(86a) How Effective Are Safety Gaps at Mitigating Explosions: Largest Scale Testing of Safety Gaps to Prevent Ddts

A large vapor cloud explosion (VCE) followed by a fire is one of the most dangerous and high consequence events that can occur at petrochemical facilities. As the size and complexity of facilities increase, designs must consider the potential adverse effects associated with vapor cloud explosions in large congested areas. In fact, if a vapor cloud within a congested region is large enough, the resulting flame or deflagration can continually accelerate within this region and ultimately reach the point where the deflagration can transition to a more devastating detonation or deflagration-to-detonation transition (DDT). As the consequences of DDTs can be orders of magnitude larger than deflagrations, facilities that are at risk need to implement mitigation measures to prevent flames from continuously accelerating in these regions. One method is to provide “safety gaps” or open areas (gaps) within the congested region to interrupt the flame acceleration and provide regions where the flame will actually slow down prior to arriving at the next congested area. The key to this design is to provide a wide enough gap or region between the congested areas so that the flame exiting the first region will decelerate or slow down to adequate levels prior to arriving at the second region.

The problem is that almost all of the safety gap tests have been performed with narrow congested regions where the width is on the order of 3 meters. Unfortunately, most practical congested areas in petrochemical facilities are much wider than 3 meters and recent tests have shown that wider congested areas may be more susceptible to DDTs. Hence, the present paper will present preliminary results of large-scale testing. The net goal of the study is to assess explosion development in both narrow (~3.5 m) and wide (~7 m) congested areas, and the effectiveness of safety gaps in mitigating DDTs. The results will be a valuable reference to facilities owners and designers in helping to provide inherently safer designs at practical scales.