Explosion Proof Fan

[Mike OMelia]

Need a good source for my guitar spray booth. I use nitro, so I want to make sure I don't wreck my shop. I'm guessing 1000-2000 cfm good. Thanks!

[Richard Coers]

I designed explosion proof electrical systems for gas turbine natural gas compressor stations decades ago. It takes a very unusual set of circumstances to have an explosion from a fan motor in a spray booth. You need the exact right ratio of explosive vapor, and then a spark. Moving air will not allow the correct ratio, unless the air is so completely saturated with the combustible gas that it remains in suspension with all that air movement. Now if you insist on getting an explosion proof fan the entire wiring system going to it must also be enclosed in explosion proof junction boxes and conduit. You see the explosion proof system not only protects from the initial explosion, but must also be able to contain an explosion inside the electrical system and prevent it from causing an explosion around the system if there should happen to be a short. I'd suggest you buy a fan that is belt driven with the motor outside the air stream. Mount the fan outside the booth so the motor is not in the hazardous atmosphere. Mount the fan switch at least 6' away from the door of your booth, assuming you have a totally enclosed booth. Have it further away if you have an open face booth.

[Bruce Wrenn]

Grain dryer fans are often explosion proof (hint, hint.) Just don't tell anybody I said they were

[William Hodge]

You could find out what the building code requires, and follow that.
I built a legal spray booth. The rules weren't that hard to follow. Getting an electrician in helped. He used EMC conduit, the right lights, and the right fan. One thing I didn't plan on was make up air, but that soon followed.

[Wayne Lomman]

Just to clarify, spray booths do move saturated solvent laden air every time you wash and spray out a spray gun, which is why explosion proof equipment is demanded by regulators. It is not difficult to comply. Belt drive is OK but expensive to set up. Motor in duct works fine. The correct motor will have the correct junction box. Use the correct category of armoured cable and as Richard says, position your switches a long way away. Cheers

[Lee Schierer]

What about mounting fans on the opposite side of the room to blow outside air into the room to pressurize the room. Then just have exhaust openings from the paint booth to outside. That arrangement would have no vapors flowing past the fans.

[Dan Hall]

This post by Mister Coers is spot on. I installed these systems in the petroleum industry. The goal is to mitigate by design so that there is no classified area to protect. A totally enclosed fan cooled motor (TEFC) completely outside of the booth driving a well grounded metallic axial fan is the usual case. In the oil industry we worried more about static electricity than electrical sparks. That doesn't mean that we didn't have classified locations but that they were engineered to be Division II or lower by design. When the LEL (lower explosive limit) is close or reached on any exposed area we just got the heck out of there until mitigation could be accomplished.

When we did tank jobs where we had to breach the integrity of the tank for cleaning and repair the planning took lots of effort. Curiously enough, in normal operation the top of the tank, or that part of the tank that doesn't have oil in it, is filled with methane (natural gas) to displace oxygen. So it's the opposite of the principle Richard is talking about. In a spray booth you want to dilute the combustible gas or liquid with massive volumes of air so that LEL is never reached. In a tank job, the inside of the tank is saturated with combustible gasses all the time. There is no oxygen to support combustion. First you empty all the oil out, then you open the top and bottom vents of the tank and then exhaust the interior of the tank with compressed air powered fans. The object is to have the tank pass THROUGH the LEL without a source of ignition available at that moment. Once the tank has been vented for a calculated period of time, the effluent gasses are tested safe and the tank is entered.

Just a little too much detail but it illustrates the principle for those interested.

[Dan Hall]

Yup. Grain elevators and woodworking shops blow up too.

[Jim Tabor]

What about mounting fans on the opposite side of the room to blow outside air into the room to pressurize the room. Then just have exhaust openings from the paint booth to outside. That arrangement would have no vapors flowing past the fans.

Yes, why not...I worked with school districts back in the 80's and 90's and that's the way asbestos abatement enclosures were set up.

[Allan Dozier]

I built my own spray booth and went ahead and installed vapor proof lights and explosion proof fan just in case. I bought my fan through Autobody Toolmart. It is a Jenny fan and I will add a plug for Jenny. After I installation it ran fine for a day or so then wouldn't turn on. I called Jenny and the rep sent my a new motor with essentially no questions asked.

[Mike OMelia]

Found this interesting. That jenny looks good for Class I Group D

http://www.zeton.com/site/pdf_articl...otor_Paper.pdf

[Mike OMelia]

I built my own spray booth and went ahead and installed vapor proof lights and explosion proof fan just in case. I bought my fan through Autobody Toolmart. It is a Jenny fan and I will add a plug for Jenny. After I installation it ran fine for a day or so then wouldn't turn on. I called Jenny and the rep sent my a new motor with essentially no questions asked.

Do you think the 16" would be good for a small spray booth? Lets say 6 foot tall. 4 feet wide. 4 feet deep.

[Dan Hall]

Would it blow dust and debris from the shop into the paint booth?

[Wayne Lomman]

Go by the cfm of the fan, not the diameter. You need to match fan capacity to the size of your booth so that you have constant flow of 0.5metres/second with no areas of still air. If the fan is too big you will be working in a howling gale and that never goes well. If the fan is too small it is a waste of money as there is no benefit. I always reference Australia/New Zealand Standard 4114 for a straightforward explanation of the requirements. OSHA should have a similar resource available that takes all the guesswork out of it. Google search a bit and you can usually find free copies of what you need. Cheers

[Allan Dozier]

Wayne's references would be the most accurate answer Mike but off the top of my head I could easily say a 16" fan should be unnecessarily big. I have a variable speed control on mine and if you used one for your size space you could turn it down quite low I think.