Testimony

Before the Committee on Homeland 

Security, House of Representatives 

United States Government Accountability Office

GAO 

For Release on Delivery 

Expected at 10:00 a.m. EDT 

Wednesday, March 21, 2007 MARITIME SECURITY

Public Safety 

Consequences of a 

Liquefied Natural Gas Spill 

Need Clarification 

Statement of Jim Wells, Director 

Natural Resources and Environment 

GAO-07-633T 
What GAO Found

United States Government Accountability Office

Why GAO Did This Study

Highlights

Accountability Integrity Reliability

www.gao.gov/cgi-bin/getrpt?GAO-07-633T.

To view the full product, including the scope 

and methodology, click on the link above. 

For more information, contact Jim Wells at 

(202) 512-3841 or wellsj@gao.gov. 

Highlights of GAO-07-633T, testimony 

before the Committee on Homeland 

Security, House of Representatives 

March 2007

MARITIME SECURITY

Public Safety Consequences of a 

Liquefied Natural Gas Spill Need 

Clarification 

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 of the studies 

also examined other potential hazards of an LNG spill, including LNG vapor 

explosions and 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. Finally, the Sandia 

study examined the potential for cascading tank 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 panel of experts 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 

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 

recently released 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 unclassified 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. 
Page 1 GAO-07-633T 

Mr. Chairman and Members of the Committee: 

I am pleased to be here to discuss the results of our recently released 

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. 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 unclassified 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 

unclassified 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. Because some additional 

studies are classified, we will be issuing a separate classified report with 

related findings at a later date. 

 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 this Committee, the House 

Committee on Energy and Commerce, and Representative Edward J. Markey. 

United States Government Accountability Office

Washington, DC 20548 
Page 2 GAO-07-633T 

The six unclassified 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. 

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 

Summary 
Page 3 GAO-07-633T 

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. 

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 

Background 

Studies Identified Different 

Distances for the Heat 

Effects of an LNG Fire, but 

Agreed on Other LNG 

Hazards 
Page 4 GAO-07-633T 

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 being released today. 

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. 

 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. 

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 
Page 5 GAO-07-633T 

• 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 6 GAO-07-633T 

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 7 GAO-07-633T 

For further information about this testimony, please contact me at (202) 

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

Herrnstadt Shulman also made key contributions to this statement. 

Contacts and 

Acknowledgments 

(360817) 
This is a work of the U.S. government and is not subject to copyright protection in the 

United States. It may be reproduced and distributed in its entirety without further 

permission from GAO. However, because this work may contain copyrighted images or 

other material, permission from the copyright holder may be necessary if you wish to 

reproduce this material separately. 
GAO’s Mission The Government Accountability Office, the audit, evaluation and 

investigative arm of Congress, exists to support Congress in meeting its 

constitutional responsibilities and to help improve the performance and 

accountability of the federal government for the American people. GAO 

examines the use of public funds; evaluates federal programs and policies; 

and provides analyses, recommendations, and other assistance to help

Congress make informed oversight, policy, and funding decisions. GAO’s 

commitment to good government is reflected in its core values of 

accountability, integrity, and reliability. 

The fastest and easiest way to obtain copies of GAO documents at no cost

is through GAO’s Web site (www.gao.gov). Each weekday, GAO posts 

newly released reports, testimony, and correspondence on its Web site. To

have GAO e-mail you a list of newly posted products every afternoon, go 

to www.gao.gov and select “Subscribe to Updates.” 

The first copy of each printed report is free. Additional copies are $2 each. 

A check or money order should be made out to the Superintendent of 

Documents. GAO also accepts VISA and Mastercard. Orders for 100 or 

more copies mailed to a single address are discounted 25 percent. Orders 

should be sent to: 

U.S. Government Accountability Office 

441 G Street NW, Room LM 

Washington, D.C. 20548 

To order by Phone: Voice: (202) 512-6000 

TDD: (202) 512-2537 

Fax: (202) 512-6061 

Contact: 

Web site: www.gao.gov/fraudnet/fraudnet.htm

E-mail: fraudnet@gao.gov

Automated answering system: (800) 424-5454 or (202) 512-7470 

Gloria Jarmon, Managing Director, JarmonG@gao.gov (202) 512-4400 

U.S. Government Accountability Office, 441 G Street NW, Room 7125 

Washington, D.C. 20548 

Paul Anderson, Managing Director, AndersonP1@gao.gov (202) 512-4800

U.S. Government Accountability Office, 441 G Street NW, Room 7149 

Washington, D.C. 20548 

Obtaining Copies of 

GAO Reports and 

Testimony

Order by Mail or Phone 

To Report Fraud,

Waste, and Abuse in 

Federal Programs 

Congressional 

Relations 

Public Affairs 

PRINTED ON RECYCLED PAPER