On 1 January 1992, the Health and Safety Executive (HSE) introduced a weaker permissible exposure standard for crystalline silica. The new maximum exposure limit for respirable quartz was 0.4mg/m3 (up from a recommended limit of 0.1mg/m3) and with the same standard applying to cristabolite and tridymite (0.05 mg/m3). According to Hazards magazine: “It has become clear that the quarry industry demanded an weakening of exposure standards because it claimed that it could not meet the existing standards. Rather than stand firm, the HSE has caved in and accepted the weaker standard, claiming that its new guidance notes would ensure that where better standards had already been achieved they would be maintained.” At the time IARC said there was limited evidence crystalline silica caused cancer in humans (IARC, 1987); it was subsequently upgraded by IARC to a group 1 proven cause of cancer in humans. HSE research in 2009 found HSE had dramatically over-estimated levels of industry compliance with silica exposure standards and under-estimated the numbers of workers over-exposed. At this point the exposure standard had reverted to 0.1mg/m3.
Reported in Hazards, number 38, 1992.