Modifying OELs for Extended Work Shifts

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