I've heard more than one person expound upon the frighteningly massive dangers of solvent explosions from motor w/brushes used in the laboratory
setting.
I'd like to put in my two cents.
It is really NOT as serious a problem as most people think it is. Vapours need to be extremely concentrated to go off.
For instance,
The Lower Explolsion limits for say.....acetone (which is pretty damn flammable is 2.5% by volume solvent-air, so.......to make a solvent explosion in
a five gallon bucket, you need to comletely vapourise a half quart of acetone.
Don't beleive me? Ask anyone who has ever built a spud gun how much hairspray they use to launch a potatoe!
I think we forget that a large open window with a normal fan or a decent breeze is almost always enough to properly ventilate a lab.
We forget that the sparkless motors and heating mantles are a relatively recent invention and that most labs used large amounts of solvents and bunsen
burners in the same space quite routinely.
The danger of a minor fire/explosion in a modern lab is mainly one of liability.
A quick scare, or a little bit of broken glassware, a scorch mark on the countertop....these things are not really a big deal.
At least that's how our progenitors used to look at it.
and the way I still look at it, (except for the costly glassware, I'm so poor that every time I break a flask I cry for three weeks!)
Now, anytime anyone gets a paper cut on the job, they sue for ten million dollars and the employer convene's a board of inquiry.Twospoons - 15-9-2004 at 18:23
Your calculation is way off.
Rough calcs give me 22l of acetone vapour from 74cc of liquid acetone. (at STP, based on ideal gas laws). If the explosion limit is 2.5% then thats
enough vapour for 800l of air. Going back to the bucket - a 10 litre bucket only needs ~1ml of liquid acetone to reach the explosion limit.
Sorry - I have to work in metric, only got 10 fingers
Moral: don't be too quick to write off vapour explosion hazards as scaremongering. Vapour explosions regularly wreck rooms where idiots are
trying to make hash oil.BromicAcid - 15-9-2004 at 18:29
My experiences:
In high school chemistry the teacher added 5 ml of methanol to a 8 gallon container and inverted it several times, he then stuck a match over the
opening an a blue shock of flame whooshed though the container leaving everyone awed.
One short spray of ether based starting fluid and a match will pop a tire back on its rim.
Carbon disulfide and diethylether have some of the widest explosion ranges for solvents I can think of, carbon disulfide will ignite from boiling
water in nearly any concentration above 2% in air.
Yes, some of the data regarding solvent explosions is over exaderated, but that is just so you don't differentiate between the potential hazards
of different solvents, you are always sure to be careful with all your solvents so you never have to worry about that one unexpectedly
flammable/explosive one.Mr. Wizard - 15-9-2004 at 19:02
You are an accident waiting to happen. You don't have to have the whole volume between the LEL and the UEL, just the part near an ignition
source; for a micro second. Then the whole of the liquid will be on fire, and if its on your clothes and skin, you will know exactly where the LEL
is; a centimeter from your skin. You only have to make the mistake once, and you will know all about skin grafting and cleaning wounds. Chances are
the potato cannons were too rich, which has been my experience. Take some cheap advice, and expect the worst, plan for the worst, and have a second
thought about what might happen. As for your math, as Twospoons said, you are way off.
CH3COCH3 gives a molecular weight of 58. This means 58 grams will give you one MOLE at STP (Standard Temperature & Pressure) if this was all vapor
it would occupy about 22 liters, as a MOLE of any gas would do. Figure the volume of a 5 gallon bucket very roughly at 20 liters. Let's just
call it 22 liters to make it easy. .025x58 grams gives us about 1.35 grams which will gives us your LEL of 2.5% This 1.35 grams at a density of .8
will take up about 1.7 cc, right where Twospoons figured it. Be careful, don't get smart after you get burned or hurt.Hermes_Trismegistus - 16-9-2004 at 02:52
Quote:
Originally posted by Mr. Wizard
You are an accident waiting to happen.
Yeah, You're probably right.mick - 16-9-2004 at 08:00
A few years ago after 2 fires in fume cupboards from people evaporating ether in a beaker on a hot plate I put out the following;
Diethyl ether (ether) is extremely flammable.
Boiling point=34.6 oC (nearly a gas).
Autoignition temp=160 oC (can be readily ignited by a hot plate or spark).
Vapour densisty=2.55 (air=1).
Evaporation rate=37.5 (butyl acetate=1).
Lower explosion limit in air=1.9%.
2.5l of ether could give 28.8 cubic meters of potentially explosive vapour (flash fire).
If anything is wrong with the figures I would appreciate.
I have always suggested that if some spilt more than a couple 100 ml ether and there is any change of a spark etc, just get out the place and let it
clear on its own. I do not think you should try and mop it up because you would be standing in the middle of a potential fire ball.
I used to try all sorts of stuff in a zippo type lighter. Alcohols were the hardest to light. I think acetone and ethyl acetate just flashed and burnt
the wick, toluene burnt but too much smoke. Some stuff called Shell rubber solvent was good or 50/50 80 to 100 pet spirits and 100 to 120 pet spirits
was the best.
Like other people have said, I think its how much you have got around you that counts.
mickTwospoons - 16-9-2004 at 13:59
Diethyl ether is particularly bad as the explosion limts cover such a huge range of concentrations - from 1.7% to 48% Diethyl ether MSDS
I guess that's what makes it ideal for starting cars, and powering spud cannons.
[Edited on 16-9-2004 by Twospoons]
Definition Problem
Organikum - 16-9-2004 at 14:36
We suffer here from a problem of definitions, as everything seems to be called an explosion.
There are rarely true explosions with inflammable solvents in the lab and only few who have experienced one are able to tell.
100ml of gasoline, ether, acetone, toluene, etc...... in a perfect mixture with air will explode in a way you, your lab and the house will suffer
severe damage. You most.
But these perfect mixtures are gladly very rare, near to not-exist in reality. (home-lab, not industrial)
Explosion:
After an explosion of a flask you will be busy picking glass-shards out of your body.
Deflagration (common):
After a deflagration you will perhaps be a little dizzy and thats it. Impressing fireballs without big harm is typical here.
Solvent fire (more common):
Dont panic and have a wet towel and a bucket full sand handy. Avoid fire-extinguishers!
Standing in a fireball of burning ether is not so bad, really. Been there done that, although not by free will...
Dripping some ether onto your palm and lighting it is a nice way to show-off. You loose your hairs there, but who needs hair on his hands anyways?
Except this it gets a little warm and thats it.
The problem with ether fires is that etherfumes are heavier than air and ignite already on a hotplate. And more dangerous that similar to methanol the
flames are almost invisible and this way prone to spread the fire further. And then its getting dangerous.
I would really prefer to see the true dangers in handling certain compounds told, told by real-world examples, told in a understandable way. All this
flash-point etc. brings nothing as it plain does address nothing related to security.
Not to take anybody down here, but to protect our hobby and all those who are new to it.
regards
ORGJohnWW - 16-9-2004 at 15:32
There is currently a FAE (fuel-air explosive) thread going on the Roguesci.org forum, which is pertinent here. It gives the URL of a PDF file on the
subject, viz. http://www.gichd.ch/pdf/TN_09_30__04__2001_FAE_Version 1.pdf .
John W.mick - 17-9-2004 at 09:07
The trick I was shown at school was putting your hand in burning CS2. A lovely cold blue flame, but then they found out how toxic it is so it is not
allowed now. It is right that every thing can get out of proportion. If there is a chance of a fire and there is nothing else near that can catch fire
easily then it should be OK.
The CO2 extinguisher is not recommended for the inexperienced because you can blow every thing all over the place and and make it worse, if you touch
the nozzle your hand freezes, but if you just play it over the fire from a distance it should go out and cool ever thing down.
Sodium choride is also good for most fires.
mick.
I think the danger of a solvent flash fire would increase if you are in an enclosed space
mick
[Edited on 17-9-2004 by mick]Dodoman - 17-9-2004 at 11:09
I think a good old bucket of sand would be perfect for any fire. Would also be alot cheaper. neutrino - 17-9-2004 at 13:08
The reason they don't use sand anymore is that its so heavy. Have something around some delicate glassware ignite, dump sand on it and
you're left with glass shards.vulture - 18-9-2004 at 03:40
Sodiumcarbonate is even better than NaCl as it'll absorb more heat through the endothermic production of CO2 which also helps to extinguish. It
should not be used with metal fires though. That's a whole different branch.neutrino - 21-9-2004 at 16:19
That reminds me of something they taught us in "health" class a few years ago: never use baking soda to extinguish a flame on your stove
(like burning food), as the CO<sub>2</sub> evolved can cause an explosion! Just goes to show you how the educational system is going in
this country. Magpie - 21-9-2004 at 18:24
Shortly after getting married my new bride was cooking bacon and started an intimidating grease fire. She promptly put it out with a sodium carbonate
fire extinguisher. Sure it made a mess on the stove and surroundings but so what.
Except this it gets a little warm and thats it.
.