Chemical Hazards in the Workplace - American Chemical Society

36 A New Passive Organic Vapor Badge with Backup Capability

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W. J. LAUTENBERGER and Ε. V. KRING Applied Technology Division, Ε. I. du Pont de Nemours and Company, Incorporated, Wilmington, DE 19898 J. A. MORELLO Engineering Test Center, Ε. I. du Pont de Nemours and Company, Incorporated, Wilmington, DE 19898 Recently, interest has been growing in sampling organic vapors with a passive sampling device (1-8). In general these devices collect organic vapors by means of molecular diffusion and adsorption onto an activated charcoal collection element. After exposure, the activated charcoal is desorbed with a measured volume of desorbing solvent. The desorbing solutions are then analyzed using gas chromatographic techniques outlined in NIOSH Analytical Method, P&CAM 127. A new passive organic vapor badge has been developed with the capability of determining when breakthrough or saturation of the charcoal adsorbent has occurred. The Du Pont Pro-Tek Organic Vapor Air Monitoring Badge with Back-Up (G-BB) contains two 300 milligram charcoal strips, one in the front section and another in the backup section. (See Figure 1.) The front section of the badge normally collects a l l of the contaminant. The backup section serves two purposes: 1) it can indicate when saturation of the front section has occurred, and 2) it can extend the total sampling time up to the point of its saturation. Experimental The dynamic contaminant generation system used has been p r e v i o u s l y described by Du Pont f o r the purpose of l a b o r a t o r y v a l i d a t i o n of sampling methods where an accurate measure of the true contaminant concentration could be determined (9*.10)· The badge exposure chamber used i n the l a b o r a t o r y t e s t i n g c o n s i s t s of a m i n i a t u r i z e d wind tunnel made of g l a s s rectangular tubing jacketed with a water condenser which permits temperature control. (See F i g u r e 2.) G-BB badges were placed i n the exposure channel chamber and held i n p o s i t i o n so that the flow of a i r remained p a r a l l e l to the face of the badges. Exposure t e s t s involved the placement of s i x badges i n the chamber and

0097-6156/81/0149-0575$05.00/0 © 1981 American Chemical Society

In Chemical Hazards in the Workplace; Choudhary, G.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.


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Figure 1.

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Pro-Tek G-BB badge components

DELRIN SHIMS

BADGE HOLDER

EXPOSURE CHANNELS

END VIEW

SIDE VIEW Figure 2.

Badge exposure chamber



36.

LAUTENBERGER

E T

AL.

Passive Organic

Vapor

Badge

577

the removal of one every hour. Exposure dose l e v e l s were, t h e r e f o r e , generated over a range of c o n d i t i o n s . Test vapors chosen were toluene, acetone, methyl chloroform, and t r i c h l o r o e t h y l e n e . Generated concentrations were approximately one to two times the TLV . A l l organic chemicals used were F i s h e r S c i e n t i f i c Company spectro q u a l i t y grade. Face v e l o c i t y c o n d i t i o n s were maintained at 100 ft/min. Temperature and pressure c o n d i t i o n s were 298°K and 760 mm Hg r e s p e c t i v e l y . R e l a t i v e humidity was e i t h e r 5 or 80 percent. For storage s t a b i l i t y t e s t s , a s u f f i c i e n t number of badges were exposed to an exposure dose l e v e l of approximately one-half the c h a r c o a l c a p a c i t y at 80 percent r e l a t i v e humidity. H a l f the samples were r e f r i g e r a t e d (40-45°F) and h a l f were l e f t a t ambient temperatures (75-80°F). Badges were then analyzed a t i n t e r v a l s ranging from one day to three weeks. Analysis A f t e r exposure, the a c t i v a t e d c h a r c o a l s t r i p s are removed from both f r o n t and backup s e c t i o n s f o r a n a l y s i s . Each s t r i p i s desorbed separately with 1.5 ml of spectro q u a l i t y carbon d i s u l f i d e and a g i t a t e d f o r 30 minutes w i t h a shaker (SKC Model Charcoal Developer). The desorbing s o l u t i o n i s then analyzed by removing a 0.5//-/ a l i q u o t and i n j e c t i n g i t i n t o a HewlettPackard Model 5840A gas chromatograph equipped w i t h an automatic sampler (Model 7672A) and flame i o n i z a t i o n d e t e c t o r . The a n a l y t i c a l column used was a 6-foot by 1/8-inch g l a s s tube packed w i t h 10 percent Carbowax 20M on 80/100 mesh Chromosorb W. The u n i t was operated i s o t h e r m a l l y w i t h column temperature ranging between 65°C and 100°C depending on the contaminant being measured. The c a r r i e r was n i t r o g e n at a flow r a t e of 30 cm^/min. C a l i b r a t i o n standards f o r the a n a l y s i s were prepared d a i l y so that known q u a n t i t i e s of the contaminant were contained i n the desorbing s o l v e n t . The weight of the desorbed contaminant i s determined by comparison with peak areas of known c a l i b r a t i o n standards. The t o t a l mass c o l l e c t e d was determined by c o r r e c t i n g the desorbed mass f o r d e s o r p t i o n e f f i c i e n c y . P r e v i o u s l y determined d e s o r p t i o n e f f i c i e n c i e s were found to be: 0.67, acetone; 0.97, toluene', 0.98, t r i c h l o r o e t h y l e n e ; and 1.01, methyl chloroform (10). R e s u l t s and D i s c u s s i o n Theory For d i f f u s i o n a l badges, according to F i c k ' s F i r s t Law of D i f f u s i o n , the amount of mass, M (ng), adsorbed on the c h a r c o a l i s a f u n c t i o n of the badge sampling r a t e , (D A/L) (cm^/min), times the ambient c o n c e n t r a t i o n , C (mg/m3) and the sampling time, t (min)(3,5,7,11-14).


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M (ng) - D

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t (min)

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(1)

The badge sampling r a t e i s a d i r e c t f u n c t i o n of the d i f f u s i o n c o e f f i c i e n t (D) of the organic vapor(s) being sampled and the t o t a l c r o s s - s e c t i o n a l area (A) of the badge c a v i t i e s . The r a t e i s an inverse f u n c t i o n of the d i f f u s i o n path or length (L) of the c a v i t i e s . (2)


where: 2 D, ^ r ^ - = D i f f u s i o n c o e f f i c i e n t a t 25°C, 760 mm Hg A, cm^ = T o t a l c r o s s - s e c t i o n a l area of the c a v i t i e s L, cm = Length of c a v i t i e s According to equation (1), i f the badge geometry i s held constant, the mass c o l l e c t e d w i l l be a l i n e a r f u n c t i o n of the exposure dose, C x t (See F i g u r e 3) up to the p o i n t of s a t u r a t i o n of the c h a r c o a l . I n a two-stage badge such as the G-BB badge the f r o n t s e c t i o n of the badge samples a t a r a t e of approximately 50 cm^/min. up to the p o i n t of s a t u r a t i o n . (See Figure 4.) No sampling should be taking p l a c e a t t h i s time i n the backup s e c t i o n . A f t e r s a t u r a t i o n of the f r o n t s e c t i o n , however, the backup s e c t i o n samples a d d i t i o n a l m a t e r i a l a t a reduced r a t e . (See F i g u r e 5.) The sampling r a t e of the backup s e c t i o n i s a f u n c t i o n of the t o t a l area and length through which the contaminant must t r a v e l from the f r o n t face of the badge to the backup s e c t i o n charcoal s t r i p . This sampling r a t e can be determined by the use of equation (3) (14).

(3)

where: d i f f u s i o n a l r e s i s t a n c e through d i f f u s e r element 1 d i f f u s i o n a l r e s i s t a n c e through charcoal

strip

d i f f u s i o n a l r e s i s t a n c e through d i f f u s e r element 2 For the G-BB badge: = 0.135 cm + .023 cm + 0.135 cm = 0.293 cm Total



36.

LAUTENBERGER

E T A L .

Passive Organic

Vapor

Badge

Exposure Dose (ppm-hours)

Figure 3.

Figure 4.

Backup badge theory

Front section sampling


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\/Total

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V /Backup


Since the (j^ of the backup s e c t i o n i s 2.2 times the of the f r o n t s e c t i o n , the backup s e c t i o n should sample a d d i t i o n a l m a t e r i a l a t 46 percent of the sampling r a t e of the front section. (See F i g u r e 3.) Sampling Data Studies of four contaminants were made to determine whether the backup s e c t i o n samples a t 46 percent of the f r o n t s e c t i o n r a t e a f t e r s a t u r a t i o n of the f r o n t s e c t i o n . The four contaminants chosen had v a r y i n g vapors pressures and adsorption p r o p e r t i e s on c h a r c o a l . (See Figures 6-9.) In a l l four cases, breakthrough was detected a f t e r s a t u r a t i o n of the f r o n t s e c t i o n charcoal and the sampling r a t e i n the backup s e c t i o n was approximately 46 percent of the sampling r a t e of the f r o n t s e c t i o n . The s o l i d l i n e p l o t t e d through the backup s e c t i o n data points i s the t h e o r e t i c a l slope assuming the backup s e c t i o n sampling r a t e i s 46 percent of the f r o n t s e c t i o n sampling r a t e . Extended Sampling Time I f s a t u r a t i o n of the backup s e c t i o n has not occurred, one should be able to add the mass c o l l e c t e d i n each s e c t i o n and determine a t o t a l mass c o l l e c t e d . T h i s t o t a l mass c o l l e c t e d should be a l i n e a r f u n c t i o n of the exposure dose, C x t u n t i l the backup s e c t i o n charcoal becomes saturated. The equation below determines the t o t a l mass c o l l e c t e d . W

(ng) = W

CT

cp

(ng) + 2.2 [ W

CB

(ng)]

(4)

Where W W

T o t a l corrected

CT

CF

=

weight

Corrected weight of exposed s t r i p i n f r o n t s e c t i o n .

Corrected weight of exposed s t r i p i n backup section. 2.2 = C o r r e c t i o n f a c t o r based on the f a c t that the sampling r a t e of the backup s e c t i o n i s 46 percent of the sampling r a t e of the f r o n t section.

W

CB =



LAUTENBERGER

Passive Organic

E T A L .

Figure 5.

Vapor

Badge

Backup section sampling

Exposure Dose (ppm-hours)

Figure 6.

Toluene sampling data: T = 298 K; RH = < 5%; P — 760 mm concentration = 125 ppm; (%) front section; (O) backup section


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Figure 8. Trichloroethylene sampling data: T — 298 K; RH = 80%; P — 760 mm Hg; concentration = 990 ppm; (%) front section; (O) backup section


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AL.

Passive Organic

Vapor

Badge

583

Weights have been corrected f o r any c o r r e c t i o n from a blank ( i . e . , c h a r c o a l s t r i p from an unexposed badge). F i g u r e 10 represents the t o t a l c o r r e c t e d mass as a f u n c t i o n of exposure dose f o r toluene from the data c o l l e c t e d i n F i g u r e 6. A l i n e a r r e l a t i o n s h i p e x i s t s out to exposure dose l e v e l s of at l e a s t 9,000 ppm-hours versus 4,000 ppm-hours f o r the f r o n t s e c t i o n of the badge. T h i s extended l i n e a r i t y allows one to increase the sampling time f o r measuring an exposure.


Storage S t a b i l i t y A f t e r a t e s t exposure, the cover was replaced on the badge and the badge r e s e a l e d i n a pouch. Then, h a l f of the samples were r e f r i g e r a t e d and h a l f were stored a t ambient temperatures. F i g u r e 11 shows that the storage s t a b i l i t y of the t o t a l mass c o l l e c t e d i s approximately two weeks f o r acetone, t r i c h l o r o ethylene, and toluene whether stored r e f r i g e r a t e d or at ambient temperatures. During sample storage, the more v o l a t i l e compounds may migrate throughout the badge u n t i l e q u i l i b r i u m i s reached. F i g u r e 12 shows that f o r v o l a t i l e compounds such as acetone and t r i c h l o r o e t h y l e n e s i g n i f i c a n t m i g r a t i o n occurs w i t h i n one to two days. T h i s m i g r a t i o n process i s somewhat reduced by r e f r i g e r a t i n g the samples. For compounds i n which m i g r a t i o n i s expected, s e p a r a t i o n of the charcoal s t r i p s immediately a f t e r exposure appears to be necessary. Conclusion To date, l a b o r a t o r y sampling t e s t s f o r acetone, methylchloroform, t r i c h l o r o e t h y l e n e and toluene have confirmed the Pro-Tek G-BB Organic Vapor A i r Monitoring Badge's a b i l i t y to: 1. I n d i c a t e when s a t u r a t i o n of the f r o n t s e c t i o n of charcoal has occurred. 2. Extend the t o t a l sampling time f o r measuring an exposure. Storage s t a b i l i t y s t u d i e s i n d i c a t e that badge samples can be stored up to two weeks e i t h e r r e f r i g e r a t e d or a t ambient temperatures. However, f o r v o l a t i l e compounds such as acetone and t r i c h l o r o e t h y l e n e m i g r a t i o n does occur and separation of the charcoal s t r i p s immediately a f t e r exposure i s recommended. Acknowledgements The authors express t h e i r g r a t i t u d e to the f o l l o w i n g f o r t h e i r a s s i s t a n c e : V i n c e Keedy and Dave Mount f o r a s s i s t a n c e i n badge design and c o n s t r u c t i o n ; John P r a t t , J u a n i t a Reeves,


584

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40 -

m


E

1000

2000

3d00

4000

5000

6000

Exposure Dose (ppm-hrs)

Figure 9. Methyl chloroform sampling data: T — 298 K; RH — 80%; P = 760 mm Hg; concentration — 400 ppw; (%) front section; (O) backup section

1

2

3

4

5

6

7

8

9

Exposure Dose (ppm-hours x 10 ) 3

Figure 10.

Total corrected mass (weight); T — 298 K; RH — < 5 % ; P — 760 mm Hg; organic vapor = toluene; concentration = 125 ppm


LAUTENBERGER

Passive Organic

E T A L .

ioop#g

o

70

TRICHLOROETHYLE

100 o*r>


585

Nominal Loading Level = 5

o

90 -

Nominal Loading Level =

o

0 -

o — I

Badge

ACETONE

8--

80 a>

Vapor

900 -80

TOLUENE

100

Nominal Loading Level = 12 mg

90 80 5

10

20

Time (Days)

Figure 11. G-BB storage stability—percent total mass retained vs. time; data points, average of two determinations: (O) ambient (75-80°F); (%) refrigerated (40-45°F)

50,

Equilibrium Value

o 40

30

20

10

fi-

10

20 Time (Days)

Figure 12. G-BB storage stability—percent mass on backup section vs. time; data points, average of two determinations: (O, %) acetone, (A, A) trichloroethylene, (C\,M) toluene; open symbols, ambient temperature; closed symbols, refrigerated


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and L o i s L i n f o r performing many of the sampling and a n a l y t i c a l procedures; A n i t a P o l l a c k f o r e d i t o r i a l a s s i s t a n c e ; and Mary Lynn Woebkenberg of NIOSH's Measurements Systems Section f o r h e l p f u l d i s c u s s i o n s and suggestions.


Literature Cited 1. Bailey, A.; Hollingdale-Smith, P. A. Ann. Occup. Hyg., 1977, 20, 345-356. 2. Evans, M.; Molyneux, M.; Sharp T.; Bailey A.; HollingdaleSmith, P. Ann. Occup. Hyg., 1977, 20, 357-363. 3. Tompkins, F. C., Jr.; Goldsmith, R. L. Am. Ind. Hyg. Assoc., 1977, 38, 371-377. 4. Nelms, L. H.; Reiszner, K. D.; West, P. W. Anal. Chem., 1977, 49, 994-998. 5. Bamberger, R. L.; Esposito, G. G.; Jacobs, B. W.; Mazur, J . F. Am. Ind. Hyg. Assoc. J., 1978, 39, 701-708. 6. West, P. W.; Reiszner, K. D. Am. Ind. Hyg. Assoc. J., 1978, 39, 645-650. 7. Montalvo, J. G., Jr. Am. Ind. Hyg. Assoc. J., 1979, 40, 1046-1054. 8. Toshiko, H.; Ikeda,M. Am. Ind. Hyg. Assoc. J.,1979, 40, 1091-1096. 9. Freeland, L. T. Am. Ind. Hyg. Assoc. J., 1977, 38, 712-720. 10. Lautenberger, W. J.; Kring, E. V.; Morello, J . A., Am. Ind. Hyg. Assoc. J., 1980, 41, 737-747. 11. Palmes, E. D.; Gunnison, A. F. Am. Ind. Hyg. Assoc. J., 1973, 34, 78-81. 12. Palmes, E. D.; Gunnison, A. F.; DiMatto, J.; Tomczk, C. Am. Ind. Hyg. Assoc. J., 1976, 37, 570-577. 13. Gossilink, D. W.; Braun, D. L.; Mullins, H. E.; Rodriguez, S. T.; paper presented at American Industrial Hygiene Conference, Los Angeles, CA (May 1978). 14. Palmes, E. D.; Lindenboom, R. H. Anal. Chem., 1979, 51. 2400-2401. RECEIVED

October 15, 1980.


Chemical Hazards in the Workplace - American Chemical Society

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