On the Potential of Mitigating Vapour Cloud Explosions Using Flame Inhibitors

Very few measures are taken to mitigate the possible consequences of vapour cloud explosions. The main attention is given to prediction of the consequences, which is used to consider strengthening structurally or re-locate occupied buildings such as control rooms. However little is undertaken to limit the consequences of vapour cloud explosions directly such as by limiting the maximum size of congested areas (in relation to the reactivity of the fuel), introducing physical (soft) barriers to limit the size of the flammable cloud or by directly affecting affecting flame propagation by e.g. the introduction of water deluge upon confirmed gas detection. The latter two measures are successfully applied on larger offshore production platforms, especially in the North Sea. The use of water in landbased process facilities appears difficult due to the large amounts of water necessary.

Recently an alternative suggestion was made, viz. the use of flame inhibitors by either injection into the flame directly (post-ignition detection) or by injection into the developing flammable gas cloud upon pre-ignition gas detection.

The potential of the use of flame inhibitors was investigated experimentally on both laboratory scale (in a 20 l sphere) and on medium scale in a 50 m3 congested vented enclosure. The 20 l sphere experiments are used to derive fundamental combustion properties in the presence of flame inhibitors. The medium-scale experiments investigated the potential of using this technology in reality both as a pre- and post-ignition agent.

Parameters that were varied include fuel concentration, fuel type, inhibitor type and inhibitor concentration.

The present paper aims at giving an overview of the experimental results, highlighting the potential of the use of flame inhibitors limiting the possible consequences of vapour cloud explosions.

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