Vapor cloud explosion experimental research

This chapter is organized as follows. First, an overview of experimental research is presented. Experimental research has focused on identifying deflagration-enhancing mechanisms in vapor cloud explosions and on uncovering the conditions for a direct initiation of a vapor cloud detonation. 

At first glance, the science of vapor cloud explosions as reported in the literature seems rather confusing. In the past, ostensibly similar incidents produced extremely different blast effects. The reasons for these disparities were not understood at the time. Consequently, experimental research on vapor cloud explosions was directed toward learning the conditions and mechanisms by which slow, laminar, premixed combustion develops into a fast, explosive, and blast-generating process. Treating experimental research chronologically is, therefore, a far from systematic approach and would tend to confuse rather than clarify. 

Because the major causes of blast generation in vapor cloud explosions are reasonably well understood today, we can approach the overview of experimental research more systematically by treating and interpreting the experiments in groups of roughly similar arrangements. Furthermore, some attention is given to experimental research into the conditions necessary for direct initiation of a detonation of a vapor cloud and the conditions necessary to sustain such a detonation. 

Experimental research has shown that a vapor cloud explosion can be described as a process of combustion-driven expansion flow with the turbulent structure of the flow acting as a positive feedback mechanism. Combustion, turbulence, and gas dynamics in this complicated process are closely interrelated. Computational research has explored the theoretical relations among burning speed, flame speed, combustion rates, geometry, and gas dynamics in gas explosions. 

Hasegawa, K., and K. Sato 1987. Experimental investigation of unconfined vapor cloud explosions and hydrocarbons. Technical Memorandum No. 16, Fire Research Institute, Tokyo. 

Research on water explosion inhibiting systems is providing an avenue of future protection possibilities against vapor cloud explosions. British Gas experimentation on the mitigation of explosions by water sprays, shows that flame speeds of an explosion may be reduced by this method. The British Gas research indicates that small droplet spray systems can act to reduce the rate of flame speed acceleration and therefore the consequential damage that could be produced. Normal water deluge systems appear to produce too large a droplet size to be effective in explosion flame speed retardation and may increase the air turbulence in the areas. 

Previous studies of vapor cloud explosions (VCE) have used a correlation between the mass of a gas in the cloud and the equivalent mass of TNT to predict explosion overpressures. This was thought to have conservative results, but past research evidence indicates this approach was not accurate to natural gas in air mixtures. The TNT models did not correlate well in the areas near the point of ignition, and generally overestimated the level of overpressure in the near field. Experiments on methane explosions in unconfined areas have indicated a maximum overpressure of 0.2 bar (3.0psio). This overpressure then decays with distance. Current propriety computer modeling programs have been improved to simulate real gas and air explosions from both historical and experimental evidence. 

Research on water explosion inhibiting systems is providing an avenue for future protection possibilities against vapor cloud explosions. Industry experimentation on the mitigation of explosions by water sprays... 

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