(11a) Suppression of Overpressure during a Vapor Cloud Explosion –

Suppression of Overpressure During a Vapor Cloud Explosion –

a New Approach

Abstract

Some of the most severe accidents in the history of the process industry have been vapor cloud explosions (VCE). The pressure waves created by VCE's can cause damage to buildings over large distances and can harm people inside these buildings.  A concept has been developed that has the potential to reduce the maximum overpressure generated by large VCE’s.

Explosion tests have been conducted on a 95 m³ testing facility to demonstrate the validity of the underlying hypothesis. Within the test rig, congestion was created by 784 vertical tubes arranged in a square pattern. The concept foresees the initiation of multiple counter fires within a vapor cloud immediately after ignition has occurred, but before the flame front can accelerate to a critical speed.

The experiments comprised the simultaneous ignition of the vapor-air mixture within the test rig at multiple locations. Compared to single point ignition, the resulting explosion pressures were reduced by a factor of two or more. In addition, directional pressure wave effects associated with ignition at one side of the rig were eliminated.

The results show that it is possible to substantially reduce the severity of a vapor cloud explosion by splitting up the explosion into multiple smaller vapor cloud fires and to consume the bulk of the fuel before the flame front arrives from the original point of ignition.

Application of this concept may be more attractive than other options for mitigating VCE damage to buildings if devices which can rapidly detect an incipient flame in a vapor cloud  and also rapidly initiate the secondary flames can be successfully demonstrated.

Authors: Norbert Baron, Chris R. Buchwald

Company: ExxonMobil Research & Engineering