THE LIMITS OF THRESHOLDS - SILICA AND THE POLITICS OF SCIENCE, 1935 TO 1990

Since the 1930s threshold limit values have been presented as an objec tively established measure of US industrial safety. However, there hav e been important questions raised regarding the adequacy of these thre sholds for protecting workers from silicosis. This paper explores the historical debates over silica threshold limit values and the intense political negotiation that accompanied their establishment. In the 193 0s and early 1940s, a coalition of business, public health, insurance, and political interests formed in response to a widely perceived ''si licosis crisis.'' Part of the resulting program aimed at containing th e crisis was the establishment of threshold limit values. Yet silicosi s cases continued to be documented. By the 1960s these cases had becom e the basis for a number of revisions to the thresholds, In the 1970s, following a National Institute for Occupational Safety and Health rec ommendation to lower the threshold limit value for silica:and to elimi nate sand as an abrasive in blasting, industry fought attempts to make the existing values more stringent. This paper traces the process by which threshold limit values became part of a compromise between the h ealth of workers and the economic interests of industry.