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Exposures and their control in radiographic film processing in British Columbia Teschke, Kay; Chow, Yat; Brauer, Michael; Chessor, Ed; Hirtle, Bob; Kennedy, Susan M.; Chan Yeung, Moira; Dimich Ward, Helen 2000

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Exposures and their Controlin Radiographic Film Processingin British Columbia                                                                                                                                                 Report to the Workers? Compensation Board of British ColumbiaFebruary 2000Kay Teschke1, Yat Chow1, Michael Brauer1, Ed Chessor1,3, Bob Hirtle1,Susan M. Kennedy1, Moira Chan Yeung2, Helen Dimich Ward21 School of Occupational and Environmental Hygiene, 3rd Floor, 2206East Mall, University of British Columbia, Vancouver, BC, Canada2 Respiratory Division, Department of Medicine, University of BritishColumbia, Vancouver, BC, Canada3 Engineering, Prevention Division, Workers? Compensation Board ofBritish Columbia, Richmond, BC, CanadaiExecutive SummaryBackground Radiographers process x-ray films using developer and fixer solutions which containsuch chemicals as glutaraldehyde, hydroquinone, potassium hydroxide, potassiumsulphite, sodium thiosulphate, acetic acid, aluminum sulphate, and ammoniumthiosulphate. Some of these agents are known to cause or exacerbate asthma, andradiographers have been diagnosed with occupational asthma due to glutaraldehydesensitization. Radiographers have also reported a wide array of symptoms whosecauses have not been identified.Objectives This study sought to quantify the airborne exposures of radiographers to a selectionof these agents, to determine whether there were differences in exposure levelsbetween radiographers working in hospitals and those working in private clinics, toinvestigate the effectiveness of general and local exhaust ventilation as means ofcontrolling exposures, and to examine other factors, such as tasks and machinecharacteristics, which might influence exposure levels.Approach The study began in the summer of 1998 with a telephone survey of 102 facilitiesrandomly selected from all radiography facilities in the province of British Columbia.A standardized questionnaire was administered to elicit information on sitecharacteristics, including measures currently in place to control exposures. Thesurvey was followed with a field study carried out in 32 facilities in the greaterVancouver area and 3 in Prince George, starting in the fall of 1998 and ending in thespring of 1999. Personal exposures to glutaraldehyde (from the developer chemistry),acetic acid (from the fixer chemistry), and sulphur dioxide (a byproduct of sulphites,present in both developer and fixer solutions) were monitored.Results On the basis of our survey results, we estimated that in 1998 about 1,770 employeesworked with x-ray film processing machines in 181 clinics and hospitals throughoutthe province. Most of these radiographers worked in hospital settings. Typically, thefacilities had more than two film processing machines on site, most of which hadautomated chemical mixing, silver recovery units, and local exhaust ventilation, andwere located in rooms with general dilution ventilation.Average full-shift personal exposures to glutaraldehyde, acetic acid, and sulphurdioxide were 0.0009 mg/m3, 0.09 mg/m3, and 0.08 mg/m3, respectively, all morethan one order of magnitude lower than current Workers? Compensation Board ofBritish Columbia exposure limits.Local exhaust ventilation of the processing machines and use of silver recovery unitslowered exposures, whereas the numbers of films processed per machine and thetime spent near the machines increased exposures. Personnel in private facilities hadhigher exposures than those in hospitals. Private clinics were less likely to have localexhaust ventilation and silver recovery units. Their radiographers spent more time inthe processor areas, and processed more films per machine.iiImplications Although exposures were low compared to WCB standards, there are good reasonsto continue practices to minimize or eliminate exposures: glutaraldehyde andhydroquinone are designated sensitizers whose exposures must be kept ?as low asreasonably achievable?; the levels at which health effects occur are not yet clearlyestablished, but appear to be lower than current standards; and health effectsresulting from the mixture of chemicals are not understood.Methods to reduce exposures identified in this study include local exhaust ventilationof the processing machines, use of silver recovery units, and minimizing time spentin the processor areas.Developments in digital imaging technology are making available options which donot involve wet-processing of photographic film and therefore could eliminate theuse of developer and fixer chemicals altogether.iiiAcknowledgementsWe would like to extend our appreciation to the managers and employees of all the hospitals, healthcentres, and private clinics for their kind and willing participation and assistance throughout thisstudy.We would also like to thank the Workers? Compensation Board Laboratory for performing theanalyses of the air samples, and Victor Leung, Manager of the School of Occupational andEnvironmental Hygiene Laboratory, for his advice during the analyses.This study was funded in part by the Workers? Compensation Board of British Columbia FindingSolutions program.ivTable of ContentsExecutive Summary ...................................................................................................................................iAcknowledgements .................................................................................................................................iiiList of Tables and Figures.............................................................................................................................vGlossary .................................................................................................................................vi1.0 Introduction ..................................................................................................................................12.0 Methods ..................................................................................................................................22.1 Facility Identification ..........................................................................................................22.2 Telephone Interview...........................................................................................................22.3 Exposure Monitoring..........................................................................................................22.4 Data Analysis........................................................................................................................53.0 Results ..................................................................................................................................73.1 Telephone Interview...........................................................................................................73.2 Exposure Monitoring........................................................................................................103.2.1 Personal Exposures.............................................................................................103.2.2 Area Concentrations............................................................................................103.2.3 Ventilation.............................................................................................................123.2.4 Relationship between Ventilation and Exposures..........................................133.2.5 Other Characteristics of the Sites in the ExposureMonitoring Survey...............................................................................................163.2.6 Relationship between Exposures and Facility, Machine, orTask Characteristics.............................................................................................204.0 Discussion ................................................................................................................................234.1 Description of Radiography in British Columbia.........................................................234.2 Exposures of Radiographers............................................................................................234.2.1 Exposure Levels...................................................................................................234.2.2 Ventilation.............................................................................................................244.2.3 Other Determinants of Exposure.....................................................................254.3 Study Limitations...............................................................................................................264.4 Conclusions and Recommendations ..............................................................................275.0 References ................................................................................................................................28Appendix A: Letter of introductionAppendix B: Telephone questionnaireAppendix C: Material safety data sheetsAppendix D: Consent formAppendix E: Data collection formsvList of Tables and FiguresTable 1:  Range of concentrations of reagents in developer and fixerworking solutions, according to manufacturers? specifications ...................................3Table 2:  Air sample collection and analytical methods.................................................................4Table 3:  Characteristics of hospital-based and private radiographic filmprocessing facilities in British Columbia .........................................................................7Table 4:  Characteristics of x-ray film-processing machines .........................................................9Table 5:  Concentrations of glutaraldehyde, acetic acid, and sulphur dioxidein the breathing zones of radiographers during a full work shift...............................11Table 6:  Concentrations of glutaraldehyde, acetic acid, and sulphur dioxideon or near film processing machines during a full work shift ....................................11Table 7:  Characteristics of the general ventilation ......................................................................12Table 8:  Characteristics of the local exhaust ventilation ............................................................12Table 9:  Personal exposures to glutaraldehyde, acetic acid, and sulphurdioxide according to the ventilation characteristics......................................................13Table 10:  Characteristics of the 19 hospital and 16 private facilities whereexposures were measured.................................................................................................16Table 11:  Characteristics of 102 film processing machines .........................................................16Table 12:  Data collected within the 86 rooms housing film processing machines ..................17Table 13:  Characteristics of 97 radiographers whose exposures were measured,and their work on the sampling day................................................................................19Table 14:  Multiple regression models for glutaraldehyde, acetic acid, and sulphurdioxide concentrations .....................................................................................................21Table 15:  Multiple logistic regression models showing odds ratios for exposures toglutaraldehyde, acetic acid, and sulphur dioxide...........................................................22Table 16:  Multiple regression models for glutaraldehyde, acetic acid, and sulphurdioxide concentrations with facility as a random variable...........................................22Figure 1:  Relationship between glutaraldehyde concentrations and local exhaustventilation flow rates.........................................................................................................14Figure 2:  Relationship between acetic acid concentrations and local exhaustventilation flow rates ........................................................................................................14Figure 3:  Relationship between sulphur dioxide concentrations and local exhaustventilation flow rates.........................................................................................................15viGlossaryAutomated Radiographic film chemistry is usually supplied by the manufacturers inChemical  a concentrated form. The concentrate must be mixed with water andMixing delivered to the processing machines. This can be done manually, but most currentsystems use automated methods which may supply several machines. Each systemhas two large tanks (about 10 gallons each), one for the diluted developer solutionand one for the diluted fixer solution. Water supply lines run directly to the tanks.When a tank is empty, a buzzer sounds. This alerts personnel in the area to mount abottle of concentrate (about 1 gallon) directly on the opened top of the tank. As theconcentrate drains into the tank, water is metered in to dilute it at the same time.Once the tank is filled, the empty concentrate bottle is removed and the tank lid isclosed. The diluted developer or fixer is delivered from the tanks as required to theprocessing machine(s) through a metered piping system.Silver  Used fixer solutions contain dissolved silver halides. These can be pumped to aRecovery  silver recovery unit which separates and collects the silver ions using electrolytic orUnit ion exchange methods.Drainage, Rooms housing the processing machines typically have floor drains. Processing?Open? vs. machines and silver recovery units have pipes which take spent fluids to this?Sealed?  drain. In a few sites, the area of the drain around the pipes was sealed with a fittedplastic cover to minimize the opportunity for gases or vapours from the drain toenter the room. In most cases the drain area around the pipes was left unsealed(?open? drainage).Local  The cabinets of most modern radiographic film processing machines are well sealed,Exhaust  so that they can be ventilated. An exhaust duct (usually about 1.5 to 5 inches inVentilation diameter) is attached to the back and bottom of the cabinet. The ducting is thenattached to a fan which pulls air away from the cabinet and exhausts it, preferablydirectly to the outdoors. This type of ventilation is typical of ?industrial? systemsmeant to exhaust contaminants directly from their source.General  The rooms housing the film processing machines may be connected to the generalRoom  building ventilation system, often referred to as the HVAC (heating, ventilating, andVentilation air-conditioning) system. This is the type of ventilation typically found in large officebuildings, with air inlets and outlets (exhaust) in the ceiling of the room. This kind ofventilation operates by diluting contaminants which have entered the room air and isless efficient than local exhaust.Exposures and their Control in X-ray Film Processing 11.0 IntroductionThe production of radiographic films involves the same methods as photographic film processing.In radiography, x-rays rather than visible light create a latent image on the film surface by reducingsilver halide crystals to elemental silver. The image is amplified and stabilized during the developingprocess using reducing agents such as hydroquinone. The image is fixed by agents which dissolveand remove the unused silver halides. Automated x-ray film processing machines achieve shortdevelopment times (seconds to minutes) by using elevated temperatures (28-35 ?C), by includingglutaraldehyde as a hardening agent within the developer solution, and by actively drying the fixedand washed films with heated air [Hewitt, 1993].The process entails potential exposures to hydroquinone, glutaraldehyde, formaldehyde, glycols,acetic acid, sodium sulphite, sulphur dioxide, ammonium chloride, silver compounds, and otherchemicals. Some of these, in particular the aldehydes, have been shown to cause or exacerbateasthma [Corrado et al., 1986; Burge, 1989; Jachuk et al., 1989; Cullinen et al., 1992; Trigg et al., 1992;Chan-Yeung et al., 1993; Hayes and Fitzgerald, 1994; Kivity et al., 1994; Gannon et al., 1995; Malo etal., 1995]. Occupational asthma has been observed in radiographers, the technical professionals whomake the radiographs and process the films [Cullinen et al., 1992; Trigg et al., 1992; Chan-Yeung etal., 1993; Gannon et al., 1995]. In addition, radiographers have reported of a wide variety ofsymptoms including headaches, sore throat, hoarseness, nasal discharge, sore eyes, fatigue, sinusproblems, painful joints, oral ulcers, catarrh, tinnitus, tight chest, skin rash, dyspnea, heartarrhythmias, chest pains, and numbness [Goncalo et al, 1984; Spicer et al., 1986; Gordon, 1987;Smedley et al., 1996]. Studies of radiographers to date have not clarified a link between theirexposures and these symptoms. An investigation is currently underway in British Columbiacomparing the respiratory health of radiographers and physiotherapists [Wymer et al., 2000].Because of the suspected occupational illnesses associated with radiography, we sought to evaluatethe levels and determinants of exposure to several common chemicals used in radiographic filmprocessing. This study was meant to serve as an initial step in the selection of control strategies tominimize occupational exposures. The specific objectives were?  to examine the potential for radiographers to have airborne exposures to film processingchemicals;?  to determine whether there are differences in exposure levels among radiographers working inhospitals or health care centres, and radiographers working in private clinics;?  to determine the effectiveness of general and local exhaust ventilation systems for controllingexposures; and?  to examine other factors such as task, facility, and machine characteristics which might influenceexposure levels.The study had two components. First, a telephone survey of a random sample of all public andprivate film processing facilities in British Columbia was conducted to describe the characteristics ofthe facilities and to determine what measures are currently in place to control exposures. In thesecond part of the study, personal exposure monitoring was conducted in a subsample of facilities inPrince George and the greater Vancouver area to assess the effectiveness of three types ofventilation systems (general ventilation, manufacturer-specified local exhaust ventilation, andventilation-engineer-specified local exhaust ventilation), and to examine other determinants ofradiographers? airborne exposures to film processing chemicals and their by-products.Exposures and their Control in X-ray Film Processing 22.0 Methods2.1 Facility IdentificationIn order to identify all public and private x-ray film processing facilities in the province of BritishColumbia, the Workers? Compensation Board of B.C. (WCB) compiled, from their records, a list offacilities that remitted x-ray films on behalf of WCB clients for compensation purposes. The list offacilities was double-checked and updated for completeness against the Yellow Pages? categories?X-ray Laboratories - Medical and Dental? and ?Hospitals and Health Care Centres.? Hard copiesof the Yellow Pages for every city or area in the province were searched. In addition, the web pagefor the British Columbia Yellow Pages was also searched (www.mybc.com/yellowpages, summer1998). In total, 181 distinct facilities were identified.2.2 Telephone InterviewFrom this list, 100 facilities were randomly selected for a phone interview to obtain informationabout the basic characteristics of the facilities province-wide. One of the study objectives was toassess the effectiveness of improved ventilation, designed by an industrial ventilation engineer, incontrolling exposures, however, we understood that only a few sites in the province might haveachieved this level of local exhaust ventilation. Therefore Ed Chessor (Ventilation Engineer,Engineering Services, WCB) identified all facilities in the province which, to his knowledge, hadupgraded ventilation according to his specifications, i.e., local exhaust from the processor cabinet at20 cubic feet per minute (cfm) or more. All of these facilities were included as phone interview sites,even if they were not included in the initial random selection. He identified 16 sites, of which 10were already included in the random selection. As a result, there were a total of 106 sites identifiedfor telephone interviews.The initial contact with each location was by a letter to the supervisor in charge (Appendix A). Thiswas followed by a telephone call to set up an appointment for an interview with the supervisor or,where the supervisor was not familiar with the x-ray processing facilities, another senior employeewith this expertise.The phone interviews were conducted in the summer of 1998 using a structured questionnaire(Appendix B). The focus was on characteristics such as facility type (private vs. hospital), thenumber of personnel employed in the film processing areas, make and number of processors, namebrand of developer and fixer chemistry, type of chemical mixing (manual vs. automatic), presence ofsilver recovery units, the number of films developed per machine and week, and the presence ofgeneral and local exhaust ventilation.2.3 Exposure MonitoringDuring the telephone interview, supervisors of the 41 facilities located in the greater Vancouver areaand in Prince George were asked whether they would be willing to have their facility participate inan exposure monitoring study. From the list of 36 facilities so identified, stratified random samplesof 15 private and 15 public facilities were selected. To this group were added all facilities identifiedby Ed Chessor as having upgraded their ventilation controls to his specifications, but not included inExposures and their Control in X-ray Film Processing 3the initial random sample. This gave a total of 19 public and 16 private facilities for exposuremonitoring.To select compounds for exposure monitoring, all participants in the telephone interviews wereasked to supply material safety data sheets (MSDS) identifying the constituents of the filmdevelopment and fixing solutions used in their facilities (Appendix C). This investigation indicatedthat the developer and fixer chemistry used in x-ray processing included a variety of chemicalcompounds formulated by several manufacturers (Table 1). Despite the number of manufacturers,there was a core list of reagents used by all: acetic acid, aluminum sulphate, ammonium thiosulphate,glutaraldehyde, hydroquinone, potassium hydroxide, potassium sulphite, and sodium sulphite.Table 1: Range of concentrations of reagents in developer and fixer working solutions, according to manufacturers?specificationsReagentDeveloper,Range ofConcentrations,in %Fixer,Range ofConcentrations,in %Vapourpressure,in mm Hg@ 20 ?CWCBExposureLimitacetic acid p 1-5 (all) 11.4 10 ppm (8-hr)aluminum chloride - 0.1-1.0 1.0* n/aaluminum sulphate - 1-5 (all) n/a n/aammonium thiosulphate - 7-15 (all) negligible n/aboric acid - 0.1-1.0 negligible n/acarbonates (potassium, sodium) 1-5 - n/a n/acitric acid - p n/a n/agluconic acid - 0.1-1.0 n/a n/aglutaraldehyde (sometime as the bis sodium bisulphite)0.5-5 (all) - 17.0 0.25 mg/m3 (C)glycols (diethylene, triethylene) 0.5-1.5 - 0.2 n/ahydroquinone 1-5 (all) - 0.0001 2 mg/m3 (C)5-nitroindazole p - n/a n/a1-phenyl-3-pyramzolidone 0.5-1.5 - n/a n/apotassium acetate 1-5 - n/a n/apotassium hydroxide 1-5 (all) - 1.0 2 mg/m3 (C)potassium sulphite 5-10 (all) - n/a n/asodium acetate - 1-5 n/a n/asodium bisulphite - 1-5 negligible 5 mg/m3 (8-hr)sodium sulphite 1-5 (all) <2 negligible n/asodium thiosulphite - 1-5 negligible n/ap = present, but in concentrations less than the lowest reported by the manufacturer- = not presentn/a = not available(all) = contained in chemistry of all manufacturers(C) = ceiling exposure limit(8-hr) = 8-hour time weighted average exposure limit* = relative humidity at 100 ?CTable 1 also lists the vapour pressures and the WCB exposure limits [WCB, 1998] for thesechemicals. Glutaraldehyde and acetic acid have the highest vapour pressures, have known healtheffects for which exposure limits have been established, and have standard air sampling and analysismethods established by the WCB Laboratory [WCB, 1984]. Acetic acid was used in the fixerchemistry of all manufacturers, and the developer chemistry of some. Glutaraldehyde was used as ahardener in the developer chemistry of all manufacturers. As a result, these two reagents wereExposures and their Control in X-ray Film Processing 4selected for air sampling. In addition, sulphur dioxide was selected because it is a gaseousdegradation product of the sulphite compounds when the fixer solution is heated or left standing forlong periods of time.Table 2 lists the collection apparatus and analytical methods for each chemical, as specified in theWCB Laboratory Analytical Methods Manual [WCB, 1984]. All sample collection tubes had twosections of sorbent to allow determination of whether breakthrough into the second sectionoccurred due to overloading or poor adsorption.Table 2: Air sample collection and analytical methodsChemicalWCB MethodNumber Collection Apparatus Analytical Methodacetic acid 2005 SKC 226-119 activatedcharcoal tubesion chromatographyglutaraldehyde 5230 SKC 226-01 silica gel tubesimpregnated with 2,4-DNPHhigh performance liquidchromatographysulphur dioxide 5280 SKC 226-80 activated beadedcharcoal tubesion chromatographyThe exposure study took place from the fall of 1998 to the spring of 1999. Each facility was visitedon two days. On the first day, all radiographers who worked in the facility?s film processing room(s)on a daily basis were informed about the study procedures and invited to participate in the personalair sampling. In addition, data about unvarying characteristics of the processing machine(s) and workroom(s) were recorded. This included mapping the room(s), recording the make and model of thefilm processing machine(s), noting the film processing chemistry used, and taking measurements ofthe ventilation system(s). Ventilation velocities were measured using a TSI thermoanemometer witha minimum of 8 measurements 0.25 to 4 inches apart across the face of each ventilation ductexhausting the processing machines or the general room air. Measurements were made at least 12inches downstream of duct changes likely to produce turbulent flow. Duct dimensions were alsorecorded. An attempt was made to determine where the local exhaust ventilation air was exhausted,by consulting building maintenance personnel and by following the ducting. Processing machineswhose local exhaust ducts were not connected to an external fan or which allowed contaminated airto recirculate were considered not to have local exhaust ventilation. All ventilation measurementswere repeated on the second field visit, using the same methods.On the second day, all willing radiographers who worked directly with the processing machines, to amaximum of 5 (randomly selected if more volunteered), were asked to wear personal samplers.Subjects were given an explanation of the sampling setup and told what to do in case there wereproblems. All were asked to sign a consent form (Appendix D). Each participant was fitted with twoMSA Flow-Lite? constant-flow sampling pumps before starting work. One pump was calibrated todraw air at 1.2 L/min through the sampling train for glutaraldehyde; the other used a flow splittercalibrated to draw air through the sampling trains for acetic acid at 0.5 L/min and for SO2 at 0.1L/min. The pumps were calibrated before and after sampling using a Gillibrator? automated soap-film flowmeter. The sampling pumps were attached to a waist belt, the collection devices wereclipped onto the employee?s lapel, and rubber tubing connecting the collection devices to the pumpsExposures and their Control in X-ray Film Processing 5was taped along the subject?s back to prevent interference with work. All samples were collectedconcurrently for a full shift (7.5 to 9 hrs).One field blank for each chemical was included for each facility. All samples were stored in arefrigerator (4 ?C) to await one of the biweekly deliveries to the laboratory for analysis. All chemicalanalyses were conducted by the WCB Analytical Laboratory. Limits of detection for the analyticaltechniques were reported by the laboratory as the lowest dilutions of standards used to calibrate themethods: 0.3 microgram for glutaraldehyde, 10.0 micrograms for acetic acid, and 1.0 microgram forsulphur dioxide. The average concentration detection limits (mass detection limit divided by theaverage air volume sampled) were 0.0005 mg/m3 for glutaraldehyde, 0.04 mg/m3 for acetic acid, and0.017 mg/m3 for sulphur dioxide.Initial results of sampling indicated that personal exposure levels were low (often below detectionlimits), therefore worst case exposure levels at 20 subsequent sites were estimated using full-shiftarea samples collected with an equivalent sampling train placed atop or beside film processingmachines.During the sampling period, work tasks performed by the subjects were recorded every 10 minutes,using the following task categories: 1) in darkroom feeding film; 2) loading film into daylightprocessor; 3) observing processed film around processing area; 4) taking picture of patient;5) waiting in processing area; 6) inputting computer data; 7) out of processor area; 8) refillingchemicals; 9) cleaning processing machine; and 10) cleaning spills. After the completion of thesampling period, each subject was asked a series of questions regarding her/his work history,complaints about odours from the processing chemicals, and whether the sampling day was a?normal? day. In addition, the estimated number of films processed by each machine throughoutthe measured shift was recorded. Forms used to collect the information during the exposuremonitoring survey are included as Appendix E. The forms allowed for collection of data aboutsubjects? use of respirators and other personal protective equipment.2.4 Data AnalysisDescriptive statistics (means for continuous data and counts for categorical) were used to examinethe characteristics of provincial radiographic processing facilities determined by the telephonesurvey. The characteristics of public and private facilities were compared using t-tests for continuousdata and chi2 for categorical data.Descriptive statistics (arithmetic and geometric means, geometric standard deviations, minima, andmaxima) were used to characterize the levels of airborne exposure to glutaraldehyde, acetic acid, andsulphur dioxide. Because examination of frequency histograms of the exposures variables suggestedthat the data were approximately log-normally distributed, all exposure data were log-transformed(base e). Data below detection limits were divided by the square root of 2, according to therecommendations of Hornung and Reed [1990]. Stratification on public versus private facility typeswas done, and inferential tests used to examine differences, as described above. Paired t-tests werealso used to compare mean concentrations of personal and area measurements taken in the samefacilities.Ventilation characteristics, including volumetric flow rates, room air volumes per hour, roomvolumes, and exhaust duct areas for general ventilation, and velocities, flow rates and duct diametersExposures and their Control in X-ray Film Processing 6for local exhaust ventilation, were summarized. The levels of personal exposures associated withthree levels of general ventilation (none, < 10 room air volumes per hour, and greaterequal 10 room airvolumes per hour) and three levels of local exhaust ventilation (none, < 20 cfm, and greaterequal 20 cfm) werecompared using one-way analysis of variance (ANOVA).Descriptive statistics were used to summarize characteristics of the sites, film processing machines,and radiographers included in the air monitoring study. Characteristics of sites included the numberof radiographers, number of machines, number of rooms in which processors were housed, and thenumber of films processed per week. Characteristics of machines included make, location, brand ofdeveloper used, brand of fixer used, presence of a silver recovery unit, method of chemical mixing,and temperature and humidity in the room where the machine was housed. Characteristics of theradiographers included the radiography experience, shift length, reported availability and use ofpersonal protective equipment (PPE), and tasks performed.To test whether any additional factors beyond ventilation and facility type were associated withpersonal exposures, a multiple regression analysis was conducted. Prior to developing the model,variables for offering to the models were selected in several steps. First, we considered whetherthere was reasonable support for the hypothesis that there could be a relationship between the factorand the exposure. Second, correlations between independent variables were examined, and wherePearson r greaterequal 0.7, only one variable was chosen for inclusion in the analysis, the variable consideredlikely to be most directly related to exposure. Third, we examined whether the variables wereassociated with exposure in univariate analyses (p < 0.25) and, if so, whether the direction ofassociation could be logically interpreted. Initially an ordinary least squares backwards regression wasconducted; all variables with p <=< 0.10 were retained. To control for correlation within facilitybeyond that explained by the factors in the model, we entered these variables into ProcMixed inSAS, designating facility as a random variable.Because more than 40% of the personal exposures to each analyte were less than the limits ofdetection of the sampling and analytical methods, we also used logistic regression models to examinefactors associated with exposures above and below the detection limits. These models werecompared to the linear regression models to determine which factors entering the models were themost stable predictors of exposure.Exposures and their Control in X-ray Film Processing 73.0 Results3.1 Telephone InterviewOf the 181 radiographic film processing facilities identified in British Columbia in the summer of1998, 106 were selected for a telephone interview. The supervisor or another senior employee of 102of the facilities (96%) agreed to participate in the survey.The reported characteristics of radiographic film processing facilities in British Columbia areoutlined in Table 3, stratified by whether the facilities were in publicly owned hospitals or healthcentres (63.7%), or in privately owned businesses (36.3%). Hospital and private facilities differedconsiderably in size. On average, private clinics had fewer employees, and fewer film processingmachines on site.Table 3: Characteristics of hospital-based and private radiographic film processing facilities in British ColumbiaAll Hospital PrivateFacilities Facilities FacilitiesN=102 N=65 N=37# of employees who work Mean 9.8 12.7 4.5with the film processing machines SD 13.4 15.9 3.7Min - Max 1 - 60 1 - 60 1 - 20*p=0.002# of employees who work Mean 11.9 15.6 5.2in the processing area SD 20.0 24.1 4.1Min - Max 1 - 150 1 - 150 1 - 20p=0.011# of film processing machines Mean 2.3 2.7 1.5on site SD 2.1 2.5 0.73Min - Max 1 - 13 1 - 13 1 - 4p=0.005# of rooms in which film Mean 1.9 2.2 1.4processing machines are located  SD 1.7 2.0 0.68Min - Max 1 - 10 1 - 10 1 - 4p=0.014# of films processed per week Mean 1243 1361 1036SD 1301 1554 621Min - Max 15 - 7450 15 - 7450 100 - 2400p=0.23Ventilation upgraded in the Yes  17 12 5last 2 years  No 85 53 32p=0.52SD = standard deviationMin - Max = Minimum to Maximum*p-values for tests for differences between hospital and private facilities, t-test or chi2If the data are representative of all 181 facilities in the province, it suggests that in British Columbiain the fall of 1998, there were about 1,770 radiographers who worked directly with film processingmachines, and about 375 other employees who worked in the vicinity of the machines. It alsosuggests that there were over 400 x-ray film processing machines in the province, and theydeveloped a total of about 225,000 films per week.Exposures and their Control in X-ray Film Processing 8Table 4 outlines the reported characteristics of the 230 processing machines present in the surveyedfacilities in the fall of 1998, again stratified by whether they were located in publicly owned hospitalsor health centres (76%), or in privately owned businesses (24%). Most machines (57.5%) werelocated in dark or semi-dark rooms where access must be restricted, but a large proportion (42.6%)were ?daylight? machines which can be located anywhere. Hospitals used daylight processors muchmore often than private facilities. The majority of machines were made by Kodak (60.4%), though afew other manufacturers had significant proportions of the market: Fuji (16.1%), Dupont (11.7%),and Agfa (8.6%). Kodak developers and fixers were also the dominant brand, but three companieseach held more than 10% of the market share for developer and fixer chemistry, including twowhich do not manufacture processing machines: Picker; White Mountain; and Dupont. Each ofmanufacturers offered the chemistry in several different formulations (see Appendix C). Thenumber of films processed weekly varied by almost 3 orders of magnitude between the processingmachines. Almost all the machines (91.7%) had automatic chemical mixing. Similar numbers hadsilver recovery units attached (92.6%). Most machines (95.2%) were reported to be placed in roomswith general room ventilation, and 83.9% had local exhaust from the machine itself. Private facilitieswere somewhat less likely to have general and local exhaust ventilation of their machines. In 17 ofthe 102 facilities (Table 3), supervisors reported that there had been upgrades to the ventilation ofthe film processing machines in the previous 2 years.Exposures and their Control in X-ray Film Processing 9Table 4: Characteristics of x-ray film-processing machines in hospital-based and private facilities in British ColumbiaAll Hospital PrivateFacilities Facilities FacilitiesN=230 N=175 N=55Location of x-ray film- Darkroom 130 84 46processing machines Daylight 98 91 7Semi-dark (yellow) 2 0 2*p<0.001Make of x-ray film-processing Kodak 139 107 32machines Fuji 37 20 17Dupont 27 25 2Agfa 20 16 4Konica 5 5 0Odelt 1 1 0AFP 1 1 0p=0.003Number of films processed Mean 510 503 697per machine per week SD 550 499 518Min - Max 5 - 3200 5 - 3200 35 - 2000p=0.014Brand of developer used Kodak 100 78 22Picker 35 25 10White Mountain  33 17 16Dupont 32 31 1Agfa 16 13 3Autex 11 8 3Fuji 2 2 0Varix 1 1 0p=0.002Brand of fixer used Kodak 90 68 22Picker 49 39 10White Mountain  32 16 16Dupont 23 22 1Agfa 17 14 3Autex 16 13 3Fuji 2 2 0Varix 1 1 0p=0.009Method of mixing machine Automatic 211 156 55chemicals Manual 19 19 0p=0.011General ventilation in processor Yes 219 171 48room No 11 4 7p=0.002Machine has local exhaust Yes 193 150 43ventilation No 37 25 12p=0.19Machine has silver recovery unit Yes 213 160 53No 17 15 2p=0.22*p-values for tests for differences between hospital and private facilities, t-test or chi2SD = standard deviationMin - Max = Minimum to MaximumExposures and their Control in X-ray Film Processing 103.2 Exposure MonitoringAmong the 102 facilities participating in the telephone survey, there were a total of 41 facilities inPrince George and the greater Vancouver area that were eligible to participate in the exposuremonitoring part of the study. 36 (88%) agreed to participate, and 19 public and 16 private facilitieswere selected for the study; three of them were in Prince George.In the exposure monitoring study, a total of 177 radiographers were present during the samplingshifts. Of these, 117 volunteered to participate in the exposure monitoring (66%). A smallerproportion of radiographers volunteered at hospital-based than private facilities (82/135=61% and35/42=83%, respectively; chi2=7.297, p=0.007). There were two reasons for the lower participationrate in hospitals: their radiographers knew that there were many employees to choose from,therefore felt less obligation to participate; and some radiographers who worked part-time or on acasual basis in several hospitals declined to participate at a second site. Because we could sample amaximum of 5 radiographers at each site, exposure measurements were made on 97 of the 117radiographers who volunteered.3.2.1 Personal ExposuresTable 5 indicates that radiographers? personal exposures to glutaraldehyde, acetic acid, and sulphurdioxide were low. The majority of glutaraldehyde samples were below detection limits, as were alarge proportion of both the acetic acid and sulphur dioxide samples. None of the samples exceededthe Worker?s Compensation Board of British Columbia 8-hour exposure limits of 24.5 mg/m3 foracetic acid or 5.2 mg/m3 for sulphur dioxide. The WCB has a ceiling limit for glutaraldehyde of 0.25mg/m3. We measured exposures throughout a full shift, so the measures are not strictly comparable.However, since the maximum full-shift glutaraldehyde exposure measured was less than 1/100th ofthe ceiling limit, it is extremely unlikely that the ceiling limit was exceeded, even for short periodswithin a shift [Rappaport and Selvin, 1988].Personal exposures in the hospital settings were significantly lower than those in the private facilities(t-tests, comparison of geometric means: pglutaraldehyde = 0.001; pacetic acid < 0.001; psulphur dioxide < 0.001).3.2.2 Area ConcentrationsBecause of the low concentrations found in the initial batch of personal samples analyzed at theWCB Laboratory, area samples were taken at 20 facilities subsequently studied to determine whetherair concentrations were higher in close proximity to the film processing machines. Table 6 indicatesthat a greater proportion of the area samples had detectable air concentrations, and arithmetic meanconcentrations of acetic acid and sulphur dioxide were 1.6 and 3.1 times higher than those ofpersonal samples respectively. Personal and area glutaraldehyde levels did not differ. In paired t-testsof the mean personal and area exposure levels in the 20 facilities where area samples were taken,only sulphur dioxide levels were significantly higher in area than personal samples (comparison ofgeometric means, pglutaraldehyde = 0.29, pacetic acid = 0.12, psulphur dioxide = 0.001). Area concentrations werealso low compared to existing occupational exposure standards.Differences in area concentrations between hospital and private facilities were not statisticallysignificant (t-tests, comparison of geometric means: pglutaraldehyde = 0.78, pacetic acid = 0.47, psulphur dioxide =0.67).Exposures and their Control in X-ray Film Processing 11Table 5: Concentrations of glutaraldehyde, acetic acid, and sulphur dioxide in the breathing zones of radiographersduring a full work shift, in 19 hospital and 16 private facilitiesGlutaraldehyde Acetic Acid Sulphur DioxideAll facilities (N=97 air samples)% < LOD 53.6 42.3 40.2Minimum > LOD (mg/m3) 0.0006 0.031 0.020Maximum (mg/m3) 0.0023 0.80 0.41Arithmetic mean (mg/m3) 0.0009 0.088 0.078Geometric mean (mg/m3) 0.0008 0.060 0.040Geometric standard deviation 1.62 1.85 2.66Hospitals (N=62)% < LOD 64.5 56.5 59.7Minimum > LOD (mg/m3) 0.0006 0.031 0.024Maximum (mg/m3) 0.0020 0.12 0.32Arithmetic mean (mg/m3) 0.0007 0.053 0.041Geometric mean (mg/m3) 0.0007 0.048 0.027Geometric standard deviation 1.50 1.51 2.24Private Facilities (N=35)% < LOD 34.3 17.1 5.7Minimum > LOD (mg/m3) 0.0008 0.042 0.020Maximum (mg/m3) 0.0023 0.80 0.41Arithmetic mean (mg/m3) 0.0011 0.12 0.11Geometric mean (mg/m3) 0.0009 0.089 0.080Geometric standard deviation 1.71 2.05 2.40LOD = limit of detectionTable 6: Concentrations of glutaraldehyde, acetic acid, and sulphur dioxide on or near film processing machines duringa full work shift, in 11 hospital and 9 private facilitiesGlutaraldehyde Acetic Acid Sulphur DioxideAll facilities (N=22 air samples)% < LOD 45.4 22.7 13.6Minimum > LOD (mg/m3) 0.0007 0.051 0.058Maximum (mg/m3) 0.0020 0.700 1.03Arithmetic mean (mg/m3) 0.0009 0.14 0.24Geometric mean (mg/m3) 0.0008 0.102 0.159Geometric standard deviation 1.78 2.35 2.89Hospitals (N=13)% < LOD 53.8 30.8 7.7Minimum > LOD (mg/m3) 0.0009 0.051 0.058Maximum (mg/m3) 0.0020 0.70 0.62Arithmetic mean (mg/m3) 0.0009 0.14 0.21Geometric mean (mg/m3) 0.0008 0.090 0.15Geometric standard deviation 1.74 2.55 2.68Private Facilities (N=9)% < LOD 33.3 11.1 22.2Minimum > LOD (mg/m3) 0.0007 0.054 0.10Maximum (mg/m3) 0.0020 0.31 1.03Arithmetic mean (mg/m3) 0.0010 0.15 0.29Geometric mean (mg/m3) 0.0008 0.12 0.18Geometric standard deviation 1.90 2.11 3.38Exposures and their Control in X-ray Film Processing 123.2.3 VentilationIn the facilities studied, there were 102 film processing machines, most housed in separate rooms.The majority of these rooms had general ventilation (77%; Table 7). Most of the machinesthemselves had local exhaust ventilation of the processor cabinet (85%; Table 8). Only 6 machines(6%) had neither type of ventilation.The quality of the ventilation was variable, with about 37% of rooms having exhaust flowsequivalent to 10 or more room air volumes per hour, and about 32% of machines having localexhaust flow rates of at least 20 cubic feet per minute (cfm). None of the machines had both highlocal exhaust flow rates and high general ventilation rates. It is interesting to note that 7 processingmachines (located in 3 hospitals and 2 private facilities) with exhaust ducts had no fan attached toexhaust the air. These were counted as not having local exhaust ventilation.Ventilation of the film processing machines was more frequently present and of better quality in thehospital facilities than in the private clinics (chi2, contingency table, numbers of machines withvarious ventilation rates, all facilities, Tables 7 and 8; pgeneral ventilation = 0.059, plocal exhaust ventilation = 0.015).Table 7: Characteristics of the general ventilation in rooms housing film processing machines in the 19 hospital and 16private facilities where exposures were measuredAll Hospitals PrivateFacilities Facilities FacilitiesNo. of rooms 86 63 23No. with no general room ventilation (%) 20  (23%) 12  (19%) 8  (35%)No. with flow < 10 room air volumes/hr (%) 34  (40%) 23  (37%) 11  (48%)No. with flow greaterequal 10 room air volumes/hr (%) 32  (37%) 28  (44%) 4  (17%)Mean room exhaust flow rate (SD) (cfm) 231  (326) 289  (359) 71  (110)Mean room air volumes/hr (SD) 10.4  (12.3) 12.2  (13.5) 5.4  (6.0)Mean room volume (SD) (ft3) 1,485  (1,419) 1,777  (1,525) 685  (550)Mean room exhaust duct area (SD) (ft2) 1.0  (1.9) 0.89 (0.84) 1.3  (3.3)SD = standard deviationTable 8: Characteristics of the local exhaust ventilation of film processing machines in the 19 hospital and 16 privatefacilities where exposures were measuredAll Hospitals PrivateFacilities Facilities FacilitiesNo. of processing machines 102 77 25No. with no local exhaust ventilation (%) 15 (15%) 8 (10%) 7 (28%)No. with local exhaust ventilation butno flow measurements possible (%) 21 (21%) 13 (17%) 8 (32%)No. with volumetric flow rate < 20 cfm (%) 33 (32%) 26 (34%) 7 (28%)No. with volumetric flow rate greaterequal 20 cfm (%) 33 (32%) 30 (39%) 3 (12%)Mean volumetric flow rate (SD) (cfm) 21.9 (26.2) 22.3 (20.8) 20.1 (40.6)Mean duct diameter (SD) (inches) 2.9 (1.2) 3.1 (1.0) 2.3 (1.3)SD = standard deviationExposures and their Control in X-ray Film Processing 133.2.4 Relationship between Ventilation and ExposuresThe effect of ventilation on the personal exposures of radiographers was examined by consideringthe ventilation characteristics of the dominant machine with which they worked. There wereproblems measuring ventilation velocities in some rooms and local exhaust ducts, therefore only 93of 97 personal exposure measurements could be used to examine the effects of general ventilation,and only 84 of the exposure measurements could be used to examine local exhaust effects.No reductions in exposure were observed with general ventilation of the rooms where the filmprocessing machines were located (Table 9).Local exhaust ventilation of the main machine used was associated with reduced exposures amongradiographers, with reductions of 20 to 46%, compared to no local exhaust (Table 9). The highestventilation flow rates (greaterequal 20 cfm) usually appeared to be associated with lower exposures than werelower exhaust rates.Table 9: Arithmetic and geometric mean personal exposures to glutaraldehyde, acetic acid, and sulphur dioxideaccording to the ventilation characteristics of the main machine used by the radiographer being sampled in 35 hospitaland private facilitiesGlutaraldehyde Acetic Acid Sulphur DioxideN (mg/m3) (mg/m3) (mg/m3)General Room VentilationArithmetic meansNone  18 0.0009 0.071 0.063Room air volumes/hour < 10  42 0.0009 0.086 0.081Room air volumes/hour greaterequal 10  37 0.0008 0.069 0.051*p=0.57 p=0.64 p=0.24Geometric meansNone  18 0.0008 0.035 0.059Room air volumes/hour < 10  42 0.0008 0.048 0.062Room air volumes/hour greaterequal 10  37 0.0007 0.035 0.059p=0.60 p=0.29 p=0.94Local Exhaust VentilationArithmetic meansNone 25 0.0010 0.10 0.094Volumetric flow rate < 20 cfm  24 0.0007 0.079 0.051Volumetric flow rate greaterequal 20 cfm  35 0.0008 0.053 0.066p=0.043 p=0.10 p=0.17Geometric meansNone 25 0.0009 0.061 0.086Volumetric flow rate < 20 cfm  24 0.0007 0.038 0.050Volumetric flow rate greaterequal 20 cfm  35 0.0007 0.033 0.049p=0.019 p=0.058 p=0.001*p-values for tests for differences in concentration by ventilation rate, one-way ANOVAExposures and their Control in X-ray Film Processing 14Figures 1, 2, and 3 show the relationship between glutaraldehyde, acetic acid, and sulphur dioxideconcentrations and local exhaust ventilation flow rates graphically.Local Exhaust Ventilation Flowrate (cfm)200Concentration of Glutaraldehyde (mg/m3).003.002.001.0009.0008.0007.0006.0005.0004.0003LegendHospitalPrivate FacilityFigure 1: Relationship between glutaraldehyde concentrations and local exhaust ventilation flow ratesLocal Exhaust Ventilation Flowrate (cfm)200Concentration of Acetic Acid (mg/m3).8.6.4.2.1.08.06.04.02LegendHospitalPrivate FacilityFigure 2: Relationship between acetic acid concentrations and local exhaust ventilation flow ratesExposures and their Control in X-ray Film Processing 15Local Exhaust Ventilation Flowrate (cfm)200Concentration of Sulphur Dioxide (mg/m3).4.2.1.08.06.04.02.01LegendHospitalPrivate FacilityFigure 3: Relationship between sulphur dioxide concentrations and local exhaust ventilation flow ratesExposures and their Control in X-ray Film Processing 163.2.5 Other Characteristics of the Sites in the Exposure Monitoring SurveyCharacteristics of the 35 facilities included in the exposure monitoring survey are summarized inTable 10. To determine how representative the subset of sampled sites were of facilities province-wide, these characteristics can be compared to those of the 102 facilities sampled in the telephoneinterview, presented in Table 3. The hospitals in the sampled subset were on average larger than theprovincial average, with more radiographers on site, more film processing machines, and more filmsprocessed every week. This is expected given that the exposure study was based in the LowerMainland, the location of the largest hospitals in the province. The private clinics included in theexposure study were similar in size to those province-wide, although they processed more films perweek, on average.Table 10: Characteristics of the 19 hospital and 16 private facilities where exposures were measuredAll Hospitals PrivateFacilities Facilities FacilitiesN=35 N=19 N=16Mean no. of radiographers on site (SD) 17.3 (16.8) 27.6 (16.9) 5.1 (2.4)Mean no. of machines on site (SD) 2.9 (2.1) 4.1 (2.2) 1.6 (0.6)Mean no. of rooms in which processing machines located (SD) 2.4 (1.7) 3.3 (1.8) 1.4 (0.6)Mean no. of films processed/week (SD) 1933 (1525) 2548 (1781) 1203 (646)SD = standard deviationTables 11 and 12 indicate characteristics of the rooms housing the film processing machines and ofthe machines themselves at the exposure study sites. The temperatures and relative humidities in thefilm processing rooms did not vary much between facilities or by facility type (Table 11). Developerand fixer concentrate were added to make up working solutions on about one-quarter to one-thirdof sampling days. In most facilities, the concentrate was added to a central working solution systemthat fed all the machines housed in a room.Table 11: Data collected within the 86 rooms housing film processing machines at the facilities where exposures weremeasuredAll Hospitals PrivateFacilities Facilities FacilitiesN=86 N=63 N=23Mean temperature on sampling day, in ?C (SD) 22.1 (1.5) 22.4 (1.4) 21.1 (1.5)Mean relative humidity on sampling day, in % (SD) 45.6 (6.9) 44.8 (7.3) 47.7 (5.3)Mean number of bottles of developer concentrateadded on sampling day (SD) 0.26 (0.54) 0.26 (0.54) 0.26 (0.54)Mean number of bottles of fixer concentrateadded on sampling day (SD)  0.33 (0.62) 0.32 (0.62) 0.35 (0.65)SD = standard deviationThe characteristics in Table 12 can be compared to those from the telephone survey sites, listed inTable 4. Once again, the hospitals in the exposure study subset differed somewhat from thoseprovince-wide: they used daylight processors more frequently; they used Picker processing chemistryExposures and their Control in X-ray Film Processing 17more frequently than Kodak; and they did not use manual chemical mixing for any of theirmachines. Private facilities in the exposure study were very similar to those province-wide, exceptthat they were less likely to use Kodak machines. None of the machines had chemical spills on thesampling days.Table 12: Characteristics of 102 film processing machines at the facilities where exposures were measuredAll Hospitals PrivateFacilities Facilities FacilitiesN=102 N=77 N=25Location of film processing machinesDarkroom  47 26 21Daylight  55 51 4Make of machinesKodak  57 47 10Fuji  14 4 10Dupont  17 15 2Agfa  12 9 3Odelft 1 1 0AFP 1 1 0Mean no. of films processed/machine/week (SD) 702 (357) 607 (255) 814 (431)Brand of developer usedKodak 28 20 8Picker 31 27 4Dupont 19 19 0White Mountain 8 1 7Agfa 8 5 3Autex 5 2 3Fuji 2 2 0VAR-IX 1 1 0Brand of fixer usedPicker 42 38 4Kodak 19 11 8Dupont 13 13 0Agfa 9 6 3Autex 9 6 3White Mountain 7 0 7Fuji 2 2 0VAR-IX 1 1 0Method of mixing chemicalsManual 0 0 0Automatic 102 77 25Machine has silver recover unit 93 70 23Machine has open drainage 96 77 19Number of spills on sampling day 0 0 0SD = standard deviationExposures and their Control in X-ray Film Processing 18Table 13 summarizes characteristics of the radiographers included in the exposure monitoringsurvey, and the tasks they performed on the sampling days. The study participants had an average of9 years of experience at the facility in which they were employed and 17 years of experience inradiography. The typical shift length was 7.5 hours.On the sampling days, the hospital facilities processed an average of 115 films per machine, ontarget for the weekly workload of about 600 films per machine reported for these facilities. The largemajority of hospital radiographers reported that the workload on the sampling day was average.Private facilities averaged 204 films per machine on the sampling days, busier than the reportedaverage weekly workload of about 800 films per machine. Despite this, only a small proportion ofradiographers from the private facilities reported that the workload was busy on the sampling day.The tasks of the radiographers were observed every 10 minutes throughout the sampling days. Themost frequent tasks recorded were taking x-rays, time outside the processing area, waiting in theprocessing area, and observing film. Relatively little time was spent in a darkroom or loading film.Cleaning the processing machine, and refilling chemicals were rarely observed, and no spillsoccurred during the sampling days.Although gloves and goggles were available at most of the facilities, especially hospitals, only 2individuals reported using gloves during the sampling days. No other personal protective equipmentuse was reported or observed.The majority of subjects reported smelling the processing chemicals on the sampling day, however,measured levels of personal exposure to glutaraldehyde, acetic acid, and sulphur dioxide were notassociated with reported odour (t-tests, all p > 0.25).Exposures and their Control in X-ray Film Processing 19Table 13: Characteristics of 97 radiographers whose exposures were measured, and their work on the sampling dayAll Hospitals PrivateFacilities Facilities FacilitiesN=97 N=62 N=35Radiography experienceMean years on site (SD) 8.9  (6.1) 8.8  (5.9) 9.0  (6.6)Mean total years (SD) 16.8  (9.6) 14.2  (9.1) 21.4  (8.7)Number female (%) 80 (82) 48 (77) 32 (91)Mean shift length (hours) (SD) 7.5 (0.48) 7.5 (0.47) 7.6 (0.50)Number of films processed in dominantmachine on sampling day (SD) 147  (105) 115  (87) 204  (111)Reported workload on sampling daySlow (%) 36 31 46Average (%) 56 58 51Busy (%) 8 11 3Mean % time spent on the sampling day*Taking x-rays (SD) 37  (14.0) 39  (15.4) 34  (10.7)Outside processing area (SD) 21  (13.8) 23  13.4) 19  (14.4)Waiting in processing area (SD) 20  (9.0) 18  (9.9) 22  (7.0)Observing film, by processor (SD) 12  (6.0) 11  (5.8) 15  (5.6)In darkroom (SD) 4  (5.8) 2  (3.5) 8  (6.5)Loading film in daylight processor (SD) 3  (4.3) 3  (3.9) 2  (4.8)Inputting data to computer (SD) 3  (9.0) 4  (11.1) 0  (0)Cleaning processing machine (SD) 0.06  (0.4) 0  (0) 0.2  (0.7)Refilling chemicals (SD) 0.05  (0.4) 0  (0) 0.1  (0.6)Cleaning spills (SD) 0  (0) 0  (0) 0  (0)Reported PPE availabilityGloves available on site, in % 88 98 69Goggles available on site, in % 56 69 31Dust mask available on site, in % 19 21 14Cartridge respirator available on site, in % 6 7 6Apron available on site, in % 12 19 11Reported use of PPE on sampling dayWore gloves, in % 2 2 3Wore other protective equipment, in % 0 0 0Reported smelling processing chemicalson sampling day, in % 66 73 54SD = standard deviation* 3 of the sampled hospital radiographers could not be tracked throughout their work day, therefore task information is based on 59hospital radiographers, and 94 in total.PPE = personal protective equipmentExposures and their Control in X-ray Film Processing 203.2.6 Relationship between Exposures and Facility, Machine, or Task CharacteristicsIn order to determine which facility, machine, and radiographer characteristics were related toexposure levels, after adjusting for other associated factors, we conducted multiple regressionanalyses with glutaraldehyde, acetic acid, and sulphur dioxide exposure levels as the dependentvariables in 3 separate analyses.To prepare for the analysis, we first examined correlations between independent variables. Facilitytype (hospital versus private), known to be associated with exposure levels (section 3.2.1 above), wasalso strongly associated with many of the other independent variables. Since the aim of themodelling was to discern which characteristics of hospital versus private facilities affected exposurelevels, facility type was not initially offered to the models.Both local exhaust ventilation (categorized as no local exhaust ventilation, ventilation flow rates > 0and < 20 cubic feet per minute (cfm), and ventilation flow rates greaterequal 20 cfm) and general ventilation(room air volumes per hour, continuous) were included in the models, because assessing theeffectiveness of ventilation was a primary objective of the study.Other variables were selected for offering in the models if there were reasonable grounds for thehypothesis that they could be related to exposure (i.e., p-value < 0.25 in univariate analyses againstexposure level, and direction of effect in univariate analyses could be logically explained). Variablesselected for the analyses included the number of films processed in the dominant machine used bythe radiographer on the sampling day; the number of processing machines per room; percent oftime spent on tasks associated with increased exposure levels (working in the darkroom, loading filminto daylight processor, waiting in processing area); whether or not fixer was added; whether or notdeveloper was added; whether the machine had open drainage; and the presence of a silver recoveryunit. Tasks associated with decreased exposure levels (taking x-rays and those involving time outsideprocessing area) were not included in the multivariate models, because they replaced the effects oftasks associated with increased exposure, yet were only passively associated with exposure.Table 14 describes the multiple linear regression models for glutaraldehyde, acetic acid, and sulphurdioxide. Only the number of films processed was a consistent predictor of increased exposure for allthree agents. Time spent in a film processing area increased acetic acid and sulphur dioxideexposures, and time in a darkroom increased acetic acid exposure. Local exhaust ventilation loweredglutaraldehyde and acetic acid exposure. The use of a silver recovery unit was also associated withdecreased exposure to acetic acid and sulphur dioxide. The proportions of exposure varianceexplained by these models ranged from 13 to 38%.Adding facility type to the models in Table 14 (data not shown) removed the number of filmsprocessed per machine from all three models because the number of films processed in hospitalfacilities was lower than in private facilities. Adding facility type also removed percent time spent ina darkroom from the acetic acid model because there was a smaller proportion of darkrooms inhospitals than in private facilities. The models which included facility type instead of the number offilms processed or time in darkroom explained somewhat more variance (glutaraldehyde r2 = 0.14,acetic acid r2 = 0.38, sulphur dioxide r2 = 0.38), especially in the sulphur dioxide model, suggestingthat there is some additional difference between hospitals and private radiography clinics whichremains unaccounted for.Exposures and their Control in X-ray Film Processing 21Table 14: Multiple regression models, coefficients (and p-values), for glutaraldehyde, acetic acid, and sulphur dioxideconcentrations (all log-transformed, base e)Glutaraldehyde Acetic Acid Sulphur DioxideNumber of films processed per machine 0.001(0.03) 0.0014(0.02) 0.0028(0.003)% time spent in darkroom  - 0.020 (0.05) -% time spent in processor area - 0.018 (0.008) 0.021 (0.05)Silver recovery unit present - -0.50 (0.04) -0.92 (0.03)Local exhaust ventilation < 20 cfm -0.27 (0.04) -0.40 (0.01) -Local exhaust ventilation greaterequal 20 cfm -0.17 (0.15) -0.44 (0.003) -Number of observations 84 82 94model p-value  0.01  0.0001  0.0003model r2 0.13 0.38 0.19- = not in modelr2 = the proportion of variance explainedTable 15 shows the results of the multiple logistic regression which compares the odds of exposureabove versus below detection limits. Once again, the number of films processed in the dominantmachine used by the sampled radiographer was a consistent predictor of increased exposures to allagents. The odds ratios indicate that the odds of exposure to glutaraldehyde, acetic acid, and sulphurdioxide above the detection limit was about 1.5 to 2-fold higher after processing 100 films. Theresults for percent time spent in the dark room were similar to those of the linear regressionanalyses. Spending 5% of one?s work day in a darkroom increased the odds of detectable exposuresto acetic acid and sulphur dioxide by 1.9- and 1.7-fold. Adding another film processing machine to aroom increased the odds of detectable exposures to acetic acid and sulphur dioxide by 3- and 2-foldrespectively. Adding developer also increased exposure to acetic acid. As in the linear regressionanalysis, local exhaust ventilation lowered exposures. For glutaraldehyde and acetic acid, the odds ofdetectable exposures were three to fourteen times lower with local exhaust ventilation than without.As with the linear regression models, adding facility type to the logistic regression models removedthe effect of the number of films processed and percent time spent in a darkroom (data not shown).Table 16 shows the results of multiple linear regression analyses, controlling for correlation withinfacility, by including facility as a random variable in a mixed effects analysis. The within-facilitycorrelation was moderate (r from 0.44 to 0.55) for all three agents. By comparing the modelspresented in Tables 14 and 16, we can observe the variables which were affected by within-sitecorrelation and therefore removed from the new models: number of films processed per machine;time spent in the darkroom; and the presence of a silver recovery unit. After controlling for within-facility correlation, local exhaust ventilation remained a predictor of decreased exposure forglutaraldehyde and acetic acid, and percent time spent in the processor area remained a predictor ofincreased exposure to acetic acid and sulphur dioxide.Offering facility type to these models did not remove any of the final variables from the models.Facility type was an explanatory variable for both acetic acid and sulphur dioxide and is included inthe model descriptions in Table 16.Exposures and their Control in X-ray Film Processing 22Table 15: Multiple logistic regression models showing odds ratios (and p-values) for exposures to glutaraldehyde, aceticacid, and sulphur dioxide, comparing the odds of concentrations above versus below detection limitsGlutaraldehyde Acetic Acid Sulphur Dioxide# films processed/machine (per 100 films) 1.6 (0.076) 1.6 (0.11) 2.1 (0.017)# machines/room (per additional machine) - 3.2 (0.005) 2.4 (0.028)Time spent in darkroom (per 5%) - 1.9 (0.035) 1.7 (0.042)Developer added (yes vs. no) - 3.2 (0.048) -Local exhaust ventilation < 20 cfm 0.28 (0.049) 0.069 (0.001) -Local exhaust ventilation <=< 20 cfm 0.24 (0.025) 0.20 (0.033) -Number of observations 82 82 82model p-value  0.012  < 0.0001 0.0009model r2 0.11 0.27 0.17- = not in modelr2 = the proportion of variance explainedTable 16: Multiple regression models, coefficients (and p-values), for glutaraldehyde, acetic acid, and sulphur dioxideconcentrations (all log-transformed, base e), with facility as a random variableGlutaraldehyde Acetic Acid Sulphur Dioxide% time spent in processor area - 0.012 (0.04) 0.022 (0.006)Local exhaust ventilation < 20 cfm -0.30 (0.026) -0.26 (0.14) -Local exhaust ventilation greaterequal 20 cfm -0.14 (0.26) -0.33 (0.05) -Facility type (hospital vs. private) - -0.39 (0.02) -0.99 (0.0005)Number of observations 84 82 94model p-value  0.0001 0.004 < 0.0001model OLS r2 0.083 0.35 0.31Within-facility correlation 0.47 0.55 0.44- = not in modelmodel OLS r2 = the proportion of variance explained; since it is not available for the ProcMixed model, the ordinary least squares r2for the same model is reported; this does not take into account the within-facility correlation.Exposures and their Control in X-ray Film Processing 234.0 Discussion4.1 Description of Radiography in British ColumbiaThe participation in the telephone survey was excellent (96%), therefore should not be affected byselection bias.Based on our telephone survey, we estimated that there were about 1,770 employees who workedwith x-ray film processing machines in the province in 1998. This compares with an enumeration of1,223 ?medical radiation technologists? who were members of the Health Sciences Association inJune of 1996. Apart from the year of enumeration, differences in these numbers could be accountedfor by inclusion in our estimate of personnel who were not radiographers, radiographers whoworked part-time in multiple locations, or radiographers who did not belong to the Association.The large majority of provincial radiographers work in hospital settings (83%), with machines thathave automated chemical mixing (92%) and local exhaust ventilation (84%). All the developingfluids used contain glutaraldehyde, hydroquinone, potassium hydroxide, potassium sulphite, andsodium sulphite; all the fixer solutions contained acetic acid, aluminum sulphate, and ammoniumthiosulphate.The reporting in the telephone interviews was in excellent agreement with our research personnel?sobservations in those sites subsequently visited. For example, ventilation is likely to be one of themost difficult items for an untrained person to assess, yet in only three of the 35 sites was thepresence of general room ventilation misreported. The same was true for local exhaust ventilation.There was no consistency in the direction of misreporting.4.2 Exposures of Radiographers4.2.1 Exposure LevelsAgreement by facilities to participate in the exposure survey was excellent (88%), as was agreementto participate in the monitoring by radiographers in private clinics (83%). A smaller proportion ofhospital radiographers agreed to the monitoring (61%); whether this lower participation rate affectedexposure measurements is not known.Exposures of radiographers to glutaraldehyde, acetic acid, and sulphur dioxide in this study were lowin comparison to current WCB exposure limits [WCB, 1998]. Arithmetic mean concentrations wereless than one-sixtieth of the standards (0.25 mg/m3 ceiling, 25 mg/m3 8-hour, and 5 mg/m3 8-hour,respectively). In two published studies of radiographers? exposures to glutaraldehyde, reportedconcentrations have also been low: 0.003 - 0.006 mg/m3 in one study [Lienster et al., 1993]; and lessthan 0.009 mg/m3 in the other [Gannon et al., 1995]. Hewitt [1993] reported that in measurementsin a radiography processing room conducted by the British Health and Safety Executive, no sulphurdioxide was detected (detection limit not indicated). We have not found reports of measurements ofradiographers? exposures to acetic acid.These low exposure levels must be considered in the context of reported health effects. In the studyof Gannon et al. [1995], occupational asthma due to glutaraldehyde was confirmed in bronchialExposures and their Control in X-ray Film Processing 24challenge tests of two individuals working in radiography, despite exposure measurements belowdetection limits. These cases appeared clinically similar to three endoscopy nurses with the samediagnosis whose airborne exposures were considerably higher (mean personal glutaraldehyde levelsof 0.041 to 0.17 mg/m3). There have been other reports of occupational asthma amongradiographers [Cullinen et al., 1992; Trigg et al., 1992; Chan-Yeung et al., 1993], as well as reports ofother symptoms of unknown etiology [Goncalo et al, 1984; Spicer et al., 1986; Gordon, 1987;Smedley et al., 1996], but no exposure data were reported in these studies.The still very sparse exposure-response data suggest that adverse health outcomes, of glutaraldehydeat least, can be observed at exposures much lower than WCB exposure limits. The current WCBRegulation recognizes this by designating glutaraldehyde as a sensitizer and requiring exposures to?be kept as low as reasonably achievable.? Hydroquinone, another constituent of developers, has thesame designation.There are other reasons why the exposures observed in this study should not be interpreted solelyon the basis of WCB exposure limits:1)  Dermal exposures, not measured in this study, may contribute to disease. Few tasks withpotential for skin-wetting exposures took place during the study period (e.g., cleaning theprocessor, refilling chemicals, or cleaning spills), however, it is possible that routine handling ofx-rays involves some small recurrent exposures throughout every work day.?  Radiography exposures involve a mixture of many agents. Glutaraldehyde itself has beenidentified as a sensitizer which can cause asthma in radiographers, but it is also possible that themixture of agents could contribute to a heightened sensitivity, or to other non-asthmasymptoms. Many agents present in the fixer and developer solutions (e.g., hydroquinone) werenot measured in this study.?  Exposure standards of some other agencies are lower than the WCB limits. For example, theWorld Health Organization recommends that exposures to sulphur dioxide not exceed 0.5mg/m3 averaged over a 10-minute period in order to protect asthmatics, nor exceed 0.125mg/m3 averaged over 24 hours [WHO, 1999]. Although exposures were measured with adifferent averaging period in this study, the data suggest that both of these guidelines could havebeen exceeded.Radiographers? perceptions of odours were not related to exposure levels, therefore lack ofperceived odour should not be used as an indicator of low exposure. Odour thresholds andolefactory fatigue vary considerably between subjects. Acetic acid has an odour threshold rangingfrom 2.5 to 250 mg/m3, and that for sulphur dioxide ranges from 1.18 to 12.5 mg/m3 [Ruth, 1986].The minima are close enough to the highest full-shift average exposures to these agents to expectthat some subjects would have smelled these chemicals during higher peak exposures over shortperiods in their work days. The odour threshold for glutaraldehyde has been reported as 0.16 mg/m3[ACGIH, 1997]. Because measured exposures to glutaraldehyde were considerably lower than this,glutaraldehyde is less likely to have been detected by the study subjects.4.2.2 VentilationLocal exhaust ventilation of the film processing machines was associated with lower personalexposures to all three agents in univariate analyses, and remained a predictor of reduced exposuresto glutaraldehyde and acetic acid even after controlling for other factors. Although this indicates thatlocal exhaust ventilation is an effective method of exposure control for radiography, the exposuresExposures and their Control in X-ray Film Processing 25were reduced by less than 50%, and volumetric flow rates greater than 20 cfm did not giveconsistently better results.The less than optimum performance of local exhaust ventilation was not expected and suggestsinvestigation of points of gas and vapour release not controlled by the current ventilation design. Apossibility is the discharge tray where heated air used to dry the x-ray films and the films themselvesexit the cabinet. Sulphur dioxide is a byproduct of the drying process, and was not controlled by thecurrent local exhaust ventilation design, supporting the idea that the film discharge tray could allowgas release. Other locations in the processor rooms which do not normally have local exhaustventilation include the floor drains to which processor chemicals are discharged and the tanks inwhich the developer and fixer chemicals are mixed and stored. These are likely to be less important,for the following reasons. Open drainage was not a predictor of exposure in any of the models. Themixing tanks were closed except on the rare occasions when developer or fixer concentrates wereadded, and these additions were not consistent predictors of exposure. A final possible explanationfor the only moderate success of local exhaust ventilation is that some of the exhaust ducts mayhave fed into the return air ducts of the general ventilation system rather than exhausting to theoutdoors. If this were the case, contaminated air could be recirculated in a diluted form back intothe building air.General room ventilation was not found to be related to reduced exposure levels. We used theroom?s volume and mechanical exhaust air flow rate to estimate the room air exchange rate. Tracergas methods of measuring air exchange rates would take into account any additional air exchangebetween adjacent rooms, as well as natural ventilation with outdoor air through poor seals. It ispossible that with this more accurate measure of air exchange, a relationship between generalexhaust ventilation and exposure would have been detected, however, our results suggest roomventilation is unlikely to be a major source of exposure reduction.4.2.3 Other Determinants of ExposurePersonnel in private facilities had average exposures 60 to 170 % higher than those in hospitals andhealth care facilities. Hospitals more frequently had local exhaust ventilation and silver recoveryunits, they processed fewer films per machine, and their radiographers spent less time in darkroomsand in the processor area. All of these factors were related to lower exposures, and are likely toexplain the lower levels observed in the hospital settings. More exposure variance, especially insulphur dioxide levels, was explained in the models which included facility type. This suggests thatsome remaining difference between hospital and private facilities remains unaccounted for.Factors which were the most stable predictors of exposure in the models were the number of filmsprocessed per machine, time spent in the processor area, and local exhaust ventilation. Other factorsappeared influential in some models, but not others. Adding developer and having more than onemachine per room were associated with a greater likelihood of exposures above the detection limit.The use of silver recovery units was associated with lower exposures to acetic acid and sulphurdioxide in the initial multivariate analysis. The reason for this effect is unknown, but it is likely thatsilver recovery units allow additional time for fixer solutions to cool and become less volatile beforethe waste fluid exits to the drain.The models explained 8 to 38% of the variance in exposure. In observational studies examining theExposures and their Control in X-ray Film Processing 26determinants of exposure to other agents in other industries, investigators have been able to explainas little as 3% and as much as 83% of exposure variability [Burstyn and Teschke, 1999]. Exposurevariance is often more difficult to explain when exposures are low and a large proportion ofexposure measurements are below detection limits, as was the case in this study. However, it is alsopossible that factors which we did not record contributed to exposure. For example, future studiescould attempt to assess flow rates of air emissions from the discharge trays of the processormachines, and conduct more sophisticated measurements of room ventilation.Some factors were not predictors of exposure in any of the models: the addition of fixer during thework shift; and open drainage of the processing machines. The addition of fixer and developerchemistry and sealed drains were only rarely observed, therefore effects of these factors may havebeen difficult to detect. Other characteristics were observed infrequently (e.g., loading films andcleaning machines) or varied little (e.g., relative humidity and temperature); effects of these factorswere not detected in this study. None of the machines in the exposure study used manual mixingand there were no spills on the sampling days, therefore the effects of these factors could not beevaluated.4.3 Study LimitationsThough the limits of detection of the exposure monitoring methods used in this study were wellbelow WCB exposure limits, the methods were unable to detect exposures in more than 40% of thepersonal measurements. More sensitive sampling and analysis methods would be extremely useful topermit exposure-response analyses which can examine whether effects occur at very low levels, assuggested by some evidence to date.Dermal exposures were not assessed in this study, so their contribution to total dose is unknown.Such exposures may be contributors to sensitization. Measurement of dermal exposures is notstandardized or simple. Although quantification of chemicals or their metabolites in biological fluids,such as urine or blood, is ideal as an indicator of total dose from all routes of exposure, suchmethods require that the metabolism and kinetics of the agent are known. When biologicalmonitoring is not possible, methods which assess skin exposure by means of patches, bodydosimeters, or tracers may be used, but these have many limitations in interpretation.This study did not measure all the possible chemicals used in radiography. Of those not included,the glycols, potassium hydroxide, and hydroquinone are the most deserving of follow-up because oftheir frequency of use and/or existing exposure standards. However, all are considerably less volatilethan the chemicals measured in this study, so it seems unlikely that airborne exposures to thesechemicals would be as high as those measured here.The exposure portion of this study included many large hospitals in the Vancouver area. It is notclear whether the results are generalizable to smaller public facilities in less populous areas. Becausethe private facilities in the exposure study resembled those in the telephone survey, their results areexpected to be applicable throughout the province.Exposures and their Control in X-ray Film Processing 274.4 Conclusions and RecommendationsThe results of this study indicate that radiographic film processing personnel in British Columbiahave exposures to glutaraldehyde, acetic acid, and sulphur dioxide at levels well below current WCBexposure limits. However, because glutaraldehyde is a sensitizer, and because there is some evidencethat health effects, including asthma, may occur at levels lower than these standards, efforts tominimize exposures remain the best practice.Most facilities in the province employ local exhaust ventilation of processing machine cabinets andhave silver recovery units. Both measures were associated with reduced exposures in this study, andare reasonable control strategies. To ensure the usefulness of local exhaust ventilation systems, theducting from the processor cabinets must be connected to a fan designed for the system, capable ofexhausting the contaminated air at a flow rate of at least 20 cfm to the outdoors.Sulphur dioxide levels were not controlled by standard processor cabinet ventilation. Wehypothesized that this may be due to contaminated air exiting the machine at the film discharge tray.Local exhaust ventilation hoods at these locations may reduce exposures, but would need to bedesigned and tested. As a preliminary recommendation, the exhaust flow rate should be at least twicethe flow rate of air discharged from the machine (or three times if the temperature of the air leavingthe processor is over 50 ?C).Radiographers who spent more time in film processing rooms had higher exposures in this study,therefore administrative measures or machine placements to reduce the time spent in proximity ofthe machines would be effective control measures. Sealing open drains would be good practice,though we did not observe an increase in exposures with open drainage in this study.Another prevention option may eventually eliminate the chemical exposures altogether: the adoptionof digital imaging processes. Digital imaging can be done using digital x-ray cameras, or usingtraditional cameras, but capturing the image on reusable "direct-capture thin-film-transistor"detectors instead of photographic film. While the digital images can still be transferred tophotographic film using traditional wet-chemical processors, the technology allows the alternativesof viewing the images on a computer screen or dry-printing them on film. Such technologies wereobserved in use at two of the 35 sites in the exposure monitoring survey. Digital imaging is slowlybeing adopted in the industry because it allows computer transfer and manipulation of the x-rayimages, improving their diagnostic utility.Any future studies of wet-chemical film processing should include measurements of dermalexposure to both the volatile and non-volatile constituents of the developers and fixers, shouldinvestigate methods to reduce detection limits of airborne exposures, and should attempt to assessexposures during spills and manual mixing. Studies investigating the relationship between bothdermal and airborne exposures and health effects would greatly improve our ability to design andlocate control measures.Exposures and their Control in X-ray Film Processing 285.0 ReferencesACGIH. (1997) Documentation of the Threshold Limit Values and Biological Exposure Indices. American Conference ofGovernmental Industrial Hygienists: Cincinnati, OH.Burge PS. (1989) Occupational risks of glutaraldehyde. Br Med J 299:342.Burstyn I, Teschke K. (1999) Studying the determinants of exposure: A review of methods. Am Ind Hyg Assoc J 60:57-72Chan-Yeung M, McMurren T, Catonio-Begley F, Lam S. (1993) Occupational asthma in a technologist exposed toglutaraldehyde. J. Allergy Clin. Immunol 91:974-978.Corrado O, Osman J, Davies R. (1986) Asthma and Rhinitis after exposure to glutaraldehyde in endoscopy units. HumanToxicol 5:325-7.Cullinan P, Hayes J, Cannon J, Madan I, Heap D, Newman Taylor AJ. (1992) Occupational asthma in radiographers.Lancet 340:1477.Gannon PE, Bright P, Campbell M, O?Hickey SP, Burge PS. (1995) Occupational asthma due to glutaraldehyde andformaldehyde in endoscopy and x-ray departments. Thorax 50:156-159.Goncalo S, Brandao FM, Pecegueiro M, Moreno JA, Sousa I. (1984) Occupational contact dermatitis to glutaraldehyde.Contact Dermatitis 10:143-4.Gordon M. (1987) Reactions to chemical fumes in radiology departments. Radiography 53:85-89.Hayes J, Fitzgerald M. (1994) Occupational asthma among hospital health care personnel: a cause for concern? Thorax49:198-200.Hewitt PJ. Occupational health problems in processing of x-ray photographic films. Ann Occup Hyg 37:287-295Hornung RW, Reed LD (1990) Estimation of average concentration in the presence of non-detectable values. Appl OccupEnviron Hyg 5:46-51.Jachuk S, Bound P, Steel J, Blain P. (1989) Occupational hazard in hospital staff exposed to 2 percent glutaraldehyde inan endoscopy unit. J Soc Occup Med 39:69-71.Kivity S, Fireman E, Lerman Y. (1994) Late asthmatic response to inhaled glacial acetic acid. Thorax 49:727-728.Lienster P, Baum JM, Baxter PJ. (1993) An assessment of exposure to glutaraldehyde in hospitals: typical exposure levelsand recommended control, measures. Brit J Ind Med 50:107-111Malo J-L, Cartier A, Desjardins A. (1995) Occupational asthma caused by dry metabisulphite. Thorax 50:585-586.Rappaport SM, Selvin S, Roach SA. (1988) A strategy for assessing exposures with reference to multiple limits. Appl IndHyg 3:310-315.Ruth JH. (1986) Odor thresholds and irritation levels of several chemical substances: A review. Am Ind Hyg Assoc J47:A142-A151Smedley M, Inskip H, Wield G, Coggon D. (1996) Work-related respiratory symptoms in radiographers. Occup EnvironMed 53:450-454.Spicer J. Hay DM. Gordon M. (1986) Workplace exposure and reported health in New Zealand diagnosticradiographers. Australasian Radiology 30(3):281-6.Trigg CJ, Heap DC, Herdman MJ, Davies RJ. (1992) A radiographer?s asthma. Respir Med 86:167-169.WHO. (1999) Air Quality Guidelines. World Health Organization:GenevaWCB. (1984) Laboratory Analytical Methods. Workers? Compensation Board of British Columbia: Richmond, BC.WCB. (1998) Occupational Health and Safety Regulation. Workers? Compensation Board of British Columbia: Richmond, BC.Wymer ML, Chan-Yeung M, Kennedy SM, Kasteel K, Dimich-Ward HD. (2000) A comparison of respiratory symptomsbetween physiotherapists and radiographers. 2000 American Lung Association/American Thoracic Society InternationalConference. Toronto, Ontario.

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