Official Luthiers Forum!

I am wanting to build a spray booth so I can use NitroCellulose if I want. Currently I use Water Based or Shellac. I read that an explosion proof fan is required. I have a few fans with the electric motor mounted on the outer casing but the motors are by no means encased. I know the Nitro is highly flammable. Is it the exposed electric motor that is the issue here? Is it the potential for some form of spark from the motor that could ignite the fumes? If so, is it possible to encase the motor from the fumes?

Sorry if this seems disjointed.

No, it is not possible to encase an open motor to be explosion proof.

My setup uses a totally enclosed, fan cooled (TEFC) motor, and an aluminum, non-sparking fan blade. In order to be an Explosion proof system, I would have to include sealed rigid conduit for the wiring, and XP switches. But the extra cost for that was beyond my means and not completely necessary as my switch is installed some distance from the spray booth.

If you want to guarantee the result to be non-explosive there are LOTS of steps to take.

1. All the receptacles should be mid-height or higher on the wall. Most explosive gasses settle rather than float.
2. All wiring must be airtight. In explosion proof rooms that are built to code, wire runs through sealed pipe....not conduit, for instance. All receptacles and junction boxes are specially made for this.
3. Electrical switches are mounted outside the room.
4. Lighting is specifically "explosion proof". A typical explosion proof fixture for flourescent ligthing can run $500 each.
5. The motor in your fan must be "fully enclosed" and hardwired.

Doing it yourself, it is almost impossible to guarantee the result but you can improve your odds the more you apply these measures.

Of course, waterbased finishes eliminate the issue entirely and some solvent based finishes are much more dangerous than others. Look at the MSDS for each material you want to spray for its "lower explosive or flammable limit". There is an upper limit but when using an exhaust fan you probably don't need to look at that. When you compare this lower limit you'll see a lot of difference between solvent based nitro and other things. Nitro is something you want to take full measures with. It's pretty flammable.

_________________
I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

You may have heard a month ago or so about an unexpected explosion on Redstone Arsenal. Technicians were demilitarizing some rocket motors (grinding down the propellant). For whatever reason, it exploded (and sadly, the two technicians were killed due to burns). The building was also designed to be explosion proof... something to think about. All the walls on two floors blew out to prevent over-pressurization (which if the searing hot gasses don't get you, will most definitely get you). All that was left standing was the original steel girders and framework of the building. Most houses are not designed to do this (at least not on purpose).

Mike Doolin bought a system that cost about $2000-$2500 that I thought was very reasonable given the risks. Please contact him for info on that.

Another consideration is where you live and your insurance policy. If you live in a "thickly settled" area, it may not be a responsible thing to do (use volitile products). If you do have an accident, your insurance may not cover this. If you check with your insurance company, you might get your policy cancelled (unless you do everything to code, and even then it might be more expensive).

Mike

I bought the small Grizzly and had it installed by an "acquaintance" electrician. It cost a bundle, and I was stunned at the prices of the materials and lighting. Don't forget you have to have replacement air and that cost a couple of $$$ too. Breakdown ran about:

Booth: $1600.
Parts and lighting: $950.
Electrician's labor:$450.
Duct exhaust: $200.
Replacement air: $400.

The replacement air is a Rube Goldberg system and in the winter it gets mighty cold for 2 minutes , but I have figured out a way to force air from outside the room into the room and out a small vent so that I can shut off the booth, and offgass the guitar. A real setup for replacement air would have run 5K.
Was it worth it? You bet!

Thanks for all the great replies. I am looking into an explosion proof fan. If anything I have a great set of guidlines to start with. Thanks. I'll try and let you know how it turns out!

When a motor or a fixture says it's explosion proof that means that if and explosion takes place inside the motor, light or switch or receptical box that the housing will contain the explosion.
When Ibuild my booth I'm using a blower from a AC or furnace . The motor is located outside of the duct. Plus the blower I have now has 3 speeds. You can also use positive pressure to the room with a blower.
As I recall you can get an explosion proof fan for about $300. Do a google search for them. You can also make your booths ceiling lower the the room it's in and put plexi glass skylights in the ceiling of the booth and seal them and hang your lights above them so that they are out of the room.

So why not just keep the room well ventilated so that the vapor concentration can never build up to the point of being able to ignite? I just run an industrial fan into a room, with a window open, and it keeps the room pretty well ventilated for spraying. Many so called tradesman do it like this (actually even less... I have seen people spray lacquer in a poorly ventilated room wearing nothing but a surgical mask! With the compressor running in the same room and I can smell lacquer for miles outside) and I never read about explosions due to paint fumes on the news, but I do hear about people passing out and die due to excessive paint fumes! Maybe in the west things like explosion proof fans or wiring is required because of insurance and other regulations so it does cost a lot more to do things. I guess that's why things are cheaper in Taiwan, because there's no stupid regulations and codes (at least one that's enforced... the electrical wiring in most new or old buildings in Taiwan would be declared unsafe according to the NEC)

_________________
Cat-gut strings are made from kitten guts, stretched out to near breaking point and then hardened with grue saliva. As a result these give a feeling of Pain and anguish whenever played, and often end up playing themselves backwards as part of satanic rituals.

Typhoon Guitars
http://www.typhoon-guitars.com

Hey Chris, would a fan like this be the type you are referring to? I have 4 of these.

I do not think I would use that fan Forbes.

When funds are tight (and your insurance is paid up), go with positive pressure. And make sure you vent to the outside...

Mike

OK Mike..thanks. I am looking into an explosion proof fan...and keeping the air flowing...

Cutting corners here is not a good thing. You need true spray booth equipment. Air exchange is a good thing but it needs to be filtered. Also if you use air conditioning or heat ,this can be expensive. You can pull all your heated air out of the shop in a few minutes.

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Guess that works fine till you go "BOOM"...
As far as wearing a surgical mask and spraying lacquer, talk to them in 20 years...they will all have emphysema.

That fan will work. Any fan is going to pull the heat out of the room. You could put that fan outside of the room and put a filter over the intake just like on you furnace or an air handler which is what it is and vent that into the room creating positive pressure and the open a window or make a lower opening just like you would for a fan and spray towards the opening and the spray will be exausted out. Then when done spraying put the fan on low if it's has speeds while it flashes off some.
Oh yeah the fans are more like $800 not $300.

Also remember the guitars have to off gas somewhere that is humidity and temperature controlled and well ventilated. They will stink up your shop. Considering that and my time and the expense in setting up an explosion proof spray booth that is up to code it's cheaper to send the nitro finished guitars to Addam Stark. I still can spray stuff that won't blow up or off gas for weeks.

_________________
It's not what you don't know that hurts you, it's what you do know that's wrong.

One thing you may want to check is your insurance . If you put in a spray booth and it causes a fire and it isn't approved or inspected you may not be covered. There are many grey areas here , especially with local ordinances . Check first , it may save you getting a citation.

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Are galvanized steel blades spark proof?

No. It would probably be OK, but like John and others said, you may have local codes, or insurance concerns if you don't have everything .....right.

My finishing room is separate from my shop. This is the fan I've got. http://www.autobodytoolmart.com/jenny-16-explosion-proof-fan-variable-control-p-14234.aspx I got mine used when a local body shop upgraded to a bigger fan. I don't have all the explosion proof switches ect. Non explosion proof switches shouldn't be a problem as long as you turn everything on before you open anything flammable, don't turn anything off until after the fan has cleared the fumes.

Again, check with your insurance company, and check local codes.

Years ago I painted cars with lacquer in a garage and a couple box fans running under the partually open door. I used a wood stove for heat. I guess I'm lucky I didn't get blown up.

_________________
I didn't mean to say it, but I meant what I said.
http://www.brackettinstruments.com/

Addam's shop is just down the road from mine. I don't think his name came up in a previous thread of "Who does your finishing?", but it should have. He sprays lacquer for a number of well known luthiers here in northern California.
I don't do spray finishing. When I did, I used a positive pressure booth. (The fan is on the outside, pushing air into the booth.) With this set up, you don't have to worry about combustible fumes moving across a sparking motor. Put a good filter between the booth, and the fan, and you've controlled dust problems in a way that exhaust fans never can. Exhaust fans pull dust into the booth through every possible leak. I'm sure the booth I sprayed in wasn't "explosion proof", but I thought it safe enough to work in. It was a big step up from the booth I learned in: three thrift store window fans in the exhaust duct. That one burned down while I was spraying.