurate estimate of true exposure. A study that measured full-day noise exposures of farmers found average exposures of 86 dBA.  In this same study 15% of all measurements taken were above 90 dBA (values adjusted to 8-hour day equivalent exposures (Christensen, Vinzents et al. 1992)). A New Zealand study which measured noise exposures of 60 farmers found average exposures to be between 84 and 86 dBA, with exposures as high as 94 dBA (McBride, Firth et al. 2003). A third study found an average 8-hour exposure of 86 dBA (range of 58-99) for 13 dairy farmers (Dennis and May 1995). These results also had to be adjusted for a longer than average work day, 13 hours on average (Dennis and May 1995). Finally, a study which measured noise exposure in 36 swine confinement workers found average exposures to range between 87-109 dBA (Humann, Donham et al. 2005). What factors can increase the risk of noise-induced hearing loss?  We have listed many common sources of farm noise previously, but there are some specific factors that have been identified that put farmers at increased risk for hearing loss. These include: amount of time spent using a grain dryer or tractor, time (in years) spent working on a farm (May, Marvel et al. 1990; Solecki 1995; Solecki 1998), time (in years) spent hunting (Nieuwenhuijsen, Schenker et al. 1996; Beckett, Chamberlain et al. 2000; Rautiainen and Reynolds 2002), having a livestock farm3 (Hwang, Gomez et al. 2001), metal-working4 (McBride, Firth et al. 2003), using older equipment5, using additional equipment attached to a tractor (Sullivan, Schnieder et al. 1980), and using self-propelled equipment (i.e., walking tillers, Sullivan, Schnieder et al. 1980). What can you do to reduce the risk? Hearing Conservation Programs  Many of the studies which investigated noise exposure and hearing loss in farmers have recommended that hearing conservation programs be implemented (Anttonen, Virokannas et al. 1994; Beckett, Chamberlain et al. 2000).  In other industrial workplaces hearing conservation programs are required where exposure to noise may exceed regulatory levels.  A hearing conservation program is useful as it lays out a series of steps that can be undertaken to decrease the noise hazard: 1. Assessment of noise in the workplace 2. Worker education and training 3. Implementation of engineered noise controls 4. Posting of signs in hazardous areas 5. Provision of hearing protection devices 6. Annual hearing tests 7. Program evaluation  3 Compared to crop and dairy farming. 4 Compared to tractor, grain crushing, chainsaw and “other” noisy work equipment. 5 More than 10 years old. Noise and Hearing Loss in Farming  page 14 of 69   14 Most importantly farmers will need to assess noise levels to understand where the danger lies. Noise assessment is typically conducted by occupational hygienists or acoustical consultants.  However, one simple test of overexposure to noise is if two people standing arms length apart have to shout to be heard – if so, the noise level is likely above 85 dBA and damage is likely to unprotected ears.  Farm hands and family members must also be educated about the hazards of noise, and noisy areas and noisy equipment posted.  The exposure of farm workers to noise can be controlled using a variety of methods.  They may involve prevention (i.e., reducing or eliminating noise sources) or protection (i.e., minimizing personal exposure by the use of protective equipment worn by the farmer). Figure 1 illustrates options for noise control along the sound pathway. Also, please see Appendix 4: ‘Noise Control Studies’ for more information on the studies below.  A short-term hearing conservation program which included educational modules and a hearing screening program for the agricultural industry was initiated in Saskatchewan in 1995 (Lupescu, Angelstad et al. 1999).  A flexible outreach educational program designed to bring health and safety information to farmers in Minnesota included a module on the hazards associated with noise (McJilton and Aherin 1982).  Figure 1. Illustration of sound pathway and options for control    Noise and Hearing Loss in Farming  page 15 of 69   15 Reducing Noise Exposure  It is always preferable if a noise source can be eliminated, or noisy equipment replaced with quieter equipment.  If elimination or substitution is not possible then engineering controls should be the next priority in order to reduce noise at the source.  Before new engineered noise controls are considered, it is worth ensuring that the noisy piece of equipment is properly maintained, and particularly that all manufacturer fitted controls are in place (e.g., muffler, doors, vibration dampers, windows, etc.). Then further maintenance can be aimed at reducing vibration, or insulating vibrating parts (e.g., vibrating pipe against sheet metal case).  Cost is a major barrier to upgrading equipment (Marvel, Pratt et al. 1991) and as such, farm equipment is often used for many years, sometimes even decades (Marvel 1992; Beckett, Chamberlain et al. 2000).  Still, with proper maintenance and engineering controls, the use of old equipment can still result in safe levels of noise exposure for farm workers.  Use of hearing protection devices should be the focus only where source control is not possible, as the attenuation of noise provided by hearing protection devices is dependant on their fit and how often they are worn, and therefore may not be sufficient to prevent hearing loss. Engineered Noise Controls  Though the term may not be familiar, engineering noise controls are very common in the agricultural setting.  The most familiar of these might be the tractor cab, which reduces the noise level experienced by the operator by separating him or her from the noise source.  There are many factors which influence the noise levels experienced inside a cab including the noise produced by the engine, the material of the cab, and the use of other noise controls on the tractor.  The amount of noise reduction varies depending on the sound frequency, but reports indicate that for the average tractor the addition of a simple cab could reduce noise levels experienced by the operator by 4 dBA (Walker 1970; Marvel, Pratt et al. 1991). The factors at the design stage of a tractor cab which will affect noise levels inside that cab can be the type of metal, the type of glass, the sealing methods, and the space available for insulation (Emme 1972; Marvel 1992).  In practice, noise levels experienced inside the cab are also affected by the operator’s use of personal stereos, or leaving windows open for ventilation or communication.  Ideally, an acoustically designed tractor will employ other conventional controls such as mufflers, sound absorption material, and anti-vibration cab mounts to more effectively reduce the noise exposure for tractor operators.  One study showed that a good muffler may reduce the noise levels sensed 1 foot from the exhaust pipe (i.e., near the operator’s ear) by 3 dBA for diesel tractors and 6 dBA for gasoline tractors (Walker 1970).  Sound absorption material such as polyurethane foam or fibreglass may reduce noise levels experienced inside the cab by up to 4 dBA (Walker 1970).   One modular cab for the White Farm A4T tractor Noise and Hearing Loss in Farming  page 16 of 69   16 which employed damping and sound absorption layers on the floor and roof reduced the noise level experienced by the operator by 18 dBA (as compared to no cab).  Levels of noise reduction in this realm should be sufficient to bring noise exposure from most tractors below hazardous levels.  Hearing Protection Devices  Hearing protection devices such as ear plugs and muffs are one method to reduce personal noise exposure.  For noise exposures from chainsaws and tractors, ear muffs and ear plugs have about the same attenuation efficiency for frequencies less than 100 Hz, but ear plugs are more effective at higher frequencies (Lague 1992). For a tractor producing 116 dBA, use of earplugs under ideal conditions has the potential to reduce noise below exposure limits (82 dBA). However, real-world attenuation is a function of appropriate use and fit of the hearing protection devices.  In actuality, the average reduction of noise achievable by wearing earplugs is closer to 10 dBA (Pessina and Guerretti 2000). In extreme situations, a combination of both plugs and muffs provides the greatest protection.  The effectiveness of hearing protection devices for preventing noise-induced hearing loss depends on the consistent use.  A telephone survey of farmers in California indicated they work around noisy machinery for 10% of their day on average (Schenker, Orenstein et al. 2002) but more than half reported wearing hearing protection ‘rarely or never’ when working under noisy conditions and 66-80% of farmers report using earplugs or earmuffs rarely or never under any conditions (May, Marvel et al. 1990; Wilkins, Engelhardt et al. 1998; Carpenter, Lee et al. 2002; McCullagh, Lusk et al. 2002).  Factors influencing a farmer’s decision to use hearing protection devices are their perception of the risk of hearing loss (Schenker, Orenstein et al. 2002) or belief that hearing loss is preventable (Wadud, Kreuter et al. 1998). Barriers to use include perceptions that protective devices are not comfortable, not available, inconvenient, or that they inhibit communication (Wadud, Kreuter et al. 1998).  Although study results are conflicting (Broste, Hansen et al. 1989), younger farmers may have a higher rate of use of hearing protection devices. A study of reindeer herders in Finland found that 76% of farmers aged 24-34 and 42% of farmers aged 55-64 wore hearing protection (Anttonen, Virokannas et al. 1994). A US study in which young farmers were taught the importance of wearing hearing protection resulted in 81% using hearing protection (Knobloch and Broste 1998). This highlights the special role of education in farm safety.  Based on the prevalence of personal hearing protection use and the influencing factors, there is a need for health promotion programs to prevent noise-induced hearing loss in the The problem with ear plugs and muffs: Ear protectors do not give as much protection in “real” work situations  as manufacturers’ claim; protectors must be fitted properly, consistently worn – though users often find them hot and uncomfortable; ear plugs should always be inserted with clean hands to avoid infection; plugs and muffs interfere with normal communication, warning signals, etc. It is always better to try to reduce the noise at the source! Noise and Hearing Loss in Farming  page 17 of 69   17 agricultural setting.  Still, it is important to remember that hearing protection devices should be secondary to engineering controls, especially as the use of hearing devices may reduce the ability to detect warning signals (Talamo 1979; May 1990). Conclusions There is good evidence that noise in the agricultural industry is a serious problem, and that farmers experience noise-induced hearing loss as a result of their occupational noise exposure.  Noise sources include agricultural machinery, particularly the tractor, but can also include animal noise and ancillary work such as hunting and the use of hand tools.  While addressing noise is a common issue in industrial settings, the agricultural sector faces additional challenges such as the exposure of children, the long work days and seasonal variation, the range of work tasks faced by the farmer, the dispersion of the work force (a barrier in terms of promoting awareness and education) and the use of older equipment.  Steps required in moving forward and reducing NIHL involve filling knowledge gaps in our understanding of the extent of risks on farms, finding effective methods of education for farmers and farm workers, and identifying and developing new and novel solutions for the reduction of excess noise and prevention of hearing loss in the farming population. Recommendations for research  In the process of completing this review several relevant areas were identified as knowledge gaps in the literature and should be the focus of future research.   These include noise exposures in animal confinement areas and in greenhouses.   Additionally, no studies of noise exposure have been completed on populations of B.C. farmers (and indeed there are very few studies completed in Canada).  Determining the appropriate strategy to address noise in the agricultural environment is a great challenge.  The design of policies and programs to prevent hearing loss are complicated by issues specific to the farming industry, as discussed above. Possible solutions in the future Active Noise Controls  One application to watch for in the future is the use of active noise control.  For a technical explanation of noise control please refer to the introduction in the article “Active Noise Control Communication Headsets” that follows this report.   Briefly, active noise control aims to reduce the noise levels experienced by a worker by emitting tones that cancel the sound waves produced by a noise source.  The recent research on active noise control in the agricultural setting has focussed on its application inside cabs, though in other industries active noise control is used in communication headsets.  Please see Appendix 4: ‘Noise Control Studies’ for more information on the studies below. Noise and Hearing Loss in Farming  page 18 of 69   18  Researchers have tested the suitability of active noise control to control the noise exposure of tractor operators (Botteldooren 1993; Yoshida 1995; Peng, Sasao et al. 2001).  It may reduce sound pressure levels at the ear of the operator by 2-3 dBA (Peng, Sasao et al. 2001). Active noise control is most effective for frequencies up to 250 Hz (Zawieska 2004); above this, conventional methods of noise control are more appropriate.  Active noise control is an area of ongoing research, and it suggested that the focus for future work should be on expanding the range of frequencies for use and on reducing the cost of controls. Pharmaceutical Treatments  We reviewed literature that focuses on the studies that have exhibited a positive effect on NIHL in humans and that have been published since 1985.  There are a number of different treatments for NIHL that have been and are being researched.  While most of these treatments are pharmaceutical in nature, some are not. Table 3 lists the treatments and the rationale for their effectiveness.  Table 3 - Treatments for NIHL Treatment Theory/Effects Reference(s) Corticosteroids Improve the microcirculation in the cochlea after acute noise trauma (Duan, Ulfendahl et al. 2002) Blood flow promoting drugs (e.g. epinephrine, dextran pentoxifylline and hydroxylethyl starch) Increase the blood flow through the cochlea when administered after acute noise trauma (Duan, Ulfendahl et al. 2002) (Miller, Laurikainen et al. 1994) Oxygen Reduces hearing threshold shifts and hair cell loss one hour following impulse noise trauma (Duan, Ulfendahl et al. 2002)  Neurotrophins (e.g. nerve growth factor, brain-derived nerve growth factor, neurotrophin-3 and glial cell line-derived neurotrophic factor) Stimulate auditory nerve regrowth and protect from sensorineural hearing loss (Miller 2004) (Duan, Ulfendahl et al. 2002) Anti-oxidants and scavengers Get rid of reactive oxygen species (ROS) which are thought to be involved in noise trauma (Duan, Ulfendahl et al. 2002) Glutamate receptor antagonists It is thought that the glutamate receptors are overstimulated during noise trauma.  Reduce this effect. (Duan, Ulfendahl et al. 2002) Gene therapy Uses viral vectors or liposomes to deliver nucleic acids (e.g. transgenic neurotrophin) to the cochlea (Duan, Ulfendahl et al. 2002)  Of these treatments, the blood flow-promoting drugs were thought to be the most promising, with the dextran pentoxifylline being tested in a randomized, double-blind, placebo-controlled human trial. (Probst, Tschopp et al. 1992)  However, the effects were not Noise and Hearing Loss in Farming  page 19 of 69   19 found to be significant different from the effect in the non-treatment group.  Since this study, the research on cochlear blood flow promoting drugs seems to have been abandoned.  Neurotrophins seem to be the “next big thing” in treatment and prevention of sensorineural hearing loss, with a new patent (Miller 2004) registered last year which proposed the use of a glial cell line to promote the regrowth of nerves in the cochlea.  While still in the animal testing phases (guinea pigs and chinchillas), the fact that they registered for a patent indicates that they are confident in their results, and we might expect some human studies to be conducted within the next couple of years.  In conclusion, it appears that there is a number of promising treatment strategies for noise induced hearing loss.   While none of the treatments have made it successfully through clinical trials yet, some treatments (most notably neurotrophins) may progress to this stage in the next couple of years. In the meantime, the best line of defence against noise-induced hearing loss is still prevention through reducing noise exposure.  Acknowledgements  We wish to acknowledge the guidance and advice provided by Ms. Cheryl Pruitt of the Farm and Ranch Safety and Health Association.  The section on pharmaceutical treatments was taken from Thom J, C Peters, E McIntyre, M Winters, K Teschke, H Davies. 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Noise and Hearing Loss in Farming  page 24 of 69   24 Appendix 1: Literature Review Methodology  Five bibliographic databases were used to identify the literature for this review: PubMed, Agricola, Web of Science, Compendex/Inspec and CCINFO.  PubMed, produced by the U.S. National Library of Medicine, specializes in health literature. Agricola focuses on agricultural research. Compendex contains information on engineering. CCINFOWeb, produced by the Canadian Centre for Occupational Health and Safety, specializes in occupational health and safety literature. The search was conducted in February 2005 and employed combinations of the following keywords: noise, hearing, hearing loss, noise- induced hearing loss, tinnitus, audiometry, dosimetry, TTS, PTS, hearing conservation program and agriculture, farm, farming, greenhouse, tractor, cab, combine, bailer, silo, farm animals, livestock, swine, cattle. In addition, a significant portion of the literature cited within this review was identified through hand searching of references found within other papers. We included all accessible scientific literature relating to noise exposure and hearing loss in the agricultural setting, but excluded articles that were written in languages other than English and French. Studies on the health impact to animals from noise exposure were also excluded. Finally, with respect to potential control measures, a Patent search was conducted using similar search terms.    Noise and Hearing Loss in Farming  page 25 of 69   25 Appendix 2: Health Studies Name Year Purpose Design Population Exposure Outcome Results Conclusion Anttonen 1994   cross- sectional 512 Finnish reindeer herders (18-65 yrs). Exclusion of those over 65, with history of ear infection or with abnormal ear drums. Assessed by questionnaire, specific questions on type of equipment/machine used. Calculated as total usage time of noisy tools. Air conduction hearing thresholds ~ NIHL Prevalence of hearing loss was 15% (ISO Standard). Hearing impairment (>20bB) in both the mid exposure (5000-10000 hrs/yr) and high exposure groups (>10000hrs/yr) at 4.0kHz. Snowmobiles (38.1% by time) and chain saws (48.4% by time) were the greatest noise exposures (range 90-115dBA). 75% of young farmers and 42% of older farmers wore hearing protection. Hearing loss noted in the youngest group. Increased with increased exposure to machinery. Hearing Conservation Program recommended. Beckett 2000 To determine sources of hearing loss in the Farm Family Health and Hazard Survey and to identify targets for prevention. cross- sectional 185 New York farmers (mean age 48 years), 157 male and 28 female, mainly of dairy farms. Interviews were conducted to assess lifetime noise exposures. Noise measurements were taken on a subset of farms (convienence samples directed at high exposure)  Hearing loss assessment (audiometry, otoscopy, tympanometry). Pure tones at 0.5, 1.0, 2.0, 3.0, 4.0, 6.0, and 8.0kHz. Mean noise measurements (dBA) by source: tractors 90.7 (range 75- 102), milk area 76.4 (range 54-93), milk house 82.2 (range 50-99), vacuum pump 91.9 (range 70- 105), milk cooling compressor 83.8 (range 50-100). High frequency hearing loss was defined as >25dB at one of the higher frequencies (3.0, 4.0, 6.0). Almost 98% of the participants had functionally significant hearing loss, 72% had high frequency hearing loss (AMA Guidelines). Poisson Regression: Years of using a grain dryer was found to be a predictor for hearing loss, but only 9% of the population reported ever using. Years of tractor use may be a predictor for hearing loss (p=0.51). The prevalence of hearing loss found was fairly high. Communication to those at risk was recommended. Noise and Hearing Loss in Farming  page 26 of 69   26 Name Year Purpose Design Population Exposure Outcome Results Conclusion Broste 1989 To study the prevalence of hearing loss among teen aged farm children cross- sectional, establishment of a cohort for future longitudinal analysis 872 students aged 12- 19 from vocational agricultural classes, in Wisconsin Four exposure groups based on questionnaire responses to exposure history and degree of participation in farm work Audiometric threshold testing done at high schools and questionnaire of health history 9% reported wearing hearing protection. 71-74% of those working on a farm had hearing loss in at least one ear versus 36- 46% of those not. NIHL found to be twice as prevalent in those working on a farm vs. those not. Adult hearing loss may begin in childhood. Agricultural workers often participate in non- occupational noisy activities. Franzinelli 1988 Estimating noise exposure absorbed by farmers, when driving machines.   21 farms and 106 male machine drivers (mean age 45 years) from them. Italy Noise dose absorbed annually by workers, calculated through personal sampling Tonal audiometry Annual noise dose measured in cereal growing was just over 95dBA while in wine growing it was just over 90dBA. Results were confirmed by results of hearing threshold shifts in machine drivers  Hwang 2001 To study self- reported hearing loss survey - New York Farm Family Health and Hazard Surveill. 1622 New York farmers (62% male), contacted via phone. Questionnaire on noise exposure, also used noise measurement data from FFHHS Questionnaire on hearing loss Hearing loss reported by 22% of population. Logistic model for self reported hearing loss: age (coef 0.05, p 0.0001), male sex (coef 0.90, p 0.0001), livestock farm (coef 0.45, p 0.012), noisy farm equipment (coef 0.09, p 0.001), past noisy farm jobs with (a) some PPE (coef 0.67, p 0.002) and (b) no PPE (coef 0.73, p 0.0001). The use of hearing protection did not influence the model for noisy farm equipment. Farm noise exposure is a serious risk to hearing. The first priority should be to decrease noise at the source. Humann 2005 To measure 8hour noise exposures for workers and noise exposure associated with specific work tasks. And to characterize the frequency distribution of noise.   Three swine production sites in Iowa measured 4 times each. Three employees randomly chosen each time for dosimetry. dosimetry measurements of daily noise doses (36 measurements)   All 36 dosimetry measurements were above 85 dBA (range:86.7- 108.6), mean levels by facility area ranged from 90.3-98.3 dBA. Out of 10 work related tasks, 2 (heat checking sows and processing piglets) produced noise levels above 90 dBA .  Noise and Hearing Loss in Farming  page 27 of 69   27 Name Year Purpose Design Population Exposure Outcome Results Conclusion Karlovich 1988 To evaluate the prevalence and characteristics of NIHL in a rural population.   812 (534 males, 278 females; aged 16-85) attendees of the annual Wisconsin Farm Progress Day Exposition. Case history information over past 5 years. Exposure estimated based on measured hearing levels. Audiometric testing (pure tone air conduction) on site. Approximately 25% of males had communication handicap due to hearing loss by age 30, and it rose to 50% by age 50. Less than 20% reported wearing hearing protection. Hearing levels for farmers and nonfarmers were similar, regardless of occupational noise exposure history. men living in rural areas have a higher prevalence of hearing loss and associated communication problems. Kerr 2003 To characterize hearing loss in 2 understudied populations as part of "Healthy People 2010" objectives   Recruited at farm show, needed to work at least 20 hrs per week Self administered questionnaire Perceived hearing loss AND measured hearing loss Measured hearing loss > 25dB at: 500Hz - 37.3%, 1,000Hz - 16.7%, 2,000Hz - 28.0%, 4,000Hz - 66.7%, 6,000Hz - 78.7%. Perceived hearing loss (5 point scale, 5=poor): 500Hz - 3.0, 1,000Hz - 3.5, 2,000Hz - 3.5, 4,000Hz - 3.3, 6,000Hz - 3.1. Perceived hearing loss NOT a good indicator of actual hearing. Knoblock 1998 To report results of a 4 year hearing conservation program 4 year Intervention study 753 students in rural Wisconsin, randomly put into intervention (n=375) and control (n=378) groups. Intervention - hearing conservation program (education, audiometric testing, hearing protection) Use of hearing protection Reported use of hearing protection - 81% among intervention vs 43% control. Predictors of use were found to be: male sex, lawn mower use and tractor use. Education level, hearing perception and paternal hearing problems were not found to be predictors. Use feedback from students to improve program. Kristensen 1988   case report - hearing impairment in pig breeders male aged 45 45 min twice a day (animal feeding) with no hearing protection for 17 years. self reported hearing loss over time, verified by audiogram Noise measurements taken, always above 90dB (95-104dB). Miller for grinding feed (88dB) and high pressure cleaner (98- 105dB) also noise sources. Many people employed in big breeding are at risk for NIHL. Also, leisure noise exposure sources (hunting) considered not to be responsible for NIHL. Automatic feeders recommended. Noise and Hearing Loss in Farming  page 28 of 69   28 Name Year Purpose Design Population Exposure Outcome Results Conclusion Lupescu 1999 To evaluate an education and screening program to promote hearing conservation among farmers program Evaluation 18,650 homes sent mailings, 3000+ had audiograms done and 1,418 returned final questionnaire (1087 males, 331 females) Educational resources & hearing screening protocol. NA 29% (21% of males and 56% of females) had normal audiograms. 31% (33% of males and 24% of females) had early loss index audiograms. 39% (45% of males and 20% of women) had abnormal audiograms. Only 47% males and 18% females wore hearing protection. Many participants had already incurred noise induced hearing loss. Marvel 1991 To assess the nature and prevalence of hearing loss randomized study from pre- established cohort, comparison to rural non- farm (age and sex matched) Full time New York dairy farmers (n=49)- randomly selected from initial telephone survey which estimated that 15% of farmers had trouble hearing Interview with registered nurse to collect info RE occupational, medical and recreational histories Hearing loss - measured through audiological examination Farmers had poorer hearing then non-farmers at ALL frequencies tested. Farmers:65% high, 37% mid, freq hearing loss. Much greater then estimates from initial screening. Non-farmers:37% high, 12% mid, freq hearing loss. Farmer hearing loss mainly in left ear. Diffference in prevalence of hearing loss between dairy farmers and non dairy farmers was due to occupational noise exposure on the farm. May 1990 To understand the noise levels associated with dairy farming randomized study 49 fulltime farmers or farm workers, 46 male and 3 female, mean age of 43.5(30-56) and mean years farming 29.4(15-44) Interview with registered nurse to collect info RE potential confounders and other exposures Medical and occupational histories taken AND audiometric testing (PTA and HFA) Loss of >20dB in either ear was considered abnormal. 37% had abnormal hearing at 0.5, 1.0, 2.0 and 3.0 kHz (PTA) and 65% had abnormal hearing at 3.0, 4.0 and 6.0 kHz (HFA). Both age (p<0.05) and years farming (p<0.05) were correlated with reductions in both PTA and HFA. Fewer then 20% routinely used hearing protection. Among farmers, there is substantial hearing loss in higher frequency ranges (right ear: 55% and left ear: 65%). Presbycusis is an important confounder. Left ear was more affected (p<0.02). Noise and Hearing Loss in Farming  page 29 of 69   29 Name Year Purpose Design Population Exposure Outcome Results Conclusion McBride 2003 To identify noise sources in farming and investigate their association with hearing loss. cross- sectional random sample 586 farmers (381 males and 205 females) Questionnaire used to assess noisy jobs, noise dosimetry for a sub-set of 60 farmers, to measure a 'normal' days exposure. Audiometry and questionnaires Median LEQ exposures of between 84.4-86.8 dBA, a significant minority of exposures were over 90 dBA. Logistic Regression: High exposure to tractor with no cab: odds ratio of 2.09(0.62-7.08) for having hearing disability. Low exposure to chain saw: odds ratio of 2.12(0.55-8.22) for having hearing disability and for high exposure odds ratio of 2.57(0.96-6.87) for having hearing disability. High exposure to grain crusher: odds ratio of 2.09(0.89- 4.92) for having hearing disability. Age, tractor driving without a cab and metal working were found as risk factors for hearing loss. Prevention through either noise reduction or isolation of the source is the best practice. Concerning ear protection, ear muffs are often better choices then ear plugs. Merchant  2002 To obtain risk factor data for rural residents (see article for full set of study objectives) Cohort - Keokuk County (Iowa) Rural Health Cohort Study 341 farm households, 461 town households and 202 rural non-farm households Environmental assessment questionnaire health questionnaire Men in all 3 residential groups were less likely to report good- excellent hearing than women (OR=0.30, CI:0.21-0.41), those who had ever smoked were also less likely to report good-excellent hearing (OR=0.81, CI:0.60-1.09). NIHL among farmers is well documented, thus findings were not surprising. Miyakita 1997 To estimate the number of workers in major industry groups with NIHL Cross- sectional, using census data Total number of workers in Japan Results stratified by industry - census data Screening audiometry Rate of workers with positive results by industry used to estimate (control for age, ear disease, non-occupational exposure) total number of workers with >40 dB hearing loss @ 4kHz for each industry. 360 000 of 2M total workers at risk were in agriculture. Workers found to be at risk for NIHL should be covered by noise hazard guidelines. Noise and Hearing Loss in Farming  page 30 of 69   30 Name Year Purpose Design Population Exposure Outcome Results Conclusion Miyakita 2004 To examine the risk of hearing loss among farmers exposed to noise from mechanized farm equipment   1538 Farmers and 4300 Office Workers in Japan Mechanized farm equipment, dosimetry measurements taken on subset of 54 farmers Hearing tests conducted through health care institutions Tests were done at the 1kHz and 4kHz frequencies for greater than 40dB. For males at 4kHz: aged 40-49 office = 9.6% and farmers = 16.4%, aged 50-59 office = 16.1% and farmers 30.3%, aged 60-69 office = 29.9% and farmers = 50.3%.  No significant difference was found at 1kHz or for women. For tea harvesting/processing 8hr exposure ranged from 81.5- 99.1dBA, for sugar cane harvesting the range was 83.2- 97.6dBA. Farmers are at risk for NIHL, hearing conservation programs needed Nieuwenhuijsen 1996 To identify the determinants of exposure to dust, noise and pesticides and use of protective equipment cross- sectional 1,947 randomly selected California farm operators Self reported percentage of time working in noisy job Determinant model for exposure and use of protective equipment Field crop farms had greater amount of time exposed to noise (30%) and nurseries had the lowest (1%). Percent of time driving a tractor was the strongest predictor of exposure (odds ratio - 1.29(1.22-1.35); 1.45(1.38-1.52). Use of protective equipment increased with noise exposure.  Plakke 1992 To compare individuals exposed to farming noise with those never exposed. case-control (?) 30 each in case (farmers) and control groups (white collar workers). Matched for age group. Case history questionnaires pure tone audiometry Control group: no individuals had >19dB average for 1000, 2000 and 3000Hz. Cases: 10% of 25- 34yrs, 30% of 35-44yrs, 50% of 45-54yrs had >19dB average for 1000, 2000 and 3000Hz. Farmers are at risk for NIHL. Rautiainen 2004 To evaluate if a safety intervention program has been effective at reducing farm injury/illness and related costs. cohort All injuries in the Iowa Certified Safe Farm Study Noise injury Injury rate was associated with noise exposure. The risk ratio of being injured when exposed to noise was 1.53(CI:1.19-1.96) unadjusted and 1.25(CI:0.95-1.64) adjusted for all other risk factors (age, general health, farm size, intervention, job, livestock, alcohol, stress, dust and gas, chemicals/pesticides, heavy lifting).  Noise and Hearing Loss in Farming  page 31 of 69   31 Name Year Purpose Design Population Exposure Outcome Results Conclusion Solecki 1995 To evaluate noise exposure and NIHL. noise survey AND case- control Polish farm tractors, combines and harvestors AND 172 tractor drivers (aged 19-52) and 33 manual workers employed on farms Dosimetry measurements of daily noise doses Audiometry: tonal air conductivity at 0.5, 1, 2, 3, 4 and 6 kHz. Mean dose for entire year was 96.6dBA. Monthly doses were highest in August, July and September. The greatest hearing loss for tractor drivers was at: 3kHz (13.7-14.8dB), 4kHz (17.1- 18.4dB), 6kHz (16.7-18.8dB). Threshold hearing values were found in tractor drivers compared to controls for the frequencies 3- 6kHz, occupational noise exposure led to NIHL. Solecki 1998 To compare the occurrence of hearing loss in farmers with that of non exposed individuals. case control 45 male farm tractor drivers or self- propelled machine operators, aged 21-50, in Poland. Controls were matched for age (within 6 months) and sex and mainly worked in administration/control. Otological interview to identify risk factors Audiometric examination (PTA and HFA) for tonal air conductivity (each ear) and bone conductivity. Statistically significant differences between the groups were noted at tested frequencies: 2, 3, 4, 6 and 8 kHz. High frequency hearing loss in oldest 2/3 of farmers was equivalent to noise related hearing loss. The control group had no clinical significant hearing loss at any age group. For farmers, both age and duration of employment in agriculture were significantly correlated with mean hearing loss. Noise present in the farming environment is the primary reason for decreased hearing among farmers. Solecki 2000 To describe the duration of exposure to noise in farming population   30 self employed farmers Time-schedule measurements over 1 year No Outcome Measure Highest time values for noise exposure occurred during harvesting months: August 5 +/- 2.7, October 4.9 +/- 2.1, average hours exposed to noisy activities per day. High variation of total daily exposure based on time of year. Noise and Hearing Loss in Farming  page 32 of 69   32 Name Year Purpose Design Population Exposure Outcome Results Conclusion Solecki 2002 To better recognize noise-related health risk among Polish private farmers. Case control 128 private farmers aged 28-65yrs who had been working for 11- 40years. Excluded based on head injury or past ear disease. Controls: 42 office workers Otological interview to identify risk factors, dosimetry measurements on tractors to estimate noise exposure. Audiometric examination for tonal air conductivity (8 pure tones) and bone conductivity (6 tones) Hearing loss defined as >20dB. Private farmers: 45% had hearing loss at mid frequencies, 78% had hearing loss at high frequencies. Control group: 0% had hearing loss at mid frequencies, 17% had hearing loss at high frequencies. When stratified by age, older farmers had progressively worse hearing. Significant correlation between period of employment and hearing loss observed in youngest age group. Noise present in the farming environment is the primary reason for decreased hearing among farmers. It was found that the most decrease in hearing occurs within the first 30 years of exposure after which the process slows down. Stewart 2003 Determine perceived effects of hearing loss   93 people (aged 18-75) actively engaged in farming Case histories of noise exposure and demographic information Medical examination, pure tone air conduction thresholds. Hearing loss increased with frequency tested, effect stronger for part time farmers at high frequencies (3000, 4000, 6000, 8000Hz) Farm noise exposure may put farmers at risk for NIHL. Teixeira 2003 Examine auditory disorders in workers exposed to insecticides   98 individuals  Questionnaire  pure tone audiometry Workers exposed to insecticides: 63.8% had hearing loss, median exposure time to detect a high frequency loss was 7.3 years. Workers exposed to insecticides AND noise: 66.7% had hearing loss, median exposure time to detect a high frequency loss was 3.4 years. Hearing thresholds were lowest for those exposed to noise and insecticides. Insecticides may have an ototoxic effect which is worsened by concurrent exposure to noise. Further research needed. Noise and Hearing Loss in Farming  page 33 of 69   33 Name Year Purpose Design Population Exposure Outcome Results Conclusion Thelin 1983 To examine the risk of high- frequency hearing loss for farmers   161 male farmers (25- 64 yrs) representing all regions of Missouri, 75 agri fair non-farmers, and 129 office workers. Noise exposure reported by participants Pure tone screening in each ear at 1.0 (20dB), 2.0 (20dB) and 4.0 kHz (25dB). Failure rates at 2000 and 4000 Hz in both ears: farmers - 16.8%, agri-fair non-farmers - 10.7%, office workers - 6.2% (p value < 0.01). Farmers at risk for hearing loss at 2,000 and 4,000 Htz (compared with office workers), failures increased with increasing frequency and for each frequency the failure rate was highest for farmers. Male non-farmers who 'associate' with farmers also had substantial hearing loss.  Both young and older farmers are at risk for hearing loss, active measures need to be directed at young farmers. Townsend 1975 To illustrate the overall hearing characteristics of residents in rural Michigan Cross- sectional 1,325 residents Noise exposure reported by residents Pure tone air conduction tests For all age groups, hearing thresholds were considerably poorer than those predicted by presbycusis (age related hearing loss) alone. Non-occupational sources of noise exposure such as snowmobiles, hunting, use of chain saw and motorcycles are of concern. Troester 1970   Clinical survey  60 tractor drivers Noise and vibration measurements taken for tractors Audiograms  Noise levels from almost ALL tractors were above 85dBA. hearing loss increased with number of years worked, greatest for 5-10 and 10+years worked. The ear was endangered by noise. Noise and Hearing Loss in Farming  page 34 of 69   34 Name Year Purpose Design Population Exposure Outcome Results Conclusion Wilkins 1998 to obtain data on a broad range of agricultural health and hazard related factors among workers on cash grain farms. mixed mode survey  (Ohio Farm Family Health and Hazard Survey) 1,782 cash grain farmers in Ohio statewide mixed- mode survey: self administered questionnaire and telephone interview Years of exposure, days per year and lifetime hours were calculated for different types of occupational and non- occupational noise exposures Longest exposures were for cabless tractor (19,846 mean LH) cab tractor (8,823 mean LH) and grain drivers (7,117 mean LH). In total, almost 62 million hours of noise exposure were reported by the 1,782 participants. 65.6% never wore hearing protection when exposed to agricultural noise, compared to 52.7% who never wore hearing protection when exposed to non- occupational noise (hunting, motorcycle, snowmobiling). Almost every farmer reported using a cabless tractor at some point. Hunting was the dominant activity associated with non occupational noise exposure (25.8 years on average), use of hearing protection was poor (~33%) for all age groups and education levels.  Noise and Hearing Loss in Farming  page 35 of 69   35 Appendix 3: Noise Source and Exposure Studies Table Author Date Purpose Design Population  Exposure Method Result Beckett 2000 To determine sources of hearing loss in the Farm Family Health and Hazard Survey and to identify targets for prevention. Cross- sectional 185 New York farmers (157 male and 28 female) mainly on dairy farms Tractors and farm equipment.  Hearing loss assessment (audiometry, otoscopy, tympanometry). Pure tones at 0.5, 1.0, 2.0, 3.0, 4.0, 6.0, and 8.0kHz.  Lifetime noise exposure was determined using detailed interviews. Noise measurements were taken on a subset of farms (convenience samples directed at high exposure) Mean noise measurements (dBA) by source: tractors 90.7 (range 75-102), milk area 76.4 (range 54-93), milk house 82.2 (range 50-99), vacuum pump 91.9 (range 70-105), milk cooling compressor 83.8 (range 50-100). High frequency hearing loss was defined as >25dB at one of the higher frequencies (3.0, 4.0, 6.0). Almost 98% of the participants had functionally significant hearing loss, 72% had high frequency hearing loss (AMA Guidelines). Poisson Regression: Years of using a grain dryer was found to be a predictor for hearing loss, but only 9% of the population reported ever using. Years of tractor use may be a predictor for hearing loss (p=0.51).   The prevalence of hearing loss found was fairly high. Communication to those at risk was recommended. Christensen 1992 To record exposures in relation to various work tasks. Cross- sectional 26 farmers at 11 large pig- breeding farms Swine husbandry. Measured noise at farmer's ear using dosimetry.  Adjusted values for longer than average work days. Mean noise dose was 86.2dBA (81.2- 94.8dBA). 15% of all measurements were above 90dBA. Loudest work tasks were cleaning with high pressure equipment (93- 100dBA) and ear marking / tattooing (mean of 92dBA). Dennis 1995 To understand the personal noise exposure experienced by those working on a dairy farm. Cross- sectional 13 farmers (12 male) on 9 different farms in New York 41 tractors and other farm equipment. Measured noise exposure over full day using dosimetry. Collected diary of activities.  Adjusted for longer than average work days. Work day found to be 11-15 hours.  Mean (adjusted) eight hour exposure was 86dBA (range 58-99). Noise levels were highest during chain saw and buzz saw use (102dBA), lower for use of bedding choppers (95dBA) tractors (90dBA), and lowest for milking (74dBA).  Tractors are a prominent source of noise exposure. Farmers need to be able to recognize potentially harmful noise exposures. Due to the seasonality of farming, studies are needed that look at yearly exposures. Noise and Hearing Loss in Farming  page 36 of 69   36 Author Date Purpose Design Population  Exposure Method Result Franzinelli 1988 To estimate noise exposure experienced by farmers when driving machines. Cross- sectional 106 male machine drivers on 21 farms in Italy. Tractors and farm equipment. Measured noise dose absorbed annually by calculations through personal sampling. The outcome measure was tonal audiometry. Annual noise dose measured in cereal growing was just over 95dBA while in wine growing it was just over 90dBA.  Results were confirmed by results of hearing threshold shifts in machine drivers. Guul-Simonsen 2000 To find a standardized method to measure noise from livestock ventilation units. Noise survey Livestock ventilation units. 12 different livestock ventilation units. Loudness and sound level at 7 points 1M from ventilation unit. The noise measurement method presented here gives comparable results (+/- 1 dBA) whether noise testing completed in an enclosed space or open air environment. Holt 1993 To measure noise exposures in rural areas. Cross- sectional Tractor operators 155 tractors on 36 farms. Measurements taken with a sound level meter Noise levels between 78-103dB were measured. 75% of tractors without cabs and 18% of tractors with cabs had noise levels above 90dB. A radio adds on average 3.1dB (windows closed) or 4.2dB (windows open) for tractors with a cab.  Hearing protection recommended when using a tractor (with cab) is more than 3-4 hours or when using a tractor (without a cab) is more than 1.5-2 hours. Kristensen 1988 To assess hearing impairment in pig breeders. Case report 1 male aged 45. Animal feeding 45 min twice a day with no hearing protection for 17 years. Recorded self- reported hearing loss over time, and verified by audiogram. Measured noise levels in the feeding area. Noise measurements taken, always above 90dB (95-104dB). Miller for grinding feed (88dB) and high pressure cleaner (98-105dB) also noise sources.  Many people employed in pig breeding are at risk for NIHL. Also, leisure noise exposure sources (hunting) considered not to be responsible for NIHL. Automatic feeders recommended. Matthews 1968 To characterize the noise environment on farms. Noise survey Tractor operators Tractors, combine- harvesters, walking tractors, chainsaws, brush cutters, livestock buildings and barn machinery Measured noise levels for tractors at different horsepower while performing a range of tasks, and levels different farm buildings. Tractor noise levels are unsatisfactory.  Cabs may or may not improve noise levels, depending on design.  Noise levels from small-engine tools are hazardous, but HPD use may be appropriate control.  Noise levels in building require more research. Noise and Hearing Loss in Farming  page 37 of 69   37 Author Date Purpose Design Population  Exposure Method Result Meyer 1993 To measure noise exposure for farm workers in bean-bar operations.  To develop a model to predict noise exposure in this conditions. Noise survey Bystanders and bean-bar riders (those who work off back of tractor). Tractor-  John Deere tractor Model 2955 Measured noise exposure levels according to Nebraska Tractor Test Laboratory method Noise levels at bean-bar are likely above 85 dBA.  Noise at bean-bar position is 10 dBA (average) higher than at bystanders.  Results indicate that HCP should be implemented for bean-bar riders. Miyakita 2004 To examine the risk of hearing loss among farmers exposed to noise from mechanized farm equipment. Cross- sectional 1538 Farmers and 4300 Office Workers in Japan Mechanized farm equipment. Hearing tests were conducted through health care institutions, and dosimetry measurements taken on subset of 54 farmers.  Tests were done at the 1kHz and 4kHz frequencies for greater than 40dB. For males at 4kHz: aged 40-49 office = 9.6% and farmers = 16.4%, aged 50-59 office = 16.1% and farmers 30.3%, aged 60-69 office = 29.9% and farmers = 50.3%.  No significant difference was found at 1kHz or for women. For tea harvesting/processing 8hr exposure ranged from 81.5-99.1dBA, for sugar cane harvesting the range was 83.2- 97.6dBA.  Concluded that farmers are at risk for NIHL, hearing conservation programs needed. Mumgaard 1977 To report noise and performance data for tractors. Noise survey Tractor operators Tractors, with and without cab. Measured bystander noise level under many operating conditions defined by Nebraska Tractor Test. Measured noise levels associated with: # cylinders, engine power, # gears, engine RPM and tractor year. Murugesan 2001 To compare noise and vibration levels produced by power tillers, and to make recommendations for duration of work for operator with fatigue. Noise survey Power tiller operator 3 power tillers: battery operated power tiller; diesel engine operated power tiller; petrol start kerosene run engine operated. Measured noise and vibration levels at 1M intervals from engine. Velocity, acceleration and frequency of vibration at right handle, left handle and body of operator. Battery operated power tiller produced 80dBA and can be operated for up to 8 hr without human fatigue.  Both engine driven tillers can be operated only 1.5 before fatigue. Diesel power tiller emitted 121 dBA and kerosene emitted 115 dBA.  Battery operated power tiller was the best for operator safety and comfort. Noise and Hearing Loss in Farming  page 38 of 69   38 Author Date Purpose Design Population  Exposure Method Result Oser 1967 To evaluate potential permanent noise induced hearing loss from prolonged exposure. Noise survey Workers in chicken dressing plants. Chicken dressing plants in US. Noise measurements (method section not complete) Excessive noise was generally found in the picking room (5 out of 9 exceeded 85dB) and lung removal station (all 9 averaged 90dB) and near the chillers. Increased sound levels from background music was also noted and in some areas caused noise levels to be just over limit.  Recommended that hearing protection be available to workers and that audiometric testing be done on each worker. Ragni 1999 To evaluate operator exposure to noise and vibration. Noise survey Operators Small implements for soil tillage used in developing countries (focus: China) Measured noise levels at user's ear, and acceleration transmitted from the handle Noise levels do not poise appreciable risk. For 10% of subjects the vibration level could cause hand disorders after 3 years use. Simpson 1969 To measure noise exposure for tractor operators. Noise survey Tractor operators 55 tractors: included 21 gas, 30 diesel and 4 liquid petroleum tractors (lists details of tractor types), and 18 other pieces of farm equipment. Measured sound pressure levels at the operator’s left ear (sitting and standing positions) for tractors running at 50, 75 and 100 percent of tractor load. For all tractors, noise levels were >85 db. Noise levels higher if farmer standing than sitting (ear closer to exhaust stack). Solecki 1995 To evaluate noise exposure and NIHL over the year. noise survey AND case- control 172 tractor drivers (aged 19-52) and 33 manual workers employed on farms. Polish farm tractors, combines and harvesters. Measured dosimetry measurements of daily noise doses. Audiometry: tonal air conductivity at 0.5, 1, 2, 3, 4 and 6 kHz. Mean dose for entire year was 96.6dBA. Monthly doses were highest in August, July and September (monthly values not converted to dBA scale). The greatest hearing loss for tractor drivers was at: 3kHz (13.7- 14.8dB), 4kHz (17.1-18.4dB), 6kHz (16.7- 18.8dB).  Threshold hearing values were found in tractor drivers compared to controls for the frequencies 3-6kHz, occupational noise exposure led to NIHL. Noise and Hearing Loss in Farming  page 39 of 69   39 Author Date Purpose Design Population  Exposure Method Result Sullivan 1980 To monitor noise exposure in typical agricultural operations. Noise survey. 67 employees of 6 Nebraska farms Tractors and farm equipment. 1 year of dosimetry measurements and spot checking with sound meters. Average noise dose exceeded 85dBA on 17% of the 10,855 days measured. Tractors and self propelled machines without cabs were at or near 90dBA, both combines and forrage choppers (with cabs) were above 90dBA and run for up to 16 hours per day.  Assuming results are generalizable, 6-18% of all farm employees will incur hearing loss by the end of their working life. Troester 1970 To examine hearing loss associated with noise exposure. Cross- sectional survey 60 tractors drivers. Tractors. Measured noise and vibration levels for tractors.  Used audiograms of personal hearing. Noise levels from almost ALL tractors were above 85dBA.  Hearing loss increased with number of years worked, greatest for 5-10 and 10+years worked. Venable 1994 To provide detailed documentation of noise exposure. Noise survey Farm workers 3 noisy agricultural settings: mowing with tractor, using power hand tools, and construction of grain drying operation. Measured noise levels and simultaneously collected videotape of work activities for 30 minute periods. Reported min, max and average noise levels for each situation.  The combination of audio and video is useful to identify activities with greatest contribution to worker exposure. Noise exposure for tractor operation (no cab) was consistent 85 dBA, grain storage construction noise levels were variable- maximum noise level associated with electric wrench.  Noise and Hearing Loss in Farming  page 40 of 69   40 Appendix 4:  Noise Control Studies Table Author Date Control Method Product Name Purpose Method Result Botteldooren 1993 Active Noise Control   To introduce new tool for ANC which allows simultaneous analyses of digital electronics, and to apply it to a simulated cab noise situation. New combined approach of finite different time domain- digital signal processing simulation.  Measured noise levels in the driver cabin of large agricultural machines. New design suited to closed cabs. Carletti 2003 "Noise solutions"   To test the effectiveness of noise solutions to reduce noise of engines and engine cooling systems for small agricultural machines. Determine effectiveness of different cooling systems and modified engines on test bench.  Of these, tested the best solutions on 2 small agricultural machines, comparing standard component with modified  component.  Carpenter 2002 PPE (including HPD)   To describe HPD use. Cross-sectional, mail-out survey of 2483 farmers in US, with telephone follow- up Farmers reporting ‘never or rarely’ use of earmuffs was 78% and of earplugs 72%. Emme 1972 Cab Design   To discuss the noise control design considerations for cabs, because "quite cabs begin at the design stage". Review in the areas of: structural design, sealing, cab absorption, cab transmission loss, lever and mechanism design. Specific examples of noise controls and subsequent noise reduction. Hakimi 1973 Resilent (anti- vibration) mounts for tractors   To determine the effect of tractor mount design on noise, vibration and safety of tractor. Measured noise levels at operators ear for 6 mount designs on 4 cylinder tractor operated at full speed.  Also tested vibration levels and impact tests of safety frames. Most effective mounts reduces noise by 5 db Noise and Hearing Loss in Farming  page 41 of 69   41 Author Date Control Method Product Name Purpose Method Result Hansson 1996 Vibration control for tractors- by cab suspension   To describe the design of an active cab suspension to minimize vibration exposure, and evaluate performance losses under different conditions. Mounted cab on suspension and simulated different observer states, damping potentials and power consumption over different ground surfaces Vibration damping potential for active suspension better than passive suspension. Hari 1999 Tested prototype cab and used sound absorbing materials   To characterize noise levels inside prototype cab. Measured noise levels with windows open and closed, and with/without sound insulating materials.  Also evaluated safety structure, suspension and materials. All measured data were within allowable limits.  Interior noise level most dependant on whether front panel window (over engine) is open or closed. Foam inside mudguards and isolation floor coats reduced noise level. Harris  1979 Insulation, mufflers, enclosures, barriers JI Case 90 series tractor non-cab 4 post ROPS To discuss the noise control technology applied to non-cab tractors in order to achieve <90 dBA exposure. Used "sound source analysis" to determine areas of noise exposure. Addressed reverberation (with sound insulation material), cooling system (airflow, fan speed), exhaust (muffler, and sound insulation material), engine noise (enclosure and barriers), engine structure and hydraulic noise (fiberglass mount), and intake. Achieved noise reduction in a cost effective manner. Hattori 2001 New alloy for circular saws SUS430 (ferritic stainless steel) To find a steel alloy for circular saws that is strong, readily available, and produces relatively little whistling noise. Tested saws made of SUS 430 (stainless steel) with SKS5 (alloy tool steel) and SIA (Silentalloy- previous quiet option) in terms of idling noise levels at rotational speeds ranging from 1000- 5000 rpm. Silentalloy saw is effective at reducing whistling noise, but has low strength and limited availability.  Whistling suppression performance/ noise levels for the SUS430 saw were shown to be similar to Silentalloy saws in idling. Koopmann 1978 cab   To review the physical mechanism of the production of low frequency tones in cabs, and to describe methods for source identification correcting the problem.   Includes case study Noise and Hearing Loss in Farming  page 42 of 69   42 Author Date Control Method Product Name Purpose Method Result Lague 1992 Ear plugs, ear muffs and both   To demonstrate a method to determine the level of protection associated with HPD, and evaluate effectiveness in agricultural setting. Reported sound levels over a range of frequencies for exposure to chainsaw and tractor, without HPD, with ear plugs, with ear muffs, or with both. HPD is generally enough to get noise exposure to safe levels Lupescu 1999 Hearing conservation program   To evaluate the success of education and hearing screening program initiated for agricultural industry in Saskatchewan. Program: phase 1- educational resource, phase 2- completion of noise exposure questionnaire and free hearing screening. Program feedback: 16% of those who received educational package replied to request and audiogram.  Of those tested, 29% had ‘normal’ hearing.  87% men said exposed to noise on farm, but only 47% wore HPD.  Program evaluation: program had better than anticipated response, achieved goals, and reasonable costs. McCullagh 2002 HPD   To describe HPD use Descriptive correlational design, interviews with 167 farmers, using Pender Health Promotion model. Questions asked the % of time using HPD when exposed to high noise in field, shop or grain-handling facility. Overall HPD use 17%.  Not related to age, gender farm role or operation size. Related to interpersonal support, barriers, and situational influences. McKibben 1971 Noise control in new cab design using: Modular concept, Isolation mounts, Nonparallel sides, Isolated roof, Acoustical headliner, and Floor Mat White Farm A4T Tractor with modular cab To design an improved modular cab that has good noise, environmental and performance control, and ease of production.  Aim to reduce major noise sources in cabs: airborne noise which is transmitted through openings in the firewall and platform, and to reduce noise which is mechanically transmitted. Tested noise levels at 50, 75 and 100% operation for White Farm A4T diesel and other commonly used cabs. Conventional cab has sharp peak of 96 dB, whereas A4T cab has only 84 dB peak.  Graphs show dB vs. frequency for conventional cab, modular cab, and no cab. Noise and Hearing Loss in Farming  page 43 of 69   43 Author Date Control Method Product Name Purpose Method Result Peng 2000 Active Noise Control ANC and TMS320C25 high-speed digital processor. To improve on ANC technology by incorporating RLS (recurrent least square) in ANC Measured noise levels for system on tractor (outdoors), with 2 speakers to generate control sound and microphones to represent operator's ear. Overall sound pressure decrease 5-6 dB, with maximum of 18 dB using the feedback-RLS system.  However RLS system not highly accurate and sensitive to calculation errors.  Also, measurements were only at 500 Hz due to processor limitations (but above this passive noise control suitable). Pessina 2000 Earplugs (54 types), earmuffs (40) and ear canal caps (27)   To measure noise levels of 60 used tractors and to ascertain what protection HPDs could provide for driver exposure. For each of the 121 HPDs, calculated single number rating (SNR) from reported mean attenuation and SD over all octave bands.  Measured noise levels at driver's ear on stationary and moving tractor operating at max speed. Simulated the use of each of the 121 HPDs for noise levels of each of the 60 used tractors. Average noise levels on used tractors is 87-88 dBA (max 101).  Theoretical reduction with HPDs could be 10 dBA. Attenuation effectiveness of HPD depends on the individual, and how they wear it. The best HPD is the one that is comfortable, effective and has minimal impact on communication.  Earplugs seem more suited to tractor drivers than earmuffs. Proulx 2004 New cutting line for weed- cutters   To design a flexible cutting line for weed- cutters that is less noisy that current designs, and also is durable and cheap to manufacture.   Describes design. Schenker 2002 PPE (including HPD)   To describe self- reported exposure to noise and use of PPE by farmers, and to explore determinants of exposure Cross-sectional, telephone survey of 1947 farmers Farmers reported working in noisy situations 10% of day.  22.8% wore HPD>50% of time, and 56.3% reported ‘rarely or never’.  HPD use associated with young age, male sex, fewer cigarettes smoked, and non- administrative farm jobs. Concern about hearing loss was predictor. Noise and Hearing Loss in Farming  page 44 of 69   44 Author Date Control Method Product Name Purpose Method Result Talamo 1979 Hearing defenders, cabs   To examine the effects of cab noise environments to (a) measure relative effects of cab attenuation and noise masking and (b) measure the ability of drivers to perceive direction and origin of warning shouts. Attenuation study: Five drivers were used for study- 2 with normal hearing, 3 with some form of hearing loss.  Pure octave tones were projected through loudspeaker and study measured driver's noise perception from inside cab for 4 tractors with engine (a) running and (b) not running.  Direction: Four drivers with normal hearing were used in study. While drivers performed simulated task, 8 shouts were projected from 8 possible directions.  Drivers reported origin of percieved shouts. Cabs and HPD have minor effect on tonal signal delectability. Low probability of driver hearing warning from >3m. HPD use increases directional errors. Wadud 1998 HPD   To identify the beliefs and practices related to the prevention of 3 farm-related occupational diseases, included noise induced hearing loss. Mail-out survey of 300 randomly selected farmers in central Missouri. Primary outcome was the association between farmers' beliefs and their work safety practices.  Also evaluated perceived barriers to preventive action. Farmers who believed that hearing loss was preventable were more likely to use HPD.  Most common perceived barriers to HPD: not convenient; not bothered by noise; need to hear machinery. Recommendations for development of Health Promotion Programs: address belief that farmers do not have control over adverse life events; address reported barriers to implementation; use existing (trusted) communication channels to get the messages to farmers. Walker  1970 Cabs   To describe noise exposures from different tractors, factors affecting noise and noise control options. Test noise levels of tractors with no cab, with partial cab, and with cab. Important data on tractors are effectiveness of muffling, type of engine (gas, diesel (subtypes of diesel)), engine operating speed, fan design and output, engine speed. Noise and Hearing Loss in Farming  page 45 of 69   45 Author Date Control Method Product Name Purpose Method Result Yoshida 1995 Active Noise Control 2 Japan-made tractors, no cab To introduce an ANC system, and to compare ANC to convention methods of sound absorption/insulation. Simulations to measure the effect 3 ANC systems on 2 tractors. ANC could reduce exposure by 15 dB. Efficient in reducing noise in low frequency up to 500 Hz; limited utility in high frequency.  Recommend to use in conjunction with conventional treatment. Zawieska 2004 Active Noise Control   To review progress of ANC in Poland.   ANC effective for frequencies up to 250 Hz.  Need work above this.  Future efforts should focus on enhancing application range, and reducing ANC costs.           ACTIVE NOISE CONTROL COMMUNICATION HEADSETS FOR THE ENTERTAINMENT INDUSTRY  August 2005      Prepared for: Safety and Health in Arts Production and Entertainment (SHAPE) Suite 280 - 1385 West 8th Avenue Vancouver, BC V6H 3V9 Prepared by: Jadine Thom, Cheryl Peters,  Elaina McIntyre, Meghan Winters, Kay Teschke, Hugh Davies* School of Occupational and Environmental Hygiene 2206 East Mall Vancouver, BC V6T 1Z3  *Corresponding author   Noise and Hearing Loss in Farming  page 47 of 69   47 Executive Summary  This literature review was produced at the request of SHAPE, the association for Safety and Health in Arts Productions and Entertainment.  SHAPE asked us to provide information on state of the art techniques in reducing noise exposure.  We conducted a systematic and comprehensive review of the scientific literature with respect to two methods: (1) controlling noise exposure, via active noise control headsets (the subject of this report) and (2) reducing hearing damage, via pharmaceutical interventions (the subject of a short report titled “Drug Treatments for Hearing Loss”, which follows).  Active noise control (ANC) headsets are very similar to regular communication except that they have built in active noise control systems that reduce the amount of ambient (unwanted) noise. In an ANC headset, a small microphone on the outside of the headset picks up the unwanted, external noise, and instantaneously emits a counter-signal that cancels it out, leaving only the desired communication signal.  ANC devices are primarily used today by aircraft pilots. However they have been tested in other occupations characterized by high levels of background noise and the need for accurate communication. These devices may be able to reduce the ambient noise in entertainment work environment, thus increasing speech intelligibility, and potentially lowering damaging noise at the ear.  This report provides a technical background to the concept of active noise control, discusses its use in the entertainment industry and provides guidance on how to select the appropriate device.  Noise and Hearing Loss in Farming  page 48 of 69   48 Table of Contents   Executive Summary ..................................................................................................................... 47 Table of Contents ......................................................................................................................... 48 Introduction .......................................................................................................................................... 49 What is active noise control? ............................................................................................................... 49 Active noise control headsets ............................................................................................................... 51 How might active noise control communication headsets be useful in the entertainment industry? ................................................................................................................................................................ 53 Is your unwanted noise external background noise?..........................................................................................53 Is your unwanted noise emitted by the headset? ................................................................................................56 Summary ............................................................................................................................................... 56 Acknowledgments..............................................................................Error! Bookmark not defined. References………………………………………………………………………………………...15 Appendix 1: Literature Search Strategy...................................................................................... 60 Appendix 2: Summary of articles that assessed noise exposure from headsets ........................ 61 Appendix 3: Summary of ANC headset articles ......................................................................... 64 Noise and Hearing Loss in Farming  page 49 of 69   49 Introduction   Is your current communication headset not working out for you?  Do you find yourself raising the volume on your headset in order to hear the person with whom you are trying to communicate?  Then, perhaps you will find this report useful.  It describes active noise control and how it is currently being used in headsets to reduce the ambient noise from your surroundings, enabling you to lower the volume on your headset, reducing your noise exposure from your ambient surroundings and from the headset itself, and lowering your risk for developing noise-induced hearing loss.  By the end of this report, you should understand the principle behind active noise control and how it is being employed in communication headsets.  You will then be able to make an informed decision, based on your type of noise exposure, about whether an active noise control headset is right for you, and which type might be best for your work situation. What is active noise control?   In order to understand how an active noise control communication headset may be useful it is first necessary to explain what active noise control is and how it works.   Sound, as you may know, has wave-like properties when it travels through air.  Just like the waves that roll up onto the beach, sound waves have crests and valleys.  How tall and how deep those crests and valleys are will determine the amplitude and loudness of the sound.  Sound waves that are very tall and deep will be very loud, and sound waves that are short and shallow will be very quiet (Figure 1).  Figure 1 - Low amplitude (quiet) sound waves compared to high amplitude (loud) sound waves   Noise and Hearing Loss in Farming  page 50 of 69   50 The distance between the crests and valleys will determine the frequency, or what is commonly known as the pitch of the sound.  If the waves are squished together, the sound will be very high pitched and squeaky and if the waves are stretched out, the sound will be low pitched, like a low hum (Figure 2).  Figure 2 - High frequency/pitch sound waves compared to low frequency/pitch sound waves   If there are two sound waves present, the waves overlap and “interfere” with each other.  When the two waves have the same frequency and directly overlap (i.e. they have the same phase) the result is constructive interference and the noise will double in amplitude.  However, if the two waves have the same frequency and amplitude but they are shifted slightly in time (i.e. they are “out of phase”), then the waves cancel each other out and you get destructive interference. The result of destructive interference is that no noise (or sound) will be heard (Figure 3).  Active noise control uses destructive interference to cancel out unwanted noise.  The frequency, amplitude and phase of the undesired sound are measured and another sound of the same frequency and amplitude but opposite phase is created.  When destructive interference occurs, noise is reduced.  Therefore, in order for active noise control to function, it is necessary to know the frequency, amplitude and phase of the undesired sound. Active noise control works best for cancelling lower frequency sounds that are continuous; higher frequency and impulse sounds are hard to control.  Noise and Hearing Loss in Farming  page 51 of 69   51 Figure 3 - Constructive interference compared to destructive interference   Active noise control headsets  Active noise control headsets are very similar to regular communication headsets (i.e. one or two-way communication) except that they have built in active noise control systems that reduce the amount of lower frequency ambient noise (i.e. the noise created by surroundings) so that the wearer will be able to better hear the higher frequency sound and speech that is being transmitted to the headset.  These headsets are available commercially and are produced by several companies for a variety of industries.  They also come in a variety of styles, from those that only cover part of the ear, to those that surround the entire ear, like an ear muff hearing protector. (Behar 2001) The latter type of headset is more useful because they can reduce the noise produced by sounds across a spectrum of frequencies (a.k.a. broadband noise).  With the active noise control turned off, the headset functions similarly to an ear muff hearing protector, which decreases the sound in the high frequency range (high pitched sounds).  This can be seen in Figure 4 taken from Feist, Mongeau et al. 2001. It shows three sound traces: ƒ The uncontrolled sound (solid line) ƒ The sound experienced while wearing the ANC headset, but with the ANC function turned off (dashed line) ƒ The sound experienced while wearing the ANC headset, but with the ANC function turned on (dotted line) Sound is on the vertical axis and frequency is located on the horizontal axis. Noise and Hearing Loss in Farming  page 52 of 69   52  Figure 4 - Effect of ANC headset on sound levels   So how does the active noise control system know the all important characteristics of the noise it is trying to reduce such as the frequency, amplitude and phase as discussed in the previous section? Well, there are essentially two types of active noise control (ANC) that are currently being researched, each with their own advantages and disadvantages.  These two types are “feed-forward ANC” and “feed-back ANC”. (University of Twente 2005)  In feed-forward ANC, the system is programmed to cancel out a specific noise.  That is, the frequency and amplitude of the sound are known, and they can be programmed into the system and a secondary noise is created which cancels out the first noise. (Pawelczyk 2003) This type of ANC is most useful when the noise exposure is continuous and predictable.  An example of such noise may be the noise created by the vibration of a tractor. (University of Twente 2005) Headsets of this type are not appropriate if the unwanted external noise is being created by a moving source as the amplitude of the noise will not consistent in this circumstance – it will vary as the distance between the source and the receiver changes. (Gan and Kuo 2002)  In feed-back ANC, a small microphone located on the earshell of the headset picks up the signal of the external noise.  This signal from the primary noise is analyzed for its frequency, amplitude and phase, and a secondary noise is created by the system that will result in destructive interference and cancel out the noise.  This type of ANC is most useful when the noise you are attempting to reduce is broadband or unpredictable in terms of frequency or amplitude.  It is a more accurate noise cancellation method than feed-forward ANC. You can have different signals being received and processed at each ear. (Gan and Kuo 2002)  It is also considered to be cheaper and more compact than feed-forward ANC. (Gan and Kuo 2002)  Figure 5 was taken from Gan and Kuo 2002 and shows the basic setup of a feed-back ANC system.  However, it may be possible to get the best of both worlds.  Researchers are currently looking at combining the two systems (feed-forward and feed-back) in a single headset.  The feed-back control is thought to reduce broadband noise while the feed-forward system reduces periodic noise. (Rafaely and Jones 2002)  It may also be possible to get ANC headsets that control the noise that is Noise and Hearing Loss in Farming  page 53 of 69   53 transmitted to the ear from vibration of the earshell using vibration actuators which produce a force that opposes the earshell vibration. (Rafaely, Carrilho et al. 2002)  Figure 5 - Basic setup of a feed-back ANC headset  How might active noise control communication headsets be useful in the entertainment industry?  Now who might benefit from ANC communication headsets?  To date, they have been used primarily by airplane pilots to reduce low frequency aircraft noise (Gower and Casali 1994; Giguere, Abel et al. 2000). They have also been tested by tollbooth operators for their ability to reduce traffic noise (Feist, Mongeau et al. 2001).  Table 2 in the Appendix provides more detail on the studies that have been conducted assessing noise exposure from headsets.  However, it seems completely plausible that ANC communication headsets, particularly those that are regulated by feed-back mechanisms, would be of use in the entertainment industry.  They may be able to reduce the ambient noise on movie sets for example, thus increasing the wearer’s ability to hear and understand the conversation being communicated through the headset itself, often referred to as speech intelligibility.  Although no studies have been conducted to date on the noise exposure from communication headsets in the entertainment industry, it is suspected that noise exposure may take one of two forms.  Either the unwanted noise is loud ambient noise that is interfering with speech intelligibility or the unwanted noise is created by the headset itself (e.g. from feed-back or static).  In order to determine if active noise control will be useful in your particular work situation, you will need to understand the nature of the source of the noise, and whether its frequency is low or high.  Is your unwanted noise external background noise?  In the first case where the unwanted noise is external background noise, the problem can be solved using active noise control.  In such instances, it will be necessary to conduct a noise survey to assess your exposure to noise.  In particular you will want to know the frequency range and the loudness of your noise source or sources, and whether or not the sound varies for any reason – for example is it stationary relative to your position. Noise and Hearing Loss in Farming  page 54 of 69   54 Are the frequency and amplitude variable?  Is the distance between you and the noise source changing?  If you find that the noise has varying frequency and amplitude, or that you or the noise source move around a lot, then feed-back ANC headsets will likely be more useful.  It is expected that most of the situations that you will encounter in the entertainment industry will fall in this category (e.g. loud explosions or people talking around you).  As can be seen from Table 1 below, there are many feed-back ANC headsets available commercially.  Of these, the David Clark website is the easiest to navigate, and their headsets come in a variety of styles for a number of different uses.  However, some of these manufacturers only produce ANC headsets for the airline industry.  It may also be possible to modify an existing headset by fitting a microphone inside the earshell connected to an analog feedback control circuit.  The Lectret headset was modified in this manner. (Rafaely and Jones 2002) Are the frequency and amplitude of the noise constant?  Is the distance between you and the noise source consistent?  If you find that the noise is relatively constant in frequency, loudness and distance, then a feed- forward ANC headset may provide adequate protection. Most situations in the entertainment industry will not fall under this category.  However, if you find that you are exposed to this kind of noise, feed-forward headsets are also available commercially, possibly by some of the same manufacturers that are listed in Table 1.  If you would like to read about further studies that have evaluated, tested or produced ANC communication headsets, then refer to Table 3 in the Appendix. (Note: This table has a high level of detail and is intended for those readers with a good understanding of noise and active noise control.) Noise and Hearing Loss in Farming  page 55 of 69   55  Table 1 - ANC headsets that have been identified in the scientific literature and reference websites where more information (e.g. prices) may be obtained Headset Description and performance Reference Website ANVT Supra-aural headset with ANC at 70-400 Hz, and passive noise control above 3000 Hz (Zera, Brammer et al. 1997) n/a Bose Aviation headset circumaural headset designed for aviation industry, feedback ANC (Gower and Casali 1994; Giguere, Abel et al. 2000) http://qualitysound.bose.com/headsetx_headset_ind ex.htm David Clark H1013X/DCNC unknown (Giguere, Abel et al. 2000) http://www.davidclark.com/ QuietMan headset by MNC circumaural headset with attenuation of frequencies below 1000 Hz (Zera, Brammer et al. 1997) n/a Noise Control Technology Group Feed-back (Feist, Mongeau et al. 2001) http://www.nctgroupinc.com/nbex.htm Peltor 7004 circumaural headset, attenuates frequencies below 300 Hz (Zera, Brammer et al. 1997) discontinued product Peltor ANR Aviation headset active personal hearing protection device (Giguere, Abel et al. 2000) Sennheiser NoiseGard Feed-back (Giguere, Abel et al. 2000) http://www.pilotstuff.com/Sennheiser.html TechnoFirst NoiseMaster unknown (Giguere, Abel et al. 2000) http://www.volez.com/store/article.tpl?ref=TECH FIRST_CASQUE1 (in French) Telex ANR 4000 Feed-back (Giguere, Abel et al. 2000) n/a  Noise and Hearing Loss in Farming  page 56 of 69   56  Is your unwanted noise emitted by the headset?  If the unwanted noise is more akin to the second case where the noise is being emitted by the headset itself, then active noise control may not be as useful.  Several noise exposure studies have been conducted on call centre operators and telephone operators who may be exposed to noise from fax machines or acoustic feedback through their headsets. (Macrae 1995; Brueck 2003; Peretti, Pedrielli et al. 2003; Bayley 2004) In one particular study, the noise exposures of 150 call centre operators were measured. (Patel and Broughton 2002) Although the authors concluded that the call centre operators had a low risk of hearing damage from their occupational noise exposure they did suggest that the instalment of acoustic shock limiters may reduce their noise exposures.  Acoustic shock limiters control noise in the form of short sound bursts.  Discussions of this method of noise control go beyond the scope of this report, but the authors refer to the work of a group of scientists in Australia that may provide more information and that are studying the adverse health effects of these acoustic shock events. (Milhinch and Doyle 2000; Patuzzi, Milhinch et al. 2000)  Summary   The following is designed to assist in choosing the appropriate noise control strategy for your headset noise problem. Figure 6 - Picking the appropriate noise control strategy   Noise and Hearing Loss in Farming  page 57 of 69   57   In conclusion, now that you know what active noise control is and how it works in ANC communication headsets, you should now be able to decide if an ANC communication headset will work for your particular headset noise exposure problem, and which one you should consider buying or modifying.  Acknowledgements We would like to acknowledge the guidance and advice provided by Ms. Linda Kinney of SHAPE, and comments and suggestions of Ms. Ingrid Turk. Noise and Hearing Loss in Farming  page 58 of 69   58 References  Bayley, A. M. W. (2004). "Acoustic limiting in telephony headset systems." Acoustics Bulletin 29(5): 22. Behar, A. (2001). "Testing of ANR (active noise reduction) headsets." Canadian Acoustics 29(3): 52. Brammer, A. J., D. R. Peterson, et al. (2004). "Maintaining speech intelligibility in communication headsets equipped with active noise control." Canadian Acoustics - Acoustique Canadienne 32(3): 132. Brueck, L. (2003). "Measurement and Instrumentation Group: Call Centres - A Measurement Headache." Acoustics Bulletin 28(5): 7. Campbell, R. H. (1975). "Electroacoustic properties of noise attenuating headsets." Journal of the Audio Engineering Society 23(10): 806. Cartes, D. A., L. R. Ray, et al. (2002). "Experimental evaluation of leaky least-mean-square algorithms for active noise reduction in communication headsets." Journal of the Acoustical Society of America 111(4): 1758. Cartes, D. A., L. R. Ray, et al. (2002). "Low frequency acoustic test cell for the evaluation of circumaural headsets and hearing protection." Canadian Acoustics 30(1): 13. Cui, J., A. Behar, et al. (2003). "Insertion loss testing of active noise reduction headsets using acoustic fixture." Applied Acoustics 64(10): 1011. Dajani, H., H. Kunov, et al. (1996). "Real-time method for the measurement of noise exposure from communication headsets." Applied Acoustics 49(3): 209. Feist, J. P., L. Mongeau, et al. (2001). "Tollbooth operators' response to traffic noise and the performance of an active noise control headset survey results: Survey results." Transportation Research Record(1756): 68. Gan, W.-S. and S. M. Kuo (2004). Integration of virtual bass reproduction in active noise control headsets, Beijing, China, Institute of Electrical and Electronics Engineers Inc., Piscataway, NJ 08855-1331, United States. Gan, W. S. and S. M. Kuo (2002). "An integrated audio and active noise control headset." IEEE Transactions on Consumer Electronics 48(2): 242. Gan, W. S. and S. M. Kuo (2003). Integrated active noise control communication headsets, Bangkok, Thailand, IEEE. Giguere, C., S. M. Abel, et al. (2000). "Binaural technology for application to active noise reduction communication headsets: design considerations." Canadian Acoustics 28(1): 3. Gower, D. W., Jr. and J. G. Casali (1994). "Speech intelligibility and protective effectiveness of selected active noise reduction and conventional communications headsets." Human Factors 36(2): 350. Macrae, J. H. (1995). "Hearing conservation standards for occupational noise exposure of workers from headphones or insert earphones." Australian Journal of Audiology 17(2): 107. Milhinch, J. and J. Doyle (2000). Acute aural truama in headset and handset users. 14th National Conference of the Audiological Society of Australia, Adelaide, Australia. Patel, J. A. and K. Broughton (2002). "Assessment of the noise exposure of call centre operators." Annals of Occupational Hygiene 46(8): 653. Patuzzi, R. B., J. Milhinch, et al. (2000). Acute aural trama in telephone headset and handset users. NeuroOtological Society of Australia National Conference, Melbourne, Australia. Pawelczyk, M. (2002). "Analogue active noise control." Applied Acoustics 63(11): 1193. Pawelczyk, M. (2002). "Feedforward algorithms with simplified plant model for active noise control." Journal of Sound and Vibration 255(1): 77. Noise and Hearing Loss in Farming  page 59 of 69   59 Pawelczyk, M. (2003). "A hybrid active noise control system." Archives of Control Sciences 13(49)(2): 191. Peretti, A., F. Pedrielli, et al. (2003). "Headphone noise: Occupational noise exposure assessment for communication personnel." Acta Acustica (Stuttgart) 89(SUPP): 49. Rafaely, B., J. Carrilho, et al. (2002). "Novel active noise-reducing headset using earshell vibration control." Journal of the Acoustical Society of America 112(4): 1471. Rafaely, B. and M. Jones (2002). "Combined feedback-feedforward active noise-reducing headset- The effect of the acoustics on broadband performance." Journal of the Acoustical Society of America 112(3): 981. Ritter, D. C. and J. L. Perkins (2001). "Noise-induced hearing loss among U. S. Air force cryptolinguists." Aviation Space & Environmental Medicine. Vol. 72(6): 546-552. Savell, J. F. and M. T. Boothby (1996). Noise exposures from earphones, Bellevue, WA, USA, Inst of Noise Control Engineering, Poughkeepsie, NY, USA. University of Twente, D. o. M. E., Laboratory of Mechanical Automation. (2005). "Course notes: 113172 - Advanced motion and vibration control. Chapter 2: Theory of active noise control." Retrieved May 23, 2005, from http://www.wa.wb.utwente.nl/Lectures/113172/avicrdr.pdf. Williams, W. and J. Presbury (2003). "Observations of noise exposure through the use of headphones by radio announcers." Noise & Health. Vol. 5(19): 69-73. Zera, J., A. J. Brammer, et al. (1997). "Comparison between subjective and objective measures of active hearing protector and communication headset attenuation." Journal of the Acoustical Society of America 101(6): 3486. Noise and Hearing Loss in Farming  page 60 of 69   60 Appendix 1: Literature Search Strategy  Four bibliographic databases were used to identify the literature for this review: PubMed, CCINFOWeb, Compendex/Inspec, and Web of Science.  PubMed, produced by the U.S. National Library of Medicine, specializes in health literature. CCINFOWeb, produced by the Canadian Centre for Occupational Health and Safety, specializes in occupational health and safety literature. Compendex contains information on engineering, and some noise measurement papers were located using this database. The search was conducted in February 2005 and employed combinations of the following keywords: noise and exposure, headphones, headsets, earphones, cryptoling*, hearing protectors, active noise control. In addition, a significant portion of the literature cited within this review was identified through pearling, or hand searching of references found within other papers. We excluded articles which were written in languages other than English and French. Finally, with respect to potential control measures, a Patent search was conducted using similar search terms.  Noise and Hearing Loss in Farming  page 61 of 69   61 Appendix 2: Summary of articles that assessed noise exposure from headsets  Author & Date Publication type Purpose Population Method Results Comments (Macrae 1995) Primary To determine an optimal method for measuring noise exposure at the eardrum to telephonists that use headphones or insert earphones while working telephonists  Proposes two methods for measuring noise from the earphones at the eardrum, a probe-tube microphone inserted into the ear canal and a coupler   Identifies telephonists as an at risk group, and lists Australian OEL for noise exposure at the eardrum (8hr-LeqA = 90 dB, and Lpeak of 143 dB) (Dajani, Kunov et al. 1996) Primary Measurement on noise exposure from communication headsets on an acousto-mechanical mannequin head. Method validation on human subjects in real-world applications mannequin head, 8 industries: air traffic controllers, telephone operator, reservations operators, telephone cable maintenance workers and airport ground crew For human measurements, measured noise levels under the headset (variety of types) with microphone and environmental noise was measured with a sound level meter People that worked in the airport had higher Leq8hr than office or street setting.  High environmental noise may contribute to noise exposure becasue it causes workers to increase levels so that they can hear.  Greater attenuation with modified circumaural hearing protector Looked at noise exposure from the headset itself and from the environment (Williams and Presbury 2003) Primary noise exposure from headphones that allow monitoring of broadcast transmission and receive information from program producers radio announcers (12) During broadcast, an identical headphone was set up in parallel on an artificial ear connected to a sound level meter Most not exposed to high noise exposures but some do have high noise exposures (Leq up to 95 dB) Radio announcers may be a special case because they are using headphones to monitor their own quality of voice transmission Noise and Hearing Loss in Farming  page 62 of 69   62 Author & Date Publication type Purpose Population Method Results Comments (Patel and Broughton 2002) Primary To measure noise exposure of call centre operators Call centre operators (150) An identical headphone was set up in parallel on a KEMAR mannequin connected to a microphone at the eardrum.  Only measured in left ear. Right ear was sealed.  Background noise levels were measured but not incorporated into estimate of Leq because not considered to be significant contribution Noise exposure unlikely to exceed 85dBA, risk of hearing damage is low.  Higher exposures from fax tones, holding tones and high pitched tones from mobile phones (but shorter in duration so don't contribute much to overall exposure) Large sample size. In discussion, mentions some control strategies:  acoustic shock limiters (short sound bursts) (legal requirement DTI 85/013).  Refers to work of Patuzzi (2000) and Milhinch and Doyle (2000) who are studying health effects of acoustic shock events. (Ritter and Perkins 2001) Primary To assess noise induced hearing loss in US air force cryptolinguists Crypto-linguists (120) Compared 1998 audiogram to reference audiogram and to enlistment audiogram. Since incidence of PTS may exceed 3%, may signal that HCP is ineffective Did not measure noise exposure itself. (Brueck 2003) Conference summary (Measureme nt and instrumentati on group) review of presenters at the conference call centre operators  (Peretti, Pedrielli et al. 2003) Primary headphone noise exposure telephone operator head and torso simulator in 3 different workplace settings Some workers may be at risk for hearing loss  Noise and Hearing Loss in Farming  page 63 of 69   63 Author & Date Publication type Purpose Population Method Results Comments (Savell and Boothby 1996) conference proceedings to assess the noise exposure of workers given personal (music) radio headsets, especially worried about workers that raise the volume of their headsets in order to hear over background noise levels two groups control and treatment (i.e. headset with adjustable volume) Headsets were of two types: walkman with headphones and headsets with radio incorporated into the headset, and were measured on artificial test fixture May result in overexposure (based on OSHA criterion of 80 dB), if headphones are turned up to highest volume for the entire 8 hour workday (range of 90 to 99 dBA TWA) Authors did not expect the headphones to attenuate any of the background noise (not even passively).  In fact, specifically avoided earmuff type headsets because they attenuate the noise.   Noise and Hearing Loss in Farming  page 64 of 69   64  Appendix 3: Summary of ANC headset articles  Author Publication type Control type Product(s) Theory/Purpose Methods Results Comments (Bayley 2004) (representa tive from Plantronics ) Review Telephone headsets, acoustic limiting Mention Plantronics as a manufacturer for these devices Noise spikes may occur in cordless telephones (analogue, digital or Voice- over-IP), longer duration noises from fax or DTMF tones, acoustic feedback or network faults.   Acoustic limiting in cordless and mobile phones puts a limit on the voltage that can be transmitted through the telephone headset. This technology is more useful if the noise is being emitted from the headset itself rather than exterior to the headset (ambient noise).  Also could this technology be adaptable from telephones to sound attenuating headsets? (Behar 2001) Primary ANR headsets one supra-aural headset, 2 circumaural headsets, one flying helmet (No brands/models specified) To compare insertion loss that is achieved from the different headset designs Acoustical test fixture (artificial head) which allows for measurement of insertion loss.  Pink noise emitted by loudspeakers in audiometric cabin circumaural headsets seem to provide greater total insertion loss (approximately 15 dB below 500 Hz) than supra-aural (4 dB below 500 Hz)  (Brammer, Peterson et al. 2004) Primary ANR headsets one feedback control headset and one feedforward control headset (brands/model not specified) Comparison of the ability of the two headsets to maintain speech intelligibility Headsets are worn by human or mannequin and noise reduction is measured using microphone inserted under earmuff.  Speech transmission index (STI) was used to determine speech intelligibility. In feedback control system, when input mic is located under the earmuff there is cancellation of noise and speech.  Not a problem with feedforward.  (Campbell 1975) Review noise- attenuating headset n/a n/a n/a n/a Describes how to measure effectiveness of noise- attenuating headsets:  acoustic attenuation, receiving sensitivity and frequency response of the headset, and microphone sensitivity Noise and Hearing Loss in Farming  page 65 of 69   65 Author Publication type Control type Product(s) Theory/Purpose Methods Results Comments (Cartes, Ray et al. 2002) J Acoust Soc Am Primary ANR headset modified prototype (Rockford Fosgate model FNQ1406) Comparison of algorithms to optimize stability and performance of ANR systems Headset is mounted with the earpieces on a flat plate in a low freq acoustic test cell and subjected to 4 noise sources. They were able to pick a candidate algorithm which resulted in overall stability and performance in measured and simulated ANR experiments. How accurate are flat plate measurements (our faces are not flat!)?  Not sure what the implications are since this is a theoretical evaluation more than an evaluation of the headset itself. (Cartes, Ray et al. 2002) Can Acoust Primary low frequency acoustic test cell   Describes the development of a low frequency acoustic test cell which can be used to evaluation circumaural ANR headsets  (Cui, Behar et al. 2003) Primary ANR headsets 5 types of headsets (brands/model s not specified) Measurement of insertion loss of ANR headsets using experimenter designed acoustic test fixture (mannequin)     This is a proposed method for the measurement of insertion loss that doesn't involve human subjects. (Feist, Mongeau et al. 2001) Primary active noise reduction headset Noise Buster Extreme open ear active noise control headphone, manufactured by Noise Control Technology Group Inc. To reduce low frequency ambient traffic noise levels through active noise control will reduce risk of developing hearing loss, increase speech intelligibility between attendant and customer and increase comfort level of attendant Using two questionnaires, evaluated subjective response of tollbooth operators to ambient noise (eg. traffic) with and without open ear active noise control headphone. Reduction in ambient noise but no increase in speech intelligibility. ANR headset attenuates noise in the low freq range (<500 Hz).  Headset itself (ANR off) attenuates noise in high freq range. Attendants did not find them to be comfortable and were unlikely to wear them while working. Subjective response to headsets (Gan and Kuo 2002) Review Integrated feedback active noise control headsets n/a n/a n/a n/a Easy to read, good background information.  Explains advantages and disadvantages of feedforward and feedback control systems. Noise and Hearing Loss in Farming  page 66 of 69   66 Author Publication type Control type Product(s) Theory/Purpose Methods Results Comments (Gan and Kuo 2003) Primary Integrated feedback active noise control headsets designed by the authors Describes the development and evaluation of an ANC headset Integrated system that has feedback control combined with off-line and on-line modelling of the secondary path (i.e. noise picked up from error microphone), additional adaptive filter that cancels near-end noise before sending it to the far end.  Had to develop algorithms to do this. Based on computer simulation results, was able to attenuate the background noise by more than 30 dB while enhancing the near-end speech level by more than 25 dB Disadvantage of combination analog feedback and digital feedforward is the limited flexibility of the analog filter. This system may be able to compensate for that. (Gan and Kuo 2004) Primary ANR headset with good bass reproduction not specified ANR attenuates low frequency environmental noise, but may also reduce wanted bass (esp in headsets for portable MP3 players, etc) Wubjective response to attenuation provided by headset when two sound tracks were played Practical, cheap, lightweight and effective, cancels noise and enhances bass  (Giguere, Abel et al. 2000) Review ANR headsets and binaural technology Peltor ANR aviation headset, Sennheiser NoiseGard, Bose Aviation headset, Bose Aviation Series II, David Clark DCNC headset, David Clark H1013X, Telex ANR headset system, Telex ANR 4000, TechnoFirst NoiseMaster Combination of ANR and binaural technology may allow for increase in speech intelligibility especially in aircraft cockpits none presented All headsets studied were analog, preferable to have digital because more compact.  More research needed. Binaural technology: signals are integrated from both ears Noise and Hearing Loss in Farming  page 67 of 69   67 Author Publication type Control type Product(s) Theory/Purpose Methods Results Comments (Gower and Casali 1994) Primary ANR and conventional headsets ANC headset - Bose Aviation, conventional - David Clark H10-76 comparison of an ANR and conventional headset to see if the ANR increases speech intelligibility and noise attenuation in environments with high ambient noise (eg. aircraft noise) Three headset configurations (ANR on, ANR off, and conventional) tested with pink (broadband) noise and M-2 Bradley Infantry vehicle (tank) (low freq bias esp at 50, 125, 250 Hz) noise emitted from loudspeakers in a lab on 9 subjects (6M, 3F) aged 19-26 Attenuation of noise with ANR headset, especially at low freq but no increase in speech intelligibility This experiment was conducted in a laboratory environment, therefore the real-world application is questionable (Pawelczyk 2002) Appl Acous Primary active noise reduction headset passive headset (Peltor H9A) equipped with loudspeaker (headphone) The authors modified a passive headset by equipping it with a loudspeaker to create an ANC headset, analog control Noise attenuation was measured using a Solartron-Schlumberger spectral analyser Attenuation of noise by 15-20 dB from 200-450 Hz.  Analog control is best for short distances between noise source an error microphone. Cheap to produce (approx 20 USD including passive headset). A highly technical review article. (Pawelczyk 2002) J Sound Vib Primary feedforward active noise control in active personal hearing protection device not commercially available, constructed by the author construction of an algorithm that will allow for attenuation of sound in APHPD quickly n/a Attenuation of 30 dB over freq range 100 to 550 Hz, adaptation takes about 0.1 s. Not sure if this device is commercially available yet…due to quick response, may be good for controlling periodic noise? (Pawelczyk 2003) Primary ANR headset with hybrid feedback control not commercially available, constructed by the author Investigation of a hybrid (analogue and discrete) feedback control system. Analogue controller attenuates broadband noise, and discrete controller attenuates dominant tones  Perform as expected. Excellent introduction on problems and issues surrounding ANR headsets. Noise and Hearing Loss in Farming  page 68 of 69   68 Author Publication type Control type Product(s) Theory/Purpose Methods Results Comments (Rafaely and Jones 2002) Primary Feedback- feedforward ANR headset modified Lectret ANR headset (circumaural with analog feedback control and digital feedforward control) Feedback control reduces broadband noise while feedforward reduces periodic noise One subject was fitted with headset and exposed to white noise that was passed through filters in range 200 to 900 Hz in reverberation chamber (reverberant sound field) and laboratory (direct sound field).  Noise measured with internal microphone. Good broadband sound attenuation in reverberant sound field regardless of subject position.  In direct sound field, best attenuation is achieved when the external reference mic is upstream of the propagating sound field. Requires modification of commercially available headset. Only one subject. (Rafaely, Carrilho et al. 2002) Primary ANR headset with earshell vibration control modified passive headset (JSP, model KMO7236) Additional noise that is transmitted to the ear via earshell vibration is reduced using vibration actuators which produce a force that opposes the earshell vibration instead of generating sound inside of the earshell as is the theory behind conventional ANR headsets Theoretical model was constructed to predict how changes to the headset (inertial force actuator or a force actuator) would cause a reduction in earshell vibration.  Followed up by experimental validation. The preferable configuration involves the placement of a force actuator between the headband and the earshell because it does not increase the inertial weight or compromise comfort. Requires modification of commercially available headset. Theoretical and laboratory based…real-world function? Noise and Hearing Loss in Farming  page 69 of 69   69 Author Publication type Control type Product(s) Theory/Purpose Methods Results Comments (Zera, Brammer et al. 1997) Primary ANC headsets Peltor headset (model 7004), Quietman headset by MNC, and NQ100 hearing protector by ANVT comparison of subjective (masked threshold, loudness balance) and objective (insertion loss) measures of active hearing protector and communication headset attenuation In an anechoic chamber, subject (n=7) was surrounded by 4 loudspeakers emitting broadband (25-20000 Hz) pink noise at a sound pressure level of 110 dB while wearing hearing protection device All three methods of measurement yielded similar results for Peltor.  Peltor headset: ANC works primarily below 500 Hz, max attenuation of 18 dB at 125 Hz, NQ100 hearing protector: max attenuation of 17 dB at 200 Hz, not very good at attenuation in the high frequency range (4000-8000 Hz), smallest attenuation of all devices, Quietman headset: ANC functions at frequencies below 1000 Hz, range in attenuation with different subjects and different measurement techniques Article has nice description and photos of all headsets.  Peltor: circumaural headset, large volume earcup, attenuates sound below 300 Hz. Quietman: circumaural headset, smaller volume earcup, lighter, attenuates sound below 1000 Hz.  NQ100:  supra-aural, lightweight, attenuates sound from 70-400 Hz (actively) and above 3000 Hz (passively)  

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