Firestorms

Abstract

Quantitative criteria are sought for onset of firestorms, severe stationary (non-propagating) holocausts arising via merger of fires from multiple simultaneous ignitions in a heavily fuel-laden urban environment. Within an hour, surface-level radial inflow from all directions sustains a large-diameter convective column that eventually reaches altitude of about 10 km (e.g., Hamburg, Dresden, Hiroshima). As the firestorm achieves peak intensity (a couple of hours after the ignitions), inflow speeds are inferred to attain 25–50 m/s; typically 12 km2 are reduced to ashes, before winds relax to ambient levels in six-to-nine hours. Here the firestorm is interpreted to be a mesocyclone (rotating severe local storm). Even with exceedingly large heat release sustained over a concentrated area, in the presence of a very nearly autoconvectively unstable atmospheric stratification, onset of vigorous swirling on the scale of 2 hrs requires more than concentration of circulation associated with the rotation of the earth; rather, a preexisting, if weak, circulation appears necessary for firestorm cyclogenesis.

Fire Induced Flow Field - Theory And Experiment

“…Here, the primary feature of interest is the fire induced convection column covering many kilometers in the horizontal directions and extending to the height of the atmosphere. Existing analyses of this phenomenon, whether analytical in nature (2), (6) or based on detailed time dependent numerical simulations (7)- (9), have represented the fires themselves as a smooth continuous source of heat.…”

Interactions and Spreading of Adjacent Large Area Fires

“…Computed ground level flows are 10 m/s at the fire perimeter ( [Carrier, Fendell, and Feldman, 1985]. The caloric equivalent of those combustibles is 1.86 .…”

Studies in Urban-Scale-Fire Thermohydrodynamics

“…The results that emerge suggest strongly that, even for a fire whose fuel bed has the scale and "loading" of a major city, the plume is confined largely to the troposphere, except possibly in cases where very humid low level air would strongly augment the liftina process ( a mechanism which has not been incorporated herein), and/or in cases where a strong, meteorological low-pressure feature was already centered near the city when the fire began (Carrier and Fendell 1983). …”