Occupational exposure to dust in slate pencil manufacture.

Slate pencils are manufactured from natural rock known as Binota Shale in small factories. Since the dust generated by stone-cutting and groove-making machines during the process contains a very high percentage of free silica and the particles are of sizes ranging up to a few microns in diameter the exposure both to respirable and to total inhalable airborne dust was assessed. Dust sizing revealed that all of the dust was respirable (less than 2.5 microns). Measurement of the intake velocity of the exhaust system in many cases showed it to be less than 10 m s-1. Suggestions are made for improvement in the working conditions.