TABLE OF CONTENTS The three major hazards fire, explosion and toxic release usually involve the emission of material from containment followed by vaporization and dispersion of the material. The treatment given here is relevant to all three hazards; in particular, the development of the emission and dispersion phases is relevant to such situations as:
Escape of flammable material, mixing of the material with air, formation of a flammable cloud, drifting of the cloud and finding of a source of ignition, leading to (a) a fire and/or (b) a vapour cloud explosion, affecting the site and possibly populated areas.
Escape of toxic material, formation of a toxic gas cloud and drifting of the cloud, affecting the site and possibly populated areas.
There is a wide range of circumstances which can give rise to emission. The situation which appears to be most frequently discussed is a failure of plant integrity, but it is important to consider other occurrences, including escape from valves which have been deliberately opened and forced venting in emergencies. Thus on a low pressure refrigerated liquefied petroleum gas (LPG) installation, for example, a large quantity of flammable vapour may be released by failure of a pressure vessel or of pipework. But loss of refrigeration with resultant forced venting could also give a large release of vapour. Finally, emissions caused by terrorist acts are of growing concern.
In view of the many different situations which can give rise to emission, it is peculiarly difficult to obtain meaningful estimates of the quantity...
