Hi everyone,
I’ve been spraying with waterborne finishes for a little while now. I’m interested in spraying shellac (in alcohol), but I’m only working in a little basement shop. Usually, I have a box fan and a simple spray booth, similar to what Dresdner sets up in the video from FWW. In the full video (which I got from the new instant video purchase – great!) he talks a lot about spraying shellac, but never mentions an explosion hazard. Is shellac relatively safe? Should I stick with water borne shellac, even though it’s not as easy to get?
Thanks,
Todd
Replies
As an antique restorer and furniture refinisher I spray a lot of shellac. It's the best base coat/sealer that I have found for most finishes. I also work in a basement shop and have had no problems in 30 years. I usually spray near an open garage door with an exhaust fan going.
furndr
As you mention, the solvent for shellac is alcohol. Depending on the type of alcohol you use, and the amount of dilution it gets with shellac, the flash point can be VERY low.
(Flash point is the temperature of ignition, given a perfect mixture of fuel vapors and air/oxygen.)
Spraying any flammable liquid allows easy vaporization, and assists with the mixing with air/oxygen.
So, maybe you're getting the idea -- you need to read up on the subject, and might nix the idea, at least in your basement.
And I'm reasonably sure that there is no such thing as water-borne shellac.
Target Coatings has a product that they refer to as waterborne shellac. This may be what the original poster was referring to.Ron BreseIf you're too open minded your brains will fall out.
Hi everyoneThanks for your thoughts. I've done a bit more thinking on this. Ethanol has a flash point of around 20% (on a hot day in my area). The density of air is about 1 kg per cubic meter, the density of ethanol is a little less than 1 kg per liter. My basement is nearly 20 cubic meters. So, four liters of ethanol should be enough to reach the flash point in the basement - of course this assumes it's evenly distributed, which it won't be, so the danger is somewhat increased.Now, that doesn't seem right. I'm pretty sure that if I were to drop a gallon of denatured alcohol on the floor, the house wouldn't blow up. Is there a problem with my math? That brings me to another thought. With alcohol, there isn't much difference between spraying and wiping, vaporization-wise, since the alcohol flashes off so quickly. It's more a matter of volume. In other words, if I wipe on shellac on, say, a couple of big doors without good ventilation, is this also risky? Or vise-versa, if it's not risky, why is spraying risky? I'm using an HVLP, with decent transfer.The water based shellac that I use is indeed from Target Coatings. It's a great product (so is their USL water based lacquer), but I can't just go to Home Depot for it - not yet anyway.Not really convinced either way yet,
Todd
I'm not an expert in this area and a wiser person would probably be smart enough to stay on the sidelines. Seems to me that although the vaporization rate with brushing and spraying might be similar, with spraying, you're introducing alchohol into the atsmophere much more quickly than you can when brushing. Also, although it seems reasonable that the explosion risk may be lower than say, lacquer, there's still a fire risk and as I recall, alcohol burns nearly invisibly. So you may have a fire going and not even know it until it's too late to control it or get out.
Todd, I'm certainly not an expert, but don't the flash point numbers refer to the volume that remains suspended in the air? If so, wouldn't one have to be spraying a much larger volume to keep the 4 liters suspended?
According to Wiki:"The flash point of a flammable liquid is the lowest temperature at which it can form an ignitable mixture in air. At this temperature the vapor may cease to burn when the source of ignition is removed. A slightly higher temperature, the fire point, is defined as the temperature at which the vapor continues to burn after being ignited. Neither of these parameters is related to the temperatures of the ignition source or of the burning liquid, which are much higher. The flash point is often used as one descriptive characteristic of liquid fuel, but it is also used to describe liquids that are not used intentionally as fuels."And I have seen sealed containers of denatured alcohol that had warning labels with the flash point being very low (less than 200F). And basements usually have ignition sources that are well above that -- water heaters, furnaces, clothes dryers, pilot lights.I stand by what I said earlier -- Spraying alcohol based shellac in such an environment is a huge risk.
Politics is the antithesis of problem solving.
Edit (again): I just checked on the flash point of ethanol, and it's _55F_ NOT 200F. That means that it _is_ possible to reach explosive concentrations. /EditThat's a good wiki page. One very important point that I took from it: that temperature (200F) is the temperature of the _liquid_, not the ignition source. The liquid temperature sets the equilibrium vapor concentration. In other words, if I flooded my basement with ethanol at some temperature below 200F, and walked in with a match, nothing would happen!That seemed ridiculous to me - but think through it. You obviously can't drop the match into the liquid, since that would ignite, but at room temperature, ethanol just doesn't have enough vapor pressure to ignite the vapor alone. Put that pot of ethanol on a stove though, and good-bye eyebrows.But! This isn't the whole story, of course, and I'm certainly not saying that spraying is safe. The spray itself (which contains little droplets of liquid) could obviously ignite, which is a considerable risk, especially with a $20 crappy box fan zapping away 3' from the gun. I think that is the only way that something bad could happen, unless I'm off in my analysis.Is there really no chemists hanging out here? Don't make me call my brother-in-law. Actually, come to think of it, he does have my planer...ToddEdit: Just for giggles, I looked up the flash point of lacquer thinner: 4F! So, definitely don't spray lacquer. Or flood your basement with it, and walk in with a match, because it _will_ explode.Edited 12/12/2008 6:11 pm ET by Qwkbrnfox
Edited 12/12/2008 7:38 pm ET by Qwkbrnfox
If I understand your latest post, wiping or brushing shellac in my shop with the ceiling furnace running should not be dangerous. I was thinking that I might have to turn off the pilot lite when finishing.
Art
This is an interesting thread. I have an electric water heater and can easily prevent my furnace coming on. With the possible exception of the exhaust fan, there are no other ignition sources. So for sake of argument, if I have eliminated ignition sources, including the fan and I spray in the basement, how long will it take for the shellac (alcohol) vapor to dissipate to a safe level.
Just a side note.... If you have a decent exhaust fan going in a basement with a running furnace, the exhaust fan will suck the furnace exhaust right back down the chimmney unless there's some other source for make up air.
Hi Quickstep,I just edited my somewhat long-winded post above, to point out that the flash point of ethanol is 55F, NOT 200F. That means that it could be possible to reach dangerous concentrations at room temperature. But the question remains: is this a practical danger? I would be willing to bet that lots of people spray shellac. However, as YesMaam points out, is the level of risk such that it's just not worth doing? I was really hoping that dozens of people would chime in with a resounding "I do it all the time", like a couple of the previous posters.And you make an excellent point that deserves to be restated: with a good exhaust fan, you'd better have a good source of make-up air, if you have a gas or oil fired appliance. I have a intake pipe of the same size as the boiler exhaust, that feeds to within 18" of the boiler. This is code around here.
"This is an interesting thread. I have an electric water heater and can easily prevent my furnace coming on."You should turn the breaker off on the WH or put the thermostat in vacation mode.The thermostat can arc enough, if you happened to have explosive mixture, top set it off..
William the Geezer, the sequel to Billy the Kid - Shoe
Good Point Bill. My furnace has a service switch. When that switch is off, the whole thing is shut down. I just need to make sure the vapors have dissipated before turning it back on.
The flash point of ethanol is 55° F. Flash point is the temperature at which an open container of a liquid has enough vapor above its surface that a match can get it to flash (but not to continue burning). Incidentally, if the room were cold enough, even a bucket of butane would not release enough vapors to catch fire.The explosive limits of ethanol describes the concentration of vapor by volume in the air that constitutes an explosive mixture. Below 3.3% (LEL) it is too diffuse to explode. Above 19% (UEL) it is too concentrated to explode. Anywhere between those concentrations a spark or flame can cause an explosion. Your calculations were based on densities of air and of liquid ethanol instead of alcohol vapor. LEL 3.3% = 33,000ppm. As a vapor, 22.4L of ethanol gas (one mole of an ideal gas) = 46g. A cubic meter is 1,000,000cc or 1,000L.http://www.chem.purdue.edu/chemsafety/Chem/solvents.htmBruceT
Gotcha, good information there. The key is that the explosive limits are by vapor volume. Here's my math, revised knowing that:Basement is 20m^3 = 20,000L3.3% (Lower limit) is 660L of vaporized ethanol (20,000L *.033)Number of Moles of 660L of ethanol = 29.5 (660L/22.4L per Mole)Mass of 29.5 Moles = 1.355 kg (29.5 Moles * 46g / Mole)Volume of 1.355kg of ethanol = 1.715L (1.355 kg / .79 kg/L)So, if we assume that my basement is warmer than 55F (I hope so), then 1.7L (half a gallon) of ethanol will evaporate to give an explosive mixture. That's a fair bit, but even smaller amounts will cause temporary, locally higher concentration, that could explode in contact with, say, a pilot light.For another point of reference, lacquer thinner has a lower explosive limit of 1%! All lacquer thinners are a little different, so there's no standard density for it, but it seems reasonable that around a half liter (about a pint) would be enough to cause an explosive concentration in my basement. Ventilation is clearly very important!Todd
The obvious solution is to have enough members of the Swedish Bikini Team to keep the shop warm, and then they can alternate operating manual vent fans with two opposing windows open. The potential distractions might result in other safety issues, however. ;-)For added practical perspective, consider the number of body-shop spray booths that are in constant operation with far more volatile finishes. Or, product-finishing chambers seen on various TV shows where it's a constant fog inside. I'm guessing their vent fans may have shielded motors, but I'm not sure.
Edited 12/13/2008 3:36 pm by RalphBarker
"Ventilation is clearly very important!"Amen to that!By the way, before you got to the LEL, you'd very likely be quite intoxicated. 3.3% is 33 times the OSHA maximum allowable limit.BruceT
Tood - Your last post (regarding the LEL calculations) is the most pertinent. There's been a fair amount of discussion on this thread about the closed-cup flash point, but flash point is only indirectly related to the hazard of an explosion. It's true that the flash point is related to the vapor pressure of a liquid at particular temperatures, and if the temperature is well below the flash point, the vapor pressure above the liquid will be low enough that the ignition point cannot be reached.
However, that doesn't mean that you cannot create an explosive mixture of air and a particular solvent below the flash point. What you can't do is create an explosive mixture of a solvent and air (or oxygen) below the condensation point of the solvent, at least in an equilibirum situation.
Regarding your calculations, they look correct (though the mole per volume term is a bit off, but not by much), though I didn't go through them in detail.
Note, however, that your calcs. assume that there is no interchange with the air volume in the basement (it's good to start with this assumption, since it usually gives you a "worst case"), and that the air in the basement is perfectly mixed. In reality, of course, neither of these conditions hold true in actual practice.
For the most part, the air very close to the sprayer and prayed surface will be above the UEL (Upper Explosion Limit), and most of the rest of the air will be well below the lower explosion limit. The chances are very low that you would actually create an explosion, though it is remotely possible. I'd also note that nearly 2 liters of Ethanol is a lot of ethanol for a spraying session - most closed-cup spray systems are limited to about a quart, and that's if the system is over-filled.
I'll note that if you were to approach the LEL for ethanol in your shop, it's likely that you'd be overcome by the fumes and possibly faint when you take off the respirator - which represents a considerably greater risk to your health than the explosion possibility.
Finally, I'll note that industrial safety departments would generally not allow the spraying of combustible fumes without a certified air-exchange rate inside a spray booth or hood, but a lot of that has to do with a zero tolerance for any risk, not actual calculations of the risk.
(P.S. - You asked for "chemists" - I've a PhD in Chemical Engineering, and a branch of CHE is vapor hazard control - I'm fairly familiar with it)
Excellent! I knew there would be someone hanging around here who actually knows what they are talking about. This is what I'm currently thinking: with my current set-up, which uses a cheap box fan, there is a small risk of fire. I don't think that I'm at risk of an explosion, because of what you pointed out - the local concentration is likely above the UEL, diffusing rapidly to below LEL. The droplets in the spray might be able to ignite from my fan, which would be wonderfully ironic.On the other hand, I believe that with an explosion proof fan, the risk drops to darn near zero. The fans I've seen could change the entire volume of air in my basement in around a minute! One more time for good measure - a fan this big would suck the exhaust from the boiler and water heater, again ruining my day. An open window would take care of that. The fans I've seen on the 'net are around $500 - expensive, but not terribly so.
"The fans I've seen on the 'net are around $500 - expensive, but not terribly so."
Explosion-proof (actually "explosion resistant", but you know what I mean) anything is pretty expensive, but that has a lot to do with the UL certification process, not so much with the expense of the materials. If you can find a fan from Grainger that uses a TENC (Totally Enclosed, Non Cooled) motor, that'll do the trick, so long as the fan shroud is metal and it's grounded to the building electrical. Frankly, and were it me, I would just not worry about it so long as there's fan evacuation of the fumes and the fan is grounded. The probability of a fire is really, really low. The sawdust that builds up in the air in a power tool shop is a heck of a lot more hazardous.
By the way - humidity has a fair amount to do with the hazard when it comes to a fan-evacuated system. Non-polar solvents like laquer thinner can generate a significant static charge when moving through something like a box fan. Humidities above about 50% R.H. dramatically reduces this potential.
On a side note, this is why you're warned never to fill a plastic gasoline container inside a truck bed with a plastic liner. The insulating quality of the truck bed liner can lead to a situation where the flowing gasoline generates a static charge, which then sparks through the metal fill nozzle, igniting the vapors above the liquid in the can - kaboom.
Like this?http://www.grainger.com/Grainger/items/1HLA2That's $160, which is definitely tolerable. And it will move about 10x what my little box fan will.
That $160 is probably Grainger's "customer-off-the-street" price. If you know someone who uses Grainger and has an account, you'll probably get a lower price.
kreuzie
I doubt that fan is explosion proof, especially at Grainger prices. I've been looking and looking; I can't find one for less than $500.
Induction motors are inherently explosion-proof. There is no sparking as happens between brushes and commutator on a "universal" motor. The only possibility of sparking is at any mechanical contacts of the capacitor start circuitry. As long as that is in a can on the motor frame, sealed by a grommet or other suitable seal, the motor is safe.Small induction motors in the fraction hp range for fan assemblies are not that expensive.Rich
I've often wondered about that. Not to hijack the thread, but my window exhaust fan has an induction motor without a commutator or brushes. With no sparks, shouldn't that be safe?
That is not the definition of explosion proof.Now there is what is know as intrinsically safe circuits which don't have enough energy in them to cause a spark.While rare a bearing could freeze and cause a spark or a wire burn off.Explosion proof equipment has to with stand and explosion IN the equipment and the any gases that come out through any movable parts has to bee cool enough that it does not ignite gases OUTSIDE the device..
William the Geezer, the sequel to Billy the Kid - Shoe
Yep - That would do the trick, though as Rich says, it's not inherently explosion-proof. There's some rather complicated requirements for true, industrial-rated explosion-proof ratings, and there's also a certification requirement from NFPA (National Fire Protection Association) and UL. That's partly why explosion-proof electrical items are pricey. One requirement, for example, is low-voltage control circuits and bronze, non-sparking bearings.
That said, it would be a rare thing for a home woodshop to have a true expolsion-proof spray booth. You're going considerably head and shoulders above the normal installation for even taking these considerations into account. I can't guarantee that there will never be an issue without going to an explosion-rated solvent-handling spray booth, but if it were my shop, I'd go with something like the Grainger fan you linked to, build a small, fold-up enclosure to handle any over-spray, and leave it at that.
Here is my 2cw on this. It really depends on your basement and how you are spraying. I've sprayed a bit of shellac and mostly in my garage shop. I built a spray tent of 4mil plastic and sprayed inside using a HVLP gun with very low overspray. I have sprayed some with a standard spray gun and it went every where and was a nightmare. In my case I had no easy flash points and I'm spraying minimal amounts and would vent well. I moved in August to a new home and now I'm in the basement with one big open area (about 1400 sqrfeet) that shares space with my furnace and gas hotwater heater. So I have to be real cognizant of that flash point threat. Fortunately I have windows on one side of the basement and I will build another plastic tent area and vent to the outside via a window. So in my opinion it depends if you have flash sources and how much you spray. You don't say but I hope you wear properly rated respiration protection.
If it moves, tax it. If it keeps moving, regulate it.
And if it stops moving, subsidize it.
The explosion hazard is quite small with shellac but adequate ventilation is still required. However, the inebriation factor is relatively high (pardon the pun). Be sure you are wearing an appropriate respirator.
Hi Howie,Our messages crossed in cyber-space. Yes, I definitely wear a respirator when I finish with anything volatile or sprayed, though it's so disappointing to let that good ethanol go to waste.Todd
>> Yes, I definitely wear a respirator when I finish with anything volatile or sprayed, though it's so disappointing to let that good ethanol go to waste.As the time gets close to 5:00 PM, just add a dollop of vermouth to your shellac. Saves you the trouble of mixing your own martini.Howie.........
And the oil from the olives helps with the shellac rub-out!
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