Spray Booth Fans and Explosion Risk

The scary stories in this thread should convince anyone that explosion-proof fans are a must in any spray operation. August 17, 2009

Is there anybody out there using non explosion proof fans in a homemade spray booth they are expensive? I am sure people are doing it Iím just curious if you could use a whole house type fan and mount it in a wall.

Forum Responses
(Finishing Forum)
From contributor W:
My first spray booth was a small corner of the cabinet shop with plastic sheeting hung from the ceiling and secured at the seams with spring clamps. The exhaust system was a used furnace fan built into a cabinet that was wheeled up to a hole cut into the garage door. I was advised by my mentor to heat the small space with a propane heater that was like a giant open lantern setting on the floor with a 5 gallon propane tank connected.

I'll never forget the day when I started spraying again, but forgot to turn off the propane heater. I looked back, through a fog of lacquer overspray only to see the flames licking the heavy fog of flammables. I leaped through an opening and quickly reached in to shut off the propane. Nothing happened, but I can imagine the worst case scenario.

My new "dream spray booth" ironically still uses old furnace fans. They are the belt driven type therefore I can keep them enclosed and far from fumes. I believe if the ventilation is appropriate than explosion proof motors are unnecessary.

From contributor G:
I use a hazardous area fan motor. The motor is outside of the stream of air (tub-axial fan) and the way my booth is built outside the booth and spray room too. If it wasn't I would have used a fully explosion proof. For the first year or so I was using three box fans underneath my garage door. As long as you keep the level of fumes below explosion level there is little danger. But all it does is take one error.

From contributor JD:

Itís a lot like the old gas stove in the movies and the bad guy with a Zippo. The concentration of air/fuel has to be at the correct concentration to ignite. Itís not very likely that itís going to happen in your house as they show in the movies. Itís more likely in a spray booth, but it is still very unlikely that it will happen. That being said, under the correct set of circumstances, you are going to have a big explosion. Take your chances or pony up a couple extra bucks and donít worry about it.

From contributor B:
This is more than a rule. Think about it, you have a flammable vapor passing over sparks. A little like Russian Roulette.

From contributor O:
I'll assume you spray waterbornes, as I do. Even so, you don't want a fan with an open motor. I use a barn fan which is completely sealed with gaskets; it's in the wall behind six furnace filters. It clears any fogging out pretty quickly.

From contributor N:
I'm sure I'll hear it but I spray post cat lacquer (CV) in my basement with a furnace fan and open window on other end. Furnace fan I believe is about 3000 cfm and keeps small shop quite clear of any overspray/fog. Also creates low pressure zone in shop that keeps smells out of house (unless someone leaves a window/door open upstairs).

Don't believe solvent-to-air ratio in shop ever gets to a combustible ratio. If anything it is worse outside than inside. I don't use filters (yet), so I need to scrape off the fan every few kitchens to keep optimal airflow. I would be more concerned about my 1000w worklight and light switch giving off that fatal arc than my cheap belt-driven furnace fan.

From contributor T:
Try throwing a lit match into any type of lacquer, it doesn't ignite! My father and I have always sprayed lacquers, oils, latex with heaters and fans of all sorts and never in 30 years have had any bad experience. I have a friend that has been a firefighter for 15 years and he says that the flash point of oils, and lacquers is very high and has never heard of anyone blowing themselves up when using common sense, such as a fan blowing overspray out a window or a kerosene heater being used with fans carrying most of the overspray out of the window. I just sprayed onsite a 40 x 50 room with nitro lacquer and I didn't see the 115,000btu kerosene shop heater until I sprayed right on top of it - nothing even happened then. I believe it's chemistry and knowledge of your flashpoints for certain products. Common sense goes a long way and too many people are so concerned about everything they ignore common sense.

From contributor G:
A fine atomization of flammables is a lot different that a liquid. Usually there will be a flash of fire and not an explosion. You need a certain set of circumstances to have an explosion. By the time you have the equation for explosion you would be passed out on the floor from lack of oxygen. A flash fire is enough to start a series of things to happen that may be catastrophic.

From contributor R:
We had a safety meeting at a shop I used to work at where I met a gentleman who used to work at a refinery. He believed a lot of the things I am reading here. One day the odds caught up with him and he was burned on 75% of his body. He told the story of the burn wards and how they scrub off the dead skin every day with bleach and the screaming. A living hell he called it and asked them to let him die. They wouldn't. I think I'll keep the odds as much in my favor as I can including static grounding for sparks.

From contributor G:
There are well written up guidelines, rules, and laws that have been crafted to make the use of flammable coating spraying as safe as possible. Then there are the people who try to get around them by stating lack of funds or they don't believe it is that dangerous. It is up to you to figure out if you want to work in imminent danger at all times or be safe and complying. Itís as simple as that and it does cost a lot of money.

From the original questioner:
I found a 3000cfm explosive proof fan and I will be ordering it for peace of mind while spraying.

From contributor H:
Explosion proof fan - are you using the proper filled conduit? You can't run open cable to an xp fan and expect it to be safe. The same goes for not using an xp on/off switch. Be careful, the solvents are atomized. Be aware of the solvent concentration and spend the money to be safe.

From contributor T:
Explosions aren't the only hazard with solvent base finishes, how about health issues. As a solo shop the large expense of all the safety equipment and heated makeup air in a Minnesota winter, along with my comfort, makes waterbornes a no brainer, along with the question of what to do with all the waste solvent. I don't care to register as hazardous waste generator and I couldn't get rid of it legally without being registered. How are the small shops getting rid of it?

From contributor G:

Turn your fan on, put the waste solvent in your gun and atomize it. Then it will be all gone.

From contributor J:
NFPA 33 is the regulation standard and explains every detail of setting up a spray operation. It is an informative and valuable read, regardless of how strapped your budget is and what you end up installing.

From contributor M:
When I was younger and starting out, I did commercial construction. We were remodeling a Target store, one of the guys was putting on FRP board on in the restrooms and I was 20' feet away framing something and using a circular saw. He was spreading glue on the walls one minute and the next thing he knew he woke up in the emergency room with severe burns and bleeding out his ears.

Hereís what happened; he was spreading glue on a 10' high wall that was only boarded up to 8' and this created a 4" pocket in the wall. The vapors from that glue somehow settled in this pocket. Like I said I was 20' away in the entrance vestibule when I hit the button on the circular saw there was the most hellacious boom you ever heard and everyone working in the store went running for their lives. I ran into the bathroom and pulled the guy that was working in there out by his legs into the parking lot and called the ambulance/fire department. Went back into the building and took my hammer and hooked it into a 5 gallon bucket of adhesive that was burning like a rocket, then backed out on my hands and knees with it into the parking lot. Afterwards we went back in to figure out what had happened, and thatís when we figured out the fumes had lay in the wall cavity as all the dry wall and FPR board was actually blown off the wall. I have to believe the spark off the brushes of my circular saw set the explosion off as the timing was perfect and there was no other explanation.

To make a long story short, I have invested thousands in explosion proof cabinets and if you get caught in the spray room without the fans on youíre fired, no questions. I really hope to never read about some of the guys who would not spend $500 on an explosion proof fan and get it hooked up right - just pure stupidity if you ask me.