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explosion proof fans

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sarg314(at)comcast.net
Guest

Posted: Sun Oct 22, 2006 11:50 am Post subject: explosion proof fans

An exhaust fan on a home made paint booth has the potential to spark an 

explosion if you get the right mixture range of a flammable solvent in 

the air and some sparks. 



However, virtually all consumer fans use brushless AC motors (don't 

they?).  And, with the fan mounted right on the motor shaft, there's no 

belt to generate static (though I guess there are other ways to generate 

static).  So, is such a fan suitable to use to exhaust a paint booth?



Also, Does any one have any idea of what fan capacity is needed for an 

RV-sized paint booth?



--

Tom S., RV-6A

larry(at)macsmachine.com
Guest

Posted: Sun Oct 22, 2006 2:10 pm Post subject: explosion proof fans

Tom,

If you were talking hi VOC paints, the fans would have to be looked at 

very closely.  In the case of AFS paints, there is no fire hazard. On 

the question of fan capacity, I found two 20 x 20 inch household fans 

more than adequate.  You can put furnace filters in front of them that 

have a #600 rating by 3M that will stop any color from going to the 

other side.  How much capacity depends largely on the volume of spray 

and how much of the plane you intend to spray at one time.  I'm painting 

in the basic disassembed state, so the capacity only requires the 

filters get changed out 5 or 6 times during the whole operation.  If you 

were to paint the whole plane at one time, I'd think you'd need 4 fans 

going all at the same time and 8 good filters at the inlet end, tho I'd 

not recommend trying such a large scope of painting if you're new to the 

task.  It's a lot different than doing a car.

I have a painting page if you're interested in an inside booth design.

http://www.macsmachine.com/html/paint.htm



Regards,

Larry  McFarland - 601HDS at 85 hours and just about done painting.



sarg314 wrote:



 	  Quote: 	
		   



 An exhaust fan on a home made paint booth has the potential to spark 

 an explosion if you get the right mixture range of a flammable solvent 

 in the air and some sparks.

 However, virtually all consumer fans use brushless AC motors (don't 

 they?).  And, with the fan mounted right on the motor shaft, there's 

 no belt to generate static (though I guess there are other ways to 

 generate static).  So, is such a fan suitable to use to exhaust a 

 paint booth?



 Also, Does any one have any idea of what fan capacity is needed for an 

 RV-sized paint booth?



 -- 

 Tom S., RV-6A

sarg314(at)comcast.net
Guest

Posted: Sun Oct 22, 2006 3:45 pm Post subject: explosion proof fans

LarryMcFarland wrote:



 	  Quote: 	
		   

 <larry(at)macsmachine.com>



 Tom,

 If you were talking hi VOC paints, the fans would have to be looked at 

 very closely.  In the case of AFS paints, there is no fire hazard.


	


Larry:

    I know what a VOC is, but what's an AFS paint?

rhdudley1(at)bellsouth.ne
Guest

Posted: Sun Oct 22, 2006 4:29 pm Post subject: explosion proof fans

Tom,

I took my "box fans'' apart and found that they were brushless. Thus, 

there should not be a concern about igniting solvent vapors.

Richard Dudley



sarg314 wrote:



 	  Quote: 	
		   



 An exhaust fan on a home made paint booth has the potential to spark 

 an explosion if you get the right mixture range of a flammable solvent 

 in the air and some sparks.

 However, virtually all consumer fans use brushless AC motors (don't 

 they?).  And, with the fan mounted right on the motor shaft, there's 

 no belt to generate static (though I guess there are other ways to 

 generate static).  So, is such a fan suitable to use to exhaust a 

 paint booth?



 Also, Does any one have any idea of what fan capacity is needed for an 

 RV-sized paint booth?



 -- 

 Tom S., RV-6A

retasker(at)optonline.net
Guest

Posted: Sun Oct 22, 2006 4:36 pm Post subject: explosion proof fans

AFS paint is a water based polyurethane paint. See 

http://www.stewartshangar21.aero/AFS.htm  Click on "Stewart Systems" to 

the left of the page.



Good paint, no hazardous fumes.



Dick Tasker



sarg314 wrote:



 	  Quote: 	
		   Larry:

    I know what a VOC is, but what's an AFS paint? 


	




-- 

Please Note: 

No trees were destroyed in the sending of this message.  We do concede, however,

that a significant number of electrons may have been temporarily inconvenienced.

--

retasker(at)optonline.net
Guest

Posted: Sun Oct 22, 2006 4:56 pm Post subject: explosion proof fans

While you are correct about the brushless aspect, there can still be a 

concern about igniting solvent vapors.  If some part of the motor 

reaches the flash temperature of the vapor in question, you can ignite 

the vapor.  Flammable vapors do NOT always need an open flame or spark 

to ignite!  Be careful!

Dick Tasker

Richard Dudley wrote:

 	  Quote: 	

 <rhdudley1(at)bellsouth.net>

 Tom,

 I took my "box fans'' apart and found that they were brushless. Thus, 

 there should not be a concern about igniting solvent vapors.

 Richard Dudley

 sarg314 wrote:

> 

>

> An exhaust fan on a home made paint booth has the potential to spark 

> an explosion if you get the right mixture range of a flammable 

> solvent in the air and some sparks.

> However, virtually all consumer fans use brushless AC motors (don't 

> they?).  And, with the fan mounted right on the motor shaft, there's 

> no belt to generate static (though I guess there are other ways to 

> generate static).  So, is such a fan suitable to use to exhaust a 

> paint booth?

>

> Also, Does any one have any idea of what fan capacity is needed for 

> an RV-sized paint booth?

>

> -- 

> Tom S., RV-6A

-- 

Please Note: 

No trees were destroyed in the sending of this message.  We do concede, however,

that a significant number of electrons may have been temporarily inconvenienced.

--

larry(at)macsmachine.com
Guest

Posted: Sun Oct 22, 2006 5:10 pm Post subject: explosion proof fans

Tom,

Aircraft Finishing Systems has a water thinned urethane paint that is 

popular among the homebuilt aircraft community.  It was

designed to satisfy EPA requirements, is nearly odor free, fireproof and 

has a better safety record than regular paints.

http://www.stewartshangar21.aero/AFS.htm



Larry McFarland



sarg314 wrote:



 	  Quote: 	
		   



 LarryMcFarland wrote:



> 

> <larry(at)macsmachine.com>

>

> Tom,

> If you were talking hi VOC paints, the fans would have to be looked 

> at very closely.  In the case of AFS paints, there is no fire hazard.

 Larry:

    I know what a VOC is, but what's an AFS paint?

rparigor(at)SUFFOLK.LIB.N
Guest

Posted: Sun Oct 22, 2006 5:11 pm Post subject: explosion proof fans

Hello Tom



"So, is such a fan suitable to use to exhaust a paint booth? Also, Does

any one have any idea of what fan capacity is needed for an  RV-sized

paint booth?"



I can tell you what I am doing, perhaps it will help.



I sewed up a 10 foot long, 8 foot wide and 6.5 foot tall paint booth made

out of PVC clear plastic on the top and sides, and thick Visqueen on the

bottom. 



On the small door of our rented hangar, I mounted an attic fan, one of

those with mushroom dome. Sorry i don't know CFM, got it from a neighbor

and it was new. If you took a look at Home Depot offerings, and went half

way between normal stocked offerings, you would be pretty close. Then I

made a 1x2" frame around it that is the precise size of furnace filters,

think they are 24 x 30 or 24 x32, just stock Home Depot stock. I have

Velcro attached to the 1x2s and have an opening in the tent that precise

size with velcro on it.



The fan is brushless AC and had a thermostat, I bypassed thermostat.

Pretty unscientific, but I had concerns of explosion, and did a bit of

fooling trying to get some propane to get set off by fan. I have a

reasonable amount of experience building Hot Air balloon burners, and

making a pilot light that is reasonable easy to light, and will not very

easily get blown out has given a pretty good insight on what and how to

set off a mixture.  Anyway I was unsuccessful to get it to set off an

explosive mixture. My plastic creating static is of more concern. Even if

it did get set off by motor, I put an expanded metal screen over hole in

door (also critter protection) that in conjunction with filter, I am

pretty confident it would act as a flame arrestor if the fan did in fact

set off a mixture.



OK back to design, I have three 10 foot aluminium tubes supported by

florescent fixture large link chains. Now the entire side opposite the

exit is velcroed in place, I figured if it works well, which it does I can

add a section to house the entire large parts of my Europa.



The end has a 7 foot wide, 6 foot high piece of quilt (or pillow) style

white woven fill. There are 2 densities sold at most fabric stores, I used

the heavier. I sewed up a transition from this huge size "Pseudo Filter"

to a 30" round that I put over my 30" floor stand 3 speed Home Depot fan.

I need to keep it on low, and choke off ~ 1/2 of the wire mesh of the 30"

fan or else it will blow out the seams with way too much pressure. This

area of fan is under suction, so i just put a piece of visqueen to act as

a choke, it stays put till fan is turned off.



The center aluminium thin tubes can hold up perhaps 25 pounds with no

pressure inside, and probably a hundred with pressure.



Works great, rolls up into a 10 foot high Q-Tip bout a foot in diameter

when not in use.



If you keep mixture too lean, it will not ignite. It takes not much time

to rid tent of fumes. 



I have far more concern, not of attic fan, or static, but I put 2 dual 500

watt quartz halogen floor stand Home depot lights inside the tent with me.

If I were to turn around and spray paint direct into the lamps, think

would be a nice blowtorchin going on or if tent was filled, worst. 



If you were to spill solvent on floor, and lamp fell onto it same effect.



I am comfortable enough with my setup. Have always another person around,

and a smother the painter on fire blanket around. 



Side note, we built a 10 foot by 20 foot tent to build plane in. To heat,

we use a 150,000 kerosene heater. It is a torpedo design but uses a Becket

burner. To get clean air into tent, made a heat exchanger. We use a

2000CFM squirrel cage blower to pull fresh air from outside through a thin

wall aluminium expandable hose, through a electrostatic filter, then it is

wound inside a stove pipe connected to heater. Works great.



Anyway as far as painting, if it is a bit cold inside hangar, I can plumb

this clean heat to 30" floor stand intake, warms things right up. 



BTW since there is so much surface area of my large filter, airspeed is

very slow through most of tent.



Ron Parigoris

echristley(at)nc.rr.com
Guest

Posted: Mon Oct 23, 2006 5:15 am Post subject: explosion proof fans

sarg314 wrote:



 	  Quote: 	
		   



 An exhaust fan on a home made paint booth has the potential to spark 

 an explosion if you get the right mixture range of a flammable solvent 

 in the air and some sparks.

 However, virtually all consumer fans use brushless AC motors (don't 

 they?).  And, with the fan mounted right on the motor shaft, there's 

 no belt to generate static (though I guess there are other ways to 

 generate static).  So, is such a fan suitable to use to exhaust a 

 paint booth?



 Also, Does any one have any idea of what fan capacity is needed for an 

 RV-sized paint booth?


	




I used a rather large computer fan, about an 8" square.  There several 

ways to attack the problem.



-use a paint system that doesn't burn

-push a lot of air through the booth to move the VOC out

-don't use as much paint so that the VOCs have time to move



Some people have given you recommendations for VOCless paints.  I 

avoided these.  I heard unfounded rumours that they don't hold up 

(unfounded rumours that I'm now propogating without foundation).



Others have given you pointers to building a paint booth that will flow 

more than sufficient air to move the VOCs out before they build to 

explosive concentrations, but this required building more support 

"stuff" than I wanted to invest in.



The route I chose was the $50 Harbor Freight HVLP sprayer.  This thing 

is pathetic with house paint.  By the time you get the paint thin enough 

to go through the sprayer, it is to thin to cover.  But that is just not 

so with  PolySpray or PolyTone.  The sprayer is amazing with this thin 

paint.  So far, I've painted my belly and control surface fabrics, as 

well as a frieds Dart ultralight.  I asked our builder's group for 

estimates on how much paint to buy before starting, and found myself 

asking, "Where did they put all that paint?" when I was done.   The true 

story was told by how much paint was NOT on the booth walls and floor.  

Even the exhaust fan only had a slight coloration from the paint. Simply 

put, the sprayer puts the paint on the airplane instead of making a 

mist.  Considering how poor a painter I am, and how much I hate it, the 

finish job is nothing short of stunning.



Less paint sprayed means less VOCs, means smaller airflow requirements.  

Less paint sprayed also means less $70/gal paint bought, but we're 

building airplanes here, so nobody really cares about that, do they?



-- 

         ,|"|"|,              Ernest Christley       |

----===<{{(oQo)}}>===----    Dyke Delta Builder      |

        o|  d  |o        http://ernest.isa-geek.org  |

Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Mon Oct 23, 2006 6:42 am Post subject: Re: explosion proof fans

One of the wonders of internet search engines is what you CAN'T find. This is frequently as valuable as what you CAN find.



In the case of paint booth explosions, there doesn't seem much to find--even with the guys with a cigarette hanging out of their mouth and a barrel of parts solvent at the elbow. 



The long and short of it is --Be careful, but don't be crazy about it. Pilots should be able to evaluate risk based on understanding and experience in ALL areas of their life. 



OT: Great old Car Talk tale about a guy who used a vacuum cleaner to suck the dirt out of his spark plug wells after taking out the plugs. Question: "How long was it before his widow remarried?"

_________________
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net

larry(at)macsmachine.com
Guest

Posted: Mon Oct 23, 2006 12:24 pm Post subject: explosion proof fans

I agree,

An explosive atmosphere has to be just right sometimes. I remember 

working after school in Smokey’s body shop sanding cars. He’d paint a 

car each day, usually with lacquer at that time. The open furnace 

setting on the floor would heat that old block building and Smokey would 

have a handkerchief and a cigarette in the left hand while spraying with 

the right. The atmosphere was positively thick, and he’d rush out 

coughing, take a drag from the cigarette, curse the cigarette and then 

put the hanky over his face and run back in to continue. I doubt Smokey 

is around any more, but his was not the way to set up painting.



We had a multi-$M flash fire in an automated spray booth at 

International Harvester some years later that nearly killed a lady 

foreman. A small electric spark ignited a leaking thinner hose that 

flushed out the electrostatic spray nozzles. Neither of these gained any 

traction in the newspapers, but there is good reason to exercise 

caution, not in a casual way, but with positive thought and deliberate 

planning.



I paint with AFS paints because there is no fire hazard, little odor and 

the distilled water as thinner evaporates the same as VOC thinners. 

Durability is determined by how well you wash, etch and clean before 

priming. If you do it right, the primer is positively as tough as any 

other. If you do it wrong, I’m sure it would peel the same as the other 

paints. My Saturn is painted with a water-thinned paint, as are some 

commercial jet aircraft.



Respectfully,



Larry McFarland

do not archive



Eric M. Jones wrote:



 	  Quote: 	
		  



One of the wonders of internet search engines is what you CAN'T find. This is frequently as valuable as what you CAN find.

--------

Eric M. Jones

www.PerihelionDesign.com

113 Brentwood Drive

Southbridge, MA 01550

(508) 764-2072

emjones(at)charter.net

N1DeltaWhiskey(at)comcast
Guest

Posted: Tue Oct 24, 2006 2:15 pm Post subject: explosion proof fans

Tom,



Have you considered taking the fan out of the equation?



I wouldn't consider an electrical device to be safe in a volatiles laden 

atmosphere unless it is UL Listed or FM Approved as "intrinsically safe" in 

accordance with the National Electrical Code.  As already related, paint 

booth explosions do occur - the company I work for (or its insuring 

predecessors) probably paid a few buck on that IH explosion.



Volatiles have what are known as Upper and Lower Explosive Limits (UEL, LEL) 

when mixed with air.  Explosions will only occur when the volatiles content 

is within those ranges with the severest explosions occurring at the right 

stoichiometric ratio.  Determining whether you will get into these ranges or 

not is a rather complicated analysis based on knowing the number of room air 

changes per minute, and the rate of release of the volatiles into the room 

environment, the latter being more difficult to determine.  The more common 

method of doing this is taking empirical measurements with a volatiles 

detector.  Obviously, all of this can become moot if there is no ignition 

source present. Static potential from the plastic or other sources will be 

reduced with higher humidity, do don't spray on a cold dry day.



Consider also, that most volatiles are heavier than air, so where you place 

your air supply and exhaust is just, if not more, relevant than what you are 

using to move fresh air through the system.



To take the fan out of the equation, consider using it to push air into the 

booth rather than to exhaust it out.  Install an air plenum on top of your 

booth into which your fan blows.  Provide large openings (to slow the air 

movement) between the plenum and the booth with filters to remove dust that 

might be drawn in.  Exhaust the air from floor level.



Regards,



Doug Windhorn

---

Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Thu Oct 26, 2006 7:02 am Post subject: Re: explosion proof fans

Guys!.....whoa.



Far be it for me to be the voice of reason. (I was 18-years old in 1965...you get the picture.) But this discussion of explosion proof painting is Way Overboard and potentially dangerous. Here's why.



Copy and paste this search field into Google:  paint explosion  -"explosion proof" -projector -tshirt -Perplex -sony -art -youtube -"you tube" -photoshop -"T-shirt"     The minus terms eliminate a lot of non-relevant stuff.



Then answer the following--



1) Do you have ANY knowledge of a painting accident/explosion with a setup similar to what you intend to use? 



2) Do published reports cite extenuating reasons for the accident--natural gas-fired heaters, pools of solvent, toluene, open flame?



My concern is that list reader will be so afraid of fans that they may elect not to risk using them. ANY box fan will be fine. The on/off switch is the only sparker. Don't allow the booth to fill with a cloud of spray. Don't spray solvent through the gun into the open. Use a rag.



Again. Be safe but not silly. 



"Ring the bells that still can ring 

Forget your perfect offering 

There is a crack in everything 

That's how the light gets in."

---Leonard Cohen

_________________
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net

frank.hinde(at)hp.com
Guest

Posted: Thu Oct 26, 2006 8:09 am Post subject: explosion proof fans

My thoughts exactly....I have known a friend who when spraying could not

see the the other side of the room and you could see sparks in the motor

of his compressor and it did not ignite.



Now I wouldn't do that but it goes to show the amount of vapour you need

to make an explosive mixture is beyond what you will get with sparying,

as Eric says the box fan will be perfectly fine and keep the mixture

well below the LEL (lower explosive limit)



Frank 



--

rvbuilder(at)sausen.net
Guest

Posted: Thu Oct 26, 2006 10:04 am Post subject: explosion proof fans

If it was that thick, he may have actually been too rich.  It really is

a narrow mixture for it to explode.  Still wouldn't recommend it though.



Michael Sausen 



--

N1DeltaWhiskey(at)comcast
Guest

Posted: Fri Oct 27, 2006 5:56 pm Post subject: explosion proof fans

Eric, et al,



I didn't want to write a dissertation on the original question asked which 

related to safe implementation of a fan for an enclosed spray room.  As Eric 

has guided us, there is a plethora of information on explosions and 

explosive atmospheres.  But my perception of the intent of the temporary 

spray booth was to successfully complete painting an airplane.  Do we need 

to read multi-hundred page books to determine whether we can do this safely 

or not?



Back to basics:



1) Assume we will use a flammable based paint.  Otherwise, most of the rest 

of this discussion is not too important.



2) We will assume the enclosed area for painting is relatively air tight. 

If it is not, make sure there is no hot electrical outside the are within 5 

ft. of the floor.



3) Further assume the purpose of the booth is to reduce dust that will 

contaminate the paint job, and to keep undesirable vapors and particles away 

from energy sources (static, electrical arcing as is switches, hot surfaces 

as in furnaces, or open flame as in a multitude of appliances) as may be 

appropriate.



4) I am assuming the builder of the booth is astute enough to know not to 

put electrical equipment inside the booth, including lights.  He also has 

enough sense to ground discharge nozzles to prevent static buildup.  This 

activity is not for idiots.



5) The "booth" should consist of 3 parts - the activity room, an air supply 

plenum, and an exhaust plenum. The interface between the supply plenum and 

the activity room will be at the top of the latter. The interface between 

the activity area and the exhaust plenum will be at floor level.  Both 

interfaces will consist of filters. Both plenums will be fed from, or 

discharge to, outside the building which contains our booth.



6) Given 5, any fan of adequate volumetric capacity will work (remember, one 

complete air change every 5 min.). It will be switched on before entering 

the booth, and off after departing, because the switch is outside the booth. 

There are few reasons to be concerned with explosive vapors migrating to the 

fan because they are heavier than air and will exit via the exhaust plenum 

even if the fan is off.  (One "safe" industrial approach is to eliminate 

electrical equipment within 5' of an open faced spray booth, and within 15' 

for a height of 5' off the floor.)



The one exception I can think of would be related to airflow through the 

booth in the opposite direction caused by wind outside the building. 

Appropriate arrangement of the intake and exhaust areas should mitigate this 

(back draft dampers might be considered if this is perceived to be a 

problem).



7) With adequate airflow through the activity area, a general "fog" will not 

occur.  If it does, stop spraying and figure out why!



 Have you gotten zapped from static today? If so, you might want to 

postpone your spray activity to another day as one added precaution.



If steps 1-8 are addressed, your chances for an explosion are next to 

nothing.  These precautions are easy to take and make good sense. They also 

are not expensive.  Going down the road of intrinsically safe or explosion 

proof equipment does not make good sense given the purpose of our temporary 

installation.  If you think you need to do more than the above, I would 

highly recommend not using a flammable solvent based paint.



Regards,



Doug Windhorn

---

bonanza(at)vodamail.co.za
Guest

Posted: Fri Oct 27, 2006 10:21 pm Post subject: explosion proof fans

Doug, this post goes into my archives. Some subtle points that I did not give much thought to! Thanks for the

heads up! That is why I love the list- always learning!



Bob Verwey

A35 Bonanza ZU-DLW



--

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