Technical Explosion-proof exhaust fan: building temp paint booth

Hi all,

I am looking at constructing a temp paint booth in my detached garage. I ran across "explosion-proof exhaust fans". With all the worries of painting a car, I did not know the risk of an explosion needed to be added to the mix ! I will certainly be going with an exhaust fan mounted down low, but not sure if I need to go the explosion proof route ? Does anyone have experience with this? I will be spraying expoxy primer and single stage urethane. Not likely to paint more than one car. (Assuming no explosions !)

 

I use one. The household box fan is sucking highly volatile chemicals right through an electric motor, I wouldn't risk my life and property to a box fan. You will get plenty of people that will say it is okay, I'm just not one of them. Vevor makes a nice fan for less that $200. In the pic the fan is poking inside the clear door, and I attached that air duct to it. The other end of the duct is ran through a box of furnace filters. Those filters were as black as night (I painted my PU black in the booth) when I cleaned up and tossed them. I will also say the amount of air being removed kept visibility in the booth at a pretty good level while painting.

 

What do you think an explosion proof fan is? If you think it means it will survive an explosion, you are wrong.
It means the fan will not ignite an explosion when being used. Might be a very good idea with paint fumes....

 

In most jurisdictions, code requirements require explosion proof motors in any duct or ductwork exhausting flammable fumes. One spark in an open motor and if the fumes are just right, it can explode.

 

I’v wired more than one paint booth, paint mixing, paint storage (not latex) and various other “explosion proof” locations. Nothing electrical in there unless it’s installed explosion proof equipment . No light fixtures, wall outlets, nothing. It’s expensive and a pita. And it’s been ignored many times and people have gotten lucky. Billy’s booth with the windows, or lights mounted on the outside is an example. Exploding vapors are extremely dangerous. As in not usually survivable.

 

As someone who has “Woofed” a pole barn or 2 painting cars. It sucks, just pay the money and get the explosion proof fan.

 

Many Thanks guys ! An explosion-proof fan it will be !

 

Bandit Billy, where did you source the structure?
Thanx,
Tom

 

Focus on explosive vapors is important to be sure, but ventilation is the main ingredient. The fog clears but keep that thing ventilating during the purge of solvents and catalyst. The "smell" is the killer. Explosion proof is really more for sealed areas and routes of ventilation like a filtered exhaust box. Simply moving air isn't hazardous but any and all safety measures are worthy. But again, ventilation is very important to YOUR PERSONAL HEALTH. Stay away from it while it's final curing for at least an hour. Yeah I know you're in there painting but I'm talking about after and you're dying to see it with no respirator or other incumbrances.

 

The guy that sprayed epoxy of my truck in an inflatable booth used positive air pressure to push air out through built-in filters made into walls of the booth.

 

I worked construction and we did just about everything. One night I received a call to get my butt up to a Savemart grocery store in Antioch, California. A coworker and I arrived to see the bakery department blown to hell, I mean blown to hell. Turns out they were gluing F.R.P. Paneling to the existing walls. The company superintendent was removing electrical outlets and switches to make cutting around them easier. There’s that word again, easier. The superintendent shorted one of the outlets a popped the breaker. Off he went to try and find the switch panel. The other two continued applying the panels to the walls. One guy was wiping the walls with lacquer thinner to remove the grease, so the new panels would stick. The other guy was applying adhesive to the panels with a notched trowel. Ok, 4’x10’ paneling on the saw horses, oil based glue, 5 gallon bucket , one guy spreading it on. The other guy ,lacquer rag in hand, wiping the wall down, vapor everywhere, including inside the wall cavity. The superintendent, who was gone a long time, finally finds the tripped circuit breaker...........throws the switch.......boom......... outlet throws a spark to the metal stud framing. Wall cavity full of vapors lights off , explodes with enough force to move the mixer across the room. Bakery Mixers are heavy SOB. The guy wiping the wall, the now on fire wall, is wiping with a ball of fire in his hand. The other guys trowel is on fire in his hand, with a 4’x10’ flaming panel, cooking his armpit and every thing else. They recovered and both quit smoking that day. They now use WATER-BASED glue. I never seen a superintendent work so hard and fast helping us repair that poor bakery. They launch potatoes with deodorant spray in a potato gun don’t they.

 

Quite the story, @Onemansjunk . Everyone involved is very lucky it wasn't worse.
How to turn a couple thousand dollar job into a potential multi-million dollar nightmare.

Everyone has a different level of safety, but a lot of hard-working men and women not just stupidity have been injured or died to teach us what not to do.

As said, a paint area needs to be ventilated well. Lots of info out there.
https://paintcatalogue.com/calculating-cfm-paint-booths-essential-airflow-ventilation/

 

Absolutely, use an explosion proof fan if it will be exposed to flammable vapors.

Also consider other sources of ignition. Lights (external lights like billy b's are great). Big one... spark from static electricity. Consider grounding everything including the car, spray gun, skin, any metal framing in a temp structure. This will also help with keeping dust off that fresh paint.

 

When I built a small building for storing easily movable stuff or a car, and that I could also use as a paint booth on occasion I bought a "squirrel cage" blower. Most of them have a motor mounted in them that draws air (and fumes) right over the motor.

There are however other ones that have an external motor mounted outside the flow and driving the impeller by a shaft. They are usually a little larger. They can be put on some casters so they can be rolled about and used as needed. They move a larger amount of air than a typical window fan type of box. They are also usually pretty cheap, maybe $50 or $75 . In my case I permanently mounted the one I bought.

Here is a picture of it . I placed a small barrel that I cut off short and placed it in the lower area of the wall so that it gave a discharge path for the air/fumes. When its not needed, I put the barrel top back on it to seal it.

Now, if you have air exiting, you need to devise a way for filtered air to enter your booth. Lots of ways to do that depending on your shop......and thats another story.

While I don't want to dis the idea of being safe by using explosion proof equipment, I will say that probably 99% of amatuer car painters have not used explosion proof lights or fans when painting their projects. Further, most have their air compressor in the same building they are painting in. Like Dirty Harry once said............"Do ya feel lucky, Punk"


Got it leveled and poured a concrete pad for it to sit on.

You can find smaller units, but this was available cheap and moves a lot of air.




Wall Vent I cut the other end off later. Put the lid on this side when I want to close it.


I think the key point here is that you want to use your non-attached garage. If you have electricity to run lights and a compressor inside it, you are already going to have to decide .

 

Hey Billy - curious as to what you used for the fresh air "intake" side of your setup? Did you use a similar set of box filters? Also, where did you purchase your "booth" . . . I'd like to get one!

 

Swamp coolers can feed air in (water off), but aren't good filters. You gotta size them too, especially if they are restricted by the filters. If you have been in a paint booth, you know the air flow is pretty high.
I'd also run the fans/blower thru the filters for a while before spraying. Let any chunks get run through before laying down paint.

 

I've wired up a lot of spray booths over the years and none of them ever had an explosion proof fan. Explosion proof is just a general terms meaning the equipment will not emit sparks or overheat enough to ignite the vapors. The required electrical equipment is actually labeled as Class 1 Div 1. A Class 1 Div 1 electrical motor by itself would cost at least $1200. To avoid this what is commonly found that the blade in the ductwork is aluminum (non-sparking) and is driven by an enclosed belt by a external general purpose motor. Other NEC rules include interlocks on the doors and a solenoid to prevent spraying unles the doors are closed and the fan is running.

Having said this not many guys will have a real spray booth in their shop. But hanging visqueen and spaying solvent based paints is a potential hazard. I like the external fan in a stand along building as shown. Just avoid dropping your trouble light in a vapor filled homemade spray booth.

 

I have painted with a box fan when I was poor. Now I have an explosion proof fan. They are expensive!!

 

This is what the guy who is painting my Ranch Wagon is using. One blower to inflate the booth and another to blow the fumes out through the filters on the outside walls. Seems to work well.

 

Even a box fan would be explosion proof IF the vapors don't pass over the fan. What I have done, and believe to be totally safe, is place the fan on an outside wall (actually two of them under a partially closed garage door), blowing INTO the room. Only fresh air over the motor. I used furnace filters taped to the back of the fans to prevent bugs/dust from being added to the room. And, same filters taped over the man door and windows where the air was exiting. One has to be sure that there is enough airflow to keep the haze down, both for the good of your health and to prevent the mist from falling back onto the paint. That really ruins the gloss!

If you think about it, there is no ignition source in a normal fan motor, no switch or relay. But most have a switch in the box and that is an ignition source when the contacts make or break under load.

For my next paint job I'll be using a similar setup, old furnace squirrel cages blowing under the for from the outside. filters in and out.

 

This is one of those subjects that to do it correctly there isn't really any middle ground. Explosive vapors are nasty as are the resultant burns when things go bad. You can outfit a space, temporary or not, with some planning. Basically identify what you are going to have inside the space and what will be outside feeding into the space. Everything inside should be explosion proof: lights, switches, fans, etc. Things typically set up outside the space: general shop air compressor (usually not an explosion proof motor and you don't want vapor filled air to be the compressor inlet air); oil less air compressor for air supplied respirator or hood ( again, you don't want vapor laden air to be the inlet air). Outside compressors need to be located so not to be able to ingest the exhaust fumes from the space exhaust fan. If you are converting a small garage area it doesn't take much to add a small shed in a suitable place for the outside equipment. The cost of outfitting the space is cheaper than the medical bills should things go wrong.

 

For a temporary outdoor booth, positive pressure doesn't need an explosion proof blower. If the booth is inside another structure, then negative pressure with an explosion proof blower is the way. As ekimneirbo posted above, the simplest explosion proof is a squirrel cage with an external motor.

 

I blow thru, the fan on my end wall sucks air from outside and pushes it thru the shop.

....

 

I’m lucky enough to have a really good friend that owns a body shop and can use his paint booth anytime I need to, just have to work around his schedule sometimes. But at home I’ve always used a large squirrel cage fan with filters and let it push the air into my garage, then have a huge filter bank that I put underneath the roll up door that lets the air out. Let me tell you if you want to push some air that’s the way to do it! Almost no cloud of paint particles/fumes floating around in there.
Honestly I prefer the booth just because I can regulate the temp and humidity also the convenience of having a complete paint mixing system (PPG) at my disposal behind it.

 

Use a fan with a brushless motor = no sparks.
https://www.homedepot.com/p/XPOWER-...EBz_on_CVKeYljm266g6zVgsomaoXlg&gQT=1#overlay

 

I bought it on Amazon. It was a Chinese company I was unfamiliar with, and I knew Amazon would refund my purchase if it was a scam. I am also a Prime member, so I got free delivery as well. I also sourced the Vevor explosion proof fan through Amazon. $1000 for the booth (and the two fans it requires) and the extra Vevor fan and duct.

Yeah, the booth requires a small fan that inflates the booth, it runs at all times, or the booth comes down rather quickly. Rolling brown outs are not your friend. The second fan provides a positive air flow through the booth. It is a large booth, and I wanted the cloud to dissipate quickly and be able to control where it went (my wife did not want the concrete in the back yard painted black) thus the excavation fan (the fan box ended up on a tarp before the wife signed off). The combination gave me a clean booth to work in and clean concrete.

The fresh air fan was in my garage and I did run it's intake through a K&N cone filter I had in the shop. I cleaned it and oiled it and rigged up an attachment for it. Like I mentioned, Amazon is your friend. All of the correspondence from the seller was in Chinese, as was my receipt. I figured it was a scam and was comfortable that Amazon would take care of me (they have had to before). It showed up as promised and worked as described.

I will mention the downside of the booth is sunshine. I picked an overcast NW day, set up, mixed my paint with mid-temp reducer, started painting in a 75 degree booth, the sun peaked out a bit later and the booth thermometer hit 90 in seconds. Solvent checking, fast flash, no run out, and no time to change reducer. I ended up re-squirting the doors and two fenders as a result the following day. If it were set up in a building or under an overhang or carport, it would be great! I have 2 garages facing each other, I designed the peaks in the roofs to be directly across from each other, next time I plan to run a cable between the two opposing gables and add a sun tarp over the top of the booth to prevent direct sunshine but allow light through the clear sides and skylights.

 

I'm glad I hang around with you guys.
I'd blow myself up for sure.

 

If the motor is isolated from the fumes or fan impeller then it doesn't need to be explosion proof as the fumes wont flow across the motor. Your typical household box fan is not going to be safe. But a fan with a shaft that runs the impeller off to one side will be safe.

 

I used a similar set-up as Bandit Billy when I painted the roadster a year ago. Being concerned about losing power and having an inflated tent come down on my fresh paint I set up a cheap 10 X 20 ft. wedding tent inside my shop. I used red rosin paper to protect the floor, set the tent up on it and used several rolls of duct tape to seal all the joints on the walls and ends. Built a plenum for the back wall for the fan inlet to fit into, and covered the front of the plenum with paint booth exhaust filters (just visible on the floor in the back of the booth). Used an explosion proof barrel fan like Bandit Billy's for the exhaust and ducted it out to the back window of the shop. Front wall had a couple of rows of furnace filters for the air intake. I used a lot of duct tape to ensure that all fumes were contained in the booth and the exhaust system. Grounded the fan, ducting and booth to reduce the chance of static electricity. I had all the lights, compressor, heat and etc. outside of the booth. Though there are a few "improvements" I'd make if I used this spray booth again it actually worked well and after spraying a couple of coats you could leave the booth and there was NO odor of paint or thinner in the rest of the shop. Worked for me and I didn't blow myself up...

 

Thanks again guys - Lots of good input that I will incorporate. (Unless I run across an attractive ((and lonely)) woman that happens to own a paint booth.) Boy that could solve all kinds of issues !