PRELIMINARY DATA ON HARD METAL WORKERS EXPOSURE TO TUNGSTEN-OXIDE FIBERS

The first personal exposure data for tungsten oxide fibres, in two har d metal manufacturing industries is presented. Occupational exposure w as studied by static and personal measurements during tungsten metal p roduction. Three different initial materials were used, ammonium-parat ungstate (APT), blue oxide and tungsten trioxide. In both factories, a irborne tungsten oxide fibres were detected both in static and persona l samples. Fibre exposure varies for different activities. Charging of raw material, changing the hammer, cleaning-work on the cyclone and t he micro-filter were found to be among the most high dusty operations. However, as workers use respirators during cleaning operations, these filters could not be related to personal exposure. The calcination of APT to the blue oxide generates fibrous dust. The raw material import ed as blue oxide is also fibrous material and both charging it into th e calcination furnace and re-charging it into the reduction furnace ge nerates unnecessarily additional dusty periods. A single reduction-sta ge is, therefore, preferable. Furthermore, the tungsten trioxide raw m aterial is non-fibrous, therefore, calcination of APT to tungsten trio xide and its reduction to tungsten metal is preferable with respect to minimising workers exposure to tungsten oxide fibres.