EXTERNAL PUBLICATIONS

SUMMARY

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 commissioned ESR Technology to develop a new version of the gas dispersion model DRIFT. The new version, DRIFT 3, includes a significant number of modelling enhancements over the version previously used within HSE (DRIFT 2.31). These include the extension of the model to treat buoyant plumes and time varying releases. Before DRIFT 3 is adopted for use by HSE, it must undergo thorough evaluation and assessment for a range of release scenarios. The initial phases of the DRIFT 3 testing programme used DRIFT 3.6.4 and are described in reports RR1100 and RR1101. Further testing is described in four reports including this one: RR1165, RR1166, RR1167 and RR1168. The four reports cover the evaluation of the model and assessment for a range of scenarios using the enhanced version DRIFT 3.6.14.

This report describes an assessment of the performance of DRIFT 3.6.14 for modelling the dispersion of flashing instantaneous releases of toxic substances. Releases of toxic pressure-liquefied gases such as chlorine, sulphur dioxide and ammonia are considered, together with flashing heated releases from pressure vessels. These scenarios are typically used by HSE to assess Hazardous Substances Consent applications and set Land Use Planning zones around major hazards sites. This report describes sensitivity tests which show that DRIFT 3.6.14 works reliably for these scenarios. As a result of this assessment and accompanying model evaluation (see RR1165), DRIFT 3.6.14 has been adopted by HSE to model instantaneous releases of toxic pressure-liquefied gases.

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