United States Government Accountability Office

GAO Testimony

Before the Subcommittee on Coast Guard 

and Maritime Transportation, Committee 

on Transportation and Infrastructure, 

House of Representatives 

MARITIME SECURITY

Opportunities Exist to 

Further Clarify the 

Consequences of a 

Liquefied Natural Gas 

Tanker Spill 

Statement of Mark Gaffigan, Acting Director 

Natural Resources and Environment 

For Release on Delivery

Expected at 10:00 a.m. EDT 

Monday, May 7, 2007

GAO-07-840T 
What GAO Found

United States Government Accountability Office

Why GAO Did This Study

Highlights

Accountability Integrity Reliability

May 2007

MARITIME SECURITY

Opportunities Exist to Further Clarify the 

Consequences of a Liquefied Natural Gas 

Tanker Spill 

Highlights of GAO-07-840T, testimony 

before the Subcommittee on Coast Guard 

and Maritime Transportation, Committee 

on Transportation and Infrastructure, 

House of Representatives

Liquefied natural gas (LNG) is a 

supercooled liquid form of natural 

gas. U.S. LNG imports are

projected to increase to about 17

percent of natural gas supplies by 

2030, from about 3 percent today. 

To meet this increase, energy

companies have submitted 32 

applications for new terminals. If a 

terrorist attack on an LNG tanker

caused a spill, potential hazards, 

such as fire, asphyxiation, and 

explosions, could result. The 

Department of Energy (DOE) 

recently funded a study to conduct

small- and large-scale experiments 

to refine and validate models that 

calculate how heat from large LNG 

fires would affect the public. 

This testimony is based on GAO’s 

report, Maritime Security: Public 

Safety Consequences of a Terrorist

Attack on a Tanker Carrying 

Liquefied Natural Gas Need

Clarification (GAO-07-316). To 

prepare this report, GAO examined

the results of six recent studies on 

the effects of an LNG spill and 

convened a panel of 19 experts to

identify areas of agreement on the

consequences of a terrorist attack

on an LNG tanker. 

What GAO Recommends

GAO recommended that DOE 

incorporate the key issues GAO’s

expert panel identified, particularly

the potential for cascading failure, 

into its current LNG study. DOE 

concurred with this 

recommendation. 

The six studies GAO reviewed examining the potential effect of a fire 

resulting from an LNG spill produced varying results; some studies also 

examined other potential hazards of a large LNG spill and reached consistent 

conclusions on explosions. Specifically, 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, with no data on large spills from actual 

events, researchers had to make numerous modeling assumptions to scale 

up the existing experimental data for large LNG spills. Three studies 

considered LNG vapor explosions and concluded that such explosions are 

unlikely unless the vapors were in a confined space. Only the Sandia study 

examined the potential for the sequential failure of multiple tanks on the 

LNG vessel (cascading failure) and concluded that only three of the five

tanks in a typical tanker would potentially be affected, and that such failure

would increase the duration of the LNG fire. 

GAO’s expert panel generally agreed on the public safety impact of an LNG 

spill caused by a terrorist attack, disagreed on specific conclusions of the 

Sandia study, and suggested future research priorities. Experts agreed that 

the most likely public safety impact of an LNG spill is the heat impact of a 

fire and that explosions are not likely to occur unless LNG vapors are in 

confined spaces. However, the experts did not all agree with the heat hazard 

and cascading failure conclusions reached by the Sandia study. Finally, they 

suggested priorities to guide future research aimed at clarifying uncertainties

about heat impact distances and cascading failure. DOE’s recently funded 

study involving large-scale LNG fire experiments addresses only some of the 

research priorities the expert panel identified. 

LNG Tanker Passing Downtown Boston on Its Way to Port

www.gao.gov/cgi-bin/getrpt?GAO-07-840T.

To view the full product, including the scope 

and methodology, click on the link above. 

For more information, contact Mark Gaffigan 

at (202) 512-3841 or gaffiganm@gao.gov. 
United States Government Accountability Office

Washington, DC 20548 

Mr. Chairman and Members of the Subcommittee: 

I am pleased to be here to discuss the results of our report on the public 

safety consequences of a terrorist attack on a tanker carrying liquefied 

natural gas (LNG).1

 As you know, LNG is a supercooled liquid form of 

natural gas, which, if spilled, poses potential hazards, such as fire, 

asphyxiation, and explosions. U.S. imports of LNG, now about 3 percent of 

total U.S. natural gas supplies, are projected to be about 17 percent of U.S. 

supplies by 2030. To meet this increased demand, energy companies have

submitted 32 applications to federal regulators to build new terminals for 

importing LNG in 10 states and 5 offshore areas. Because of the projected

increase in tankers carrying LNG to these terminals, public safety 

concerns have been raised, including the consequences of a terrorist 

attack. In light of these concerns, access to accurate information about the 

consequences of LNG spills is crucial for developing risk assessments for 

LNG siting decisions. Despite several recent modeling studies of the 

consequences of potential LNG spills, uncertainties remain about the risks 

such spills would pose to the public. One of these studies, conducted by 

Sandia National Laboratories (Sandia) in 2004, is used by the Coast Guard 

to assess the suitability of waterways for LNG tankers traveling to 

proposed LNG facilities. In this context, DOE has recently funded a new 

study that will conduct small- and large-scale LNG fire experiments to 

refine and validate existing models that calculate how heat from large LNG 

fires would affect the public. 

My testimony today summarizes the results of our report. Specifically, I 

will (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 issues, we examined six studies of the 

consequences of LNG spills. We also convened a Web-based panel of 19 

experts to identify areas of agreement and disagreement on LNG spill 

consequence issues, including consideration of a terrorist attack. 

 1

GAO, Maritime Security: Public Safety Consequences of a Terrorist Attack on a Tanker 

Carrying Liquefied Natural Gas Need Clarification, GAO-07-316 (Washington, D.C.: Feb. 

22, 2007). This report was prepared at the request of the House Committee on Homeland 

Security, the House Committee on Energy and Commerce, and Representative Edward J.

Markey. 

Page 1 GAO-07-840T
The six studies we reviewed all examined the heat impact of an LNG fire 

but produced varying results; some studies also examined other potential 

hazards of a large LNG spill and reached consistent conclusions on 

explosions. Specifically, the studies’ conclusions about the distance at 

which 30 seconds of exposure to the heat could burn people—also termed 

the heat impact distance—ranged from less than 1/3 of a mile to about 1-

1/4 miles. These variations occurred because, with no data on large spills 

from actual events, researchers had to make numerous modeling 

assumptions to scale up the existing experimental data for large LNG 

spills. These assumptions involved the size of the hole in the tanker, the 

number of tanks that fail, the volume of LNG spilled, key LNG fire 

properties, and environmental conditions, such as wind and waves. Three 

of the studies also examined other potential hazards of an LNG spill, 

including LNG vapor explosions, asphyxiation, and the sequential failure 

of multiple tanks on the LNG vessel (cascading failure). All three studies 

considered LNG vapor explosions unlikely unless the vapors were in a 

confined space. Only the Sandia study examined asphyxiation and 

concluded that asphyxiation did not pose a hazard to the general public.

Finally, only the Sandia study examined the potential for cascading failure 

of LNG tanks and concluded that only three of the five tanks on a typical 

LNG vessel would be involved in such an event and that this number of 

tanks would increase the duration of the LNG fire. 

Summary 

Our panel of 19 experts generally agreed on the public safety impact of an 

LNG spill, disagreed on specific conclusions of the Sandia study, and 

suggested future research priorities. Experts agreed on three main points: 

(1) the most likely public safety impact of an LNG spill is the heat impact 

of a fire; (2) explosions are not likely to occur in the wake of an LNG spill 

unless the LNG vapors are in confined spaces; and (3) some hazards, such 

as freeze burns and asphyxiation, do not pose a hazard to the public. 

However, the experts disagreed with a few conclusions reached by the 

Sandia study that the Coast Guard uses to assess the suitability of 

waterways for LNG tankers going to proposed LNG terminals. Specifically, 

all experts did not agree with the study’s 1-mile estimate of heat impact 

distance resulting from an LNG fire: 7 of 15 thought Sandia’s distance was 

“about right,” 8 were evenly split on whether the distance was “too 

conservative” or “not conservative enough,” and 4 did not answer this 

question. Experts also did not agree with the Sandia National Laboratories’ 

conclusion that only three of the five LNG tanks on a tanker would be 

involved in a cascading failure. Finally, experts suggested priorities to 

guide future research aimed at clarifying uncertainties about heat impact 

distances and cascading failure, including large-scale fire experiments, 

large-scale LNG spill experiments on water, the potential for cascading 

Page 2 GAO-07-840T
failure of multiple LNG tanks, and improved modeling techniques. DOE’s 

recently funded study involving large-scale LNG fire experiments 

addresses some, but not all, of the research priorities the expert panel 

identified. 

As scientists and the public have noted, an LNG spill could pose potential 

hazards. When LNG is spilled from a tanker, it forms a pool of liquid on the 

water. As the liquid warms and changes into natural gas, it forms a visible, 

foglike vapor cloud close to the water. The cloud mixes with ambient air 

as it continues to warm up, and eventually the natural gas disperses into 

the atmosphere. Under certain atmospheric conditions, however, this 

cloud could drift into populated areas before completely dispersing. 

Because an LNG vapor cloud displaces the oxygen in the air, it could 

potentially asphyxiate people who come into contact with it. Furthermore, 

like all natural gas, LNG vapors can be flammable, depending on 

conditions. If the LNG vapor cloud ignites, the resulting fire will burn back 

through the vapor cloud toward the initial spill. It will continue to burn 

above the LNG that has pooled on the surface—this is known as a pool 

fire. Small-scale experiments to date have shown that LNG fires burn 

hotter than oil fires of the same size. Both the cold temperatures of spilled 

LNG and the high temperatures of an LNG fire have the potential to 

significantly damage the tanker, causing a cascading failure. Such a failure

could increase the severity of the incident. Finally, concerns have been 

raised about whether an explosion could result from an LNG spill. 

The Federal Energy Regulatory Commission is responsible for approving 

applications for onshore LNG terminal sitings, and the U.S. Coast Guard is 

responsible for approving applications for offshore sitings. In addition, the 

Coast Guard reviews an applicant’s Waterway Suitability Assessment, 

reaches a preliminary conclusion on whether the waterway is suitable for 

LNG imports, and identifies appropriate strategies that reduce the risk 

posed by the movement of an LNG tanker. 

Background 

Studies Identified Different 

Distances for the Heat 

Effects of an LNG Fire, but 

Agreed on Other LNG 

Hazards 

The six studies we examined identified various distances at which the heat 

effects of an LNG fire could be hazardous to people. The studies’ results 

about the distance at which 30 seconds of exposure to the heat could burn

people ranged from less than 1/3 of a mile (about 500 meters) to about 

1-1/4 miles (more than 2,000 meters). The studies’ variations in heat effects 

occurred because (1) different assumptions were made in the studies’ 

models about key parameters of LNG spills and (2) the studies were 

designed and conducted for different purposes. Since no large-scale data 

Page 3 GAO-07-840T
are available for LNG spills, researchers made numerous modeling 

assumptions to scale up the existing experimental data for large spills. Key 

assumptions made included hole size and cascading failure, waves and 

wind, the volume of LNG spilled, and the amount of heat radiated from the 

fire. For example, studies made assumptions for the size of the hole in the 

LNG tanker that varied from less than 1 square meter up to 20 square 

meters. Additionally, the studies were conducted for different purposes. 

Two studies were academic analyses of the differences between LNG and 

oil spills; three specifically addressed spills caused by terrorist attacks, 

which was a concern in the wake of the September 11 attacks; and the

final study developed appropriate methods for regulators to use to 

estimate heat hazards from LNG fires. Results of these studies can be

found in our report. 

Some studies also examined other potential hazards, such as explosions, 

asphyxiation, and cascading failure, and identified their potential impacts 

on public safety. Three studies examined the potential for LNG vapor 

explosions, and all agreed that it is unlikely that LNG vapors could 

explode if the vapors are in an unconfined space. Only one study 

examined the potential for asphyxiation following an LNG spill if the 

vapors displace the oxygen in the air. It concluded that fire hazards would 

be the greatest problem in most locations, but that asphyxiation could 

threaten the ship’s crew, pilot boat crews, and emergency response 

personnel. Finally, only the Sandia study examined the potential for 

cascading failure of LNG tanks and concluded that only three of the five 

tanks would be involved in such an event and that this number of tanks 

would increase the duration of the LNG fire. 

The 19 experts on our panel generally agreed on the public safety impact

of an LNG spill, disagreed with specific conclusions of the Sandia study, 

and suggested future research priorities.2

 Specifically: 

• Experts agreed that the main hazard to the public from a pool fire is the 

heat from the fire, but emphasized that the exact hazard distance depends 

on site-specific weather conditions; composition of the LNG (relative 

percentages of methane, propane, and butane); and the size of the fire. 

Experts Generally Agreed 

That the Most Likely 

Public Safety Impact of an 

LNG Spill Is the Heat 

Effect of a Fire, but That 

Further Study Is Needed to 

Clarify the Extent of This 

Effect 

 2

 We considered experts to be “in agreement” if more than 75 percent of them indicated 

that they completely agreed or generally agreed with a given statement. Not all experts 

commented on every issue discussed. 

Page 4 GAO-07-840T
• Eighteen of 19 experts agreed that the ignition of a vapor cloud over a 

populated area could burn people and property in the immediate vicinity 

of the fire. Three experts emphasized in their comments that the vapor 

cloud is unlikely to penetrate very far into a populated area before igniting. 

• With regard to explosions, experts distinguished between explosions in 

confined spaces and in unconfined spaces. For confined spaces, such as

under a dock or between the hulls of a ship, they agreed that it is possible, 

under controlled experimental conditions, to induce explosions of LNG 

vapors; however, a detonation—the more serious type of vapor cloud 

explosion—of confined LNG vapors is unlikely following an LNG spill 

caused by a terrorist attack. For unconfined spaces, experts were split on 

whether it is possible to induce such explosions under controlled 

experimental conditions; however, even experts who thought such 

explosions were possible agreed that vapor cloud explosions in 

unconfined spaces are unlikely to occur following an LNG spill caused by

a terrorist attack. 

Our panel of 19 experts disagreed with a few of the Sandia study’s 

conclusions and agreed with the study authors’ perspective on risk-based 

approaches to dealing with the hazards of potential LNG spills. For 

example: 

• Seven of 15 experts thought Sandia’s heat hazard distance was “about 

right,” and the remaining 8 experts were evenly split as to whether the 

distance was “too conservative” (i.e., larger than needed to protect the 

public) or “not conservative enough” (i.e., too small to protect the public).

Officials at Sandia National Laboratories and our panel of experts 

cautioned that the hazard distances presented cannot be applied to all 

sites because of the importance of site-specific factors. Additionally, two 

experts explained that there is no “bright line” for hazards—that is, 1,599 

meters is not necessarily “dangerous,” and 1,601 meters is not necessarily

“safe.” 

• Nine of 15 experts agreed with Sandia’s conclusion that only three of the 

five LNG tanks on a tanker would be involved in cascading failure. Five 

experts noted that the Sandia study did not explain how it concluded that

only three tanks would be involved in cascading failure. 

• Finally, experts agreed with Sandia’s conclusion that consequence studies 

should be used to support comprehensive, risk-based management and 

planning approaches for identifying, preventing, and mitigating hazards 

from potential LNG spills. 

Page 5 GAO-07-840T
The experts also suggested priorities for future research—some of which 

are not fully addressed in DOE’s ongoing LNG research—to clarify 

uncertainties about heat impact distances and cascading failure. 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. As part of DOE’s ongoing 

research, Sandia plans to conduct large-scale LNG pool fire tests, 

beginning with a pool size of 35 meters—the same size as the largest test 

conducted to date. Sandia will validate the existing 35-meter data and then 

conduct similar tests for pool sizes up to 100 meters. Of the top 10 LNG 

research priorities the experts identified, only 3 have been funded in the

DOE study, and the second highest ranked priority, cascading failure, was 

not funded. One expert noted that although the consequences of cascading 

failure could be serious, because the extreme cold of spilled LNG and the 

high heat of an LNG fire could damage the tanker, there are virtually no 

data looking at how a tanker would be affected by these temperatures. 

It is likely that the United States will increasingly depend on LNG to meet 

its demand for natural gas. Consequently, understanding and resolving the 

uncertainties surrounding LNG spills is critical, especially in deciding 

where to locate LNG facilities. While there is general agreement on the 

types of effects of an LNG spill, the study results have created what 

appears to be conflicting assessments of the specific heat consequences of

such a spill. These assessments create uncertainty for regulators and the 

public. Additional research to resolve some key areas of uncertainty could 

benefit federal agencies responsible for making informed decisions when 

approving LNG terminals and protecting existing terminals and tankers, as 

well as providing reliable information to citizens concerned about public 

safety. 

To provide the most comprehensive and accurate information for 

assessing the public safety risks posed by tankers transiting to proposed 

LNG facilities, we recommended that the Secretary of Energy ensure that 

DOE incorporates the key issues the expert panel identified, particularly 

the potential for cascading failure, into its current LNG study. 

DOE concurred with our recommendation. 

Mr. Chairman, this concludes my prepared statement. I would be happy to

respond to any questions that you or Members of the Committee may 

have. 

Conclusions 

Page 6 GAO-07-840T
For further information about this testimony, please contact me at (202) 

512-3841 or gaffiganm@gao.gov. James W. Turkett, Janice M. Poling, and

Carol Herrnstadt Shulman also made key contributions to this statement. 

Page 7 GAO-07-840T

Contacts and 

Acknowledgments 

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