Studies in Urban-Scale-Fire Thermohydrodynamics
Technical rept. 22 Feb 1983-22 Feb 1984
TRW ELECTRONICS AND DEFENSE SECTOR REDONDO BEACH CA
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Incendiary effects of thermonuclear weapons on urban and wildland environments can involve multiple simultaneous ignitions in the presence of heavy loading of combustibles, blasted into strewn debris. Subsequent merger of fires from initially separated ignitions results in large-area fire. Generalization of conventional integral-type modeling of buoyant plumes to encompass strongly buoyant convection through a significant depth of the troposphere permits three items to be address 1 the limit on, and mechanism for, enhancement of entrainment into the lower, flaming portion of the plume 2 the plausible degree of necking in of the plume in the lower troposphere and 3 the height to which the plume rises found to be below the tropopause unless quite exceptional ambient conditions andor fire size hold. However, two special preexisting atmospheric conditions could alter the nature of the large- area fire significantly, and these are also examined by simple approximate analyses. First, preexistence of a well-developed atmospheric cyclone over the fire area could bring conservation-of-angular-momentum considerations to paramount importance criteria for onset of a combustion-heat-intensified cyclone firestorm are proposed. Second, preexistence of a strong sustained wind of fairly well-defined direction could permit the fire to propagate rapidly beyond the area encompassing the initial ignitions, with only an exhaustion of fuel, noteworthy change of weather conditions, andor significant topographic fire break terminating the flame spread.
- Safety Engineering