explosion proof fans and finishing

[arbarnhart]

Not to beat a dead horse (I hope), but I was talking to a woodworking buddy about the discussion on finishes we had here and how someone brought up the point that the concentration required for an explosion would be more than what it took to cause you to pass out and probably die anyway. He brought up a counterpoint. He said it is correct that if you run the fan and then start spraying you won't have a problem. But if you start spraying in a small booth and then remember to turn on the fan when the fumes get bad it could be a very different story.

[thistle3585]

General rule of thumb is to start the fan before spraying and let it run for awhile after spraying. Most fans will spark when first turned on. I had OSHA in my shop a year or so ago, and they cited me for an electrical outlet within 15 feet of the opening of the spray booth because of the risk of a spark.
I think there is more danger in the overspray that builds up on the fan blades than anything else. That will easily overheat the motor and you risk an electrical fire.
I have my fan hooked up to a light switch, so when I turn on the lights in the booth the fan comes on also. Keeps me from spraying without the fan on.

[dunwell]

Just a quick clarification on the "Explosion Proof" notation on fan motors. The way the motor shop explained it to me is that it means that if the motor has problems and the inernals try to come apart, that the case is strong enough to contain the explosion. The next grade down is a "totally enclosed" which means that the case totally encloses all the moving and electrical parts. This is probably good enough for most spray booths. You for sure want a non-sparking fan blade though and it should be cleaned off every time you clean the booth. You do clean your booth, right? http://www.mandolincafe.net/iB_html/non-cgi/emoticons/wink.gif

Alan D.

[PaulD]

He said it is correct that if you run the fan and then start spraying you won't have a problem. But if you start spraying in a small booth and then remember to turn on the fan when the fumes get bad it could be a very different story.
I would make sure to check this with a qualified expert rather than relying on a "woodworking buddy's" expertise. I'm sure the risk is greatest when the fan is switched on; you get a spark in both the motor and the switch, and you would have fumes hanging in the air. I don't know how many of you have watched the commutator ring in an electric motor while it's running (that ring of copper bars that the brushes contact), but it's constantly throwing small sparks as the brush moves from one bar to the next. It's like throwing a switch hundreds of times a second. I'm not saying that your buddy is wrong, I just wouldn't take his word for it without knowing the source of his information.

I don't know if it's "kosher" or not, but I've set up temporary spray booths by placing a fan and filter outside the room and having good ventilation. As long as the fan is started first and the air flow is such that the exhaust can't circulate around to the fan, I think you've got a very safe system. Keep in mind that this is just conjecture on my part... I'm not qualified to say for sure it's safe. You don't want the fan blowing directly on you, but you want good crossflow to move the fumes away. This also keeps finishes from building up on your fan blades and enclosure.

Paul Doubek

[Chris Baird]

If you have your motor near the fumes it is wise to have a squirrel cage type motor. They don't have brushes and don't spark. Explosion proof doesn't mean that an explosion won't happen but it does mean that the motor is designed to contain the explosion if it does occur.

[arbarnhart]

I may have a gift for oversimplification, but when he described this scenario to me it seem so accurate that it didn't require much of an expert opinion to believe it. I was describing my idea of a box fan in a window with a box with no top or bottom sideways against it. This would be big enough for my scroll saw projects. I have decided to go with shellac for mandos, but I am not sure about my scroll stuff and I have a few cans of various products to use up. This would only work 7-8 months a year. I can keep my garage warm in the winter only by keeping windows and doors closed. I am still considering it a viable alternative but with that major caveat.

[sunburst]

My explosion proof fan is belt driven. There is a tube, or "tunnel" for the belt to get to the shaft, and seals on the bearings. If the fan is correctly installed, with a gasket, The motor is never in the overspray or the fumes. That, and the aluminum construction, are what make it explosion proof. The motor, by necessity, however, has to be well within 15 feet of the booth, so it needs to be a TEFC motor.
There are "hazardous location" motors, with all electic parts enclosed and gasketed, sealed conduit for the wires, etc., but the type of fan I'm talking about doesn't require one.

Proper filters, or mist arrestors, or whatever they're called, will keep the fan blades clean, so buildup on the fan shouldn't be a problem. (Yes, it should be cleaned if there's anything on it.)

If the switch is mounted correctly, in the wall or somewhere, the recommended distance from the booth, you can't turn it on once you're in there. You have to turn it on before you go in. I think it's best to get suited up, turn on the fan, go in, mix your material, prepare the gun, spray, then leave the booth. Remove all your protective gear and clothing, turn off the fan, and leave the building.
If you're still working in the shop, flipping on the fan once in a while will help keep fumes from seeping into your work space.

[Jim Hilburn]

As a 25 year electrician who has done commercial spray booth work, I would guess very few small-time spray area's conform to the National Electrical Code. A spray booth is considered a Class 1 Division 1 hazardous location and 20' all around it and 10' above it is considered Class 1 division 2. What that means is rigid conduit with seal-offs, explosion-proof motors and fans, adequate explosion-prooflighting to avoid the need for unrated temporary lighting to be used and explosion-proof switches and receptacles, often a good distance from the actual spraying operation. They take keeping us safe to extremes and that's a good thing till you have to write the check.
Anyway, you have a good deal of reading ahead of you to know and understand everything that's involved.

[Dave Cohen]

Just to add to what John and Jim said, they also want you to wire such that the spray equipment won't operate unless the explosion-proof fan is running. I built my shop from the ground up, & so needed a permit. The electrical inspectors went absolutely nutso about the spray booth. They would park in front of my house, and sit in the car reading the regs for an hour before they came up the driveway and gave me a bad time. Over time, I have come to think that there is good reason for what they did. Nitro & the like is such dangerous stuff. Your safety demands that you do your homework and do everything right. And even then, be careful.

[sunburst]

When Huss and Dalton moved to a their second building, they built a spray booth in the city limits (!).
The inspectors just handed them a 3 or 4 inch thick book and told them to read it themselves, then gave them a bad time! http://www.mandolincafe.net/iB_html/non-cgi/emoticons/tounge.gif

[JGWoods]

"Spray" is a nasty word in the OSHA vocabulary. it comes with many rules and lots of ways to spend money, all of them appropriate for auto spray booths and many industrial situations.

As far as dangerous concentrations are concerned look at the MSDS which came with your finish- varnish. lacquer, whatever- you did get an MSDS right?

Usually the section on firefighting measures lists the "lel" which is the "lower Explosion Limit" concentration necessary to get the fumes to go bang.
using acetone as an example- it has an lel of 2.5% in air by volume- notice also the PEL- pemissible exposure limit for people which is 1000 parts per million (too much).
2.5% works out to 25,000 parts per million- 25 times the allowable exposure limit and frankly you will be passed out, or have run away long ago from fumes that strong.

Most of the time you will find that there's no way you can get an explosive concentration in the air without ferocious amount of fumes- waaaay past what you want to tolerate and so you can operate with common sense- safely in any atmosphere you are comfortable in, even if it has some fumes. - wave a match around if you are curious http://www.mandolincafe.net/iB_html/non-cgi/emoticons/tounge.gif

If you have an organized shop about he only place you will find an atmosphere above the lel is inside the flammables trashcan where you have been throwing all your solvent soaked cloths- but seeing as that can has an auto closing top it's no big deal, even if a fire starts it goes out when the top closes back down on it....

Are there exceptions? sure, are there scary stories? sure.
Would I put together a $30,000 spray booth to make the local FD happy when I am spraying 1 instrument a week/month- heck no.
We had a similar problem at work where we spray out of a spray paint can little blasts of black paint- maybe 1/4 of a can each day and OSHA wanted us to put in a $30,000 spray booth. Several letters and arguments later they said they would have no further comment if there were no ignition sources with 6' of the spray operation. I keep a copy of that on file for the next visit....

Compliance and safety are often different things- be safe.

[thistle3585]

My OSHA inspector was an enviromental hygenist. Meaning he was more concerned about air quality. He monitored air quality while we performed certain tasks related to chemical use, such as spraying lacquers, staining and even the expandable foam packaging machine we used. The biggest failure was aerosol spray cans. We would spray some parts on occasion in a three sided box. The residual chemicals from aerosol cans didn't disperse, but hovered in a cloud, without any sort of airflow. It was pretty amazing to watch the guy's meter. It took several minutes for it to get to a "safe level" and that was just from a few quick spurts. He suggested we get a tabletop booth for the aerosol cans, but we had to stop doing it the way that we were up to that point. Since that inspection, I have been more attuned to the health risks associated with fumes more than the fire risk.

[JGWoods]

We already had a tabletop booth- exhaust fan, steel box, paint spray filters etc. and they still wanted the outlets and switches to be >6' - overall not a bad settlement.

[PaulD]

WOW!!! Lots of great information... I like JG's story about the spray can. http://www.mandolincafe.net/iB_html/non-cgi/emoticons/smile.gif A lot of it obviously depends on the OSHA, building, fire, or whatever inspector. When I worked in the welding shop I would crank through several spray cans of primer per day within 3 or 4 feet of my welder and probably 10 feet from the next guy's table. OSHA and the local fire inspectors never freaked on that... only on some of the ratty extension cords and OSHA made us hang screens to contain grinding byproducts.

While I would never be able to afford a $30K spray booth investment I think it pays learn from the electrical, building, and OSHA codes. They are based partially on decades of fire investigations. Even if you're not going for the inspection and you think it unlikely that you're going to level the neighborhood I would try to err on the conservative side. If you're working out of your home as a hobby, will your insurance pay if you blow up or burn down the garage? Or the house with your basement shop? What if you're building for a customer... does that take you out of the "hobby" stage as far as the fire marshall and insurance adjuster are concerned? That said, I've always gone with the "common sense" ventilation and kept a fire extinquisher in the shop just in case and I have yet to burn down or blow up anything accidentally.

To get back to Andy's recent posts; you've stated that you're trying to avoid the really noxious stuff. I found the reference to the LEL in the MSDS interesting... I'd never known (or thought) to look at that. Most of the alcohols I read about were 3.3% LEL, but it's probably worth checking the brand that you purchase.

pd

[arbarnhart]

I am not going to spray shellac - just brush or pad. No significant worries there. But I might spray Deft from a can near a fan, or I thought I might, for other projects. I also have some Polycrylic and whatever the WalMart 88 cents a can lacquer is (their cheap spray paint comes in clear and looks pretty good as a clear coat on craft items). I use it on scroll saw work. I think I will just use up what I have outside when the conditions are right and start using shellac on other projects also.

[Mario Proulx]

With regards to LEL, keep in mind that you don't have to have the entire booth at that saturation, but only the air stream to the fan, switch, or other ignition source. In other words, while the air in most of the booth may be way below the LEL limits, the air flow to the fan(or whatever) can easily be above it. And if you don't have sufficient air flow, or even ill-placed containers impeding proper air flow, there can be pockets in the booth that will be way over the LEL limits.

There's a house 50 miles from here that blew up twice. They were installing a new hardwood floor in the basement, and the owner insisted the contractors use some nasty finish on it. The contractor wasn't used to finishing hardwood floors(most are pre-fin these days), so they didn't think everything through. About an hour after the were done applying the first coat, the house blew! All the basement windows blew out, and fire took. The fire dept. contained it and saved the home, but it had to be gutted. In the re-construction, the final step was, drum roll...., the basement's floor. Again, the owner insisted on this nasty stuff(Gym-Cote, I believe), and again, shortly after this contractor was done, boom!

What happened was that the fumes were held in suspension as long as there were people in the basement moving around, circulating the air. But when everyone cleared the room and left, the vapors settled down and concentrated near the floor, being heavier than air, where the water heater set it off. Both times! <bg> Both contractors had checked for a pilot light(natural gas heater), and when they saw there wasn't one, they thought they were safe. What they didn't do was kill the power to the water heater; when it came on to cycle, the electronic ignition lit the floor finish's vapor.

The insurance adjuster that handled both claims is a good friend of mine; the above story was in the papers, as well as recounted by my buddy over a few beer, and I promise it's not an urban legend. Do not under estimate how vapors can concentrate themselves.

[JGWoods]

put 1910.107 in Google and you will get the OSHA regulations on spray booths.

A good point was raised above- that about solvent fumes being heavier than air- and all of them are even though we often think they are not. Best exhaust location for the fumes is down low, not up high as one often sees.

The hot water heater story is too common- mostly with natural gas leaks when no one is home. The basement fills with fumes, the hot water heater comes on, and boom, the walls fall down. Floor refinishing is another all too common cause.

[Chris Baird]

The only time I ever blew up was when I was working at the fuel docks at Lake Powell. My job was to fill up all those big house boats. We always ask the owner of the boat to turn off all electricity at the main breaker because there are all kinds of automatic sparks for lighting all the gas powered appliances. This particular guy just went in and pretended to turn off the breaker when I asked him. I was fueling up, which displaces about 100 gallons of fumes from the tank, and boom. I got blown into the lake. One of the autopilot starters sparked it. When I came up for air it was like the apocylypse, fire everywhere in the water and the whole side of the house boat was on fire. I guess when I got blown off the dock the gas nozzle came out spraying in the locked position. I just went back underwater and swam away. Luckily the fire boat was docked only about 100 feet away. Got all the hair burned off one side of my face and arm but was only lightly toasted due to falling into the water.I don't like to think about what may have happened to me if I were on dry land.

[arbarnhart]

I remember hearing on the news a few years ago (I think it was a local story, but it was something that I personally heard on a real newscast) about a couple of guys blowing themselves up using Liquid Nails on sub flooring. I think the problem was fumes between the ceiling below and the floor.

The worst I personally did was when I was a lab tech many years ago. I was doing protein tests on chicken feed (real exciting stuff - zzzz) and we always did parallel runs for accuracy (the numbers got used on the package so we had some liability if they were wrong). I had not mixed enough sodium hydroxide solution for the second sample, but I figure I am pretty smart guy - I can just figure out how much water and how much of the pellets to weigh out and let them dissolve in the mix. I pour it in the flask and turn on the burner (basically like a distillation process). The first run is looking normal but the second one went Vesuvian on me - it erupted the contents and melted a ceiling tile. We always used fume vents for the really volatile stuff like ether. I never even thought about sparks; I thought the concern was more about other side effects (this was not petroleum ether; it was the good stuff... )

[thistle3585]

Well, since we've moved on to explosion stories. My neighbors decided to remove their gas tank on their car, but thought it was too cold outside to do this, so they pulled it into the garage where they had set up a kerosene space heater to keep them warm. Well, as you can imagine it wasn't but a few minutes into this venture that their garage erupted into flames. I wasn't around at the time, but based on the extent of the damage I don't know how anyone survived.

[Jim Hilburn]

You have to keep in perspective what you get when spraying lacquer on a mandolin compared to some of these horror stories. Sure, the inspectors are going to want you to take the same precautions as if you were an oil refinery, but in the real world, it's overkill. Sure you want to use common sense, but you can be safe without fulfilling all the requirements.
I bought the full-blown (so to speak) explosion proof fan, but for lighting, I used some sealed lights meant for exterior use. Are they explosion proof? No, but they are sealed with gaskets. While I have the explosion-proof motor, no vapor of any amount has ever come near it because it's hidden away behind the booth. The vapor went out the fan like it's supposed to.
The addition of a HVLP gun also helps because you don't just fill up the atmosphere with vapor.

[sunburst]

"Common sense". Yep.
If you re-read any of these explosion posts, you'll see that there is a glaring lack of the use of common sense in each one. I would be amazed at the lack of common sense used in a couple of them, but ever since NASA had one group working in in kilometers and another working in miles, and crashed a zillion dollar space ship, not much surprises me anymore.

So, when even the educated and intelligent do things like these, can you really blame OSHA for trying to save us from ourselves?

[GTison]

I used to get a kick out of Explosion proof phones when I first started work at the phone company. But then I learned that "explosion proof" means that the sparks wouldn't CAUSE an explosion not that they wouldn't explode. I always thought that to be a funny thought somehow... exploding phone. visions of Monte Python or something.:p