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Operational Awareness for Advanced Firefighters & Fire Behaviour Analysts | ||||||
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On a day of elevated FDI, the lifting condensation level, also called the cloud base, may be over 5km above the ground. In general terms the burning of vegetation releases a lot of water vapour which may form a cloud within the plume, called a pyro-cumulus or pyro-cu. A rising smoke plume will resist mixing with the air that it passes through for a distance broadly equal to the flaming depth. If the resistance is still occurring when the cloud base is reached, then a fire thunderstorm may result. Such a cloud is called pyro-cumulonimbus or pyro-Cb. Pyro-Cbs are dominated by the heat released as the water vapour condenses and freezes (the latent heat). This may be up to three times the heat release of the fire. This is now a coupled fire-atmosphere event, and its movement is determined by the upper level winds pushing on the plume. Within the plume, conditions are extremely violent and disconnected from the prevailing weather outside. Fire suppression is impossible and a Red Flag Warning (Plume-driven fire) must be issued. . |