I am planning on adding a spray room to my woodshop, 7′ x 10′, will work with shellac and lacquer. Research tells me I want an explosion proof fan, and possibly the same for lights.
If this is true, where do I find such items? Any brand recommendation, size recommendation?
My outside wall is 10′. Any recommendation as to fan placement?
Thanks in advance for any info/help you can send me. Rand
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Replies
Dear Rand,
Here, spray lacquer and use a regular fan. Have not had, nor expect any problem. It's not a production, high volume deal.
To have 'explossion proof' you'd need to have all electrical items in that room, including switches, lights, conduits, and boxes explossion proof rated and it'd be quite expenssive to do.
Typical fans do not spark. Switching them on and off, or changing speeds can cause sparks.
You might want to go look at some automotive small shops in your area and see how they do it.
Good luck.
-mbl-
I opted for a TEFC fan motor instead of an exsplosion proof motor. The explosion proof rated fan, 16"/2200cfm, was about $425; the TEFC about $125. While not recommended, I have had no problems. My "booth" is configured so that I spray almost right into the fan, so there is little that escapes the exhaust. Can't even smell the spray solvents in the basement. Not sure I would recommend this, but it has worked for me.
Alan
http://www.alanturnerfurnituremaker.com
Rand,
I have been trying to work out the same issue. I talked to someone who knows alot about production equipment, and a little about explosion proof fans. He told me to get the 12 or 24 volt blowers that are used to ventalate engine conpartments of boats with inboard motors. These blowers are designed to exhaust gas fumes prior to starting the engine. I checked the prices and found they are $50-$100 each. You will have to convert to the proper voltage for the blower. Far cheaper than other alternatives.
Just passing on what I learned so far. I don't know if it is the best/safest solution.
squirrel cage blower - the exhaust does not pass through the electric motor thereby lower the explosion risk. Arrangement used in chemical exhaust hoods and most commercial exhaust systems and dust collection systems. commonly found in home furnaces which means you can either get a used one from a heating and cooling contractor friend or buy it new as a replacement part from a supplier.
Binks makes and sells explosion proof spray booths. Expensive, made of heavy gauge sheet metal and bolted together. Squirrel cage blower and a couple of furnace filters, vented outside. Bilge blowers don't move enough air to really do a good job. If someone wants a used squirrel cage blower, find a used or discarded furnace at a scrapyard.
"I cut this piece four times and it's still too short."
Wilson -I have a couple of old squirrel cage blowers scrounged from old furnaces. The type I have have the motor inside the cage thus the air flows almost totally across the motor. Just mentioning this so's we be sure to get a belt driven external motor type of centrifugal blower............
From Beautiful Skagit Co. Wa.
Dennis
Maybe someone can clarify - A synchronous motor was mentioned earlier as "safe." I assume that is just an induction motor. I would assume that ALL induction motors are safe as there is no arcing from brushes happening. Is that not correct?If an induction motor were wired so that its power switch is far from the booth, wouldn't that emininate all sources of electrical sparking? Or is there switching action going on regarding the capacitor starting circuit?Is the spinning motor itself a danger to ignite an explosive solvent by its friction in the bearings? Is an explosion proof motor made safer in mechanical ways other than the possibility of electrical sparking?Or is the only safe design one in which the motor is out of the air stream entirely such as a squirrel cage design with external motor or a prop type fan belt driven by an offset motor?A booth with a fan blowing INTO the space (positive pressure) with fumes pushed out, not pulled through a filter seems ideal except that such a design is much more complex (sealing all potential leaks) and completely eliminates temporary quick set-up designs or "open" designs.Rich
Rich -I always considered such a design, positive pressure 'clean room' approach to make more sense. One can control dust filtration much better by cleaning the air that's introduced into the space plus any dust that's in there will be effectively pushed out any cracks and crevices along with through the main exhaust. I used such an approach in the design for my photographic darkroom years ago and worked well. Although with a spray booth for finishing you'd need more air flow to deal with the volume of exhaust required, perhaps............
From Beautiful Skagit Co. Wa.
Dennis
Rich,
All but the smallest single phase induction motors have starter windings that are cut out by a centrifugal switch when they reach full speed. The switch contacts arc when they open and they are exposed to the air flowing through the motor. Note that on many totally enclosed air cooled motors the switches are still outside of the sealed housing and fully exposed to the atmosphere.
In addition, some induction motors have thermal cut out switches which will arc when they open. Also, the switches on window fans are open to the atmosphere and would be able to trigger an explosion when the fan is switched on or off.
In short, single phase induction motors are quite capable of triggering an explosion in the right atmosphere.
Personally, if someone is going to spray highly flammable finishes, having the correct safety equipment is part of the cost and they need to bite the bullet and buy it, or find an alternative way to do finishing.
John W.
Thanks John.It would seem that one could make a "marginally safe" motor safer by eliminating those unneeded electrical events. A window fan's switch could be hard wired closed or left untouched in favor of a remote switch. The capacitor starter circuit could be removed (just clip or unscrew one of the capacitor's leads) - the motor will simply start more slowly, but run normally. I'm not familiar with thermal overload circuits, but I doubt a fan motor gets stresed to the point of thermal overload.Of course, the safest measure is to mechanically offset the motor out of the air flow.I wonder if anyone has information about actual solvent/air mixtures that are explosive. I find it hard to imagine that the overspray of a woodworking finishing booth, pulled along with a high volume of air is actually explosive. Perhaps if one sprays atomized solvent/air from the gun as when cleaning it directly into an electical spark . . . ?Rich
it been awhile since I did these type of calculation but I think they are right. The technical information was obtained from the CRC Handbook of Chemistry and Physics. The lower explosion limit is the percent of atmosphere required to support an explosion - for those mechanic types - the leanest mixture that will allow an internal combustion engine to operate. The vapor pressure is the amount of material that is found as a gas (evaporated) in an atmosphere for a given temperature. one atmosphere = 760 mm Hg so if a material had a lower explosion limit of 1%, any atmosphere where the vapor pressure of exceeds 7.6 mm Hg is subject to explosion. From the data you will note that any lacquer (solvent) or shellac could produce an explosive atmosphere IN A CLOSED SPACE at room temperature. The key here is in a closed space. The ventillation of a spray booth purpose is to provide dilution (and removal) of the evaporated solvent to prevent the vapor pressure from reaching the lower explosion limit. The liquid mist in the air will not explode - it only increases the evaporation rate by increasing the surface area of liquid.The bottom line is that ventillation should be used if using lacquer or shellac finishes - that includes brushing in small enclosed spaces. Spraying increases the solvent load so ventillation is mandatory. It is unlikely, BUT NOT IMPOSSIBLE, solvent vapor pressure in an exhaust stream exchanging 1/2 to 1 volume per minute would reach the lower explosion limit.
Wilson,
Thanks. I can't understand that data in any meaningful quantitative way. But it still appears to me that any effective ventilating system in any conceivable wood working shop where solvent finishing materials are sprayed is of extreme benefit to the worker. And the possibility of an explosion, with even the most casual of attention, such as using an induction motor, and certainly moving it out of the air stream reduces the probability of explosion to insignificant levels.
Rich
Dear R14,Keep in mind that induction motor do spark inside when startup and stopdown because of centrifugal, mechanical action switches that connect/disconnect capacitors.In a true environment that needs explossion switch design, even the clothes, the tools, and EVERY THING that goes on there has to meet no-spark criteria.That's beyond a wood working shop needs.-mbl-
mbl,
Yeah. I can't imagine that any kind of exhaust system, made for spray finishing in a wood working shop is any thing but good. I really don't think there is a down side. Unless the worker wants to do something REALLY dumb. And we don't need no stinkin' exhaust system to do THAT. Do we?
Rich
Don't ever learn anything new. Rather than give you satisfaction that you know more than you did, it will only confirm you know less than you thought by opening horizons to things of which you had never dreamt and which you now must explore.
Edited 2/2/2005 6:17 pm ET by Rich14
Rand ,
You can find fans and such in the Grainger catalog or look up Grainger in your local phone book.
I just can't believe any one wants to cut safety when it comes to your well being, especially if its your home. The reason for explosion proof equipment is because of EXPLOSIONS...... There are reports I use to collect from around the country of houses blowing up. NOT all of them were gas leaks. Paint solvents was the #2 cause.Lets suppose you are not so lucky how does that effect your family? Would you spray gasoline into an non explosion proof fan. Lacquer is RED LABEL for a reason. Come on, use some common sense. I have seen the results of such an explosion. I could go on for hours, but never mind.
Call your insurance company and see if there ok with it. Ron from Mass.
Personally, I wouldn't work with solvents that release hazardous fumes in my house, anyway. I have in the past, but not in a long time.
"I cut this piece four times and it's still too short."
As others have said, explosion proof installations are expensive, both the hardware and then installation. All the conduit is rigid, and sealed with epoxy at the teminations, and all the boxes have special seals.
So, without specifically suggesting this to anyone, what I've done is use those box window fans that you can get at most home stores. I'm talking about the ones that are about two foot sqare, and 5" thick. These fans use synchronous motors. like clock motors. They have no brushes or contacts to arc or spark, and they move a fair amount of air. Not as much as a squirrel cage fan, but enough that when combined with a suitable booth it can extract as much vapor as a small touch up gun can throw.
Tom
Yes.That's what is used here. They are only about $30.00.Just don't switch speeds while spraying and turn it on BEFORE spraying.-mbl-
People are often confused about "explosion proof" versus "intrinsically safe." Explosion proof (XP) means the equipment is designed to contain an explosion - but not to prevent one. Intrinsically safe (IS) equipment is designed to prevent sparks from causing an explosion. XP is waaaay more expensive than IS, and less safe for you. IMHO, IS is a much better solution. But not all equipment is available in IS configurations, so compromises may need to be made.
I doubt you will develop an explosive atmosphere within a well-designed spray booth anyway. The fan should be moving enough air to prevent the vapors from building up to an explosive concentration. Just use IS switches so if the fan fails, the switch won't throw sparks.
"Everything should be made as simple as possible, but no simpler." A. Einstein
http://www.albionworks.net
What about putting the fan on the upstream side & going positive pressure?
Curious you should mention this option. I have spent a bit of time imagining such a system, but can't find any info as to its effectiveness. Have you used such a system? Does it work? I'd love to hear more from those who have tried it, are using it.
I am not a professional, rather a serious hobbyist. I will never do production work, rather one nice piece at a time. I don't want to invest $$$ for something I don't need, but at the same time I don't want to blow myself up.
Again, thanks to all willing to share ideas. Rand
Grizzley Tools offers a couple of spray booth set ups for around $1,100.00 to 1,400.00. They are not an entire room, but about a 4'-0" X 4'-0" exhaust area. I would tend to want to be sure I was working safe when it comes to explosive fumes. I have been considering one for my shop, does anyone have experience with the Grizzley booths ?
Robert
I've read all the replies, just wondering if a compressed air driven fan is available .I've never heard or seen one, seems possible and probably less expensive.
Mike
Dear Mike,Such item would up the demand for compressed air and be against the use of compressed air for spraying. Just going by efficiency fundamentals, no more air can be moved than is used-up, would say.Also, keep in mind that a compressor itself is by no means spark proof. It's got the motor and the pressure cut-off switches.The compressor can be mounted remote, but many, many users don't and there's no problem.As said by others, the concentration of fumes is not that high, for most typical woodwork spraying, specially for a small shop.A HVLP gun is more efficient than a conventional spray gun. That means that much less waste goes to the air, including less fumes, because at higher pressures of spraying more bouncing off the surface of what's being sprayed (waste) takes place. It's, therefore, safer for both the environment, hazard-wise, and health-wise, and it's more economical to use.-mbl-
I was just reading the newest posts and with all of the different types of motors out there, I noticed that nobody mentioned using a TEFC motor. They're (T)otally (E)nclosed but I think it's more for keeping dust out than suppressing sparks. Another way to eliminate the start-up arcing is, as was mentioned earlier, flip the switch before the spraying starts and turn it off after the fumes are gone. I remember the instructions for the Binks booth we had at one place I worked for, and I think it had a timer that would lock out the compressed air till the fan was already on and wouldn't turn the fan off till about 5 minutes after the switch was flipped off. I'm not sure the motor was anything special and it was an OSHA approved booth. Having a pressurized room would carry a lot of dust into the booth, right onto the surface that has been sprayed. Blowing through the exhaust duct is a lot more efficient, too. For safety, the mechanism has a vacuum sensor which shuts the air off if the filter gets clogged and the vacuum reading goes too high.
"I cut this piece four times and it's still too short."
Highfigh,
Pulling the air OUT of the room/booth with an "extraction" fan, pulls just as much air into the room as would happen with a fan that presurizes the room by pushing it IN. Mechanically, the 2 systems are the same. Same dust consideration. The advantage, though, with pushing the air in is that the fan and motor are entirely out of the solvent/spray mixture.
You need to filter and deflect the stream for dust coming in, and probably filter the stuff going out to capture all the solids possible. But any electrical arcing at the motor becomes moot.
Rich
Think of a spray booth as a big vacuum cleaner. You don't blow air and dirt into one of those, do you? No. The fan blows air out of the canister, creating negative pressure inside, which then sucks the dirt through the hose. Yes, you move as much air into/through the room, but just moving air isn't the point. The booth is there to evacuate the toxic fumes from spraying, chemical reactions, etc so they don't contaminate the room air. Have you ever used an approved booth? The fan is in the exhaust duct. "I cut this piece four times and it's still too short."
Edited 2/3/2005 11:05 pm ET by highfigh
Highfigh,You're not thinking this through. There is no difference as far as the volume of air inside the box is concerned between the two configurations. If you force it out the exit by a fan in the exit path (whatever the exit type), more air will come in the entrance (whatever the entrance type).If you force air in the entrance, the air volume inside will flow out the exit. The net effect is identical either way and the acutal airflow patterns can be made identical in every way.The only diference is the effect of the exiting air/spray mixture on whatever might be in its path. If you get the motor that's driving the system out of that path, you eliminate the potential for explosion.Rich
Don't ever learn anything new. Rather than give you satisfaction that you know more than you did, it will only confirm you know less than you thought by opening horizons to things of which you had never dreamt and which you now must explore.
And as a matter of fact, in an upright vacuum cleaner such as a Hoover, Eureka or Kirby, yes, you actually do blow all the dust and air into the bag, and filtered air exits the bag through its pores.There's an impeller fan just behind the beater bar which sucks the dirt released from the carpet through itself out the back of the base and up into the bag on the handle.
In an upright, yes. Which type moves more air? What happens when you have a fan blowing into a box with an outlet that has a filter covering it? Some of the air blows back. Yes, I have thought this through. I assembled the booth where I worked. I even read the manual. You didn't answer the question. Have you used a spray booth that was rated as explosion proof? They don't blow the air into the booth. They blow it out the exhaust duct. I haven't lived under a rock. I have seen those new fangled carpet sweeping machines before. I have even repaired a bunch of them. I'm looking at one now. Again, the point of a spray booth is MOVING A LOT OF AIR! That's the reason the exhaust duct is about 18" dia, unless it's a really big booth and high output fan. An upright vacuum provides suction, not high volume air movement. If someone wanted to make their own booth, they could use a squirrel cage blower with the external pulley. That way, they can attach the intake duct to the side opposite the pulley and blow the exhaust out the rectangular opening. If the fan is started before the spraying and turned off a few minutes after the spraying stops, there really isn't much chance of a problem. "I cut this piece four times and it's still too short."
Edited 2/3/2005 11:39 pm ET by highfigh
OK,You're not getting it. We're spending too much time in spray booths.Rich
Bub bye!
"I cut this piece four times and it's still too short."
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