how to extinguish a fire of sodium, lithium or potassium?

what is the best way to extinguish a fire of one the alkali metals such as sodium, lithium or potassium?
water would not be a good idea as all of these burn it, but which substance would be?
nitrogen?
carbon dioxide?

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Sand.

You could use a CO2[sub]2[/sub] extinguisher; N[sub]2[/sub] extinguishers are not common. The reactions of alkali metals with H[sub]2[/sub]O are increasingly violent, but the greatest danger is not from flames (Li is a rather slow reaction and they do not become truly violent until Rb and Cs) but rather the products of the reactions, LiOH, NaOH, and KOH which are all caustic.

that is because hydroxides of alkali metals burn your skin for example, right?

would it make sense to neutralize hydroxides with acids?

That wouldn't be favourable as when acids (nomatter what, even citric acid in oranges) touch strong alkalis (KOH, for example), strong heat is released and may cause even greater fire danger than the metal itself.

LiOH is used as a depilatory, but yes, the alkali hydroxides react with the oils in skin and "burn" it; neutralizing with acid would be a good idea (the CO[sub]2[/sub] acts as an acid and forming carbonates. Since the entire reaction is aqueous, fire isn't an issue, but remember that when something hits a liquid, it will splatter. That's why good lab technique is ALWAYS pour caustic materials into the neutral or less caustic materials. Spraying hydroxides with CO[sub]2[/sub] extinguishers is likely to splatter NaOH all over the inept, smothering it with sand is the best solution.

People often overestimate the amount of damage that chemicals can cause. In my own experience, the only serious chemical burn I ever saw happened when my younger brother sat on my lab table in a watchglass of nitric acid and copper nitrate and then afraid to tell anyone kept quite until the acid ate through his pants and burned his butt. My eighth grade chemistry teacher used to blow glass and like fire-walkers handled the red hot glass with only his fingers.

If you only take the glass for a few seconds or so, it won't be a problem as both your body and glass are bad conductors of heat.

[quote="Martin17"]You could use a CO2[sub]2[/sub] extinguisher;...[/quote]
From the sign on the door to the DP lab:
[color=red][size=18][b]NEVER USE CO[sub]2[/sub] TO EXTINGUISH A METAL FIRE[/b][/size][/color]

So yea, use sand. Or cover it with something if that's possible. Better still, don't let it catch fire ;)

Using a CO2 fire

Using a [url=http://www.fireprotectiononline.co.uk/co2-fire-extinguishers/]CO2 fire extinguisher[/url] on a metal fire is definitely a bad idea...

Because common alkali and alkaline earth metals react with carbon dioxide.

4Mg + CO2 ---> 2MgO + Mg2C

What about oil?...

:?:

The heat produced by the fire will make the oil catch fire by itself.

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