Spray Booth Explosion or Fire

[Spokerider]

Yes, another DIY spray booth thread.........

I have made a home-made spray booth from a 10' x 20' portable car shelter. I will be painting one vehicle in it.

One end is sealed with plastic vapor barrier, and it has two 20" box fans blowing filtered air into the booth.
The other end, where one would drive a vehicle into, has a 6300 CFM tube fan with a Baldor motor [ yes, inside the fan tube ], to exhaust the vapors. I have some polyester material over the exhaust fan intake to catch the over spray mist. I know that the polyester does nothing to collect vapor. This end of the shelter with fan, is not sealed air tight, nor does it need to be. It works well loosely closed up.

This booth is running negative pressure, and has a nice even cross flow breeze when the the 3 fans are running. Running roughly a 1:2 positive / negative air flow.

There will be no lighting, and no heating in the booth, just the 3 fans.

I will be spraying with a HVLP gun.
Epoxy Primer, Imron Rival paint, urethane primer / surfacer, and POR 15 and similar paint will be sprayed.


My question is;
Has anybody done any spraying in a similar booth WITHOUT problems? Ever had an explosion or fire? Used a non-explosion proof fans in a booth without any incidents?

Looking for 1st hand experience here fellas, not some reiteration of "what not to do" found everywhere on the internet. Anyone can find pages upon pages of that for themselves........ What I cannot find, is real proof that a fire or explosion was caused from over spray going through a fan motor. I have read of a few booth fires in the weeks I have researched this, but ignition was caused by heater sources, not from fan motors.

I doubt that the exhaust fan I have is explosion proof. It's what I have and what I'll use unless I can summon real proof that I ought not to....yep, I'm going to be a gambling man.

Again, looking for first hand experiences / proof please.

 

[Lee Celtic]

I'm Not an expert. I repeat not an expert.. the only thing I would think about with all that wind blowing through a plastic tunnel is static electricity.. but as long as everything is earthed up including the car it shouldn't be an ignition source.. But then again I'm not and expert and I'm prepared to be shot down on the static thing..

Though I did work with a guy who used to smoke a pipe while spraying.. we had flash overs in the spray room at least once a week.. he was old school and just used to duck.. wait for the flash to burn out and then carry on. Flames would roll across the ceiling and then they were gone. Never knew if it was the pipe that caused it..

 

[My Old Tools]

I will tell you I helped build a spray booth for a friend starting his body business. We taped and bedded everything, used fliters, explosion proof fans, explosion proof lights, etc. It didn't work worth a damn. Dust in everything he painted. Ended up tearing it out and buying a real booth.

 

[38Chevy454]

So the real question in scientific terms is will you reach the lower combustion limit. In other words, will you get sufficient fumes built up that an ignition source will potentially cause combustion. If you have enough airflow, you will never reach that limit. I can;t tell you what that limit is, but from your description it sounds like you have pretty good amount of clean air entering. This dilutes the fumes to help keep them below the combustion limit. So does taking a break from spraying and letting it flash off before adding more solvent when spraying.

 

[rlitman]

So the real question in scientific terms is will you reach the lower combustion limit. In other words, will you get sufficient fumes built up that an ignition source will potentially cause combustion. If you have enough airflow, you will never reach that limit. I can;t tell you what that limit is, but from your description it sounds like you have pretty good amount of clean air entering. This dilutes the fumes to help keep them below the combustion limit. So does taking a break from spraying and letting it flash off before adding more solvent when spraying.

Good point. That limit BTW depends on the vapors in question. Spraying from Krylon cans for example may be worse than you expect, because they use a butane/propane pressurant in addition to the solvents.

Is the Baldor motor in the fan ODP or TEFC? TEFC is not quite explosion proof, but at least it doesn't **** vapors through the motor.

 

[sberry]

With a modern spray gun shouldn't need to worry. If it clears fast its good. You don't always need fans on the intake, I don't use it on mine. I actually had too big exhaust fan for a while but mine is tuned quite well and dont filter any air coming in but pull it mostly over top of the end wall, makes for a warm downdraft.
It taks a bit of experience for tuning a room to become second nature. A good experiment is a simple twin box fan in a common bedroom, use the door as a regulator and notice too tight and no air movement, too loose and no "pull" or air clearing.
Used to smoke in dorm rooms.

 

[Marctrees]

Sorry, but what does how "modern" a spray gun have to do with the vapor in the air depending on compound sprayed?

"Airless", HVLP, or whatever, even brushing on, still applies the material that then offs into the surrounding airspace.

Just confused why that was said.

Marc

Marc

 

[rlitman]

...mine is tuned quite well and dont filter any air coming in but pull it mostly over top of the end wall...

That's a sort of filtration in a very smart way. The biggest dust particles (and stuff that's most likely to be visible in your finish) spend most of their time in the air near the ground. Air higher up is going to be cleaner, so sourcing your air from over the top of the wall will separate out the biggest stuff.

Ever notice that a computer sitting on the floor will fill up with dust bunnies, but when sitting on a desk it doesn't (unless it's in a particularly nasty environment)?

 

[Marctrees]

Sberry - I like your roll up curtains. Marc

 

[rlitman]

Sorry, but what does how "modern" a spray gun have to do with the vapor in the air depending on compound sprayed?

"Airless", HVLP, or whatever, even brushing on, still applies the material that then offs into the surrounding airspace.

Just confused why that was said.

Marc

Marc

Yes, but an old time rattle can or conventional spray gun may have a transfer efficiency of under 30% (with losses both due to overspray and bounceback), whereas HVLP can be above 65%. So by switching from conventional to HVLP, you're spraying half as much material to cover the same painted area.

The amount of flammable vapors depend upon both the amount that you spray, and the surface area of the sprayed material. Overspray from conventional spraying not only accounts for more than half of what you're spraying, but also greatly increases the surface area and emitted vapors.

 

[sberry]

Looking for 1st hand experience here fellas, not some reiteration of "what not to do" found everywhere on the internet. Anyone can find pages upon pages of that for themselves........ What I cannot find, is real proof that a fire or explosion was caused from over spray going through a fan motor. I have read of a few booth fires in the weeks I have researched this, but ignition was caused by heater sources, not from fan motors.

One guy now owns the most $ body/collision shop around had a fire back in the day, got drunk and something to do with heating paint on a wood stove etc but I seen it so bad you cant see the other side and they didn't blow up.
Not recommended though and no need to be so careless.
Mine is big and I don't paint a lot or paint out of position but the low vapor guns and so much may be water in the future. There is a lot more overspray in equipment where a guy can get it on a car.
If you don't need heat can paint with a single room or enclosure, if you want heat need a divided room. I have wood stove and infared unit and try to pick warm days even in winter time.
Google paint booth basics and there are a couple tutorials well worth reading which really help with fundamentals.
I am sure it has happened but personal knowledge never seen it. I painted a lot of stuff with 3 box fans and some cheap furnace filters in front of them and even without.

 

[sberry]

Thanks for talking about efficiency and vapor. An operator also effects the transfer rate. My scheme is about as simple as it gets and completely out of the way or installed in under 5 minutes. I have never replaced the plastic and the only damage was a careless fug with trouble light. Plastic is a nice to tune. I pre run it to pull any cobwebs out.
I painted a bit off and on but the beauty is this same space is completely open when not using it and has floor drains for 3 or 4 cars for winter parking. Its a multiple use area, use more for other stuff and no investment is something costly to build and in the way.
It works super good and is quite clean considering I barely sweep the floor.
It clears so well that I have some stock shelves at the intake end, no over spray.
By the time I got to this had some concept. I really wanted a way to paint, it was high on the list, I wanted to be able to paint a full size truck. Despite the simplicity it would be a costly process to make it significantly better.
Last 2 pics are an after and a before from a remodel this last winter that reduced 20 yrs of junk, some not used since it was parked there and reduced to the point there is wall space, has since filled a little again.

 

[sberry]

The paper machine was awkward anyway. I cut it up and made it wheel under the bench. I toss old shirt over it. In hindsight would have reversed the wheels, a minor matter. Made it wayyyyy easier to use and store.
This first pic in post above has a small boat winch with 3 3/16 nylon lines to the main curtain roll.

 

[Red Box]

I know you want to do this but for just one car? At the cost of paint now, I would consider hiring a painter w/clean booth to shoot it. You do the prep and masking. If you don't spray this stuff regularly, it's very easy to get orange peel, runs, splotches, fish eyes, etc. Then you get to wet sand everything and buy another $800-$1K in materials.

Couple of ideas for you anyway. First, depending on the size of the car, 10' wide may not give you enough room along the sides to work and see the paint going on. Side lighting is super important.

Be sure the floor is wet and also shoot early in the am as less bugs and wind. Next I would consider no fans due to the fire factor. If you use a slower reducer will help melt in the overspray as it settles.

I wouldn't discount the potential fire hazards. I'd move compressor outside and switch off anything else that could become an ignition source.

 

[johninct]

I will tell you I helped build a spray booth for a friend starting his body business. We taped and bedded everything, used fliters, explosion proof fans, explosion proof lights, etc. It didn't work worth a damn. Dust in everything he painted. Ended up tearing it out and buying a real booth.

I had kind of an opposite experience. My friend had a commercial down draft spray booth with a 4' deep pit in the center, etc. He just painted it, everything was clean and I taped all of the doors shut and I still got a few specs. That is why you block and buff when done. I also used Imron and yes, I blocked and buffed Imron. Is that Imron you are using still mixed 3:1? You also should have a special air pump to bring you clean air to breath.

 

[gahrajmahal]

The main problem with the home built spray booth besides the safety aspect, is no control over the temperature. When I sprayed the Chrysler in my avitar there was a 30 deg. Temperature difference from the time I started to spray until I finished. Hard for even a pro to get great results with those challenges.

http://www.jalopyjournal.com/forum/threads/pictopaintsaga-flat-pearl-fades-winfield-style.539437/

 

[BADSIX]

I have a home booth and been in the auto restoration business for over 30 years. my booth exits at one end with filters at the other I get real clean paint jobs. it more than the booth its how clean you are. you can't go in there with a tee shirt and spray paint, also wetting the floor helps. your vehicle needs to be clean ether rinsed under the bottom or you need to mask from the car to the floor. when your spraying the lower rocker area your blowing dust and dirt from under the car. most of your products are not very volatile and if you get good flow that's good. I would try and get that open motor fan out of the exhaust system.
Jay D.

 

[ScottsGT]

I've done it many times and I'm still here to talk about it. I had a body shop about 30 years ago. Used an old direct drive AC fan or an old squirrel cage fan I still have. Just three or four years ago I did it once again. Lined my garage with plastic, huge window fan forcing air in and that same 40 yo squirrel cage fan helping to push air out. I was still working in a thick cloud of overspray. I needed more ventilation out.

 

[MP&C]

Was in VA Beach yesterday at a business close out sale, there was a paint booth sitting inside the building, already dismantled, complete with explosion proof fan. Anyone interested PM me for contact info. I was there to pick up other items.

 

[Spokerider]

With a modern spray gun shouldn't need to worry. If it clears fast its good. You don't always need fans on the intake, I don't use it on mine. I actually had too big exhaust fan for a while but mine is tuned quite well and dont filter any air coming in but pull it mostly over top of the end wall, makes for a warm downdraft.
It taks a bit of experience for tuning a room to become second nature. A good experiment is a simple twin box fan in a common bedroom, use the door as a regulator and notice too tight and no air movement, too loose and no "pull" or air clearing.
Used to smoke in dorm rooms.

All good points fellas, thanks for the input.

Having just tried the booth out for air flow yesterday, it does **** the shelter walls in. Not really taught, but the negative pressure is there. I will be able to unzip the front "door" zippers, allowing for air to be recirculated through the exhaust fan, effectively reducing it's air flow from the booth. The intake filters that I made do restrict the efficiency of the box fans and the negative pressure helps to pull air through them.
The Baldor exhaust fan does not have variable speed settings, just on / off.

Will I have too much air flow causing turbulence as is? Dunno until I try it. Never painted in a booth before, just outside with the gnats and dust.

 

[sberry]

This obviously doesnt apply to everyone, some of the principles are the same though but this is way easier to work from than a conventional booth.

 

[Spokerider]

I know you want to do this but for just one car? At the cost of paint now, I would consider hiring a painter w/clean booth to shoot it. You do the prep and masking. If you don't spray this stuff regularly, it's very easy to get orange peel, runs, splotches, fish eyes, etc. Then you get to wet sand everything and buy another $800-$1K in materials.

Couple of ideas for you anyway. First, depending on the size of the car, 10' wide may not give you enough room along the sides to work and see the paint going on. Side lighting is super important.

Be sure the floor is wet and also shoot early in the am as less bugs and wind. Next I would consider no fans due to the fire factor. If you use a slower reducer will help melt in the overspray as it settles.

I wouldn't discount the potential fire hazards. I'd move compressor outside and switch off anything else that could become an ignition source.

I'm building a DD / Expedition 4x4, not a show car. Nothing on it is perfect.....neither will the paint job be. Using Imron paint ought to have tipped you off.

I looked to rent a booth locally, no one stepped up, leaving just the autobody repair shops that need to make their thousands.......

As DIY'er, you know that with our own shop and tools,we can work at our own pace, on our own schedule without the constraints of business deadlines and time frames and associated costs.

Thank you for the ideas. I will try to incorporate them in to this project.

 

[sberry]

Pick nice weather for a 1 off job, the Imron is dangerous to spray. I agree the 10 ft tent will be a problem.

 

[Spokerider]

I had kind of an opposite experience. My friend had a commercial down draft spray booth with a 4' deep pit in the center, etc. He just painted it, everything was clean and I taped all of the doors shut and I still got a few specs. That is why you block and buff when done. I also used Imron and yes, I blocked and buffed Imron. Is that Imron you are using still mixed 3:1? You also should have a special air pump to bring you clean air to breath.

Yes, a positive pressure hood is the industry standard for 2 part urethanes......$2000 or more, that I can ill afford.

3M has a tech bulletin on spraying urethanes. In short, they do not recommend cartridge respirators because, once you smell the fruity aromatic aroma associated with the isocyanates, the exposure limit has already been breached. They do not say the the organic vapor cartridge does not work effectively however. The 3m organic vapor cartridge respirator has worked for me so far. Replacing the cartridges often is key.

Imron Rival is mixed 6:1

 

[Spokerider]

Pick nice weather for a 1 off job, the Imron is dangerous to spray. I agree the 10 ft tent will be a problem.

A 10ft wide shelter isn't very wide, and neither is a suzuki samurai.

It's what I've got to uses and so will go with it.

 

[Spokerider]

The main problem with the home built spray booth besides the safety aspect, is no control over the temperature. When I sprayed the Chrysler in my avitar there was a 30 deg. Temperature difference from the time I started to spray until I finished. Hard for even a pro to get great results with those challenges.

http://www.jalopyjournal.com/forum/threads/pictopaintsaga-flat-pearl-fades-winfield-style.539437/

I know.
Painting time is right now, with our outside temps 25-30 deg. The October rains [ BC Canada on the coast ] are right around the corner.......

 

[Spokerider]

I have a home booth and been in the auto restoration business for over 30 years. my booth exits at one end with filters at the other I get real clean paint jobs. it more than the booth its how clean you are. you can't go in there with a tee shirt and spray paint, also wetting the floor helps. your vehicle needs to be clean ether rinsed under the bottom or you need to mask from the car to the floor. when your spraying the lower rocker area your blowing dust and dirt from under the car. most of your products are not very volatile and if you get good flow that's good. I would try and get that open motor fan out of the exhaust system.
Jay D.

Good tips Jay thanks.
I did frame off resto and painted the tub underbody last summer. Running gear is all freshly stripped and painted. It IS dusty from working on it outdoors, but it will get a good pressure washing before bringing it into the booth for paint.

I plan on painting the doors and hood off the vehicle, in the booth.
Yup, clean clothes, and a wetted floor are in the recipe.

Yes, I know the exhaust fan is not ideal, but as mentioned, unless I can dig up some proof that that I am about to have a fire / explosion from using it, I will gamble on using it.

 

[Spokerider]

I've done it many times and I'm still here to talk about it. I had a body shop about 30 years ago. Used an old direct drive AC fan or an old squirrel cage fan I still have. Just three or four years ago I did it once again. Lined my garage with plastic, huge window fan forcing air in and that same 40 yo squirrel cage fan helping to push air out. I was still working in a thick cloud of overspray. I needed more ventilation out.

lol.
Another "gambling man" and still alive too.

 

[sberry]

Having just tried the booth out for air flow yesterday, it does **** the shelter walls in. Not really taught, but the negative pressure is there. I will be able to unzip the front "door" zippers, allowing for air to be recirculated through the exhaust fan, effectively reducing it's air flow from the booth. The intake filters that I made do restrict the efficiency of the box fans and the negative pressure helps to pull air through them.
The Baldor exhaust fan does not have variable speed settings, just on / off.

Sounds like you are getting the idea, it must "draw" fumes out in order to clear the air.

Will I have too much air flow causing turbulence as is? Dunno until I try it. Never painted in a booth before, just outside with the gnats and dust

 

[sberry]

As I mentioned, I don't use any pressure. A more sophisticated booth often involves make up air and heat and uses a forced intake matched with exhaust to still maintain a draw. Its often mistakenly called a pressure booth and its not. There is no need for fans in a stand alone tent.

 

[BADSIX]

Good tips Jay thanks.
I did frame off resto and painted the tub underbody last summer. Running gear is all freshly stripped and painted. It IS dusty from working on it outdoors, but it will get a good pressure washing before bringing it into the booth for paint.

I plan on painting the doors and hood off the vehicle, in the booth.
Yup, clean clothes, and a wetted floor are in the recipe.

Yes, I know the exhaust fan is not ideal, but as mentioned, unless I can dig up some proof that that I am about to have a fire / explosion from using it, I will gamble on using it.

you should use a paint suit the paper ones. why don't you just use the positive pressure set up and no exh. fan ,it will work just as good. I have a couple of friends with positive pressure booths they work great the neat thing is that you can go in and out with out sucking in dirt or if you have any leaks your not sucking dirt and dust in there. if you have good air going in and plenty of area for air to go out it will work good.
Jay D.

 

[BonzoHansen]

Yes, a positive pressure hood is the industry standard for 2 part urethanes......$2000 or more, that I can ill afford.

3M has a tech bulletin on spraying urethanes. In short, they do not recommend cartridge respirators because, once you smell the fruity aromatic aroma associated with the isocyanates, the exposure limit has already been breached. They do not say the the organic vapor cartridge does not work effectively however. The 3m organic vapor cartridge respirator has worked for me so far. Replacing the cartridges often is key.

Imron Rival is mixed 6:1

spraying por15 has similar concerns. isocyanates. when i researched spraying that stuff years ago the por folks told me air supplied mask was required.

 

[Falcon67]

When I sprayed my car I used the old shop, so about 20x24 area. Hung drop cloths to protect everything and the floor (it didn't - overspray goes everywhere with a conventional gun) and put a 20" box fan in each of the two windows on one end. The fans had house air filters taped over them. Water floor, turn on fans, open 8x7 overhead door at opposite end of building from fans, shoot, wait just a minute for fog to clear, close overhead door. Mix, get ready for 2d coat. Worked well. Later, I used a HVLP setup for some hood and fender work - just used the fans. I recently shot the hood on my car again. Did it outside, over wet gravel, in the sun, no booth. Used too fast a reducer so it's a bit of an orange peel finish but no issues with dirt and what not.

Note, I only shoot with a single stage paint. I don't do base/clear. These are hot rods and race cars and need to be easy to repair rather than "show purty". Also - full face mask, head sock, filters and suit if you are in the booth. When I shot my car last, it was 95F outside. Had about 1" of sweat in each of the suit legs after 3.5 hrs of painting.

 

[sberry]

There is no such thing as a positive pressure spray booth. Positive pressure is for a clean room, like a balloon forces air everywhere equally and the only flow out is thru cracks.

 

[sberry]

Managing the airflow is probably the most important element of a spray booth and its design. Creating a laminar airflow envelope in the spray area at an engineered velocity separates a "spray booth" from a "tin box".



This managed airflow enables a painter to get maximum efficiency of the paint sprayed while directing overspray away from the painted finish. In a superior design, air is controlled to flow in unidirectional layers, either in horizontal, semi-downdraft or downdraft flow patterns, while maintaining an even velocity.
The above was a quote, finishing academy had a beautiful simple over view at one point, must have been too good. I got it on pdf but need to figure out how to post part of it. The older version on the net was so simple a guy could read in about 20 minutes.

 

[sberry]

In my own can feel it warm up when turning on fan if I am heating, the fan pulls warm air in a downdraft then almost horizontal fashion across the floor.
In a tent booth there wouldn't be a long room to get the lazy S developed, might have to let air in vertical as in the fashion of a cracked open door. In a fairly sealed room used a rubber band on the door knob and cracked an inch or so with twin window fan on hi, probably need 2x the power to spray a small car in a tent. I don't recall the cfm math etc but maybe 1/3 hp or so, You need a little wind on this if spraying bad paint. I don't use pressure air but its rare and I can stay upwind and outright clear, full face mask and gloves. Stand up wind mixing and pouring, keep neat and clean a bit between coats and am ready to rinse gun when done.
I use some Imron and am careful with cut in, about 10 minutes of picking around on a pickup, can shoot the inside of a bed mostly single pass and the outside in 10 minutes or less a coat.
Tractors take longer, a car an hour, tractor over 2 and discipline is everything. A fast overall coat as much as possible first, color anything not got color then another wet cover its done. I use a paint pot on them so we can spray all position.

 

[Zeke]

I have a home booth and been in the auto restoration business for over 30 years. my booth exits at one end with filters at the other I get real clean paint jobs. it more than the booth its how clean you are. you can't go in there with a tee shirt and spray paint, also wetting the floor helps. your vehicle needs to be clean ether rinsed under the bottom or you need to mask from the car to the floor. when your spraying the lower rocker area your blowing dust and dirt from under the car. most of your products are not very volatile and if you get good flow that's good. I would try and get that open motor fan out of the exhaust system.
Jay D.

This is probably the best post here, information on explosions notwithstanding. I have painted many times in a temporary enclosure and found that fans only exacerbated the dust issue. I tend to go in, do my business and get the hell out ASAP. I'll use the fan in a minute or 2 after the coat just applied begins to flash.

I have been known to wet down the area 20 or even 50 feet all around my painting set up. I sometimes run a mister as well to bring down airborne particles. (we have very low humidity so premature flashing capturing moisture is seldom a problem). As mentioned. temperature control is very important.

 

[58Yeoman]

I guess I'm surprised that I'm still alive. I've painted dozens of VW's and a couple antique cars in my garage with only a window fan under the overhead door, windows open for intake air. Cartridge mask shooting Centari with hardener, sometimes in the cold weather with the wood stove burning; all paint jobs turned out great. The only time it got to me was when I painted the inside of an 8' PU box outside w/o the mask...I broke out in hives.

The last thing I painted was a fiberglass cover for my Ranger PU about 10 years ago.

 

[BADSIX]

There is no such thing as a positive pressure spray booth. Positive pressure is for a clean room, like a balloon forces air everywhere equally and the only flow out is thru cracks.

why is there no such thing as a positive pressure booth?

on a positive pressure booth you force air through a filter system in at one end and it naturally exits the other end bringing with it paint fumes. it works exactly as a draw through only in the opposite. its much better as you can exit the room if needed and you don't **** in dust. also if your using a visqueen booth it helps hold it up and won't let dust in any little cracks there might be.
Jay D.

 

[RobSmith]

I've built temporary spray booths and only used exhaust fans and filters on the intake. That creates a flow from one end to the other. The intake is up high and the fans are low. The exhaust fans have no filter but a deflector outside forces the dirty air into a shallow tray of water. That catches most of the paint particles.