An Assessment of the Appropriateness of the Prescribed “Safe Distances” for Siting Hazardous Process Units to Prevent Domino Effect

Abstract

One of the most dangerous consequences of an equipment failure in process industries resulting in a fire and/or explosion is the triggering off of the “domino effect” or “chain of accidents.” An accident in a unit may trigger an accident in another unit which, in turn, may lead to yet other accidents. To prevent such an occurance, it is imperative that hazardous units are kept safe distances away from each other. Of the types of accidents that can occur in chemical process industries, the boiling liquid expanding vapor explosion (BLEVE) is perhaps the most destructive of the forms of accidental explosions that can occur during the manufacture, storage, or transportation of chemicals in a pressure-liquefied state. The resulting blast wave, missiles, and fire or toxic release can cause great damage to life and property. There are several standards and codes which prescribe minimum safe distances to be maintained between equipment to prevent the domino effect from occurring. Of these the code prescribed by the National Fire Protection Agency (NFPA), USA, is among the ones most widely adopted for locating hazardous units. This paper evaluates the effectives of the safe distances prescribed by the NFPA 58 code in preventing a BLEVE in one vessel from causing other vessels and nearby structures to fail. The study reveals that the distances presented by NFPA are not sufficient to prevent the domino effect when the primary accident is a BLEVE.