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Prevention, Control and Mitigation of Explosions

Background

A wide variety of measures may be employed to prevent, control and mitigate the effects of explosions. Whilst the emphasis should always be on explosion prevention (e.g. through prevention of leaks or elimination of ignition sources), the possibility of accumulation and subsequent ignition of a flammable hydrocarbon-air mixture cannot always be eliminated. Therefore control and mitigation measures may additionally be required.

Current position

Current standards for the selection and specification of measures to prevent, control and mitigate the effects of explosions comprise:

UK

International

Corporate

The Interim Guidance Notes have been updated (above), whilst the API RP2A standard has been replaced with a new standard Design and Assessment of Offshore Structures for Fire and Blast'. The recent BP guidance (see above) forms the basis for the new API standard.'

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Industry practice

Since the Piper Alpha disaster installations in the UK sector of the North Sea have undergone significant modification to prevent, control and mitigate the effects of explosions. From Safety Cases reviewed recently, significant modifications continue to be implemented as the understanding of explosion hazards improves. For new installations a wide variety of measures are being employed with the emphasis on measures to prevent explosions or reduce explosion overpressures through good ventilation and installation layout.

Key issues

Explosion development barriers (e.g. to control pressure piling effects or turbulence generation).

Some of these types of barrier have been implemented, e.g. 'weak wall' gas barriers and membrane gas barriers, whilst others are only at the concept stage. Some of the outstanding technical issues include the choice of materials for the barrier, the impact of the barrier during and after collapse, the impact on natural ventilation and consideration of equipment layout conducive to the implementation of barrier methods.

Water mist suppression systems utilising superheated water have been tested at medium scale under partial funding from HSE. This has demonstrated that such devices can suppress a developed explosion in a partially-confined module. However the proponents of this method recommend that a greater understanding of the interaction of mists and flames is obtained and that further testing is undertaken with different geometries and scales. The question of effectiveness of initiation the system on gas cloud ignition is also outstanding.

The efficacy of blast-induced atomisation from water containers has been demonstrated at small scale. Further work is required to develop and then test a device at large scale. A key advantage of this system is that it is passive (no activation required). The outstanding concerns are that are that it does not mitigate the effects explosions within a module (i.e. acts at the end of a duct or module boundary) and that it represents an additional mitigation system with an associated maintenance requirement.

Strategy development issues

Scope of current guidance on explosion prevention, control and mitigation

Activation of water deluge on detection of gas

Emerging technologies

Industry adherence to existing guidance on the explosion prevention, control and mitigation

Updated 2012-12-13