My interest is in the design of dust control systems.

1. Manual handling of powders releases fugitive dust, even when done carefully. In the dispensary, only small quantities are handled and emissions are easily controlled using local exhaust hoods. Spillages are easy to clean up.

In production areas, hand loading of larger quantities (from 200 L drums for instance) into blenders or feed hoppers is problematical for cleanliness and possible contamination of adjacent rooms. I prefer to see bulk powders loaded manually from paper bags into hoppers fitted with local exhaust, from elevated platforms if necessary. Filling and tabletting machines of modern design are generally well enclosed so that there is little dust released during operation. Cleaning should be done using a vacuum cleaning system, separate from the dust collection system.

Fugitive dust which remains airborne finds its way to the HVAC system with possible contamination consequences or, at least, increased maintenance of the filters.

2. There are no major knowledge barriers in dust control. All of the standard principles apply, with care to be economical with exhaust quantities because of the consequences for HVAC. After good equipment design, manual handling procedures and housekeeping are next in importance and need to be well defined.

3. Many people seem to be unaware of the potential for explosions when handling combustible powders. All of the conditions for a dust explosion exist within a dust collector, except a source of ignition. Although the risk is generally regarded to be small, care should be taken to locate dust collectors outdoors or to design them so that a deflagration can be safely vented outside the building.

4. I can see no emerging technologies which will benefit this subject.

I hope this discussion is helpful.

Michael Reid. ■