FOCUS
Suppression options
in the form of two discharges, which each last 15 minutes.
Hydraulic power units Hydraulic power units are present in numerous guises at waste handling facilities. The largest units are usually found on shredders, breakers and balers, but can also be present on numerous other items of equipment with moving parts. In themselves, hydraulic power packs have
a good reputation for reliability and with basic maintenance can operate trouble free for many years. However, the fire load of large hydraulic power packs can be several thousand litres of hydraulic oil. This oil when new will have a flashpoint of 250°C to 350°C, but this does reduce as the oil degrades. In normal operating conditions the presence of the oil inside the power pack and even some leakage onto the exterior or into the catchment tray is not normally a problem. With it operating under pressure, leaks in the hoses or at the fittings are not uncommon. Leaking oil only becomes a problem if a fire occurs nearby, such as in a waste pile, as the oil could become part of the fire, risking the involvement of the whole power pack. Pinprick holes in hoses, however, are much more problematic. These cause the oil to be atomised, and in this form the mini droplets of oil can be ignited at much lower temperatures by any nearby hot surface. Passing mobile plant with hot engines, for example, or trucks with hot exhausts,
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or nearby hot light fittings, can all become the ignition source. Fire suppression should be considered for hydraulic oil packs containing more than a few hundred litres. This can consist of low level automatic sprinklers positioned above the pack, but they should be hung beneath a solid ceiling so that the sprinkler heads can be relied upon to operate. However, sprinklers are relatively slow
to operate, and more effective systems would be flame detector activated deluge waterspray or watermist. The flame detector activation should trigger shutdown of the unit via a machine interlock at the same time as the fire alarm is sounded and the waterspray or watermist is released. If possible, large hydraulic units should
be enclosed within their own chambers. This not only protects the unit and its associated equipment from the harsh environment of a typical waste handling facility, but also allows containment of any leaking oil and far more effective fire detection and fire suppression. In enclosed spaces, watermist and
other clean agent fire suppression systems come into their own. They are designed to smother the fire to remove oxygen and cool the surfaces below ignition levels, and solid containment around the hydraulic power pack is ideal to maximise their effectiveness. Inside such an enclosure, fire detection would usually be standard heat detection, linear wire heat detection or aspirating fire detection
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