CRR 433/2002 - Gas release attenuation within buildings
Effects of temperature and stratification
On certain industrial sites (such as water treatment plants), chemicals which are gaseous at atmospheric pressure and temperature are stored as a liquid either by refrigeration (at ambient pressure) or pressurisation (at ambient temperature). If such a vessel develops a small rupture, pressurised liquid escapes as a jet into the local environment, or if a large rupture forms, the material may 'spill' onto the ground. If the chemical is stored at ambient temperature and at its saturation pressure, and a jet release occurs, it will quickly vaporise upon entering the lower pressure regime of the local environment. This may be justified since a fraction of the pollutant flashes to the vapour phase immediately whilst the remaining liquid constituent vaporises within 2-3 metres . For a release into an enclosed space, the vaporised pollutant mixes with the air in the room, resulting in the reduction of the overall temperature of the room contents, accompanied by a further drop in pressure. This has the effect of producing a small vacuum, which draws in fresh air from outside the building through any available openings.
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