Seems Dennis Brady wishes to re-invent the wheel:

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.

## 4 thoughts on “Scratching my head…”

1. Raymond says:

Mike,

it is pretty coincidental that you should comment on this, as I read his post the other day and thought the very same thing.

What other formula could POSSIBLY be needed to figure-out the volume of air needed to be ventilated/exhausted for a given area? (Is mother nature going to pass a typhoon 2 blocks away, blocked by a multi-story warehouse? Is the dog going to run past the torch at 15 MPH while passing gas? Etc, etc…).

I like his Dennis’ ideas, and I like his website…but this comment really caught my attention as well. I also noticed a few other things he said in the past (which were not totally wrong), but definitely sent me vibes that he was not from the good ‘ole USA.

Anyhoo…good points, Mike.

I’ll be tugging on your ear a little later, as I would like your help on a little something…and would also like to patronize you in the purchase of protective eyewear. But more on that later.

In Christ: Raymond

2. Raymond — it seems that Dennis believes in the ‘not invented here’ principle — it is obvious to me that when he talks to his so-called professional contacts about ventilation issues, he’s not asking the right questions or presenting the information in the proper framework.

This shows his lack of even the most basic understanding of the principles of ventilation and the laws of air movement which are basic physics — no one can change the physical world…

3. Tim Ramsden says:

hey mike thanks for all the info,definately dig the all tek approach to glassblowing,especially ventilation,i read your blog a couple times before i realized you are the aura lens guy as well ( i bought my shades from you bout ten years ago)i have a pair i need to get the frames fixed on but i’ll go thru the proper channels for thanks again for the physics lesson

4. So am I to understand that I need a hood like the one over my stove for the exhaust and another source of fresh air to replace the air that has has been removed by the exhaust fan.

Please keep it simple for me and it’s going to be winter here in Ohio.

Thanks for help!

Pat