Safety distances for physical explosions of LNG releases on water

Massive offshore storage of fuel let international community arising questions about the hazards on people and other installations either onshore or on-board. Among the different possible accidental scenarios, when a cryogenic gas such as LNG, is spilled on water at a very fast rate, the phenomenon of Rapid Phase Transition (RPT) may occur. The prevalent theory for RPT is the superheat theory related to direct liquid/liquid (LNG/water) contact. Following this theory, rapid evaporation let available large amount of energy and explosion behaviour is likely. Furthermore, RPTs were also found to increase the distance corresponding to the lower flammability limit (LFL) by as much as 65% due to the increase in the expansion rate [Luketa-Hanlin, 2006]. These two effects are analysed in the present study, and results are compared with the indications given in a recent guidance by Sandia National Laboratory (2004), which assessed that significant impacts to public safety and property from accidental spills may exist within 250 m. Furthermore, as expected, the experimental tests reported in the same guidance clearly indicates that RPT explosive behaviour is linked with spill rate and water temperature. In the present paper, the effect of those two parameters has been investigated by means of acoustic theory at least in the far field. To this regard, special attention must be devoted when applying this theory in the near-field where, due to density differences, deviations from ideal acoustic assumption must be taken into account