Comparative threat from LNG and fuel oil maritime accidents

Abstract

ABSTRACT The U.S. Energy Information Administration estimates a 3–4% increase in U.S. production levels of natural gas in 2017 from 2016 production rates, themselves increased from 2015. While much of this increase will be used domestically or sent by pipeline to Mexico, some will need to be shipped as a cryogenic liquid to distant ports on specially designed ships. Spill responders are familiar with the hazards faced from unplanned fuel oil releases but have less experience with the threat of a large maritime liquefied natural gas (LNG) accident. Fortunately, considerable new research has been done assessing such threats. Based upon such research, it is now possible to compare expected hazards from fuel oil and LNG tanker accidents. The paper compares behavior of both fluids in no-fire and fire-involved scenarios. LNG shows significantly different behavior than traditional oil products in either situation. In the no-fire case, LNG presents less of a direct environmental chemical hazard than fuel oil since methane, its main hydrocarbon constituent, is relatively benign compared to many of the hydrocarbons in typical fuel oils. However, it offers new safety threats to crew and vessel due to (1) its cryogenic behavior and (2) over-pressure caused by rapid phase transition of liquid to gas. The fire/explosion hazards between the two fluids are also quite different. While fuel oil fires have larger footprints and can generate a large airborne particulate hazard, LNG burns relatively cleanly with little soot. However, heat radiation from LNG is much larger, increasing the risk of secondary fires and increased damage to the vessel itself. Moreover, confined natural gas or LNG undergoing rapid phase transition can lead to an internal detonation overpressure in the vessel, also expanding the damage. Experts are divided on a boiling liquid expanding vapor explosion (BLEVE) risk from LNG maritime operations.