A3 Self-powered firestorms

Topic

The process of urban destruction has established how secondary fires spread across a damaged zone. This anomaly emerges when the density and extent of simultaneous fire sources surpass a certain threshold: the hot air rising from so many sources at once creates a suction current that draws fresh air from the periphery toward the center; this suction feeds the fire with additional oxygen, generating a self-sustaining wind system that reaches gale-force speeds and temperatures far exceeding those of a conventional urban fire.

This renders the firestorm a phenomenon qualitatively distinct from the ordinary fire described by standard processes: whereas a common fire can be fought from the outside or burns out once the fuel in its immediate vicinity is exhausted, this type of storm is self-feeding—the more the fire burns, the more suction it generates, and the more suction it generates, the more oxygen it receives. Consequently, it becomes extremely difficult to control as long as fuel remains available throughout the affected area, rather than just at the original ignition point.

For this reason, in a scenario where fire density exceeds a critical threshold, shelter zones cannot be planned based solely on structural resistance to mechanical damage; becoming trapped within an area where such a storm develops presents a distinct and additional risk—which is why early evacuation, rather than sheltering in place, is recommended for certain zones with high fuel density.

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