EXTERNAL PUBLICATIONS

SUMMARY

This study concerns the methodology used by MSDU, HSE in assessing Land Use Planning cases (LUP) near Hazardous Installations storing LPG and presenting a Vapour Cloud Explosion (VCE) hazard. The work is also relevant to all risk assessment and consequence models that are used to assess the hazard posed by blast.

The methodology currently used by MSDU assumes that the blast propagates without interaction with any buildings or terrain features that may lie between the explosion source and the proposed site. Thus the estimate of the incident peak positive overpressure is likely to be conservative. The probability of fatality is then inferred from the peak positive overpressure using war-time data. This allows the vulnerability of the public to be assessed from which consultation distance and hazard zone boundaries are determined.

The leading shock wave is the highest frequency component of the blast wave and will, therefore, be the most affected by interaction with obstacles. A revised methodology which takes account of obstacle interaction will, therefore, exhibit sheltering effects. Thus there are situations where buildings that lie between the explosion source and the proposed site will provide substantial sheltering in the region of the proposed construction. In such situations it is conceivable that the existing methodology places the hazard zone boundaries at substantially larger distances than is required to maintain an acceptable probability of fatality. A revised methodology, therefore, which takes sheltering into account could potentially free-up substantial areas of land around existing and future hazardous installations.

This report and the work it describes were funded by the Health and Safety Executive (HSE). Its contents, including any opinions and/or conclusions expressed, are those of the author(s) alone and do not necessarily reflect HSE policy