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Reprinted irum AMERICAN INULSTRIAL HYGIENE ASSOCIATION JOURNAL Volume 30. NovemDer-December, 1969 Monitoring Exposures to Vinyl Chloride Vapor: Breath Analysis and Continuous Air Sampling EDWARD D. BARETTAA RICHARD D. STEWART. M.D.,* and JOHN E. MUTCHLERf Department of Environmental Medicine. Marquette School of Medicine, Milwaukee, Wisconsin, and Environmental Heaitn Section. Biochemical Research Laboratory, The Dow Chemical Company, hdland, Michigan eg] An environmental survey was conducted to determine the time-weighted average exposure (TWA) of a group of chemical plant workers to vinyl chloride (VCD vapor. This survey featured continuous multipoint air sampling and analysis using an infrared spectrophotometer. The inhalation exposure data were digitized and record ed on paper tape for subsequent computer analysis and derivation of daily TWA values for each worker. A breath sampling program was conducted concurrently with the environmental survey, and a series of breath decay curves relating postexposure breath concentration to vapor exposure were derived from the data- To validate the breath curves derived from on-the-job data, postexposure breath curves were also constructed from breath data obtained following experimental human exposures to carefully controlled concentrations of VC1 vapor. The close agreement between postexposure breath concentrations at the corresponding TWA's obtained by each of the methods suggests that either continuous air monitoring or breath analysis is valid for estimating the worker's individual daily exposure to VCI, and provides further evidence that breath analysis is a useful industrial hygiene technique for evaluating vapor exposure. Introduction whether the chemical vapor concentrations measured arc truly representative of the ex posure being experienced by the wot kitten. Evaluation of the ranges of atmospheric con centrations and estimates of time-weighted average concentration i TWA. are ail too often based on a few spot samples obtained under conditions which arc not representa tive of ail phases of a given operation. A more exact measurement of vapor exposure would have to be based on continuous moni torin': of air in the workman's hreatiunt: zone durimr his entiic work shitt. Obviouslv this task is made difficult and often impossible This paper was presented at the American lmfuHftal Hvaicne Conference. St. Loui*. Missouri. Mi* 13-17. Marquette School of Medicine, Milwaukee. Hwroann. Dow Chemical nmoatw, Michigan. by die large number and variety of tasks per formed by today's modern chemical plant worker. Recent improvements in automatic moni toring and data processing equipment have provided a means for a more satisfactory so lution. Sequential samplers and automatic analyzers and recorders can now be used to continuously monitor several locations or operations to provide more valid data on which to base estimates of chemical exposure. Computers can be utilized to manage the large volume of data generated by continu ous monitoring.1 Meanwhile a technique itas been under de\elopmcnc which more precisely defines the level of individual exposure. The realization that the total body burden of a volatile cheu ical is directly related to its concentration in expired air led to the development of tech niques for collecting and analyzing breath samples useful in estimarine the more inn,- R&S162636 53a A oveinbcr-Dectitnber. 106!) viauaiized exposure eXDerience of each work man. Studies fav Stewart et ai. hate shown that the excretion or "decay'' of vapor in the breach can be used to characterize the ex posure. Breath decav curves constructed for several chemical solvents have proved clinicailv useful as an index to chemical expo sure. These breath decay curves, for the most part, were constructed from postexposurc breath data obtained from experimental hu man exposures to caretuily controlled and reiativelv constant vapor concentrations. However, breath decay curves have recently been constructed from breath data collected from workers whose work environment was being continuously monitored/ In this study of human exposure to vinyl chloride (YCT vapor, breath decay curves constructed from data obtained during ex perimental exposures to the relatively uni form concentradon within an exposure cham ber were compared with those derived at the theoretically equal, but broadly fluctuating, concentrations encountered in a chemical piant atmosphere. A measure of the validity of continuous monitoring data and the use fulness of breath analysis in assessing timeweighted averasre exposure was reflected by a ciose similarity between the two sets of breath decav curves. Procedures Monitoring the Plant Atmosphere The chemical installation surveyed was a closed structure housing several separate chemical processing operations. First, a job survev was conducted for each of four job classifications to determine the work areas frequented by the workmen and the time they spent in each area. For each job ciassidcacion. five sampling prooes were strategically placed in the work area, A sixth probe was placed outside the building, and charcoal and siiica gel fibers were placed in the sampling line to assure a clean air reterence. The sample probes were 5/16-inch I.D. Saran tubing through which air samples were drawn bv a vacuum pumo at a rate of 1~.5 liters/'min to a cemraily located infrared spectrophotom eter. Tiie spectrophotometer was equipped with a i 0-meter path-length gas cell sensi tive to 5 ppm of YC1 at a wavelength of 10.63 microns. The YC1 concentration was linearly related to absorbance up to approx imately 1000 ppm. A schematic diagram of the sampling sys tem is shown in Figure 1. Sampling was ex ecuted sequentially with a set of six two-way solenoid valves controlled by a timer which advanced the sampling location every 5 min utes. A visual account of transmittance was recorded on a strip chart recorder. Mean while the data were recorded in digital form on paper tape by a tape punch and digitizerprogrammed to record three equally spaced transtniaances during the last half of each 5-minutc sampling period. The transmittance data furnished by the spcctroDhotometer was converted to absorb ance and reduced to concentration according to Beer's law: TIME - WEIGHTED MEAN EXPOSURE * 0.01 ^ P, "2 Whert C, 1 mgn OftCtnirat>n gt Station Pj pr cent of lung tpgnt et lecetion during normal wore activity Figure 1. Schematic diagram oi the infrared continuous monitoring system. w here A X. A" .V, i A, (X-X~) 09,0 (X-X") = absorbance -- base-tine response. = response at total absorption. = response at location i. = 2. 5. 4. 5. 6. American Industrial Hygiene Association Journal 5.39 Finally, C= KA wheto K -- a proportionality constant. C = concentration The taoed data were processed bv a Bur roughs 5500 computer at The Dow Chemi cal Comoanv ComDUiation Research Labora tory. The computer was used to calculate the mean and standard deviation ot concen trations at each location for eacn 3-hour work shift. Finallv. time-weighted average concentrations were calculated tor eacn job classification using the time-location cata obtained from the job surveys. As described elsewhere.* the welgntea percentage o: time during which concentrations exceecec sev eral Drechosen levels was also comouted for use in establishing exposure profiles. Figure 2 describes the exposure profiles i.frequence distributions) for the tour job classifications studied during this survey. These profiles show the percentage oi time that concentrations exceeded the levels shown. They summarize several tens o: thou sands of tndividuailv measured concentra tions and reduce them to singie curves. Fig ure 3 shows the corrective trend brought about by actions undertaken to reduce the atmospheric concentration of YC1 over the 7-month period during which the studv was conducted. Oniv two job classifications war ranted extensive studv. but men in ah four classifications were asked to partirinate in tiic breath sampling program. On-the-job Breath Sorntdine - - cot 3.1 as I 2 i '0 20 10*090*070 10 90 94 J991999 999 Ttw*ejGrip % & time r coct*rjur>o* tjcrrcco r*r shqwm Ficure 2. Exposure profiles expressed as VC! vaoor concentration versus the exposure frequence distribution for the four job classifications. can glass viai i Figure 4!. The overall lengtn of the pipe: was about 9 inches, so it couia be conveniently and inconspicuously trans ported to and from work in a lunch bucket. Tiie plastic caps were lined with six layers of Saran film identical to that used for the construction of Saran air sampling bags. A 3. 32-inch hole predrilled through one of the caps provided an access for withdrawing samples. The Saran liners provided an ef fective gas barrier so that vapor losses were held to less than 10rc for a holding period of 3 days. When collecting a sample the subject was asked to remove the caps, place the pipet to his lips, and breathe normally in through hi* nose and exhale through the pipet three :*0f-- 1201- Three separate breath sampling programs were conducted concurrently with the envir onmental plant survey, designated bv the boxed portions in Figure 3. Each worker collected three breath samples dailv--me first on his arrival home tram work, the second 5 to 10 hours later, and a final sample be fore returning to work the following dav The samples were collected in pipets constructed from short lengths of 20-tnm soft glass tubing to which had been welded at eacii end the threaded portion at a 2-dram t 3-mi wrew- Fie.eRE 3. Weeklv mean vapor exposure concen trations measured during the survev. Periods dur ing which breath sampling was conducted are retjn-sented bv the boxrd-in area'. R&Si 62638 540 Xovember-December, 1969 Figure 4. Giass pioet (50 ml1! used :or collect* \ne breatn samples. One cap has a predriiled hoie for aas sampling. Both caus have Saran liners .vnich seal the piper cnamber. limes. Alter excelling the fourth breath he auicklv cans the tube, trapping a portion of aiveolar air. The imDortance of writing the name, date, exact time of sampling, and the workshift most recently completed, on the label attached to each pipet. was stressed. Aliquots were drawn from the pipets with a 1-ml Hamilton gas-tight syringe and ana lyzed in an Aerograph A-bOOB gas cnromatograph using X- carrier gas and a hydrogen dame detector. Separations were made with a 6-foot, J/a-inch I.D. stainiess-steei column packed with Carbowax 20M alkaline on Chromosorb W 60/80 mesh arid-washed. Exposure Chamber Operation Three experimental human exposures to VC1 were conducted at nominal vapor con centrations of 50. 250, and 500 ppm. The exposure chamber was a room measuring 41 feet by 6 feet wide by 7.5 feet high. The room had a continuous positive air supply and exhaust system capable of maintaining a slight negative pressure within the cham ber. Continuous distribution of the cham ber air was achieved by recirculating the air with a squirrel cage fan through a series of inlet and outlet ducts spanning the length of the chamber. The VC1 was metered into the duct carrying air exhausted by the squirrel cage fan and entered the room atmosphere via the recirculation svstem at a rate sufficient to maintain the desired atmospheric concen tration. The vapors were introduced from a pressurized storage cylinder through 6 leet of Jg-inch I.D. stainless-steel tubing into a rotometer prior to entering the circulating air "duct. A heating tape wrapped around the stainless-steel tubing prevented condensation of the YC1 and stabilized the flow ot the vapor. The concentration of VCI in the chamber was constantly monitored with a Perkin-Fd- mer infrared spectrophotometer eauipped with a 10-meter path-length gas cell. A sam pling probe, consisting of 5/16-inch I.D. Sa ran tubing, was centrally located during the exposure to represent the breathing zone of ail subjects within the chamber. The probe was moved about prior to each exposure to detect imbaiance of vapor concentrations within the chamber so that necessary cor rections in the recirculating system could be made. Air sampies collected periodically within the chamber throughout the exposure day w-ere analyzed by gas chromatography for added assurance of analytical accuracy. Both the infrared spectrophotometer and the gas chromatogrann were calibrated before each experiment and at intervals throughout the exposure dav. Each 7.5-hour exnosure day included a 0.5-hour lunch period in an uncontaminated area outside the exposure chamber. The TWA concentration was calculated on the basis of 7.5 hours of exposure. Clinical and Laboratory Procedures Each subject had been under careful medi cal surveillance by the medical department for a number of years, and each was given a complete medical examination a few days prior to the VCI exDOSures. Included were a complete urinalysis and 24-hour urine for urobilinogen, complete blood count with sed imentation rate, reticulocyte count, SCOT. SGPT. LDH. alkaline phosphatase. BUN. creatinine, and bilirubin. Each subject received a repeat physical examination 1 hour before entering the ex posure chamber. This examination included measurement of temperature, blood pressure, and pulse rate, a neurological examination, and collection of blood and breath samples. A questionnaire noting the presence of any symptoms of illness , for example, headache, nausea, dry throat i completed the pre-ex posure medical evaluation. After the subject entered the chamber, total expired breath samples wore collected everv hour by having him breathe out through a Satan tube leading to a Saran plastic col lection bag located outside the chamber. Tidal volume and total expiratory capacity American Inuusmai Hvcicne A-sut.:u::oii i-iunim 341 were measured in die mornina and again .ate in tr.e afternoon exposure periods. Subjective and neuroioeicni responses were measured before the subject entered me chamber. !5 minutes after entrance, and at i-hour intervals thereafter, F'.annagan Co ordination and Craw tom Manual Dexter, tv Tests were conducted at midmornmsr and atrain in the afternoon. Bream jamming oesran immediate:'.' after the suoiec: ie:t me exposure chamber. A 24-hour postexnosure urine sampie was collected and a biood sam ple was drawn tiie foiiowina moraine for SG?T, LDH. aikaiine ohosor.atase. 3L'N". creatinine, and biiirubm determinations. Analysis of Breath Data Tile decav curves for :he bream '.me,i emoride concentrations were constructec av stepwise muitipie learession using a digtta. com puter. An empirical reiationsnip of tr.e form Concentration = / 'TWA. time1 was select ed from a choice of several terms, earn based on TWA and. or time. The resuitins regres sion equation best represents tr.e orcered re lationship between bream vinvi chlorine con centration. time-weiirnted average exposures, and postexposure time. Each breath decav curve lias an associated standard error of regression which can be used to compute the confidence band for any chosen level of significance. The 95rc con fidence band for tire mean of a group of ob servations was chosen in this case to describe the statistical error associated with tin- breath data anti the ieyre-winn technique. Tvble I Experimental Human Exposure to Vinvi Chloride CoCnhceanmtbraetrion ppm; X i D. :syij a: 44l'J.ni :; iianfff ppmi 65- 33 i5:a21985---24t747531 mppmv( SSuumonieecrisol 424445*831** b 44 7 JTimc*weicrueb average concentration baita on 7.5 hours nemumg a j.5-hour iunen pertod ;n an unconcammateq area. "Continuous exposure for 3 5 hours. Tabie I shows the analyzed concentration to winch the subjects were exposed. Calcu lations of the mean and standard deviation of exposure concentration are based on chart readings from the infrared spectrophotometer taken at 5-minute intervals over the two 3.5hour exposure periods. The TWA is based on the total 7.5 hours which inciudea a 0.5hour lunch period in an uncontaminated area. The final breath decay curves intended for use as an index to VC1 exposures were ad justed to TWA concentrations of 50. 2a0. Results Exr rimcntal Breath Curves A total of 13 men participated in the three experimental chamber exposures at nominal concentrations of 50, 250, and 500 ppm pro ducing a total of 160 vaiid breath data points. Five of the six subjects exposed to 50 pom were re-exposed at 500 ppm 2 davs later. There was no measurable residua! vmvl chloride detected on the breaths of the sub:ec:s prior to the second exposure. Serial breacii sampling was initiated immediatelv after the subiccts left the exposure chamber ana continued up to 20 hours foilowmtr the exposures. Figure 5. Breath decav curves based on experi mental human exposures to 50, J50, and 500 ppm ol VC! i 7.5-hour TWA). R&S162640 542 Xovember-December, 1969 2L.LY VAnUTCN :M EXPOSURE ~C '/CL ,-FCF ;a r.r twa > with confidence bands oniv siightlv wider than those from controlled human experi ments. The close similarity between these curves and those constructed from controlled exposure data are further illustrated in Fig ure 8. Human Responses t;v$ ; ife vanm -.... Figure 6, Variation in VC1 vapor exposure for three shifts. ana 500 ppm (Figure 51. A 100-ppm decay curve was Interpolated from the available data using regression analvsis. These curves are presented with the caicuiated 95fc con fidence bands for the mean of a group of ob servations. On-the-job Breath Curves Ten workmen participated in the on-thejob breath sampling program, producing a total of 91 usable sets of data. Ten percent of the breath sampies collected were discard ed because of pipet leakage or poor sampling techniques. Absolute breath levels ranged from about 20 pom m one sample taken less than l hour after an 3-hour TWA of 250 ppm. to barely detectable levels (<0.05 ppm; in samples taken after exposures at TW.Vs below 50 From a subjective standpoint no significant untoward affects were noted at any of the exposure concentrations. The only complaints were those of two subjects who reported mild headache and some dryness of their eves and nose durine the 500-ppm exposure experi ments. Xo odor was detected bv anyone entering the exposure chamber at 50 ppm. At 250 ppm ail four subjects entering the chamber initially reported that they could detect a very slight odor of the chemical. Five of the seven subjects entering the exposure cham ber at 500 ppm were able to detect the odor of YC1. but after 5 minutes of exposure those five were unable to detect it even with forced inspiration. Three of the four subjects reenterins the chamber after lunch were able PPmThe extremely broad variation in the TWA's experienced by workmen during one of the periods in which breath sampling was bein': conducted is demonstrated for three shifts of men bearing the job classification "coagulator operator' (Figure 61. Minute, hourlv, and daily fluctuations in the concen tration of a contaminant are most descriptive ly revealed by continuous monitoring. This method of sampiine quickly points out the fallacy of judsrintr TWA and peak exposure "concentrations on the basis of spot samplin': or periodic survets oi briet duration. The remarkable correlation between breath concentration and corresponding TWA val ues made it possible to construct the series of breath decay curves shown in Fieure 7. Fiuvre 7. Breath decav curves derived from breath data collected from workers following onthf-|un exDosurcs to VCI vapor '3-hour TWA!. American Industrial Hygiene Association Journal JtJ to detect a faint odor ot VCi. One subject couia detect a faint odor on deep inspiration for aoproximateiy 15 minutes after entering the exposure chamber. The exposure had no noticeabie etfect on neuroiogicai responses. nor did it procuce sig nificant changes in the resuits of mentai. co ordination. or manual dexterity tests conduct ed during the exposure period. All chnicai laboratorv studies penornied in the postexposure period were normal ana not signiricantiv different from pre-exnosure vaiues. coc so r Discussion Tiie object of the environmental neaitr. survey is to identify the atmosnheric contam inant. determine the exposure ievei. and re late this to the health hazard it presents, li one is to judge hazard by ambient concen tration measurements, then those measure ments must accurately cescribe the exposure on a continuing individual basis. A carefully conducted survey combining continuous anal ysis of the work room atmospnere with a comprehensive job sraav wiii provice data vaiid for estimating timc-weignted average exposure. On the other hand, breath riecav curses constructed from breath data collected dur ing continuous piant monitoring arc m ciose agreement with those obtained !rom exposure chamber experiments with VC'.. These curves should therefore tic useful ns a second meth od for assessing exposure to VC-1 vapor. The choice of whether one or noth, meth ods should be used depends on prevailing circumstances and on the thoroughness de sired. For examnle. data useful in describ ing peak exposures are obtained trom con tinuous monitoring. Concurrentlv, exnosure trends and concentration gradients mav heip identify piant operational inefficiencies and equipment malfunctions bv re\ caiing speciric sources of emission. Correcting these prob lems not oniv :estorcs a iieaithtui work en vironment 'rmt ouen results in bonus saving? by reducing losses of raw matessai and nroduct. Cotuinuous monitoring, hot?ever. ,3 extretneiv costiv both in time anu in the c-uumment rcotiireti. The g one of data aenuued o BREATH . NYL CHLORIDE CONCEHTRATIOH. ppm ooz I----------- 1--------- oot 0 --- 2 i 5= ---- --. !0 12 IA 16 18 20 ROST EXPOSURE TIME, HOURS Ficcke 3. Comparison of breath decay curves derived from the on-the-job data and the experi mental human exposure data. limited bv the number of sampling ptobes. and these probes arc not always canabie of accurateiv measuring the individual's daiiy exposure experiences, esoecially should these invohe unusual incidences such as chemical spiils or exposures outside the monitored area. Breath analysis has die advantage of in dividualizing each worker's integrated daiiy exposure. Breath decay curves, as an index of exposure. offer a means of estimating the average daiiy individual exposure on the basis ot a lew breath samnies taken seriailv in the tsostexnosure period. Consequently breath analvsis can be used to diagnose as weil as quantitate an exposure whicii lias already occurred. It is a relatively inexpensive and simpie method which can be put into opera tion without extensive and costiv preliminary preparations. However, postexposme breath analysis does not pioviae information on tile daiiv fluctua tions o{ exnosure. and the peak exposure con centrations are not made evident by breath data. Finally, breath anaivsis is not nppiica- R&S162642 544 A on mot r-Dt'ccmht r. 19HQ bie to ail chemicais. and breath decat curves established for one chemical are not usetui as an index of exposure to any other cnemicai. The decay curves presented here are in tended to serve as an index of exposure to vinvi chloride vapor and are based on an exposure duration of 7.5 hours for the experi mental exposures, and 3 hours lor the on-thejob study. The dose agreement between the two sets of curves and the narrow confidence bands obtained in each case demonstrate the usefulness and accuracy of both metnods for estimating TWA exposures ana indicate the importance of breath analysis and the need for expanding its use in evaluating ex posures to other widely used voiatiie organic chemicals. References 1. Petejuo.v. J. E., 11. R. Hoyle, and L. f, Sciinmof.r. The Application oi Computer Science to industrial Hv^iene. Amer. Ind. Hrf. Assoc. /. 27; 180*185 < March 1%6j. 2. Stewart, R. D.. H- H, Gay. D. 5. Euj-y. C. L* HaKf.. ana \V Schaffer: Human Exposure to TetrachlorocthNienc Vapor: Reiationsnio nt Expired Air and Biona Concentrations to Exposure ana Toxicitv. Aren. Environ. Hcmth 2, 516-522 :Mav iMl., 3. Stewart, R. D,, H. H, Gay, D. 5, Eu_Y. C. L. Hake. and J. E, Peterson: Observations on me Concentration oi Tnchloroetnvlene in Blood and Exoirea Air follow ing Exposure of Humans- .imtr. Ina. Hvg. Assoc. J.23: 167-170 (April 1962 j. 4. Stewart. R. D.. and V R. Rowe: Quinze d'Etudes tur le 1.1,1-Tnenioroetnane. Arch. Maiadus Proust. 23: 194-201 1967 `., 5. Stewart. R. D.. H C. Dooo. E- D Basletta, and \ W Schaffer: Human exposure :o Styrene Vapor. Aren. /i:von, Heaitn to No. 5 Mav i9ts3'. 3 Stew art_ R, D.. E. D. BaRettv. H. C. _Dqdo and R. iCftKiUos: Experimental Human Exposure to Tetrachloroetnuenc. AMA Aren, Environ. Health. In print]. 7. Stewart. R* D.. H. C. Dopo. E. D. Baretta. a. W Schaffer, ana J. Z. Mittchler: Chronic Overexposure to Benzene Vaoor. Presented at the Sixth Annual Meet ing ot the Sociecv oi Toxicoio^v, Marcn 23*Z5. 1967. Atlanta. Georgia. Received Mav 26, 1966