More Spray Booth Questions

[Joe Lasch]

I am in the process of updating my shop to include an area for a spray booth. In a previous thread I was advised by many that I need to have an explosion proof fan and lighting if I plan to use non-water based sprays.

My plans are to spray bows (longbows and recurves) with a catalized varnish or two part epoxy finish. The amount of finish I would use at any one time is small, probably equivilent to no more than what I could do with a couple of cans of urathane from the local building supply store.

I have talked with a number of custom bow makers and none are currently using any type of explosion proof fans or lighting in their shops. Are they taking a big risk or am I being overly worried about a very small amount of spray?

[Jon Dieterlen]

I spray conversion varnish on a regular basis. My first exhaust arrangement consisted of a direct drive venturi fan w/aluminum blades. I was spraying with a Fuji turbine and 2 1/2 gal. pressure pot at the time.

I mounted the fan in a piece of OSB that fit snuggly in a 36" man door.

This set up worked pretty well. Venturi fans do a good job of pulling the air from the intake side. Some fans leak too much air from the output side to the intake side to do a good job of moving the air from the room.

I have since installed a 8x10 paint booth, so i have the venturi fan available if you are interested.

This is the one I have http://www.grainger.com/Grainger/items/3XK57?Pid=search

Remember that you need to provide for make up air. Through an open window, door etc.

I now pull make up air from the attic through a hinged door operated with a pull rope and pulley affair. That helps temper the air in cold weather.

As long as you have good air flow, (4000+ CFM) the chance of explosion from vapors I would think would be low.

Jon

[Von Bickley]

I have talked with a number of custom bow makers and none are currently using any type of explosion proof fans or lighting in their shops. Are they taking a big risk or am I being overly worried about a very small amount of spray?

They are taking a big risk. I personally know of a case where some children were playing in their father's shop and broke a light fixture.
The man lost his daughter in the fire.

[Joe Lasch]

Von, Those are the kind of stories that scare the heck out of me. What I can't seem to understand is why having a spray booth to control dust is different than just buying a couple of 12 oz. spray cans at Home Depot. It's hard to imagine that an explosion proof fan would be recommended in order to use products sold at every home improvement center in the country. What makes what I am planning to do different? Not trying to argue the great advice here - just trying to understand what I am doing.
Thanks!!

[Glen Butler]

The fan is to exhaust paint fumes. Motors create sparks. Thus explosion proof motor.

If you want to breath the fumes, and let overspray fall on your project then set up your newspaper and go to town on the kitchen table with your spray paint. Paint fumes are not going to ignite in 99.99% of cases, and even the .01% I left is high. Use plenty of ventiliation, and no open flames. Preferrably spray outdoors.

[johnny means]

If your strictly spraying that small an amount, you would never reach the kind of saturation levels that create an explosion risk. Unless your shop is like 27 cubic feet.

Ventilation is still a good idea.

[Wayne Cannon]

If it's any help, I just finished disassembling a 24" box fan, mounting the fan blades on a shaft inside of a 24-1/4" tube made of metal flashing, cut a slot for a V-belt in the intake (suction) end of the tube, mounted the motor outside/atop the tube, and used a belt-drive to spin the fan inside the tube. It's not "explosion proof", but it makes me feel more comfortable spraying flammables. My booth is three sides plus top of foam insulation panels.

FWIW, my $40 fan wound up costing about half the cost of a nice explosion-proof fan not counting labor. Counting labor, it probably cost ten times as much!

[Brett Nelson]

My understanding is that a spray booth that operates with positive pressure does not require explosion proof fans. That seems logical to me as the fan is simply feeding clean air into the booth and fumes are just vented outside through a particle filter to capture the dust particles.

If I'm mistaken, can someone please explain to me how flamable fumes would be able to reach sparks in the fan under this type of setup. :confused:

[Phil Smith]

My understanding is that a spray booth that operates with positive pressure does not require explosion proof fans. That seems logical to me as the fan is simply feeding clean air into the booth and fumes are just vented outside through a particle filter to capture the dust particles.

If I'm mistaken, can someone please explain to me how flamable fumes would be able to reach sparks in the fan under this type of setup. :confused:

OSHA has very strict requirements for spray booth setup and operation. There are requirements related to vapor, overspray, solvent, and electrical connections just to name a few. For example, there are very specific requirements on how close nonexplosion proof equipment can be to a spray booth.

Here is a link to OSHA standards for "Spray finishing using flammable and combustible materials. - 1910.107."

http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=9753

For anyone looking to set-up a spray booth I suggest you read through the requirements before starting. I you deviate from the OSHA requirements and have a fire, I would not count on the insurance company paying off.

I've done lots of spray finishing at home, but have always sprayed outside because I did not want to deal with the issues of running a spray booth.

[Brett Nelson]

OSHA has very strict requirements for spray booth setup and operation. There are requirements related to vapor, overspray, solvent, and electrical connections just to name a few. For example, there are very specific requirements on how close nonexplosion proof equipment can be to a spray booth.

Here is a link to OSHA standards for "Spray finishing using flammable and combustible materials. - 1910.107."

http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=9753

For anyone looking to set-up a spray booth I suggest you read through the requirements before starting. I you deviate from the OSHA requirements and have a fire, I would not count on the insurance company paying off.

I've done lots of spray finishing at home, but have always sprayed outside because I did not want to deal with the issues of running a spray booth.

Yeah, spraying outside is great, but I've only got about 4 months of the year where that is possible. Then during the months when it is possible, the wind knocks out half of those days and the heat knocks out most of the rest. Try spraying lacquer at 105F.

[Jeff Nolan]

The insurance point is a valid one but it's not as clear cut as you violate a code requirement and the insurance company gets an out. There are many other factors that are considered in such an instance and FWIW I don't think many of us would disagree that OSHA requirements are often a case of "belt and suspenders". If insurance companies could get out of paying a claim because of a code violation then they would employ an army of code inspectors and investigators who would descend on every claim like the TSA on a crotch bomber... uh never mind, bad example.

I make no claim of knowledge about the fan question and my last shop had a finish room that was pre-existing so I never had to do the research.