In 2005, 13 countries shipped natural gas to  14 LNG-importing countries. LNG imports, as a percentage of a country’s  total gas supply, for each of the importing countries ranged from 3 percent  in the United States to nearly 95 percent in Japan. Studies Identified Various Distances That the Heat Effects of an LNG Fire Could Be Hazardous to People because of Assumptions Made

The studies’ conclusions about the distance at which 30 seconds of  exposure to the heat could burn people ranged from about 500 meters  (less than 1/3 mile) to more than 2,000 meters (about 1-1/4 miles). The  results—size of the LNG pool, the duration of the fire, and the heat hazard  distance for skin burn—varied in part because the studies made different  assumptions about key parameters of LNG spills and also because they  were designed and conducted for different purposes. Volume of LNG spilled. The longer the fire,  the greater potential for damage to the tanker and for cascading failure. The 2004 Sandia study was intended to develop guidance on a risk-based  analysis approach to assess potential threats to an LNG tanker, determine  the potential consequences of a large spill, and review techniques that  could be used to mitigate the consequences of an LNG spill. In  these cases, the LNG spill from one tank, as well as the subsequent fire,  causes the neighboring two tanks to fail on the LNG tanker, resulting in  LNG spills from three of the five tanks on the tanker. Some Studies Examined Other Potential Hazards and Identified Their Impact on Public Safety

Three of the studies also examined other potential hazards of an LNG spill,  including LNG vapor explosions, other types of explosions, and  asphyxiation. Experts Generally Agreed That the Most Likely Public Safety Impact of an LNG Spill Is Fire’s Heat Effect, but That Further Study Is Needed to Clarify the Extent of This Effect

Our panel of 19 experts generally agreed on the public safety impact of an  LNG spill and disagreed with a few of the conclusions of the Sandia study. These  priorities include large-scale fire experiments, large-scale LNG spill  experiments on water, the potential for cascading failure of multiple LNG  tanks, and improved modeling techniques. Experts Disagreed with a Few Key Conclusions of the Sandia National Laboratories Study

Experts disagreed with heat hazard and cascading failure conclusions of  the Sandia study. As table 2 shows, DOE’s recently funded study involving large-scale LNG  fire experiments addresses some, but not all, of the research priorities  identified by the expert panel. Appendix I: Scope and Methodology

To address the first objective, we identified eight unclassified, completed  studies of liquefied natural gas (LNG) hazards and reviewed the six studies  that included new, original research (either experimental or modeling) and  clearly described the methodology used. Detonation in a  confined setting  (BLEVE)
If experts answered that “under controlled experimental conditions, it is  possible to induce this type of explosion in this type of setting,” they were  asked to answer the following question:  What is the likelihood of a each type of explosion of LNG vapors in  each setting described occurring following an LNG spill caused by a  terrorist attack on a tanker?
Why GAO Did This Study

The United States imports natural gas by pipeline from Canada and by tanker as liquefied natural gas (LNG) from overseas. LNG--a supercooled form of natural gas--currently accounts for about 3 percent of total U.S. natural gas supply, with an expected increase to about 17 percent by 2030, according to the Department of Energy (DOE). With this projected increase, many more LNG import terminals have been proposed. However, concerns have been raised about whether LNG tankers could become terrorist targets, causing the LNG cargo to spill and catch on fire, and potentially explode. DOE has recently funded a study to consider these effects; completion is expected in 2008. GAO was asked to (1) describe the results of recent studies on the consequences of an LNG spill and (2) identify the areas of agreement and disagreement among experts concerning the consequences of a terrorist attack on an LNG tanker. To address these objectives, GAO, among other things, convened an expert panel to discuss the consequences of an attack on an LNG tanker.

What GAO Found

The six unclassified completed studies GAO reviewed examined the effect of a fire resulting from an LNG spill but produced varying results; some studies also examined other potential hazards of a large LNG spill. The studies' conclusions about the distance at which 30 seconds of exposure to the heat (heat hazard) could burn people ranged from less than 1/3 of a mile to about 1-1/4 miles. Sandia National Laboratories (Sandia) conducted one of the studies and concluded, based on its analysis of multiple attack scenarios, that a good estimate of the heat hazard distance would be about 1 mile. Federal agencies use this conclusion to assess proposals for new LNG import terminals. The variations among the studies occurred because researchers had to make modeling assumptions since there are no data for large LNG spills, either from accidental spills or spill experiments. These assumptions involved the size of the hole in the tanker; the volume of the LNG spilled; and environmental conditions, such as wind and waves. The three studies that considered LNG explosions concluded explosions were unlikely unless the LNG vapors were in a confined space. Only the Sandia study examined the potential for sequential failure of LNG cargo tanks (cascading failure) and concluded that up to three of the ship's five tanks could be involved in such an event and that this number of tanks would increase the duration of the LNG fire. GAO's expert panel generally agreed on the public safety impact of an LNG spill, but believed further study was needed to clarify the extent of these effects, and suggested priorities for this additional research. Experts agreed that the most likely public safety impact of an LNG spill is the heat hazard of a fire and that explosions are not likely to occur in the wake of an LNG spill. However, experts disagreed on the specific heat hazard and cascading failure conclusions reached by the Sandia study. DOE's recently funded study involving large-scale LNG fire experiments addresses some, but not all, of the research priorities identified by the expert panel. The leading unaddressed priority the panel cited was the potential for cascading failure of LNG tanks.