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O' Exposures to Vinyl Chloride Vapor: alysis and Continuous Air Sampling r i* EDWARD D. BARETTA,* RICHARD D. STEWART, JOHN E. MUTCHLERf and Department of Environmental Medicine, Marquette School of Medieina, Milwaukee, H'isconrin, and Environmental Health Section, Biochemical Research Laboratory, The Dow Chemical Company, Midland, Michigan 0 An environmental survey was conducted to determine the thne-weighted srtrtff exposure (TWA) of a group of chemical plant workers to vinyl chloride (VCI) vapor. This survey featured continuous multipoint air sampling and analysis using an infrared spectrophotometer. The inhalation exposure data were digitised and record ed on paper tape for subsequent computer analysis aad 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 *erc derived from the data. To validate the breath curves derived from on-tbo-job data, postexposura breath curves were also constructed from breath data obtained following experimental human exposure* to carefully controlled concentrations of VCI 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 individi'.al daily exposure to VCI, and provides further evidence that breath analysis is a useful industrial hygiene technique for evaluating vapor exposure. Introduction <T1 HE QUESTION THAT MAY ARISE *- following an environmental survey is whether the chemical vapor concentrations measured are truly representative of the ex posure being experienced by the workmen. Kvaluation of the ranges of atmospheric con centrations and estimates of time-weighted average concentration. (TWA) are all too often based on a few spot samples obtained under conditions which are not representt- t've of all phases of a given operation- A more exact measurement of vapor exposure would have to he kfemdoa continuous moni toring of air in workman's breathing rone during his enrfjte work shift. Obviously thi- task is made difficnlt and often impossible ti wi pnvnlri at the American Industrial ",\re Si. Lout., Mwouri, May 13-17, 1968. larqurtie School of Mediant, Milwaukee, Wfocon*'*. ,r D** Chemical Company, Midland, ilkhifa*. by the large number and variety of tasks per formed by today's modem 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 has been under de velopment which more precisely defines the level of individual exposure. The realization that the total body burden of a volatile chem 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 estimating the more indi- 537 t -L i t i 4l t I, ii i y hi *i[ f r, ii f' ii Wi >1 u ij i I) t i -in iOt-. , ,, BOR 011297 ir mber-December, 1969 Atmosphere ' ation survived- was- a ng several separate ^rations. First, a job for each of four job nine the work areas nen and the time they ach job classification, re strategically placed :th probe was placed d charcoal and silica in the sampling line ference. The sample I.D. Saran tubing ties were drawn by a :e of 17.5 liters/min rared spectrophotomrneter was equipped ength gas cell sensiat a wavelength of cr -ntration was p to approx* of the sampling sys* 1. Sampling was exa set of six two-way d by a timer which ocation every 5 minif transmittance was irt recorder. Meanirded in digital form punch and digitizerthree equally spaced le last half of each i ta furnished by the tonverted to absorb* centration according <,"X<P) X.-X00) esponse. t total absorption, t lot ns. American Industrial Hygiene Association Journal 539 Finally where C- KA K = a proportionality constant. C -- concentration The taped data were processed by a Bur roughs 5500 computer at The Dow Chemi cal Company Computation Research Labora tory. The computer was used to calculate the mean and standard deviation of concen trations at each location for each 8-hour work shift. Finally, time-weighted average concentrations were calculated for each job classification using the time-location data obtained from the job surveys. As described elsewhere,1 the weighted percentage of time during which concentrations exceeded sev eral prechosen levels was also computed for use in establishing exposure profiles. Figure 2 describes the exposure profiles (frequency distributions) for the four job classifications studied during this survey. These profiles show the percentage of time that concentrations exceeded the levels shown. They summarize-several ten* of thou sands of individually measured concentra tions and reduce them to single curves. Fig ure 3 shows the corrective trend brought about by actions undertaken to reduce the atmospheric concentration of VC1 over the 7-month period during which the study was conducted. Only two job classifications war ranted extensive study, but men in all four classifications woo asked to participate in the breath sampling program. Fiovaa 2. Exposure profiles expressed a* VO vapor concentration versus the exposure frequency distribution fas the four job classificatioait cap glass vial (Figure 4-). The overalllfest^h of the pipet was about 9 Inches, so ia ttosaM be conveniently and inconspicuously ported to and from work in a lunch bucket. The 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 air ef fective gas barrier so that vapor losses were held to less than 10% for a holding period of 3 days. When collecting a sample the subject was asked to remove die caps, place the pipet to his lips, and breathe normally in through his nose and exhale through the pipet three ^^the-Job Breath Sampling " Time separate breath sampling programs were conducted, concurrently with the envir onmental plant survey, designated by the boxed portions in Figure 3. Each worker collected three breath samples daily--the first on his arrival home from work, the second 5 to 10 hours later, and a final sample be fore reluming to work the following day The samples were collected in pipets constructed from short lengths of 20-mm soft glass tubing to which had been welded at each end the threaded portion af a 2-dram (8-ml) screw- Fiona* 3. Weekly mean vapor exposure concen trations measured during the survey. Periods dur ing which breath sampling was conducted are rep resented by. the boxed-in areas. BOR 011298 540 Nopember-Decembcr, BcmegM--r " iTBtims mer infrared spectrophotometer equit with a 10-meter path-length gas cell. A * '""............ pling probe, consisting of 5/16-inch I.D ran tubing, was centrally located, during Flow* 4. Glau pipet (SO ml) ujed for collect* ing breath lamplei. One cap ha* a predrilled hole for gai lampling. Both capi have Saran liner* which leaf' the pipet chamber. exposure to represent the breathing zon all subjects within the chamber. The p was movetf about prior to each exposut detect imbalance of vapor concentrat times. After expelling the fourth breath he quickly caps the tube, trapping a portion of alveolar air. The importance 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-600B gas chromato graph using Nz carrier gas and a hydrogen within the chamber so that necessary recrions in the recirculating system couk made. Air samples collected periodic within the chamber throughout-the expo day were analyzed by gas chromatographs added assurance of analytical accuracy. 1 the infrared spectrophotometer and the chromatograph were calibrated before t experiment and at intervals throughout exposure day. flame detector. Separations were made with a 6-foot, /g-inch I.D. stainless-steel column packed with Carbowax 20M alkaline on Chromosorb W 60/80 mesh acid-washed. Each 7.5-hour exposure day includec 0.5-hour lunch period in an uncomamiru area outside the exposure chamber. TWA. concentration was eqfadated on Exposure Chamber Operation basis of 7.5 hours of eqmehff Three experimental human exposures to Clinical and Laboratory Procedures VCL were conducted, at nominal, vapor con>- Each subject,had been under careful m< centrations of 50, 250, and 500 ppm. The cal surveillance by the medical departm exposure chamber was a room measuring 41 for a number of years, and each was give; feet by 6 feet wide by 7.5 feet high. The complete medical examination a few d room had a continuous positive air supply prior to the VCI exposures- Included w and exhaust system capable of maintaining a complete urinalysis and 24-hour urine a slight negative pressure within the cham urobilinogen, complete blood1 count with s ber. Continuous distribution of the cham imentation rate, reticulocyte count, SGC ber air was achieved by recirculating the air SGPT, LDH, alkaline phosphatase, Bt with a squirrel cage fan through a series of creatinine, and bilirubin. inlet and outlet ducts spanning the length of Each subject received a repeat physi the chamber. The VC1 was metered into the examination 1 hour before entering the duct carrying air exhausted by the squirrel posure chamber. This examination incluc cage fan and entered the room atmosphere via lh*recirculation system at a rate sufficient to maintain the desired atmospheric concen tration. The vapors were introduced from a pressurized storage cylinder through 6 feet of {4-inch I.D. stainless-steel tubing into a rotameter prior to entering the circulating air measurement of temperature, blood pressu and pulse rate, a neurological examinati and collection of l^lood and breath samp A questionnaire noting the presence of z symptoms of illness (for example, headac. nausea, dry throat) completed the pre-t posure medical evaluation. duct A heating tape wrapped around the stainless-steel tubing prevented condensation of the VC1 and stabilized the flow of the vapor. The concentration of VCI in the chamber was constantly monitored with a Perkin-El- After the subject entered the chamb total expired breath samples were collect every hour by having him breathe out throu a Saran tube leading to a Saran plastic c lection bag located outside the chambr Tidal volume and total expiratory capac V 011299 ' ''" ? r 538 November-December, ]<n, vidualized exposure experience of each work man. Studies by Stewart et al. ** have shown that the excretion or "decay" of vapor in the breath can be used to characterize the ex posure. Breath decay curves constructed for several chemical solvents have proved clin ically useful as an index to chemical expo sure. These breath decay curves, for the most part, were constructed from postexposure breath data obtained from experimental hu man exposures to carefully controlled and relatively constant vapor concentrations. However, breath decay curves have recently been constructed from breath data collected from workers whose work environment was being continuously monitored.7 In this study of human exposure to vinyl chloride (VC1) vapor, breath decay curves constructed from data obtained during ex perimental exposures to the relatively uni form concentration within an exposure cham ber .were compared with those derived at the theoretically equal, but broadly fluctuating, concentrations encountered in a chemical plant atmosphere. A measure of the validity of continuous monitoring data and the use fulness of breath analysis in assessing timeweighted average exposure was reflected by a close similarity between- the two sets of breath decay curves. -fci f WORK AREA 1 STATION 3 ___S_T9Ai T.ION ft statioh z jSTATIOR 4 j STATION ft ii1--9i--- t* f i 6 S, SPIENCFTRRAORMEEOTER \WC1T12ER RECORDER*^ 1 EXPOSURE SUMMARY 001 > TIME* WEIGHTED MEAN EXPOSURE WS*n I, -Mf WWMfrttiM St*liM I F| pr Milt. tHM fpMil tocatitfi i durtaf trawl work tctivilf Figure 1. Schematic diagram of the infrared continuous monitoring system. i Procedures Monitoring the Plant Atmosphere The chemical installation surveyed was closed structure housing several separat chemical, processing operations. First, a jo survey was conducted for each of four jc classifications to determine the work are: frequented by the workmen and the time the spent in each area. For each job classification five sampling probes were strategically place in the work* area. A sixth probe was place outside the building, and charcoal and silic gel filters were placed in the sampling lir, to assure a clean air reference. The. samp, probes were 5/16-snch IT). Saran tubir. through which air samples were drawn by vacuum pump at a rate of 17.3 liters/mi to a centrally located infrared qteetrophoton eter. The spectrophotometer rtrm equippe with a 10-meter path-length gar cell sens tive to 5 ppm oi VC1 at a wavelength c 10.63 microns. The VC1 concentration w; linearly related to absorbance up to appro: innately 1000 ppm. A schematic diagram of the sampling sy tem is shown in Figure 1. Sampling was e: ecuted sequentially with a set of six two-v e solenoid valves controlled by a timer whic advanced the sampling location, every 5 mii utes. A visual account of transmittance w: recorded on a strip chart recorder. Meat while the data were recorded in digital fon on paper tape by a tape punch and digitize programmed to record three equally space transmittances during the last half of eac 5-minute sampling period. The transmittance data furnished by tl spectrophotometer was converted to absorl ance and reduced to concentration accordh to Beer's law: where A X, X Xi (X,-X) A = Loglo- (X.-X00) = absorbance = base-line response. = response at total absorption. = response at location i. = 2, 3, 4, 5, 6. 01*3 mher-Dectmber, 1969 photometer equipped mirth gas cell. A samof 5/16-inch I.D. Sa lly located during the die breathing zone at chamber. The probe r t each exposure to vapor concentrations > that necessary cor ating system could be rollccted periodically oughout the exposure is chromatography for lyrical accuracy. Both >tometer and the gas ilibrated before each Tvals throughout the sure day included' a n an uncontaminated sure chamber. The as calculated on the aosure. t under careful medimedical department md each was given a lination a few days ures. Included were id 24-hour urine far food count with sedacyte count, SGOT, phosphatase, BUN, I a repeat physical ore entering the exxanrination included ture, blood pressure, logical examination, and breath samples, the presence of any example, headache, npieted the pre-exn. tered the chamber, tples were collected breathe out through a Saran plastic colside the chamber, iry capacity Jmiliean Industrial Hygiene Association Journal 541 were measured in the moming and again late in the afternoon exposure periods. Subjective and neurological responses were measured before the subject entered the chamber, 15 minutes after entrance, and at 1-hour intervals thereafter. Flannagan Co ordination and Crawford Manual Dexterity Tests were conducted at midmoming and again in the afternoon. Breath sampling be gan immediately after the subject left the exposure chamber. A 24-hour postexposure urine sample was collected and a blood sam ple was drawn the following morning for SGPT, LDH, alkaline phosphatase, BUN, creatinine, and bilirubin determinations. Analysis of Breath Data The decay curves for the breath vinyl chlo ride concentrations were constructed by step wise multiple regression using a digital com puter. An empirical relationship of the form Concentration -- f (TWA, time)' was select ed from a choice of several terms, each based on TWA and/or time. The resulting, regres sion equation best represents the ordered re lationship between breath vinyl chlonde con centration, time-weighted average exposures, and postexposure time. Each breath decay curve has an associated standard error of regression which can be used to compute the confidence band for any chosen level of significance. The 95% con fidence band for the mean of a group of ob servations was chosen in this case to describe the statistical error associated with the breath data and the regression technique. ITable Experimental Human Exposure to Vinyl Chloride Chimbc Concentration (pps) X sjj. 59 2 261 S 493 7 491 S <PP> 6S-3S 289-243 31S-I7I 323-473 TWA* (pp) 48 24S 439 491* Nuahar at Subject* 6 4 4 7 Tim*<wflitsd >( (iweimiin bwd on 7.5 Houq ineludint a 0.5-boor lunch pariud in fta unconummr^d ma. kCMuittuoa wpaiin for 3.5 kowt Table 1 shows the analyzed .concentration to which 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 die hour exposure period* The TWA is on the total 7.5 hours which included hour lunch period in an niKUUtaiuinated area. The final breath decay curves intended for use as an index to VCI exposures were ad justed to TWA concentrations of 50, 250, Results Bssperimental Breath Curves A total of 13 men participated in the three sytiiiiiBiial chamber exposures at nominal concentrations of 50, 250, and 500 ppm pro ducing a total of 160 valid breath data points. Five of the six subjects exposed to 50 ppm were re-exposed at 500 ppm 2 days later. There was no measurable residual vinyl chloride detected on the breaths of the sub jects prior to the second exposure. Serial breath sampling was initiated immediately after the subjects left the exposure chamber and continued up to 20 hours following the exposures. mnvassmpor BOR 011301 am M2 November-Deeember, 1969 DA&y VARIATION N EXPOSURE TO VCL VAPOR with confidence bands only slightly 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 Doys of MoAtfi JMmffawQsm ttmm Figure 6, Variation in VCt vapor eapotuM fox. three shifts. * and 500 ppm (Figure 5). A 100-ppm decay curve was interpolated from the available data using regression analysis. These curves are presented with the calculated 95% con* fidence bands for the mean of a group of ob servations. On-tlie-Job Breath Curves Ten workmen participated in the on-thejob breath sampling program, producing a total of 91 usable sett of data. Ten percent of the breath samples collected were discard ed because of pipet leakage or poor sampling techniques. Absolute breath levels ranged from about 20 ppm in one sample taken less than 1 hour after an 8-hour TWA of 250 ppm, to barely detectable* levels- (<0,05 ppm) in samples taken after exposures at TWA's below 50 ppm. The extremely broad variation in the TWA's experienced by workmen during one of the periods in which breath sampling was being conducted- a demonstrated for three shifts of men bearing the job classification "coagulator operator" (Figure 6). Minute, hourly, and daily fluctuations in the concen tration of a contaminant are most descriptive ly revealed by continuous monitoring. This method of sampling quickly points out the fallacy of judging TWA and peak exposure concentrations on the basis of spot sampling or periodic surveys of brief 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 Figure 7, From a subjective standpoint no significant untoward affects were noted at any of the exposure concentration*. The only complaints were those of two subjects who reported mild headache and some dryness of their eyes and nose during the 500-pvm exposure experi ments. No odor was detected by anyone entering the exposure chamber at 50 ppm. At 250 ppm all 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 chare her at 500 ppm were able to detect the of VC1, but after 5 minutes of exposure there five were unable to detect it even with forced^ inspiration. Three of the four subjects re entering the chamber after lunch were able Fiouaa 7. Breath decay curve* derived from breath data collected from workers following onthe-job exposures to VC1 vapor (8-hour TWA). 1969 / wider human experibetween these rom controlled stratcd in Fig* : no significant at any of the nly complaints reported mild their eyes and xwure experiyone entering apm. At 25 the chamber >uld detect a 1. Five of the posure cham'tect the odor xposure those n with forced subjects re* ch were able is ta 20 derived from following onur TWA). H iwriniw Journal faint odor of VC1. One subject faint odor on deep inspiration foe apgMftmlately 15 minutes after entering the expoftrie chamber. The exposure had no noticeable effect on neurological responses, nor did it produce sig nificant changes in the results of mental, co ordination, or manual dexterity tests conduct ed during the exposure period. All clinical laboratory studies performed in the post exposure period were normal and not signifi cantly different from pre-exposure values. -> 54J Discussion The object of the environmental health survey is to identify the atmospheric contam inant, determine the exposure level, and re late this to the health hazard it presents. If one is to judge hazard by ambient concen tration measurements, then those measure ments must accurately describe the exposure on a continuing individual basis. A carefully I" conducted survey combining continuous anal ysis of the work room atmosphere with a comprehensive job study will provide data Fionas 8. Comparison of breath decay curves derived from the on-the-job data and the experi mental human exposure data. \aiid for estimating time-weighted average exposure. limited, by Uml number of probes, On the other hand, breath decay curves and these probes are not always capable constructed from breath data collected dur of accurately measuring the individual's daily ing continuous plant monitoring arc in. close exposure experiences, especially should these agreement with those obtained from exposure involve unusual incidences such as chemical chamber experiments with VC1. These curves spills or exposures outside the monitored should therefore be useful as a second meth area. od for assessing exposure to VCl vapor. Breath analysis has the advantage of in The choice of whether one or both meth dividualizing each worker's integrated daily ods should be used depends on prevailing exposure. Breath decay curves, as an index circumstances and on the thoroughness de of exposure, offer a means of estimating the sired. For example, data useful in describ average daily individual exposure on the basis ing peak exposures are obtained from con of a few breath samples taken serially in the tinuous monitoring. Concurrently, exposure postexposure period. Consequently breath trends aa4*CMmntrarie* gradients may help analysis can be used to diagnose as well as identify nfelBXt operational inefficiencies and quantitate an exposure which has already equiptnnipJkBlfunctions by revealing specific occurred. It is a relatively inexpensive and sourcefejKpamion. Correcting these prob simple method which can be put into opera lems restores a healthful work en tion without extensive and costly preliminary vironment but often results in bonus savings preparations. by reducing losses of raw material and prod However, postexposure breath analysis does uct not provide information on the daily fluctua Continuous monitoring, however, is ex tions of exposure, and the peak exposure con tremely costly both in time and in the equip centrations are not made evident by breath ment required. The scope of data acquired is data. Finally, breath analysis is not apptica- i wfmi iiwwaipmii. J -----hi-WV i..H-- 'I i'vr iWx mil' BO* O^1303 r V 4^ 544 Nov*mbtT-Dec*mber, Me to ell chemicals, and breath decay curves established for one chemical are not useful as an index of exposure to any other chem ical. The decay curves presented here are in tended to serve as an index of exposure to vinyl chloride vapor and are based on an exposure duration of 7.5 hours for the experi mental exposures, and 8 hours for the on-thejob study. The close agreement between the two sets of curves and the narrow confidence bands obtained in each case demonstrate the usefulness and accuracy of both methods for estimating TWA exposures and indicate the importance of breath analysis and the need for expanding its use in evaluating ex posures to other widely used volatile- organic chemicals. References 1. hwaM, J. E., H. R. Hovu. and E. 1. Saturn-a The Application ( Computer Seiem to Indiutna! It.. ficiM. Amat. /ad. Hyg. Ant. ]. 27: ISOtlU (Uji. !. 1966). 2. SnwAiT, R. D-, H. H. Car, D. S. Etuar, C. L. H*. and A. W. Settaarm: Human Euooun to TctncMoni. cthrkna Vapor: JUkltonihip of Expired Air aod Bl...| Conecutradonr to Exposure and Tweity. Artk. Ean'" Haalik 2: J16J22 (May 1961). 3. Snwut. R. D., H. H, Gay, D. S. Eaur. C. L. Him. and I. E. PxrzaaoM: Observation, on the Conceniriti.'i. of TYiehiotoothylcoo io Blood and Ltptrtd Air Win,, inx Expoem* of Humana. Anar. /ad. Hyg, Ante. J- < 16%t7(f(Ai>a 1962). 4. Stxwaht, R. D.. and V. K. Row*: Quinn \i.d'Etudaa tur la l.l.l'Trichiornethana. Artk. Haiti. frofan. 2t: 194-201 (1967). 3. SrtWAKT, R. D., H. C. Dsn x. O. >Aaxm, and A. W. SotAffmt: Home* Fapruiuu to Swaioi Vapr. Arek. Emviran. Haaitk IE: Ha, 5 (Mar 1968). 6. Smtaar. R. D., E. D. T. R. ToanuoNt . , TetrachloroaOryicno. AMA Aftki (In print). 7. SnttAtt, R. D.. H. C. ItaR I- D. . A. M ScKAma, and J. E. UvsiUBi Gh to Benacno Vapor. Pvmated at tha ! in* of the Spacer o( Todeelepy, . i%t Auaao * * RnMttW*. I*** Notices and Deadlines . It is the policy of the AIHA Journal to accept and publish notices and short items of import and interest to our readers subject to the limitations of available space. This is done as a service to our profession and no fee is charged for such announcements. Some notices are received too late to be carried to advantage in our Jour nal. Persons supplying announcements to us should keep in mind the time schedule of our publication. The Journal appears six times per year with the copies being mailed about the 20th of February, April, June, August, October, aaefc-December. While emergency or urgent notices can be inserted up to three or four weeks before the mailing date, such cannot be assured. Normally the announcements should be in the Editors hands at least two months or more before die issue in which they should appear. Perhaps these guidelines will aid you announcement generators. BOR 011304 ir