Security Length Associated with the Risk of Ammonia Tank Leak Using CTOA Criterion and ALOHA Software

Ammonia is a toxic gas and can cause tragic consequences for humans. The damage level depends on concentration and duration of exposure. The security length associated with the risk of a tank leak at the acute exposure level of 30 ppm (AEGL-1) has been computed. Two tools have been combined: the CTOA criterion and the ALOHA software. The CTOA, a measure of fracture resistance against ductile crack propagation, is implemented in Abaqus software to compute the size of a breach in a tank submitted to internal pressure. This breach is assumed to be initiated by a gouge-dent defect provoked by a shock. The ALOHA software introduces the tank's characteristics, contents, and breach size. This allows us to determine and visualize the security length. The security length depends on geographic and climatic conditions, and for an incident localized in Metz (France), a value of 436 m was found. The effects of internal temperature, wind speed, and breach position are studied. A comparison for the same reference state with hydrogen is also made.