I work on fire extinguishers, and I've just had something happen I can't explain. A customer of mine had a pretty bad fire and the fire extinguisher mounted to a forklift (which burned) exploded--blew out the side of the extinguisher.

 

Fire extinguishers are pressurized with nitrogen to 195 psi. Assuming that the o-rings on either the valve stem and/or the neck did not melt first and allow the pressure to escape, and knowing that there is no "escape valve" on a fire extinguisher, and assuming that the aluminum head did not melt prior to the steel shell warping and allowing the pressure to escape--all of which do not seem to have happened......the question is: How hot would a fire extinguisher have to get for the nitrogen inside to expand sufficiently to rupture the cylinder?

I'm thinking this may have been caused by wear.

 

Would need the manufacturer's information to work back from maximum pressure to a temperature.

Edited November 29, 201312 yr by Endy0816

It's a difficult question.

You can calculate the pressure at any given temperature quite easily, but the steel will weaken a lot as it gets hotter. That second factor is difficult to guess.

 

What you need is an expert in failure analysis.

Curves exist for many steel composition giving the proof stress versus the temperature. More often so for steel designed to work hot. A typical Fe-Mn-C alloy looses much strength at 500°C, well attained within a good fire over some time.

 

The same reason lets steel buildings collapse during a bad fire.

In very rough terms, at 500C the thing will be red hot, the pressure will have trebbled and the steel will have lost something like 20% of its strength.* The aluminium will also have weakened considerably, but it might not have been working so near it's limits in the first place.

 

Based on this

http://ro.uow.edu.au/cgi/viewcontent.cgi?article=1345&context=engpapers