It’s a structural test of the extinguisher’s cylinder, checking whether the shell can safely hold pressure well above its normal operating level.
The cylinder is emptied, pressurized to one and a half times its rated working pressure, and monitored for expansion or leaks. This is separate from the annual inspection or 6-year maintenance, testing the physical integrity of the shell itself rather than the extinguisher’s internal components or charge.
The interval depends on the cylinder type, generally every 5 years for water, foam, and CO2 units, and every 12 years for stored-pressure dry chemical units.
Exact intervals vary by manufacturer and construction, which is why the specific requirement gets confirmed against the stamped manufacture date during service rather than assumed from a general rule of thumb.
A cylinder that fails hydrostatic testing is condemned and removed from service immediately, with no partial pass or repair option.
This isn’t a deficiency that gets patched. If the shell can’t safely hold pressure, the unit is replaced rather than returned to service under any circumstances.
We’ll check your units’ manufacture dates and confirm what’s actually due.