All types of extinguisher require a basic inspection annually to check weight, externally validate the correct pressure, and find any signs of damage or corrosion. Cartridge extinguishers are to be opened up for internal inspection, and to have the weight of the cartridge tested. Labels must be inspected for legibility, and where possible, dip tubes, hoses and mechanisms must be tested for clear, free operation.
Water, wet chemical, foam, and powder extinguishers require a more detailed examination every five years, including a test discharge and recharge. On stored pressure extinguishers, this is the only opportunity to internally inspect for damage/corrosion.
Maintenance Inspection :
All types of extinguishers should be inspected at least once a year. The extinguisher is checked that it has the correct volume and pressure of extinguishing agent, that it is within the required hydrotest and internal maintenance intervals, that it is in good condition, and that all external parts are still serviceable
Water - annually (some states) or 5 years (NFPA 10, 2010 edition)
Foam - every 3 years
Wet chemical, and CO2 - every 5 years
Dry chemical and dry powder- every 6 years
Halon and clean agents - every 6 years.
Cartridge-operated dry chemical or dry powder - annually
Stored-pressure dry chemical mounted on vehicles - annuall