A new study was recently released by the US Government Accountability Office (GAO), which focused on the consequences of a possible terrorist attack on a tanker carrying liquefied natural gas (LNG). Concerns have increased since September 11, 2001, about the potential effects of a large-scale spill from an LNG tanker, as previous studies have only examined the hazards of a smaller sized spill. Specifically, authorities are concerned about the heat impact of an LNG pool fire. When LNG leaks from a tanker, it forms a pool of liquid on the surface of the water, which vaporizes and forms a cloud just above the surface. These vapors are flammable, and should the cloud ignite, the fire will burn through the cloud toward the initial spill, and will continue to burn just above the water surface, forming a pool fire.
Understanding the risks associated with LNG tankers is particularly important due to projections for a significant increase in US demand for LNG in the coming years. Authorities have speculated that LNG imports will increase by 400% in the next 10 years, indicating the necessity for officials to completely understand the possible consequences of a spill whether by an accident or by a terrorist attack. The devastation of either event has the potential to be disastorous due to current levels of preparedness.
Report Findings
Six previous unclassified reports were examined by the GAO, who were concerned about the overall hazards of LNG spills. Each of the reports reviewed by the GAO looked at the effects of an LNG pool fire, however each found different results. In particular, the studies varied on the distance from which 30 seconds of exposure to the heat from a fire could burn individuals. The conclusions ranged from approximately 500 meters to greater than 2,000 meters. These discrepancies occurred largely due to assumptions by those conducting the individual studies. As there has been no large-scale LNG spill, researchers must make assumptions on important factors, such as the size of the hole in the tanker, wind speeds, and spill volume.
Additionally, several of the studies addressed other possible effects of an LNG spill, to include LNG vapor explosions and cascading failure.
– Three of the studies agreed that it is unlikely that LNG vapors would explode, except if the vapors were in a confined space.
– One of the studies examined cascading failure, or the potential for multiple tanks on a ship to fail due to significant damage from an LNG fire. The study concluded that only 3 out of 5 tanks would fail in such an event.
Expert Findings
A panel of 19 experts were also consulted in order to conduct the study. In general, the panel of experts agreed that the most significant threat to public safety from an LNG spill is heat generated from a pool fire. The experts stressed that the extent of the threat would depend on specific conditions at the site of the spill, to include weather, location of the hole, spill volume, and size of the tanker.
The experts did not agree with the distance of heat impact put forward by one of the six studies at 1,600 meters. Several experts believed the distance was “about right,” several “too conservative,” and several “not conservative enough.”
The experts also disagreed with the cascading failure finding put forward by one of the studies. Several stated that the conclusion appeared unfounded, while others believed that all tanks on a ship could be involved in such a failure.
The panel also believed that it is unlikely that vapor explosions would occur, except if the LNG vapors were in a confined space.
Further Research Warranted
The GAO recommended that the Department of Energy undertake additional research to better understand the impact of an LNG spill, specifically the distance of heat impact from an LNG fire and the extent of a possible cascading failure. The GAO concludes that there are still numerous uncertainties and disagreements over the effects of LNG spills.
Long-term implications
At this time, there are five LNG import terminals in the US, however 32 applications were submitted for new terminals in 10 states and 5 offshore areas, with a large number of the proposed terminals in the Northeast. The Federal Energy Regulatory Commission and the US Coast Guard have approved at least 13 of these applications. Since several of these proposed terminals are in urban areas, it is important for additional studies to be initiated in order to prepare for and/or prevent a large-scale disaster from an LNG spill. Without such information, the ability to prepare for and react to a LNG spill or terrorist attack will be diminished.
