Document rpDMg9KM3B1xREx90E4gzRnx0

The Monitoring of Benzene Exposure by Air Sampling R. J. SHERWOOD Err0 Europe Inc.. Err0 Research Centre, R bingdon, Berkshire, England The information prcunted shows that it h not possible to ensure compliance with an absolute ceiling threshold limit for benzene. The ANSI standard can be dightly modified to provide practicable working criteria of IO pprn timcweightcd average and not more than 2% probabiliq ol a c e d i n g 25 ppm. It would. however, be simpler Cor the hygienist to work to a daily exposure dose limit of 5000 ppin-minuter, which u proposed here. Thu criterion is tested against wn\c typical log-normal distribuciom and h aub m i t t d to toxicologists for consideration. Introduction BENZENE HAS BEEN described as radiomimetic. It would seem that this description is appropriate to the incidence of chronic disease which nianifests itself by blood changes comparable to those p r e duced by ionizing radiation and, as recently reported, by chromosomal damage. While both benzene ant1 radiation can cause acute poisoning, the effects are not similarperhaps due in pnrt to the differing routes of access to the body. While the effects of overexposure to benzene are commonly assessed by hematology, the possible risk arising from occupational exposure can k determined by one or more of three techniques. Tlie5e are detemination of the concentration of benzene in the air the man breathes, measurement of concentration of benzene in tlie breath he exhales after exposure may have occurred, and analysis of his urine for the principal metabolite-conjugated phenol. T h e first is a measure of his exposure, the second ;I measure of [lie atiiount absorbed, the third a measure of the amount of benzene metab olized in the body. Imprwements have been made in these techniques and have been evaluated by a test exposure to a controlled C O I ~ ~ ~I I ~ I I tion;' typical application in a field >IIII!~ using personal air samplers has I K W ~ *!I scribed.` This paper considers tlie problcrii f.u ii: the practicing hygienist in the intcqiit t tion of air sampling results usitig ( i i r t ~ ! criteria. It does not present new tosiittl$, i d information, and toxicity n q ~ " .I!. introduced only insofar as t h y i i r h I\ air sampling criteria. Air Simpling At the prese-nt time the inclitrtri.il !, gienist is presented with a l n w i l d ~ ~ i i i assortment of standards for asws4iiy 9 p u r e . Some of the various ir;rrilli. standards recently reportedx sliow IIV: varying from 6 to 100 ppm. I n the United States all tlic f111111t.~ standards are currently valid: Threshold Limit (1970)` ANSI Standard (1969)c 25 ppri 1 1 I!: 50 p p i ~I I C . ~ ~ 25 pprii I t li 10 p p t i 1: wcigtiirtl cr;gc 840 American Ilidri~ Hygienic Guide While it ib en` limits "should I only by a per: pline,"' some 3 on the signifimr desirable. Summary of Air As concentratl places typically ticcessary to collr ;rig zone if resti: irilialed by a ma, A5 concentrat ctlly in time, it i ofmeasurements ol time to r e p I ontlitions. Kcpresenta tive lcrtctl by mean, iwifiiiial person; iiicriiisically safe . -' - F-- I A ure liancc wiili ing criteria cxcediiis y cxposurc Ind b SUI,. ie intlustri:il 11). I a bewilclcriii; for assessing cx various n:i tiori;i i etP show lint i t * lm. 111 the folloivii val icl : 25 i'pn cciliiiK 30 p p i p k 25 pplll cciliiis 10 ppm tinic. weighted nv. crage I I!l;icnic Guide (I 970)a 25 pprn c e i h g 100 ppm short- exposure tolerance \\'Iiile it is entirely proper that threshold tinits "should be interpreted and applied . d y by a person trained in this disciiliiiic,"' some guidance from toxicologists 1111 the significance of these values appears tlr4rable. air at a constant rate of 1 literlmin through cartridges containing silica gel attached to a harness on the shoulder. Cartridges are changed every 10 or 15 minutes, and the benzene subsequently is eluted With ethanol in the laboratory. Tlie quantity of benzene is determined by gas chromatography, and the concentration in the air calculated for each sample period. The Dis+ribu+ion of Air Sample Results Summary of Air Sampling Technique .\s concentrations of substance in work- pl,ircs typically vary widely in space, it is iictcwwy to collect tlie air from tlie brwth- 111: Lotie if results are to represent the air dinled by a man moving about at work. .is concentrations typically vary mark- tdly in time, it is necessary to take a series a l i measurements over a long enough period III time to represent average and extreme 4 oiiditions. ... Kcpresentative samples have been col- Irtictl by means of a modification of the llriginal personal air sampler7 which is iiitrinsically safe (Figure 1). This draws It has already been shown' that a series of observations oE air concentrations of 3 radioactive aerosol arising in workplaces can be desaikcl reasonably accurately by a lognormal distribution, though this does not. represent the sequence of samples with respect to time. This is also observed-in outdoor pollution studies0 and could be expected for vapor concentrations which men breath while at work. Tlie average concentration to which a man is exposed is best described by the arithmetic mean of all the samples collected, weighted for the duration of the samples unless this is held constant through- out the period. T h e variability of the concentration, which may be at least as important a factor, is best described by the geometric stan- danl deviation (GSD)which is applied to the median (geometric mean) to determine tlie probability of a given concentration's being exceeded. i FK.IW I . Intrinsically safe removal air sampla. Field Results Personal air samples. each ol 15-minute duration, have been collected during a variety of operations wlierc men are exposed to benzene vapor. Each series of samples has covered a whole working shift or a complete operation, with total times varying from 2 to 8 hours. Each set of results has been placed in rank order and plotted on logarithmic probability paper according to the system of Lirsen.10 Some typical results arc shown in Figures 2 and 3 with the computed distribution curves supcriniposed. In Figure 2, which refers to exposure to pure benzene, cume 1 shows tlie marked f :*.; 3 842 December, / I t ; .I American Industriai carbon mixture containing benzene is emir. scribed by Iog-nom: ted from a single source in a partially t w it impossible to a p p i closed area. For two men working ar~iiii~,! value, as there is a fir I the opening (curves 1 and 2) the GSI)'., NI concentration's beino, I 2.9 and 3.8. For one man working iii .I corresponding to r11e I confined space below the source of c t i i i a r i t ~ ~ l wre, which is abont I ! the CSD is 4.5 (curve 3). T h e evduation of i Hypothetical Distributions riiiist therefore be mr xceptable risk-th: T o enable comparisons to be mntlc wit!. probability of a 4 the criteria published in the Unitctl-Si:lit.. exceeded to an accepr three hypothetical distributions haw I1C.C 11 Such a limit can he plotted in Figure4. All three have ;I iiiiw amendment of the -11 weighted average value (arithmetic IIIC.III ccptable maximum fo: of 10 ppm and have geometric s i m t . ~ ! ~ : pcar reasonable to pr deviations of 1.5, 3.0, and 4.5 to re1li.u\t.r!* (ration of 25 ppm aver least. typical, and most variable C ~ J I I ~ C I I I I . ~ iiiay be exceeded on11 tions likely to be met in practice. 1'11t~i m i * hour working perioc: line proposed by Jones and Brief," W I ~ I ~ IO-minute p e r i d s tlur is also shown, is discussed later. , > , , . , , ,,CLI ,[ ),, t w - R V W I .)I a so m m m m a s a m m s z 0 O I O I L I , c o (I5 1 ? l O M D I u T I 0. CIVZW COw2s.NmATIoIu WXNC I X Q w D (%) Interprofation of Results Using Current FIGURE 2. Distribution ot air sample m u l t r for Criteria i four men exposed to benzene in various operations. Provided that sufficient numbers ol I variability (GSD 3.7) found when a man ples are taken under conditions rcplr*.I~: moves around point sources of emission in ing long-term exposure, no difficiiliv 4 1 1 ~ 1 . :he open air approaching each very closely. arise in interpretation using 111c I I I ~ ! Curves 2 and 3 show slightly lower values weighted average value of IO :]i~Jlll 4 of GSD (3.4 and 2.9) for similar operations should be noted that in a log.nol111.1(11 undertaken iri more windy conditions. In tribution the arithmetic mean is nt11 it!< contrast, curve 4 shows the small variability tical with the geometric mean (nictll.irt, (GSD 1.6) when a man works in a confined T h e interpretation of results iisiiiy >!) iI \pace. . term criteria is less straightforw.ttc! 4: I .Figure 3 shows exposure when a hydro- cifically, tlJe fact that results C;III ftc I ! ! thy, this can be restatc wracy in the form t k . vscceding 25 ppm ove: r i d should not be gre: Such a criterion In: I w i b l e to assess sliorr;I log-normal p!ot or cs wiiple results. If the Irittions having 'a tiin of 10 ppm shown in F' IiV this standard, i t cnn . I I F ~ where the air cor lively uniform (GSD 1 ( d the ceiling value's be d i m 1%. I n more t?; oiittloor work the probai : t i i d therefore the COR jM*;tks is more importar Ilie time-weighted averag From Figure 4 it can klr concentrations havin .i\ct-r~geof 10 ppm and I8tohability that the =\I1 w m c e of 100 ppm wou ll..?:; (one sample in fo. r\itcme case of a CSD Iiiliiy is 1% (that is, 01 drifts). It is not possible I Irilrlogiral significance of 111 a recent paper, Jone ivclirohcd a rational 1C \ u t iilg air sanipling restti r-t . .-- .I. sing Current u iillcd by lognormal distributions makes .I iiiilxmible to apply an absolute ceiling .J ~ I I C a, s there is a finite probability of any .m-ciitration's being exeeded (up to that criteria using the 10-ppm time-weighted limit and the 50-ppm maximum for a single 10-minute value. They make use of Larsen's method for plotting log-normal .tirrcsponding to the saturated vapor pres- curves and have taken account of the ef- t ~ i ~ vw, hich is about 100,000 ppm a t 20c). fect of sampling time on geometric stan'!'he evaluation of short-term exposure dard deviation which has been ignored w i \ t therefore be made on the concept of here. .A wptable risk-that is, restricting the T h e limit line they derive for 15-minute ;miIiaI)ilityof a given concentration's being sampling periods is also shown in Figure I\(crtied to an acceptable value. Siicli a limit can be developed by slight triitwtlment of the ANSI criteria for the ac~ q ~ i d )ml eaximum for peaks. It would ap;war reasonable to propose that 3 concenit;ltion of 25 pprn averaged over 10 minutes 4; it indicates that by this criterion the time-weighted average limit is more significmt than the ceiling value only for distributions having GSD's below 2.3. For typical distributions the short-term limits for exposure are more restrictive. I I I ; I ~ be exceeded only once during an' 8- From this analysis based on typical per- !loiir working period. A s there are 48 sonal air sampling results it is apparent Ill-iniiiute periods during such a working that the need to limit peak exposures -is h y , this can be restated with nclcqunte ac- likely to be more restrictive than the need 4 rimy in the form that the probability of to limit the long-term average. It is dif- wceding 25 ppm over any 10-minute pe- ficult to assess die biological significance of r i i d should not be greater tiinn 2y0. controlling a chronic hazard in this way. S d i a criterion makes it inimediate1y pi4ble to assess short-term exposure from .I IiTnonnal plot or calculation of the air The Significance of Short-Term Peak ..lniple results. If the hypothetical distri- Concen+ra+ionr Imt ions having a time-weighted average The principal reason for limiting peak 10 ppm sliown in Figure 4 are assessed concentrations would appear to be to pre- 11) this standard, it can be seen that in an vent the irritation of the upper respiratory .iicn where the air contamination is rela- tract and eyes, and to control the risk of rivcly uniform (GSD 1.5) the probability acute effects of intoxication. In the Hy- 111 the ceiling value's being exceeded is less gienic Guide it is stated that a concentratlm 1%. I n more typical conditions of tion of 3000 ppin is irritant, but the author uuttioor work the probability is about IO%, believes that 5000 ppin can be tolerated on a n d therefore the control of short-term a purely subjective basis. . .l d i s is more important than control of T h e concentration that produces nar- I IIC time-weighted average concentration. cotic symptoms IS less clearly defined. It is From Figure 4 it can also be seen that certainly dependent on t-h--e- d-_u_ra-tI-io--n._o-f[t~rconcentrations having a time-weighted exposure and is probably best expressed as c . ~ v c r q eof 10 ppm and a GSD of 3.0, the an exposuredose-that is, the multiple of Itrolnbility that the AIHA short-term tol- the concentration to which exposure occurs vrnnce of 100 ppm would be exceeded is and the duration of the exposure. Review 0.5% (one sample in four shifts); for the of published literature suggests that the Iwrcine case of a GSD of 4.3, the proba- danger limit for intoxication from short- Iiiliiy is 1% (that is, one sample in two term exposure is of the ordcr of 1 0 0 , O hifts). It is not possiblc to coinmcnt on thc ppm-minutcs. It tlicreforc appears desirable I,iological significance ol such valucs. that for any exposure exceeding about 2 In a recent paper, Jones and Brief" have minutes and less than S hours the permis- proposed a rational procedure for com- sible concentration should be inversely prolmring air sanipling results with the ANSI portional to the duration of exposure. f L .. t 1 t ../ American Intlrral rin There remains the question of whether slow and dependent on time-weigktal ~ t . directly related to c exposure to occasional short-term peak erage exposure. colIected by the fz concentrations can cause chronic benzolism. 5000 ppm-minute 1 This is suggested in the contribution made cccded, then the r i s by Gerarde in patty's Industrial Hygiene A Single Criterion to Control Chronic and tliseasc i\ tinlikcly arid Toxicology12 wliicli is not precisely Acute Hazards If short-teriii SI quoted in the Hygienic Guide. Review of T o meet varying environmental CIJII~!~ probability ot ;I b i n the literature does not reveal any specific tions it at first appears necessary to q u o t t . exceeding 500 ppin evidence that chronic disease has been range of appropriate acceptable C~IICCWI ., ppm-minutes) c.in produced by short-term peak exposures in tions for various exposure pericxls. the absence of a significant time-weighted However, a single criterion for cF[nnlltl -a [ticfnannineexdtrefmroeinly Fviagru: exposure. Where brief exposures to high dose can be derived from the prcl\cltt iiilltconcentrations have occurred, these are weighted average limit, which i\*.orlltl y i \ v I \ n o more than 0.05 .tverage is not to likely to have been repetitive and accom- adequate control of both clironic : ~ t t t l;I( 111, panied by more prolonged exposure to low hazards. Thus, an exposure-dose of :p~~i corresponds to a sir tiionths; for more levels. Although a sudden death has been reported following an unknown short e x p surela (and the post mortern results suggest ppm-minutes corresponds closely to t h 111 ppm time-weighted average limit for ;III hour exposure, and for short exlms~irc1" 1 1 ods is well below the concentratioti i ciitrations the pro! I C ~ S than once per y A further advant. o f criterion is that. 3 that a longer period of exposure must have to produce narcotic effecu. IO a fixed amount 01 occurred), the principal acute effect to be For single daily exposures of rltir o t , ! , ~ witpler of given flow controlled is commonly taken to be narco- for periods as short as 1minute the liitiiiitt: 4 d e to construct si1 sis. Recovery following a severe exposure parameter may be irritation, I)w+~ I I d e warning if excc may be complicated by later ~equelae,~' of the difficulty of safely contmllirig M) rliatr! From a series OE s though Elkinsis suggests that the risks of a time limitation, exposure ofnial is,iiIt,,:.! wlmsures for period severe aftereffects following a single severe respiratory protection could not Ix it :ippars that an e exposure are less than with most of the sidered good practice. ilH)O ppm-minutes i organic hrrlogegeli compounds. If benzene is indeed radiomiiricric., I!~., puIlice concen tra t If i t can be assiinied that the chronic consideration- might be given to CoiitrIbtIit. Ihmol in urihe in 1 blood dyscrasias can be related to the exposure over much longer periwls. 11 i t I.. itig/liter. This is bel amount of benzene taken u p and retained he noted that radiation stant1;irtIh t ~ , ~ - . ~ 3 M ) mg/liter p r o p 1 in the bone marrow, i t would appear un- changed from a ceiling value C O I H C ~ ~ I t i t \i7-19 for the c t n t likely that sliort-term exposure alone can pressed in roentgens per mirrute i l l l!v:* I I Iriit sufficient to Shc make a .significant contribution. exposures averaged over three niotltlr,. ll~!l From breath sampling results following year, a generation, and even a likhlc.. 1 \powre can probabl tiiied by encl-of-shif experimental and occupational exposure It is pertinent to ask whether t11c fllltl! III ICllOI. (to be reported), there appears to be a b o d y compartment in which benzene is very sloivly absorbed and excreted. There is reason to believe that this is fatty tissue and that it probably includes the bone marrow i n which the blood cells develop. T h e excretion half-life has been found to be of the order of 24 hours, and it is likely that mental standards for benzene C S ~ M ~ , I ~ C should be set 011 similar long-tintc pi,.. even if short-term criteria to C O I I ~1I1 ~I ~ I risk of acute poisoning are ;ilso rccl\iir-cc! 11 is certainly economically (1esil;lljlc I ! ; , some relaxation of present critcri:1 In. ., lowed for intermittent operations iiivt,I\li, benzene. .\lthougli end-of 511 1itlc ;i very sensitive i cp:wtitative mposurt \t..r\cd from samples rliiit is. immediate1 h i i t . An exposure C l t ri1c7 coiild be expect 1) 1' p p i i n breath at uptake is similarly slow. In dog experiments Schrenk et aLl8 showed long-term retention T h e Application of the Propo~crl of benzene during and following long ex- Criterion to Field Sampling The Significance of 5, posure. T h e use of the single exposurc-tltl,c. While benzene uptake by the blood is terion permits routine monitoring of ill, very rapid, and fairly rapid absorption oc- vidual men at risk by means of siiiglc curs in muscular and well-perfused tissues, ples collected over the work shill. I:~,I the uptake by bone marrow is probably very given sampling rate the expurc.lll.,u .I .r 845 I t on time-weiqllcrti ,I$ .t~ccdyrelated to the quantity ol benzene mean concentration is maintained at a level 1 4 x t e d by the s a m p h g device. Xf the 1 standard deviation below the threshold *FIN@ ppm-minute limit lias not been ex- limit, tlie risk of the threshold b o d y burden )O Control Chronic and ncr.tlcti, then the risk of chronic and acute being exceeded at any time wouId be less Oliccasc is unlikely in these .conditions. than one in a million. This is perhaps an If short-term samples are taken, the 2 environnie1it;Il ~ ~ I I ~ I ~:,ml~abilityof a single 10-minute sample's tars necessary to .,( ~ I I I I I I . \rcmling 500 ppm (expslire-tlose = 5000 te acceptable COIICI-IIII ;p-minutes) can be approximately tie- overconservative approach. From Sahinann's work" it can be deduced that fluctuations in the quantity of the vapor retained in the body are adequately r e p .posure periods. wriined from Figure 4. Even in the case resented if sampling time is one to two co criterion for cxl)tt\tlrl 9 1 f iiii extremely variable concentration this times the biological half-life. 1 from the prcacllr 1 i l 1 t 1 - I* JJOmore than O.OS(r, if tlie time-weighted T h e biological half-life for benzene in h i t , which woiii~l! ; i \ a I\cmge is not to exceed 10 ppm. This the brain is not well established, and it does h t h chronic ant1 CI; I I I , torresponds to a single sample every two not appear p i b l e to set an appropriate exposure-dose or .;JIIIII llioiitlis; for more typically varying con- sampling period to control the hazard of .ponds closely tu tII(. III t cnira tions the probability corresponds to acute poisoning. Zf, however, the suggestion average h i t for ;III s IC%t\han once per year. to establish a maximiim exposure of 5000 for short expostirc j1t.l t .\ lurther advantage of using this type ppm-minutes is accepted, then a sampling he Concentration ktlcl\\ II d criterion is that, as the limit corresponds system could readily be developed to give effects. it) 2 fixed aniount of benzene trapped in a warning when such an exposure may occur. exposures of this ol.clt.1 wipler ofgiven flow rate, it sliould be pos- Olxervations of benzene elimination (to as 1 minute the liliiiiil1:: Ale to construct simple monitors to pro- be reported) show a half-life for excretion irritation, Imt. ill vi#.!\ iitlc warning if excessive e x p u r e occurs. of phenol sulfate in urine of about 7 hours, ifeiy controlling so k11t11I From a series of studies of occupational wliicli may be related to the concentration sposiire of men wiilic)lll rqmures for periods from !A2 to 3 hours. of benzene in the liver. If this is a signif- on coiiltl not be ;I t'oII. it appears that an exposure dose limit of icant biological parameter, then sampling ce. .;OIN) ppm-minutes could be expected to periods as long as a whok shift will reveal leer1 radiomimetic, i 1 ~I 1 ltrotliice concentrations of conjugated fluctuations adequately. I be given to controllilt:: 1 longer periods. It i\ i t l .tiation standards d i n g value concept c\. pltenol in urine in the range of 20 to 60 iiix/liter. This is below the value of 70 to 3 0 mglliter proposed by various auth. tifir7-10 for the controi of chronic hazard T h e significance of l o n g p e r i d retention of benzene in fatty tissue to air sampling procedure has already been discussed. s per minute in 1928 I ( , Init sufficient to show that risk of acute Statistical Aspects over three months, olllarid even a lifetime. ask whether the funt1;rfor benzene exposll1.c. riiilar long-time perioclh criteria to control tljc. ing are also required. 11 bm ically desirable tha I present criteria be nlpiit opcrations invoIvir1~ rxlmure can probably be adequately monicorcd by end-of-shift urine sampling for plienol. Although end-of shift breath samples provide a very sensitive indication of exposure, cpntitative exposure can really only be aswssed from samples taken 18 hours later -that is, immediately before the following h i f t . An exposure dose of 5000 pprn-minu ~ c scouid be expected to produce about I),!! ppm in breath at that time. Samples of air are taken to estimate the concentntions of substances "sampled" by workers; it is too commonly assumed that they are identical. Personal sampling reduces errors due to variation o concentration with distance; statistical methods are needed to determine the likely magnitude of errors due to fluctuations in time. While a single sample over a shift can provide a measure of a man's exposure during that shift, it provides no indication I llrc Yq9o.tc~rl Sampling The Significance of Sampling Time of likely fluctuation. If conditions do not change signilicxntly bctwecil sliilu, tlwi itn estimate ofthe possible error iu assessirlg ingle esposure-dose criine monitoring of indiby means of single sa111- the work Shih. For I :e tile exposure-dose is Iliological Aspecls Roachzohas suggested that the sampling h i e might be set at one-tcnth the biologitxl half-life and, assuming a nonnal distriI d o n of results, has shown t h t , if tlie exposure can be iiiade by observing fluctuations during a shift. This is coiiimonly done by a simple rule based on the range of the results observed which assumes their norn d tlistributioii, but it is k t t e r made by 846 December, 1371 calculstioii oC standard error as described by Gale" and applied to radioactive particle sampling. Unless preliminary results show that tlie Ievcl of exposure is likcly to be very far away from the criterion, a t least 25 samplcs will Le required to obtain adequate statistical accuracy. J f routine monitoring is found to be necessary, i t is important that proper statistical control of the program be maintained. Conclusions The practical difficulties found in the application of a ceiling limitation to the threshold limit for a clironic poison leads to the proposal tliat tliresliolrl limit values for acute and chronic exposure be separately assessed. By introducing the concept of a permitted day's exposure based on a time-weighted average thresliold limit of 10 ppm, it appears that both acute and chronic liazarrls can be controlled by n single limit of 5000 ppm-minutes. Air saniplers to provide warning of acute overexposure could readily be constructed, and 1onFpcriorl personal air samplers will provide adequate information on which to assess the chronic Iiatnrd. .Is the introduction of this single cri- terion would greatly simplify monitoring exposure, it is hoped tliat toxicologists will consider its acceptability. References I. SHrnwooD. R. J., and F. C CASTU: The hfcmuremeni of Occupational Exposure to knxene Vapour. Ann. Occup. H y g . I I : 125 (1970). 2. SnLnwoou. K. J.: Evaluation of Exposure to &.iuria Vapour durina the Loading d Petrol. Brit. J. Indurr. M i d . 2 9 6 5 (1972). 3. Pomiuiblc LnnL of Toxic Subrtancra in Ihe Workinr: Environmmt. Ocriipational .%ifctv sir1 Hcdth L ~ i u r . Iirtcriiatiotial 1.abottr Ollice, Cctrcvr (1970). 4 . 7'hrc.~liold l.iiiiiI I`ultin 01 ..Jirbornc Contaminant<. Aiticricait ( h i f c r c w c . ol i h v c r t i n w i i i d Inclii,i~~~l Ily((irnins, (:iiiviisiixi (1370). 5 . Amcriqn N ; i i h a I Staitilnrcli liiuiiotc: Acrrplnblc i.un rcnlratioiis uf llrnrcne (IWiy). 6. Hygienic Guide Scricrlknzcne. .firirr. Ind. / f \ : dwur. J . 31: U f (197U). Ann.7. S i i u r v c m o , R. J.. and D. Sf. S. C ~ E N ~ & L G\ I I1'1.1 wtral Air Sampler. Ocrup. H y g . 2: 127 (i`JClui 8 . S~IUWOW. R. J.: On the Interpruaiion of Air S.IIIII, ling for Radroaccivc Panicles. drnrr. Ind. H y g . . 4 ~ J . 27: 98 (IWG). 9 LAU!?I. R. L : , A Method for Determining Source Ka ductron Required T o Blm Air Quality S ~ a t i d ~ t h I. 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Au I Detector t u b e s the detection o vidcd h a t the t four lima the i t and precision CI tube type nor I Introduction DETECTOR T U B industrial hygier siinple measurements 14s of certain gaseous ii;iiits i n the air of a iltc speed and ease 1% iliqus are made witi: witleniable advantage >ticIi measurements ha. \Vith the objectives t I id hygienists about i.icy a n d precision c!: awouraging tube nian L ilic performance of de: ti';iii of Occupational S rlic U.S. Public Healt I t d u c t i n g a detector I Iwt. T h e project is a 1 iitm program and is nc .I ccrtification program The Perchforoe+hylens `4, System I'crchloroethylene KI (*I c generated dynan? . ~ i i w i r emethod (Figure ,I 11. the carrier gas, was ~c.:itedd, ouble-effect ev: liloroethylene liquil