Adjustment of permissible exposure values to unusual work schedules

Research activities sought development of a method to adjust exposure limit s for 694 substances for unusual work schedules. A consensus was establishe d on the basic toxicological principle for adjustment; criteria for adjustm ent were selected by a panel of scientists coordinated by a committee of in ternational experts and supported by toxicokinetic modeling; and a group of toxicologists attributed primary health effects and related adjustment cat egory to each substance, A consensus among scientists and employers' and wo rkers' representatives was established on the protocol of the application, in the field, of the adjusted exposure limits. The guiding toxicological pr inciple for adjusting exposure standards to unusual work schedules is to gu arantee an equivalent degree of protection for workers with unusual schedul es as for workers with a conventional schedule of 8 hours per day, 5 days p er week. The process of the adjustment is inspired from the Occupational Sa fety and Health Administration logic for attribution of primary health effe cts and adjustment categories ranging from no adjustment to daily or weekly adjustments. The adjusted exposure limits are calculated according to Habe r's rule. Decisions on attribution of adjustment categories for the followi ng toxicological effects were reached: respiratory sensitizers (asthma); sk in sensitizers; tissue irritants versus tissue toxicants; methemoglobinenia -causing agents; cholinesterase inhibitors; and reproductive system toxican ts and teratogens. A simple procedure is presented to facilitate the calcul ation, application, and interpretation of the adjusted exposure limits.