For some time I have been wanting to train my wife on the use of dry chemical fire extinguishers. I have a never used dry chemical fire extinguisher that is dated 1984. First, I want to explain a bit about dry chemical fire extinguishers.
They normally consist of monoammonium phosphate powder inside a pressurized container. You merely pull the pin, point the hose at the base of the flames and squeeze the handle. They work well, but they do have a few things that you should watch for.
Always get a dry chemical fire extinguisher with a gauge that shows the pressure. I personally like ones that are five pounds or larger. They have a rating on the label that shows how much fire they are rated to put out. Always get one that is marked 3A 10BC or larger.
If an extinguisher is placed in a commercial building, they have to be serviced once a year. During a normal servicing the tech will bleed off the pressure, open the extinguisher and sift the powder. This is to make sure that the powder has not settled to the bottom of the extinguisher and hardened. This will often happen to an extinguisher that has been in a vehicle. This is caused by vibration.
If the powder hardens, only the gas will come out and no powder, the extinguisher will not work. Now the one I am about to let my wife use is dated 4/84 which is just less that 30 years old. Now this one has never been serviced other than that every few months I would turn it over and shake it or tap it with something hard to try to keep the powder loose. This extinguisher has always been in the house and never in a vehicle. It is one of several I have and I recently decided that I could no longer trust this one.
When we took it outside, I was not sure if it would still function. My wife pulled the pin, squeezed the handle and it worked like new. Still I would not recommend that you keep an extinguisher this long, I should have replaced it years ago. If you have any that are rusty or damaged, replace them right away. But if you have any old ones, at least check the gauge and see if the pressure is still up, then turn them upside down and shake them and see if you can feel the powder moving.
You can also take them to a fire extinguisher company and have them serviced, but this is often more expensive than buying a new one. If you have any that are being taken out of service, use them for training.