Yes they are indeed fire extinguishers. It is standard AF
procedure to have a bottle (or bottles) with any parked airplane. The fire fighting agent is pressurized with nitrogen over the agent, and pushes the agent out when the hose is charged and nozzle opened. The stuff used to be CB
, some sort of nasty toxic crap. Then it changed to halon. That went away due to the greenhouse gas isssue. I really don't know what the stuff is now. I think it is a non greenhouse halon type of agent. You have about 30 seconds of flow time per bottle. If used correctly, can put out a lot of fire. They are always a good thing to hang a shirt, lean on, etc. I always take time to read the grafitti that is written on each one, some bottles have some extensive world travels! Also if you don't get caught, can be used as a field expedient step ladder. There is your useless facts for today!