Fire and explosion hazards are inherent to any fuel storage system. The National Fire Protection Association has therefore established strict guidelines on fire and explosion protection of these systems. ASTs are exposed to fluctuating temperatures and vehicular traffic and are thus more hazardous, from a fire and explosion standpoint, than USTs.
Fuels expand and volatilize when heated and contract and condense when cooled. Expansion can cause high pressures in a poorly vented tank. ASTs require larger vents than USTs. The National Fire Protection Association provides minimum ventilation requirements for ASTs. Shading ASTs reduces daily temperature fluctuations in tanks. If properly vented and shaded, the explosion hazards associated with fuel expansion are similar for ASTs and USTs.
A vehicle colliding with an AST can also cause a fire, explosion, or leak that may lead to a fire or explosion. A secondary containment structure designed to contain spills and leaks from an AST also provides a barrier against collisions. Fuel pumps and dispensing equipment for all fuel tanks are placed above grade and can be struck by vehicles. An UST only provides a marginal degree of protection from collisions compared to a diked AST system. Fuel dispensing system leaks pose a fire hazard.
Smoking and open flames should be prohibited near all fuel storage and dispensing systems. No smoking signs must be posted. The debris and fireball from the explosion of an UST would cover a smaller area than that from the explosion of an AST. Therefore, required separation distances to property lines and buildings are smaller for USTs than for ASTs. Neither tank type provides an appreciable degree of protection for persons in the immediate vicinity of a tank explosion.
Petroleum products mixing with fertilizers and pesticides could potentially lead to explosive mixtures and fumes. Fuel storage tanks must be kept separate from pesticide and fertilizer tanks. Such tanks are not allowed to share secondary containment areas.
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