From my chemistry class at school I can remember that powdered substances can be ignited easily no matter what the substance, I think because the relatively large surface area lends itself to combustion.
How then is it possible to use fire extinguishers that work with “powder”?
Do they really use a powdered substance as the name suggests?
If they do then how- a fireman visiting the school just said it was a trade secret.
powdered materials burn well, even explosively, only if they are oxidizable in the first place, and well mixed with oxygen. If they are not, they act as a great smothering agent. Even flour, which can be explosive in a silo, will tend to smother flames rather than burn, unless the particles are suspended in a sizeable volume of air
Yes, powder fire extinguishers use actual powder. One of them is potassium bicarbonate, I believe. Is that K2CO3?
http://www.fire-system.co.kr/pro_fire5_eng.htm
http://www.armandproducts.com/BiEndUses.htm
Then there’s this, a long scholarly discussion on a chemist’s MB. http://www.finishing.com/61/81.html Evidently there are different types of powder fire extinguishers, depending on what kind of fire you’re dealing with (electrical, wood, grease, etc.)
Serious firefighting equipment website. Cool. http://www.fireteks.com/drychemical.htm
Whatever the chemical they use, it makes a mess. http://www.granular.com/wwwboard/messages/180.html
BTW, run “fire extinguisher powder” through Google and tons of websites selling them come up. If you have some spare venture capital sitting around, you can invest in the “Strongly Launching Dry Powder Fire Extinguisher” Company. http://china-window.com/Fujian_w/hot/fz98-127.html
Yes, we use a powder to extinguish fires. Actually, we use a few different types of powders for extinguishers (monoammonium phosphate, potassium bicarbonate, sodium bicarbonate, and potassium chloride). Technically, the name “powders” is kind of a misnomer in the fire service. These extinguishing agents are considered “dry chemical” type agents. “Dry powder” type agents are used on Class D (combustible metal) fires. I’ll talk about them later. But first, dry chemcial agents.
Dry Chemical agents are, indeed, a powder (firefighters never call something by what it really is). The powder has the quality of being able to be pushed through a hose or pipe, allowing it to be discharged where you need to put it (ie, on the fire). It extinguishes fires in a few different manners. Some types (sodium bicarbonate) release CO2 when they’re heated, smothering the fire. Monoammonsum phosphate leaves a residue on the burning material, excluding oxygen. Also, the powder forms a big dust cloud around the fire area, limiting the amount of radiational heating that will spread the fire. None of these effects really put the fire out, though. For that, we look to Mr. Chemical Chain Reaction.
I’ve talked about the Chemical Chain Reaction before, mainly here. Dry Chemical agents extinguish a fire the same way the Halons extinguish a fire…they get in between the baby chemical reactions going on inside the fire and stop them. No more reaction = no more fire. Check that thread…I did a good job of explaining how Halons work, if I do say so myself, and dry chemicals work the same way.
In short, no, not all dusts burn. The dry chemical agents are a dust, but they react differently when heated than a “normal” dust does.
Now, for Dry Powders, which are a scary bunch if you ask me. Dry Powders are for use on combustible metal (magnesium, sodium, postassium, titanium, zirconuim, uranium, plutonium, lithium, etc) fires. There are a ton of different dry powder agents, such as Met-L-X, Na-X, TEC, Lith-X, Boralon (all commercial agents found in extinguishers), and stuff like graphite powder, talc, cast iron turnings/borings, soda ash, and (believe it or not), water. Each type of agent is for use on specific metal fires, and they’re used in different ways. Some are sprayed onto the fire, some are shoveled on, and (in the case of TEC) a plastic bag of the stuff is placed onto the fire. These agents either melt down and form a coating over the fire, or cool the material down. None of them really get into that chain reaction stuff.
I’ve only had the opportunity to use dry powder once, Met-L-X on a magnesium fire. Yeah, it went out. Normally, we’ll just let the metal burn itself out. Its a lot easier that way.
Any questions?
KCB615, I have been told that if one has a grease fire in a frying pan and a salt canister handy (something where you can pour a lot fast, not just a salt shaker) the salt will put out the fire. I had occasion to do that once, and fortunately it worked. Does the sodium chloride just smother the fire, or does it interrupt the chemical chain reactions too? Or is it an urban legend and I just got very lucky?
Quoth Duck Duck Goose:
Almost, that’s potassium carbonate. Potassium bicarbonate is KHCO[sub]3[/sub]. Please don’t ask me why bicarbonate is HCO[sub]3[/sub] instead of (CO[sub]3[/sub])[sub]2[/sub].
nebuli, grease fires are a whole different animal from a fire protection standpoint. Even more so when you have an appreciable depth of grease, like in a fryalator. Dry chemical agents, when put on a grease fire, cause this nifty thing called “saponification.” The dry chemical takes the grease and turns it into a soap-like solid. The problem is that heat will break those soap-like solids apart, and the dry chemical didn’t cool the grease down. So a minute or so after the fire is out, poof! The fire is back in full force (and you’re out of dry chemical, since you dumped it all on the first fire).
As for sodium chloride as an extinguishing agent, it is one. Its used for Class D fires (sodium, postassium, and magnesium, according to my Fire Protection Handbook, 18th ed, pg 6-403), and is not rated for A, B, or C fires. Personally, I have no clue how that one works. Perhaps one of our chemistry gurus will stagger in here to explain it further. If I had to guess, I’d say you poured enough of it into the pan to dilute the burning grease. But since I wasn’t there, I can’t be 100% sure.
[public service message] And remember, folks, if a fire is larger than a wastebasket, its too large to use a fire extinguisher on. Get out of the house and call the fire department. [/public service message]
KCB615 "Any questions?"
How come you can use graphite powder to extinguish fires? Isn’t that pretty close to using powdered coke?
Using sodium chloride to put out fires.
http://www.rge.com/1913.html
http://www.taunton.com/fc/features/basics/issue10kitchenfires.htm
Also, my mother and grandma taught me that you can use flour to smother a grease fire. However, the Tyler Fire Department says not to do this. http://www.tylertexas.com/city/Fire/FR_MRSHL.HTML
OTOH, this Home Safety website says flour is okay. http://www.peachtreecityfd.org/public-education/homesafety_chklist.htm
So?
[KCB615** and DDG, thanks for the info. The grease fire I experienced wasn’t in any great pool of grease, actually it was more like just a film of grease at the bottom of the frying pan. I had also heard about using baking soda, but at the time my baking soda was in a cabinet at the other side of the kitchen and the salt was right at arms length.
From the Fire Protection Handbook:
At least thats what NFPA says about it. I tend to agree with you, matt, its kind of counter-intuitve to use graphite. With that said, I haven’t used it, seen it used, or heard of it used before I read it in the Big Green Book.
Flour in kitchen fires
The nature of the job is that I don’t find out about stuff that works very often. Normally I find out when something didn’t work like someone expected it to (thus my sig). One of those things is flour. A girl I went to high school with tried using flour to put out a grease fire by tossing the flour at it. As the OP had noted, dusts are easier to ignite than a packed solid. The dusty flour cloud that had formed ignited and lit her kitchen on fire. As if it wasn’t embarrasing enough to have your kitchen on fire, imagine knowing the firefighters who are putting it out. Back to the flour…if you can get a big lump of it onto the fire, it will smother it. I wouldn’t reccommend trying it, though. Stick with the baking soda, dry chemical, or a CO2 extinguisher.
KCB615, where did you get your firefighting experience? I learned about Met-L-X and TMB in the navy but fortunately never had a need for them. I did get a fair amount of experiencs with dry chemical (navy calls Potassium Bicarb PKP or purple K) and wet foam in the navy’s excellent shipboard firefighting school and when we tried to burn the Ranger down.
Dry chemical works very well on liquid fuel fires thought it doesn’t prevent flashback. A quick shot of powder in the air will also make for a temporary heat sheild so a fire can be more easily approached.
I have absolutely nothing to contribute to this thread; I just wanted to say
Plutonium and uranium?!? Yikes! Not exactly your typical smoldering-cigarette-butt-in-the-couch, huh?
7 years as a firefighter in southeastern Massachusetts. Thats where my “ugg…break door, drag hose, squirt water, make mess” caveman-type firefighting experience comes from. I also have my bachelor’s in Fire Science (concentration in investigation), and I’m working towards my MS in Fire Protection Engineering (still some years left for that one, though). The technical stuff I got from college, the cromagnon (read: fun) stuff from being a firefighter.
Per ISO (Insurance Services Organization, not the ISO 9000 people) regulations, engine companies are required to carry a Class D extinguisher. Since its expensive as anything, we don’t like to use it. Better off letting the metal burn itself out and protecting exposures. At school, we had the opportunity to use Met-L-X to put out a lump of magnesium in a lab setting. It put the fire out. Nothing fancy, I thought. Didn’t convince me to use them, I still just watch the stuff burn itself away.
Dry Chemical is another story, though. I’ve used it quite a few times for “real” fires, but the best was a class at the Massachusetts Fire Academy called Flammable Gas Firefighting. Take a 12’ x 12’ pit 1’ deep and fill it with liquified natural gas (LNG). Light it on fire. Then take 4 of your close friends and put it out with fire extinguishers. Its the biggest fire I’ve ever seen come out from such a small source, and by god we put it out. That was a fun day.
Ive been a Fireman for 20 years in a rustbelt city in Ohio and am of the “wet stuff on the red stuff school”(with exeptions that K mentioned.They use magnesium in steering colombs(spelling) and once I get the major body of fire out on the car I entertain myself with putting that out with water.You have to use LOTS of it and it makes a nice light show.note: we have found in the last 2 months 2 car fires with nitrous oxide tanks in the trunk.Our concern was the tanks getting hot and letting loose.I’ve put out probably 6 or 7 hundred car fires and have yet to see one blow up a la "chips"The dangers are bumper pistons letting loose,and a few other safety features that arnt so safe when on fire.I’m ex army but have noticed that the navy vets make some of the Best Fireman.Went to a week long maritime firefighting school in Toledo and got a small taste of what all navy guys learn for shipboard firefighting.Bilge fires,and simulated aircraft fires done w/afff (good stuff maynard)Any way, enjoyed the GOOD info in the posts.One suggestion,after youve put out your kitchen fire,have your local F.D. send up a pump to double check it anyway.they can write you a report for insurance use, and ventilate it bettor than you can.Stashua
Almost all Fords have (it could be “had” now) magnesium steering columns, and of course we can’t forget the magnesium Volkswagen engine blocks. Add in “mag wheels” to that list. Lots of Mg in a car fire. Its funny…you can have a car burning bumper-to-bumper and completely extinguish it with less than 100 gallons. Add in a magnesium steering column, and now you’re up to 300 gallons. Its still fun to make fireworks, though.
Thanks for mentioning the bit about calling the fire department after you’ve had a kitchen fire…I should have said that myself :::hangs head:::