Major hazard risk assessment over non-flat terrain. Part II. instantaneous release

Hankin, R.K.S. (2004) Major hazard risk assessment over non-flat terrain. Part II. instantaneous release. Atmospheric Environment, 38 (5), 707-714. (doi:10.1016/j.atmosenv.2003.10.022).

Record type: Article

Abstract

This is the second part of a two-part paper which considers the risk of being exposed to accidentally released toxic gas; part one considered continuous releases and this part considers instantaneous releases. The risk estimated is RI; the probability at any point of receiving a non-zero dose given an instantaneous release (probability language is needed because wind direction is assumed to be a random variable). On flat ground, simple analytical techniques show that for an instantaneous release of buoyancy B with a uniform windrose, RICð4=p5Þ1=4F1=2 r1=2 u1=2 B1=4 at radius r; where F is the front Froude number and u the windspeed. In this paper RI is estimated over non-flat terrain using shallow layer modelling for a range of windspeeds and slopes. The source term is identical to that of Thorney Island Trial 08. In a windspeed of 1 m s1 a slope as little as 2% substantially affects the risk in the sense that the predicted risk contours are far from circularly symmetric; continuous releases showed similar trends. The real terrain data used is from Little Barrier Island, New Zealand (latitude 36110 S; longitude 17540 E), chosen on account of its being uninhabited, and having steep slopes and complex topography. As the windspeed increases from 1 to 10 m s1; risk contours become less affected by terrain in both instantaneous and continuous releases.

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