hi i’m trying to figure out without actually testing it myself could liquid nitrogen put out a fire.
Welcome to the SDMB, John.
Since this doesn’t seem to be a comment on one of Cecil’s columns, I’ll move this thread to General Questions, our forum for factual queries.
bibliophage
moderator CCC
Probably, depending on the size of the fire.
Fire needs fuel, oxygen, and heat. Liquid Nitrogen would do a pretty good job of removing heat.
And also a pretty good job of removing oxygen.
Can’t think of a reason it wouldn’t. If it stayed a liquid then it would act like water. If it converted to gas it would still smother the fire. Both states would deprive the fuel of oxygen, and possibly heat. All this assumes enough liquid nitrogen since you can put out a house fire with a blanket (a really big blanket.)
You would have a hard time keeping the nitrogen in a liquid state.
May times while waiting for a part to cool in liquid nitrogen we would have time to play:D.
Just to see how far into the container we could lower a burning match, burning cigarette, before the nitrogen would displace the O2, and on the ground around the container while the gas spills out.
I have thought introducing liquid nitrogen into a garbage dump (years back) would be effective in controlling the vermin.
It’s used to put out oilwell blowouts. It works well on the smaller ones as well.
That depends on what is burning. Magnesium metal will burn in pure nitrogen to produce magnesium nitride. Aluminum will also burn in N[sub]2[/sub], but iron will not.
Depending on the conditions of the fire, some of the nitrogen might itself react with the oxygen and produce nitrogen oxides, which you wouldn’t want to breathe.
there is some interest in using liquid nitrogen in putting out real fires and has been tested with a full scale fire engine http://www.innovations-report.de/html/berichte/biowissenschaften_chemie/bericht-34911.html. There are some sort of fun videos exploring the idea Frostbite Theater - Liquid Oxygen and Fire! http://www.youtube.com/watch?v=Yex063_Fblk
hmm there is always lots of nitrogen in the air so I doubt whether this is really a problem
Also, even if some things can react with nitrogen, they’ll probably do so a lot less energetically than with oxygen.
Well, I know car engines can produce a certain amount of nitrogen oxides. Maybe that’s because the reaction is occurring under pressure? I don’t really know what conditions cause it to happen.
… or carbon dioxide.
Nitrogen gas is one of the most stable molecules around. It’s notoriously difficult to split apart thanks to its triple bond. That’s why fertilizers are used to get nitrogen into plants in a usable form. That’s also why so many explosives are nitrogen based. They release nitrogen gas, and in dropping down to that low energy level, they release lots of heat. Anyway, I don’t think you’re going to get a lot of dangerous nitrogen species under most conditions.
The magnesium nitrogen reaction is weak enough that I suspect enough liquid nitrogem will cool it down to not reacting. I don’t even know that magnesium can react with nitrogen in it’s liquid state. Nitrogen oxides require oxygen which will be quickly dispersed by the expanding nitrogen. You may initially get some nitrogen oxides, but not a lot.
Generally, I think liquid nitrogen would be very good at putting out most fires if you had enough of it. Depending on the size of the room and fire, I wonder if suffocation might be a hazard.
Sort of. The main determinants of how NOx forms in combustion are a combination of factors, involving such things as stoichiometry, turbulence, temperature and time. Temperature is probably by far the greatest of these factors for NOx production, with a spike at atmospheric pressures starting near the 2300F mark (note this varies due to many factors).
Liquid nitrogen dumped on a fire is unlikely IMO to produce a substantial amount of NOx due to the relatively low resulting temperature of the nitrogen.
Should work, both for cooling and as a barrier to oxygen, though nitrogen won’t work quite as well as carbon dioxide or other fire suppressant gases that work by displacing oxygen near the fire. Dedicated fire suppressants are going to be heavier than air so that they settle down on top of the fire rather than drifting away. Nitrogen is pretty much exactly the same weight as air, so it will disperse a little more quickly than Halon or equivalents.
Using liquid nitrogen, as stated in the OP, is also going to scatter whatever is burning as it flashes to a gas.
Plus, if the fire is big enough, you might get some hellacious overpressures.