Investigation of obstacle effects on heavy gas dispersion

Assessment of risk attending the manufacturing, storing and transportation of flammable and toxic gases involves the quantification of ensuing dispersion in case of accidental release. Worst case considerations have to be applied in order to obtain conservative estimates. The report describes a method for the determination of lower flammability distances for gases heavier than air under unfavorable atmospheric conditions. The method is based on the results of a wind tunnel study investigating the dispersion of instantaneous as well as continuous releases into a boundary-layer shear flow disturbed by surface obstacles. The results compare generally fair with those from corresponding field trials. Meanwhile, the method has been converted into a guideline (VDI 3783, Part 2, 1990) which constitutes the standard procedure for dispersion calculations within risk assessment studies in Germany. (orig.)