One reason is that, over time, the seal on the neck will weaken and allow compressed gas to escape. Extinguishers that have lost much of their pressure will not operate. Pressure within an extinguisher can be conveniently checked through a pressure gauge. “ABC” class extinguishers (ammonium phosphate) have the tendency to fail due to solidification of the chemical in the canister base.

Homeowners and inspectors can delay this process by periodically shaking the extinguisher. Expensive extinguishers that have expired, especially those designed for commercial use, can be refilled and resealed by companies who specialize in this service. Inexpensive models are disposable.Unfortunately, an expiration date cannot be fully trusted and there is no foolproof way to know if an extinguisher is no longer functional. Due to the extremely destructive potential of fires and the relatively low cost of extinguishers, it is advisable to replace or recharge questionable extinguishers.