Question

Why is carbon dioxide commonly used in fire extinguishers?

Answer 1

`"(i) The gas comes out of the can COLD;"`

`"(ii) The gas is fully oxidized, and thus reasonably inert."`

Explanation:

I think, and you check this, that you are not supposed to use carbon dioxide extinguishers with metal fires. That is the carbon dioxide would react with say an alkali metal, and might cause problems. This being said, I have seen carbon dioxide extinguishers successfully used in these scenarios.

Now clearly you would not use a water based extinguisher with an alkali metal fire (why not?), but in the event of a fire in a laboratory, you will not have too much time to consider your options, and are too busy having kittens.

The first consideration is your own safety, and then the safety of your colleagues. If in doubt, get out of there, and ensure your colleagues get out of there. If you think you can tackle a fire, consider also the utility of a bucket of sand (very useful), or (EVEN BETTER) a dewar of liquid nitrogen, which you could pour on the flames.

The liquid nitrogen is very useful from the consideration of clean up. Of course, after the liquid nitrogen boils off, the flame might start again, so be prepared. (I always liked the liquid nitrogen option, because it boils off pdq and the eventual clean up task is not so messy!). Fire extinguishers cause an unholy mess upon discharge, and guess who is going to clean it up?

Chemistry departments often have lectures from officers of the campus fire department (and they often get to know mavericks and cowboys VERY well!). They often do demonstrations (with for instance a `CO_2` extinguisher), and are very good sources of practical knowledge. Try to take advantage of these opportunities before having to call the fire department in earnest.