Safety Assessment Program Evaluator Student Manual

CA Emergency Mgmt. Agency Safety Assessment Program Evaluator Manual April 2011Photo courtesy Cal EMAFigure 6-23 – Red-tagged house, 2010 San Bruno Explosion/Fire6.4 ExplosionsMost explosions historically have been accidental in nature, either occurring from a domestic gasleak or boiler mishap, or in industrial settings in the routine storage and handling of dangerouschemicals. A few explosions have been caused by terrorists and other criminals bent on politicalor financial gain. Regardless of how explosions may occur, the effects to structures are similar.Large explosions in urban settings can cause lateral forces to rack nearby buildings, anddepending on the degree of force, even at some distance from the center of the explosion (alsotermed the „ground zero‟). Structures that are not completely destroyed at the ground zero maybecome very unstable, being unsafe for anyone to approach and subject to imminent collapse.Projectiles can cause damage to other structures and set fires at great distances from the initialblast site. In addition, powerful explosions can generate seismic shock waves; if set off in abody of water, surface waves resembling tsunamis can spread damage to places far removedfrom the blast site. It is quite likely that there will be much to do for SAP evaluators after anexplosion disaster.Figure 6-24 shows a granary built of reinforced concrete that was blown apart in a dustexplosion. Flammable dusts present an explosion hazard when in the right fuel-to-air ratio and inthe presence of a spark or flame. Flammable dusts can include flour, paper or wood dust, oreven the dusts of certain metals.203