EXTERNAL PUBLICATIONS

SUMMARY

The Health and Safety Executive (HSE) uses gas dispersion modelling in its assessment of the hazards and risks posed by toxic and flammable substances stored at major hazards sites. To update its dispersion modelling capability, HSE recently commissioned ESR Technology to develop a new version of the gas dispersion model DRIFT (Dispersion of Releases Involving Flammables or Toxics). The new version of the model, DRIFT 3, includes a significant number of modelling enhancements over the version of DRIFT previously used within HSE (DRIFT 2.31). These include the extension of the model to treat buoyant plumes and time varying releases. Prior to DRIFT 3 being adopted for use by HSE, it must undergo thorough evaluation and assessment for a range of release scenarios.

This report considers the dispersion of vapour from pools of toxic liquids, such as methyl iodide and ethylene oxide, and presents an assessment of the performance of DRIFT 3.6.4 for modelling such release scenarios. Sensitivity tests have shown that DRIFT 3.6.4 works reliably for the types of toxic pool scenario typically used by HSE to assess Hazardous Substances Consent applications and set Land Use Planning zones around major hazards sites.

As a result of this work and accompanying evaluation studies (see Research Report RR1100), DRIFT 3.6.4 has been adopted by HSE to model the dispersion of vapour evolved from pools of toxic liquids.

This Research 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 authors and do not necessarily reflect HSE policy.