Adjustment of Occupational Exposure Limits to Non-Standard Work Schedules

Abstract

Abstract Non-standard work schedules differ from eight hours per day, five days a week, which is the basis for the occupational exposure limits (OELs). This implies the possibility of increased exposure to agents in the workplace and increased risk of adverse health effects. As a consequence, adjustment factors may be used to provide the same degree of worker protection as the original OELs. There are basically two different approaches for calculating adjustment factors for extended work shifts, either simple linear equations or toxicokinetic models. The toxicokinetic models take into account uptake and elimination of chemical compounds in relation to the daily work period, the number of consecutive working days, and the off-duty periods between tours of duty. For a typical offshore work schedule this implies 12 h per day for 14 consecutive days with off-duty periods of four weeks. Linear models, on the other hand, only take into account either the daily or the weekly exposure which provide different adjustment factors. Furthermore, the linear models do not take into consideration neither work periods exceeding one week nor the off-duty periods. As a consequence, toxicokinetic models are recommended for calculating adjustment factors. In Statoil the requirement has been to use an adjustment factor of 0.6 which is in agreement with the Activities Regulation (§ 36). An adjustment factor of 0.6 is consistent with the worst case adjustment factor obtained from the toxicokinetic model described by Hickey and Reist (1977). The application of the worst case adjustment factor was suggested by Eide (1990) for offshore work schedules and is later referred to as the maximum half-life (MAHL) model. This factor is recommended as an adjustment factor since it will always provide at least the same degree of worker protection as the original OELs, also for most non-standard onshore work schedules. The approach implies that knowledge about the biological half-life of the chemical agents is not required. However, when the biological half-life is known, a more accurate and less conservative adjustment factor can be calculated.