Posted By ken stevens
Can anyone tell me if wood chips & wood dust can be mixed in a Local Ventilation system. Obviously wood dust is very explosive compared to wood chips. if the system is made with explosive enclosures etc then is it ok to use the system for wood chips also. The maintenance people tell me that it is illegal to mix them but i can find no law or guidance to this effect.

Posted By Jay Joshi
As wood dust has the potential for explosion, explosion relief would be required for an integrated system. I cannot go into the details of LEV design. There is some basic information in "An introduction to local exhaust ventilation" HS(G)37 from HSE books. Any design text in pneumatic conveying systems will cover it. Wood chips will be heavier than wood dust and the total power, velocity & duct dimensions are factors to be considered. Also, there you will have to dispose the waste--and there could be different rates for dust and chippings. Generally, a competent consultant should give you the various options with relevant costs.

Posted By Denis Hands
Ken,

In my experience (workshop engaged in carpentry & joinery + furniture manufacture, using hard and soft woods) the two systems are seperated. The relatively low volume of wood dust from sanding operations was captured in black bin sacks for safe disposal. The dust extraction system, as you say, had intrinsically safe electrical components and an explosion release vent. By comparison, the much higher volume of wood chippings and shavings from saws, planers, tenoners etc. was collected via a separate extraction system into a totally enclosed skip that could be removed by a lorry. I suppose, depending upon the relative volumes of dust and chippings, the whole lot could pose an explosion risk if mixed.

You could contact the HSE Woodworking National Interest Group (WOODNIG) on 024 7669 6518, who may be able to give you a definitive answer.

I hope this helps.