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Build a spray booth

Download a PDF of instructions on building an affordable spray booth for large-scale trains
Possible fire caution

In the spray booth article on page 42 of the December 2017 issue, there's an issue that should be addressed.
 
One reason that purchased paint spray booths are expensive is because they have safe motors.  This means the system is designed around at least a "totally enclosed fan cooled" motor (TEFC), or in cases where the motor is in the air stream, an explosion-proof motor.
 
https://www.pittsburghsprayequip.com/product-category/paint-booth-fans/paint-booth-fan-motors/
 
http://www.autobody101.com/forums/viewtopic.php?f=5&t=7435
 
The motor in the Fasco blower used in the article is an ordinary ventilating motor.  It is not safe for this application. This kind of motor makes sparks from dirty "brushes" or if the steel fan blades ever hit the steel housing. Any sparks in the airstream, if they occur during spraying a solvent-based product, can cause an explosion or fire.
 
The system in the article has the air being sucked out of the booth and through the fan. At the very least, I would have designed the system the opposite way, to blow fresh air through the booth and through proper filters, and then exhaust outdoors. That way, the solvent vapors and mists never get to the fan motor.  But please don't recommend that solution on my say-so alone.
 
As for the position that the amount of solvent used is small, I recall the demonstration the local fire department used to give at my elementary and junior high schools.  They had a sealed pipe with a cork in one end and a spark plug in the side. They would put in one drop of gasoline, shake up the pipe with a short piece of small chain inside to help mixing, and then touch a battery to the spark plug. The cork would blow out and hit the ceiling with a very impressive thump.  It could easily put out an eye.  If it was a sharp piece of an exploding spray booth, it could hit an artery and cause severe personal damage or death.
 
The point is that an unsealed fan motor should not be used in a spray booth because of the possibility of an explosion resulting in a fire or personal injury.
 
Please don't think that I'm over-reacting and crying wolf.  In my former days as a mechanical engineer, I saw and investigated numerous minor, serious, and even fatal accidents resulting from practices that were "done this way for years". I have even had some near-misses myself.  I can envision somebody building a spray booth like this one, using miscellaneous parts from his/her junk bin, and getting hurt.

Otherwise, keep up the great work. Every issue is hugely important to me, especially the "how-to" articles.  And you can tell your advertisers that I even read and use the ads.
 
Charles A. Jordan


Jim Kottkamp responds

I appreciate Charles Jordan’s note on the fire safety problem with the bower system in my article on building a spray paint booth.  I agree with Charles’ assessment, and believe I have found a reasonably affordable solution.
 
The least expensive ignition free industrial blower system I found was just over $1,200.00 and it used an 8 inch duct system. This is clearly not affordable. I found an off-the-shelf solution in the boating industry. Large boats need exhaust fans that can remove gas fumes from the bilge to prevent explosions. After an extensive search I found a Delta Systems - 4 inch blower that is ignition free. The Lil’ Champ Blower provides air flow rates up to 350 CFM (a significant increase over the original blower) and it performs well even under static pressure loads. The price of this blower is around $250.00.  Below are the links to two low-cost suppliers.
 
Fisheries Supply:  https://www.fisheriessupply.com/delta-t-systems-dc-centrifugal-blowers-ignition-protected
 
Boat Store USA: http://www.boatstoreusa.com/ducting-ventilation/clam-shell-cowl-vents/delta-t-systems-500-3042421p-blower-flge-4-350cfm24v/
 
The only issue with this blower is it runs on 24 Volts DV at up to 8 AMPS. A suitable AC/DC converter is available for $20.00 from Amazon at:
https://www.amazon.com/Aiposen-Transformer-Security-Computer-Project/dp/B01B1PREK6/ref=sr_1_1?ie=UTF8&qid=1510826930&sr=8-1&keywords=ac+to+dc+24+volt+power+supply
 
I believe this combination of ignition free blower and AC/DC converter will provide a safe solution for interested parties.
 
Thanks for the prompt notification and for providing me the opportunity to provide a solution to a potentially dangerous flaw in my original plan.
 
Jim Kottkamp

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