Document Rp0GYyQ6Zd9eOYvO63KLzZL8v

ABDOOO18276 OCCUPATIONAL SAFETY AND HEALTH _____________________ X1H-A INDUSTRIAL HYGIENE FOM CHAPTER XIII MODIFICATION OF PELs FOR PROLONGED EXPOSURE PERIODS A. Purpose and Scope. The 1968 ACGIH Thresh* old Limit Values (TLVs) adopted by OSHA as per missible exposure limits (PELs) are directly related to assumed conventional exposure periods or no more than 8 hours/day, 40 hours/week. 1. The 8-hour exposure limits for some sub stances may not provide appropriate protection from health hazards when novel work schedules are utilized; e.g., exposures longer than 8 hours/day, four 10-hour days/week, six 7-hour days/week, etc. This chapter identifies those PELs which may inadequately protect workers for prolonged exposure periods and describes how an "adjusted PEL" may be calculated. 2. Instructions on sampling and citation pro cedures shall be sought from the Assistant Re gional Administrator (ARA) for Technical Sup port who shall in turn contact the Directorate of Technical Support. B. Procedure. 1. Each substance listed in the Substance Toxicity Table in Chapter II has been assigned to one of the six "Work Schedule" categories de scribed in Figure X1II-1 on the basis of the 1968 Documentation of TLVs published by ACGIH. 2. During a health inspection, the Industrial Hy gienist has the responsibility of documenting any work schedules resulting in excessive exposures to a hazardous substance caused by exposure periods longer than 8 hours/day or 40 hours/week. This would include routine overtime shifts. 3. The Industrial Hygienist should determine an "adjusted PEL" as necessary for each hazardous substance samples, according to the specifica tions given for the category to which it is as signed. 4. No adjustment should be made to the PELs of substances in category 1. For all other categories, the equivalent PELs should be calculated ac cording to the methods described in paragraphs C.l through 6 and used as a professional guide or in the evaluation of actual employee risk. 5. In all situations, the equivalent PEL will be equal to or lower (i.e. more restrictive) than the PEL values listed in 29 CFR 1910.1000. 6. The Industrial Hygienist should also elicit from the employees and document any symp tomatology that may be related to the exposure. C. Work Schedule Categories. 1. Category I A. Ceiling Limit Standards. Sub stances in this category (e.g., butylamine) have ceiling limit standards which were intended never to be exceeded at any time, and so, are in dependent of the length or frequency of work shifts. The ceiling PELs for substances in this category should not be adjusted. 2. Category IB. Standards Preventing Mild Irrita tion. Substances in this category have a PEL designed primarily to prevent acute irritation or discomfort (e.g., cyclopentadiene). There are es sentially no known cumulative effects resulting from exposures for extended periods of time at concentration levels near the PEL. The PELs for substances in this category should not be adjust ed. 3. Category 1C. Standards Limited by Technologic Feasibility.The PELs of substances assigned to this category have been set either by technologic feasibility (e.g., vinyl chloride) or good hygiene practices (e.g., methyl acetylene). These factors are independent of the length or frequency of work shifts. The PELs for substances in this category should not be adjusted. 4. Category 2. Acute Toxicity Standards. a. The substances in this category have PELs which prevent excessive accumulation of the substance in the body during 8 hours of ex posure in any given day (e.g., carbon mon oxide). XIII-1 XIII-C4a ABDOOO18277 XIII-C4bOCCUPATIONAL SAFETY AND HEALTH INDUSTRIAL HYGIENE FOM b. The following equation determines a level which ensures that employees exposed more than 8 hours/day will not receive a dosage (i.e. length of exposure X concentration) in excess of that intended by the standard. Equivalent PEL=8-hour PEL X 8 hours (Equation XHI-1) hours of exposure in one day c. The Industrial Hygienist should normally conduct sampling for the entire shift minus no more than one hour for equipment set-up and retrieval (e.g., at least 9 hours of a 10-hour shift). In situations where an employee works multiple shifts in a day (e.g., two 7-hour shifts), and the Industrial Hygienist can docu ment sufficient cause to expect exposure con centrations to be similar during the other shifts, the sampling should be done during only one shift. 5. Category 3. Cumulative Toxicity Standards. a. Substances assigned to this category present cumulative hazards (e.g., lead, mer cury, etc.). The PELs for these substances are designed to prevent excessive accumulation in the body resulting from many days or even years of exposure. b. The following equation ensures that work ers exposed more than 40 hours/week will not receive a dosage in excess of that intended by the standard. Equivalent PEL=8-hour PEL X 40 hours Equation XIII-2) hours of exposure in one week c. It is the responsibility of the Industrial Hygienist to conduct sufficient sampling to document exposure levels for the entire week when evaluating conditions on the basis of this equivalent PEL. For most operations the In dustrial Hygienist will be able to sample during one shift only and then document suf ficient cause to predict exposure concentra tions during the other shifts. 6. Category 4. Acute and Cumulative Toxicity Standards. Substances in this category may present both an acute and a cumulative hazard. For this reason, the PELs of these substances should be adjusted by either equation XIII-1 or XIII-2; i.e. whichever provides the greatest pro tection. 7. Refined Adjustment Equations for Specific Stan dards. The adjustment equation presented for categories 2 and 3 reflect an oversimplification of the actual accumulation and removal of a toxic agent from the body. Additional research, how ever, is needed in order to apply more complex equations to estimate resulting body burden and health risk due to] prolonged exposure periods. This chapter will be updated when the necessary data become available. Industrial Hygienists having sufficient data to validate adjusting PELs by a more rigorous method such as those pro posed in the following articles are encouraged to do so following approval from the ARA for Tech nical Support: Brief, R.S. and R.A. Scala, "Occupational Exposure Limits for Novel Schedules," Amer. Ind. Hyg. Assn. Jour. 36:467, 1975. Roach, S.A., "A Mors Rational Basis for Air Sampling Pro grammes," Ann. Occup. Hyg. 20:65, 1977. Hickey, J.L.S. and P.C. |Reiat, "Application of Occupational Exposure Limits to Unusual Work Schedules," Amer. Ind. Hyg. Assn. Jour. 36:613, 1977. XIII-C7 XIII-2 ABDOOO18278 OCCUPATIONAL SAFETY AND HEALTH _______________ Figure XU 1-1 INDUSTRIAL HYGIENE FOM Work Schedule Category 1A IB 1C 2 3 4 FIGURE Xm-1 Summary of Work Schedule Categories Principle Group Characteristic Conditions Resulting In Adjustment Adjustment Formula Ceiling limit standards None None Irritants None None Technologic limitations None None Acute toxicity only Exposed greater than S hours/day Adj. PEL= PEL x 8 hours/ hours exposed/day Cumulative toxicity only Exposed greater than 40 hours/ week Adj. PEL = PEL x 40 hours/ hours exposed/week Both acute and cumulative toxicity Exposed greater than 8 hours/day and/or exposed greater than 40 hours/week The equation for category 2 or 3, whichever results in the greatest protection XIII-3 Figure XIIM INDUSTRIAL HYGIENE FOM ABDOOO18279 OCCUPATIONAL SAFETY AND HEALTH XIII-4