(88a) Don't Believe the Hype: Using Case Studies and Experimental Evidence to Show why the HSE is Wrong about Excluding DDTs

A recent report by the UK's Health and Safety Executive postulated that severe explosions can propagate at subsonic speeds but generate overpressures of several bar in open areas and this "new" type of explosion is episodic in nature. The HSE paper based their findings on a specific interpretation of historical data and "empirical evidence" from previous incidents and selected experimental data. They indicate that their results should guide plant design and risk assessment. The report fails to take account of key evidence from recent large scale experimental studies and incident investigations in proposing a hypothetical explosion mechanism over those that are known to occur and are well understood. This has the potential to significantly misdirect efforts to manage such events.
This first part of the paper will review a number of incidents and demonstrate that each of these incidents can indeed be explained by fast deflagrations or transition to detonations, in complete contradiction to the HSE findings. These will include findings from Buncefield, Jaipur, and the CAPECO explosions. The results found at the incident sites will be directly compared against results from recent DDT work and the resulting damage. In addition, new experimental results will be presented that further support the idea that explosions can transition more easily than expected when the "width" of the region plays a role in impeding the side venting of the deflagration event.
The second part of the paper will present a novel technique for determining the DDT transition velocity from high-speed video footage of experiments performed at large scales (like those found at chemical facilities). Flame position versus time from an advanced tracking routine will be presented in this paper. This technique allows for significantly more accurate results and insight into DDT because the data isn’t limited to the fixed positions of fixed sensors (e.g., ion pins). This new method revealed that the transition to detonation may occur at significantly different velocities under the different conditions of these experimental campaigns, which included: (1) the RPSEA campaign, where large-scale tests with near stoichiometric propane-air mixtures ignited within a moderately low-congestion test rig made up of rigid steel beams; and (2) DNV GL Spadeadam Testing and Research in the UK to help understand the cause of the explosion severity observed at the Buncefield incident, including the effects of dense vegetation.