The use of a safety factor in setting health based permissible levels for occupational exposure

SummaryWhen adequate human observations are not or scarcely available, permissible levels for occupational exposure have to be extrapolated from animal experiments. Taking into account experimental conditions, e. g., duration of exposure (⩾ 3 months), animal species, knowledge of no- (adverse-) effect level or minim al-(adverse-) level, presence of data on human observations, the authors worked out a procedure for extrapolation. This procedure should only be applied for systemic non-carcinogenic effects. The proposed procedure is to be regarded as tentative and as suggestion for international discussion.The evaluation starts with a safety factor = 10 for extrapolation from dose/kg b. w. in long-term animal experiments to exposure of adult workers (40 h/wk); this factor corresponds to a safety factor = 3–10 for extrapolation from doses presented as concentrations in air. If long-term experimental exposure is 24 h daily, the safety factor can be lowered to the minimum value of 1. If only short-term exposure studies are available, the safety factor may have to be increased to a maximum of 400.