Kindly re-read your question, especially the part 'v=capture velocity'. It ought to be self explanatory: ought it not? ■

“V”, the capture velocity is an arbitrary figure based largely on experience. Various handbooks will give similar figures. American Conference of Governmental Industrial Hygienists “Industrial Ventilation” gives “50 to 500 fpm”.

Hemeon in “Plant and Process Ventilation” says that the selection of V is basically experimental, based on practical experience and observation of actual operations, depending on:

•The nature of the operation

•Drafts in the workspace

•The violence of dust generation

•The relative quantity of dust

•The toxicity of the dust and consequences of its release into the workspace.

Hemeon gives guideline numbers of between 40 and 100 fpm, depending……

“Industrial Ventilation” also recommends applying a factor of safety of 50% for “dry, dusty materials”.

The relative density of dust does not appear to be relevant.

If you have a specific operation in mind, you need to get advice from an expert.

Michael Reid. ■