5-Year Pressure Testing
It is the requirement of AS1851 that fire extinguishers get pressure tested every 5-years. This process basically means that added pressure is applied to the vessel in order to determine the integrity of the fire extinguisher vessel. In some extreme cases the vessel will rupture if it has week points in the metal.
Fire extinguishers generally have a high internal pressure as a result of gas injected into the vessel (the gas is normally the discharging agent). In normal everyday operating conditions the fire extinguisher may be knocked off the wall where it is mounted to or be dropped during transport. Under these situations the operator needs to be safe from cylinder explosions caused by ruptured metal. Thus the reason for the 5-year pressure test.