Suppression options
a fire and discharging the suppressant directly onto a fire at the equipment level. Examples of places where such suppression is beneficial include the following: •
shredders/bag breakers
• hydraulic power units •
trommels
• electrical panels • on conveyors • under conveyors, platforms and picking cabins
Shredders/bag breakers At waste handling sites where shredders or bag breakers are installed, these are the most common item of equipment to experience fires. This is due to the fact that the operators who are loading the waste into the hopper of a shredder or bag breaker cannot always separate out gas canisters, aerosols or batteries. In addition, discarded hot barbecues, hot coals or similar hot materials can remain hidden deep within a pile of mixed waste and do not reveal themselves until the pile is broken out, lifted in a loader and dropped into a hopper. Operators work tirelessly to prevent this and to separate out obvious fire and explosion hazards, but things do slip through from time to time. Fires on shredders or breakers will spread inside the hopper, through into the rotating equipment and out onto the exit conveyor. The most effective fire suppression for a
shredder or bag breaker is to have flame detectors watching over the hopper and looking down the exit conveyor to detect hot spots, to raise the alarm and to stop the exit conveyor through a machine interlock. Installing waterspray or watermist deluge
nozzles over the hopper will douse the fire from above, whilst nozzles on the exit conveyor close to the shredder mouth will extinguish burning material as it falls onto the conveyor. Some fires in shredders have been rather fierce. If a gas cylinder gets cracked inside the body of the shredder/ breaker, it will create a mini ‘pop’ that ignites much of the mixed waste in the hopper simultaneously. This scenario becomes a large fire within seconds and cannot be tackled easily by firefighters. The key therefore is to detect the presence of a hot spot or fire as soon as possible, to shut down the machinery and exit conveyor immediately, and to apply firewater, foam or suppressant agent liberally for an extended period. The design of the fire suppression system should permit activation within seconds, and should swamp the hopper contents and the exit conveyor for 15 minutes at least. Deluge waterspray systems connected to traditional sprinkler fire pumps can operate for hours discharging several hundred litres per minute if necessary; whereas bespoke watermist systems should be designed for at least 30 minutes of discharge capacity
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www.frmjournal.com NOVEMBER 2018
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