What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Paint booth question; possible ignition source?

goatflieg

Well Known Member
While fine-tuning my paint booth components, something occurred to me. I will be painting my aircraft with polyurethane paint. I'm using three box fans in a homebuilt enclosure to pull the air out of the booth, and filtered incoming air is drawn from the opposite side of the booth. I did some testing today, and I've got very good airflow, so no worries there. But I started to think about the fans, and how they're wired. As you can see from these photos, all three fan power cords plug into a switched power strip, which links to an extension cord run to a wall plug. I realize that I'll be switching the fans on long before there will be fumes present, and turning them off long after the fumes are evacuated. But I wonder if the presence of the power strip inside the confines of the booth on the end where fumes will be drawn constitutes a potential fire/explosion hazard. The solutions are obvious; hard wire the three power cords to one extension cord, and have any switching or plugs outside the booth. I could also mask in such a way that the power strip is outside the booth envelope, which would be somewhat awkward. But I wonder how necessary this is... am I over-thinking it, as usual? Has anyone ever experienced fume ignition from a fan motor or power strip? I'll do more research... but I'm interested in any input expressed here.
Aon1xs0j-IEghrWGfg5P5QRzzs5GJ3iyDbgNJkVOQqj40uVHfsIf1nh6zoJD9gS_opOKSmY4y78kEQ=w1920-h1080-rw-no

ZAWaKmf3ROraj9WO-Vm3HA9fgj5gpk0dms1vNX026ppPa0XHd4zXCLK9odyNgw22L4HApDsbZZldSg=w1920-h1080-rw-no
 
Paintbooth

Hello Martin,

I painted my -14 with a paintbooth exactly as you described. I had the wiring outside the booth and turned the fans on before spraying and off well after spraying.

I understand this is only one data point and explosion proof everything is always better! But, it worked for me.

One thing I would add to your setup. Set up a water sprinkler aft of your exhaust vents. You can put filters in front of the exhaust fans, but at some point you will remove them because of blockage. The spray exhaust will travel a VERY long distance without the water to knock it down. Your neighbors will thank you!
 
Fans

Maybe a little obsessive but aren't the fan motors an ignition source unless they are intrinsically safe. Compressor motors as well.
 
Last edited:
Consider using some old squirrel cage furnace fans. The motors are not in the airflow so less likely to be an ignition source
 
Just my method.

I might have this backwards but in my last temporary paint booth I built it within my garage and pushed air IN with box fans and filtered the exhaust air OUT to try to catch all the over spray. I figured the incoming air through the fans was less likely to cause a flash fire since it was paint free air. I wetted the floors down inside and out of the booth with a garden hose before I started and didn't have any problems with dust particles in the paint. The plane turned out great. I'm still here but when I think about what I did and the potential for a explosion, it scares the **** out of me. :eek:
About ready to paint my next plane and I'm going to try the Stewart system. One of the guys in my chapter used it and his job came out beautifully.
 
more data point(s)

I painted a lot of things in my Dad's shop...using a couple of those cheap cube fans to exhaust the fumes.

note #1. you can double the output of these fans by ducting them.
#1a - you'll flow much more air thru the booth if you have double the inlet area as outlet. I built an entire man-door frame of filters, and that was barely adequate...you still heard the fans rev a bit when you opened the door, which means you are sucking dirt from every crevasse in the zone.

note #2. these are very low pressure, high volume fans, so it doesn't take much of a breeze to pretty much 'stop' the flow.......so a cautionary note if you think the fumes will never reach the sparky little motors because they are blowing fresh air 'in'.

thankfully my ignorance didn't end in a big 'kaboom', but there are a lot of potential ignition sources...fluorescent lights, the drill you are stirring paint with, etc.
I think we are generally lucky that we don't seem to hit the right ratio very often for combustion.
...probably cleaning the gun and blasting a ton of lacquer thinner/gunwash through it is the more dangerous operation?
( which I usually did outdoors, for obvious reasons)
 
You really want your booth to be positive pressure, higher than outside pressure, which means pumping air into the booth with the fans. A negative pressure booth sucks dirt and bugs under the sills, around the doors, etc.

Filter air both in and out.

Beware circulating flow, like round and round the room. It's usually due to a jet of inlet air, or outflow in just a few spots. Inlets and outlet that span the room are best.

Homebuilders have been talking about paint booth explosions as long as I can remember, but I've never heard of anyone actually blowing one. Any stories out there?
 
You really want your booth to be positive pressure, higher than outside pressure, which means pumping air into the booth with the fans. A negative pressure booth sucks dirt and bugs under the sills, around the doors, etc.
Filter air both in and out.

This makes great sense Dan. However, many commercial paint booths are open faced and exhaust after the filter bank. They are designed to catch particulate, not necessarily to keep contaminants off the work. Doesn't do a thing for VOC's.
Essentially, this isn't any different than painting outdoors, with the exception that your particulates get trapped and don't fly into open air. If the environment the booth is located in doesn't have a lot of air born particulates or flying insects, you can do good work. My paint booth is this type, but I don't use it for fine exterior work, only for priming or painting structures as I build. I leave the final painting to the experts.
So, it just depends on what kind of work you want to do with your booth, but for even top coating, you can get excellent results if you can control the conditions of the room your booth is located in.
This type of booth doesn't allow any build up of explosive gasses except in the exhaust chamber, which requires an explosion proof fan to be "legal".
This is the booth I have now. 8' x 8'. You can "tarp" it out further as the fan has plenty of CFM's to handle it, but again, I just use it for parts work. http://prod.globalfinishing.com/products/autorefinishpartspainting/motorcyclepaintbooth
My first booth was an office attached to the hangar. My second was a Van's shipping box. All open faced designs.

I have never heard of anybody blowing themselves up. Just like any other combustible, it takes just the right mixture of air to fuel and an ignition source. I wouldn't want to be the first though....
 
I could be wrong

but I believe most if not all household box fans use shaded-pole induction motors that lack any sparking ability except in their on-off and possibly bi-metal thermostat switches. Very unlikely ignition source if switched remotely.
 
If the environment the booth is located in doesn't have a lot of air born particulates or flying insects, you can do good work.

Good point Jon...location is going to make a lot of difference regarding filtration.

Here in the wet part of Deep South, flying bugs seem to be enemy #1. I've been known to say really bad words after finding one doing the backstroke in my clear coat ;)

Flip side; Randy Pflanzer was at SERFI this weekend with his red RV-12. Absolutely gorgeous, and painted in an open hangar on the west coast.
 
Back
Top