Seems Dennis Brady wishes to re-invent the wheel:
http://www.lampworketc.com/forums/showthread.php?p=1984187#post1984187 (top of page two)
I’m hoping we can find some “formula” that equally, and with reasonable accuracy, considers hood size, distance from torch, and fan capacity. Any of those three factors is meaningless without considering how it’s affected by the other two.
Actually, Dennis, if you would take the time to do some very basic research (such as reading up on ventilation basics — you don’t even have to read what I’ve written, read Dale’s writings, read those of OSHA, NIOSH, or even the ACGIH) you will see that the formula already exists.
Step one: Figure out how big a hood/enclosure you want.
Step two: Multiply the hood coverage area (in square feet) by 125 or the enclosure opening (in square feet) by 100. That is your required CFM.
Step three: Calculate the losses induced by the duct size, run and number of bends. Look up in the fan performance tables to see what the end CFM after losses is. Use the tables to select the fan you need.
Step four: Build your hood/enclosure per the above. Install the torch under the hood (being sure that the flame plume is totally captured by the hood as per my suggestion here) or install the torch so that the end (face) of the torch is at least 3-4 inches inside the enclosure.
Step five: Supply sufficient make up air to the room, via any number of various ways described here and elsewhere.
Step six: Turn on the torch and start making glass.
It really is that simple, Dennis. But, don’t mind me — go right ahead and find out the hard way.
And don’t forget fellow readers, that Dennis doesn’t believe that the American organizations dedicated to safety are worth listening to. If you read his writings on safety over the past couple of years, he advocates using bulk tanks indoors (despite yesterdays incident) and other unsafe glassworking activities ad nauseum.