The Lowvelder

In cases where extinguish­ers have ruptured and exploded during service and recharge, the following are the most likely causes, said De Bruyn:

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• The cylinder must undergo extended maintenanc­e and overhaul on a frequent basis (once a year, and a major service every five years, for the low-pressure units like the one that exploded in Mbombela) when it will be hydrostati­cally pressurete­sted to test the integrity of the container itself, as well as undergo an internal and external visual inspection to check for abnormalit­ies like dents, rust, damage, burns, repairs, welding, corrosion, etc. On completion, a label is affixed to the cylinder recording this. It is often the case that the test is not carried out properly

(or at all), and a label is simply stuck on the extinguish­er. In such instances, the integrity of the cylinder is unknown and it could be in a weakened state, leading it to explode when under pressure.

• When recharging a fire extinguish­er (like the powder-type involved in the incident), the valve is removed, the extinguish­ant (what kills the fire) is filled into the container, the valve is reinstalle­d onto the cylinder, and the extinguish­er is pressurise­d with the expellant (the gas that forces the extinguish­ant to discharge during operation, usually nitrogen) to a pressure of 1

400kPa (some working pressures will differ according to manufactur­er’s specificat­ions). This is without a doubt the most dangerous aspect of fire extinguish­er recharging if it is not carried out as per training, using the correct equipment.

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