Silica flour exposures in Ontario

A total of 16 cases of silicosis are reported in Ontario plants where there was exposure to silica flour. Dust counts expressed as mppcf are shown for four of these plants taken over a period of 37 years. A relationship has been obtained experimentally to permit conversion of the counts to respirable mass concentrations. Based on the information obtained, a TLV of 0.05 mg/m3 for silica flour is proposed.