Vapor Cloud Explosion at Nil Wind

Overview

Main Objective

This project will review available weather data for the U.S. to determine which criteria could define "nil wind" conditions, as opposed to "low wind" conditions as already included in LNG facility siting studies, and their historical frequency of occurrence. Once nil wind conditions have been defined, computational fluid dynamics modeling will be performed to quantify the potential increase in the severity of consequences (flammable dispersion distances and overpressures) from accidental releases under nil wind conditions as compared with the current regulatory requirements. The weather data and consequence modeling results will then be used to inform a recommendation on whether nil wind conditions should be included in facility siting requirements. Separate recommendations on the inclusion of nil wind conditions will be made for prescriptive and risk-based siting approaches.

Public Abstract

This project will develop criteria to define "nil wind" conditions and to determine whether such conditions should be included in the siting requirements for LNG facilities. The nil wind inclusion criteria will be evaluated separately for prescriptive and risk-based siting analyses (based on NFPA 59A, 2019 edition), and will take into account the relevance of the large vapor cloud incidents described in the 2017 HSE study to LNG facilities designed and built according to current PHMSA regulations.

Summary and Conclusions

This project developed a definition for nil wind, executed a statistical analysis of wind speeds across the United States, performed a critical review of the 2017 HSE report titled "Review of Vapour Cloud Explosion Incidents" (RR1113), and evaluated the effect of nil wind conditions on flammable hazards through prescriptive and risk-based approaches using extensive modeling on a broad range of realistic scenarios. The conclusions determined through the research led the project team to not recommend any changes to siting regulatory requirements regarding wind speeds. Details of the research are included in the final report.

Relevant Files & Links