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

• 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.