Dust concentration will depend on many variables (particle size, particle density, moisture content, hood capture velocity, design of the hood enclosure) and is not predictable. Minimise the concentration by allowing adequate stilling volumes in the hood enclosures and above all, follow the guidelines of the ACGIH manual. Experienced dust collection system manufacturers will know what to expect in any given situation. Performance guarantees may be tied to particle size distribution and concentration and in that case, dust sampling in an actual system may be needed.

Michael Reid. ■