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Modifying Occupational Exposure Limits for Extended Work Shifts: A Practical Approach

This guidance explores the modification of Occupational Exposure Limits (OELs) for individuals working extended shifts. The best models for extrapolating Threshold Limit Values (TLVs) require a substance-by-substance analysis based on health effects, pharmacokinetics, and biological half-life. It emphasizes that exposure limits aiming to prevent excessive irritation typically don't need modification for unusual shifts unless the toxicant's biological half-life falls within specific ranges. Various models, including OSHA, Brief and Scala, and Hickey and Reist, can be utilized for these assessments.

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Modifying Occupational Exposure Limits for Extended Work Shifts: A Practical Approach

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  1. Modifying OELs for Extended Work Shifts • The best models for extrapolating TLVs are complex. • Must be done substance by substance. • Based on critical health effects, pharmacokinetics and biological half-life. • Often, detailed information is not sufficient for the models.

  2. Extended Work Shifts Guidance • Exposure limits whose goals are to avoid excessive irritation or odor will, in general, not require modification to protect persons working unusual work shift. • Adjustments to TLVs are not generally necessary for unusual work shifts if the biological half-life of the toxicant is less than 3 hours or more than 400 hours.

  3. Adjusting TLVs • OSHA Model • Brief and Scala Model • Hickey and Reist Model

  4. OSHA MODELEquivalent PEL T is the duration of exposure

  5. Brief and Scala Model T is the duration of exposure

  6. HICKEY and REIST MODEL t1 = hours worked per day on unusual schedule t2 = 24 times days worked/week on unusual schedule

  7. Example • Assuming that 1,2-trichloroethane has a biologic half-life of 16 hours in people, what modified TLV or PEL would be appropriate for persons who wished to work 3 days, 12 hours per day for the work week. • The present ACGIH TLV and OSHA PEL for 1,2-trichloroethane is 10 ppm.

  8. HICKEY and REIST MODEL t1 = hours worked per day on unusual schedule t2 = 24 times days worked/week on unusual schedule

  9. Modified OEL Solution

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