I’m building a new shop. I have a dedicated corner for a knock down spray booth. I intend to use waterbase finishes and petroleum base finishes. I’ve been searching for a explosion proof exhaust fan which I can install through the wall.
So far my results have turned up fans for about $380, but with an enormous amount of cfm (800 to 3000). My suspicion is that at that rate no material would ever land on the project.
I also found a company called VA EQUIPMENT CORPORATION. They have a 6 inch explosion proof exhaust fan with 100 cfm for $1,400.
Can any one help? First is explosion proof necessary? If yes, are there any sources out there that have the right size explosion proof exhaust fan without costing an arm and leg? If not, is it possible to do some type of work around this problem? Are house box fans a viable alternative? If they are how is the explosion possibility handled?
Replies
There is more to it than just an exhaust fan and spray booths are about the only way that I would recommend anyone should go. They are engineered to exhause and this involves both air flow rate and air pressure at various critical points.
To be safe, you need both an explosion proof fan and an explosion proof motor. I think Granger has them in their catalog but they are pricey.
Graingers does have them. Another resource for learning what you actually need is the fire inspector with your local codes dept. You may not "legally" need one just for home use (or maybe this is your business) but they would not only be able to answer your questions, they ought to be able to do so quite specifically to what you actually need given what you spray and the volume of air in the space. Would probably also be able to refer to to somewhere local to but the stuff. I wouldn't anticipate finding any bargains on an explosion proof fan.
The only way I've heard around it (from a fire inspector) was to mount only the fan body with the blades in the space, and have a belt drive through the wall to the motor outside. Your local guy (or gal) might have similar headache savers for other things (like lighting).
" Clothes make the man. Naked people have litte or no influence in society" - Mark Twain
You might look at a TEFC rated motor, which is less expensive than "expolsion proof" but they are used in this application, informally at least, I have heard.
A single phase TEFC motor is not a good substitute as it still produces an arc. A 3 phase TEFC motor would be a better choice as they are allowed in hazardous areas when combustable vapors are present as a result of a failure. In areas where combustible vapors are present as a normal part of the process (e.g. a spray booth) the motor should be explosion proof and the blower should be spark proof. That means that even if it fails and the impeller crashes into the housing or if you fed it a bastard file it won't spark. This, UL listing and product liabilty premiums is why they are so expensive. The last place I'd go to is my fire department for advice. Chances are they'd have you on their and the AQMD, zoning enforcement, and everyother agency's radar. A poorly designed, ill-equipped both for shooting lacquer is probably more hazardous than shooting into an open garage. The containment will tend to concentrate the vapors until they reach the LEL and with the wrong blower and lighting you've introduced an ignition source. You're much better off spraying in an open, well ventillated area - just like it says on the can.John O'Connell - JKO Handcrafted Woodworking
Life is tough. It's tougher if you're stupid - John Wayne
I probably shouldn't have posted as I haven't tried this, but have heard that it is done. Which, of course, as with so many things, does not mean that it is advisable. Thanks for the info.
Try W.W. Grainger, I bought one about five years ago I think I paid about $300 or so. It has an 8"fan mounted in a 12" w/ a 12 square opening. With fiberglass shuttters. I made it portable with Plywood extension wings to fit the width of my garage door. I simply lift the door about a foot an place the fan with wings under the door and spray away. I use a product called zip wall to fabricate a 8 mil clear barrier around the spray area ( see @ zipwall.com)
In a spray booth, the size of the fan is figured using the formula HxWx100. This is the height multiplied by the width of the room multiplied by 100. This will tell you how many CFM the fan should be rated at. You want air flow to be 100 CFM throughout the booth. This may sound like a lot of air flow, but it isn't.
In a home-made spray room/booth, you can design the air flow at a lower rate - you don't have to meet the same requirements as an approved booth. If you are blowing 2500 CFM (for example) out of the building, there should be an opening somewhere to allow 2500 CFM of fresh air to flow into the building - you can't create a vacuum, and if you don't have a fresh air inlet, you won't exhaust very much air.
Paul
F'burg, VA
Some years ago, when I bought my first HVLP set-up, I conferred with an expert about setting up some sort of spray booth (with an explosion proof exhaust fan) inside my house.
In plain words he told me it would be really stupid and dangerous to do so if I planned to use any sort of solvent based finishes.
From what he told me, the fumes would eventually accumulate around the lights and other surfaces and create a very hazardous environment for fire.
I would think very carefully about doing this. If you decide to proceed, I would get a plan together, and call your insurance people to see if a spray set up might invalidate your coverage in the event of any kind of fire.
OK, I too have a small wood shop in a seperate garage and want to set
up a spray booth for finishing.
I can't see spending $2000 - $3000 for a premade booth.
I don't mind buying the fan and covering a section of walls with
something.
Has anyone got some good suggestions for a spray booth.
I've done all my spraying outside up to now, but can't do it in the
winters here.
Jeff
Actually, if a complete spray booth was only $2-3K, it would be almost feasible for a one man shop. However, if you live in a cold climate, you have to also add a air make-up unit. The heating load for 2500 cfm of air going up the stack can be prohibative. It is also important to think about local codes and insurance.Just did a quick calculation and for my climate, you would need a 300k btu input furnace to keep up with that cfm.
Edited 2/3/2003 10:35:24 AM ET by VERMONTERKEN
Jeff - Jeff Jewitt's book "Great Wood Finishes" has a plan for a collapsible spray booth. Uses a 16" through-the-wall exhaust fan (hazardous location/explosion proof)to exhaust the fumes. A guy I was talking to about some finishing emailed me a couple pictures of his - seems to work great for him.Paul
F'burg, VA
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