United States Government Accountability Office

GAO Report to Congressional Requesters

MARITIME SECURITY

Public Safety 

Consequences of a 

Terrorist Attack on a 

Tanker Carrying 

Liquefied Natural Gas 

Need Clarification 

February 2007 

 

GAO-07-316 
What GAO Found

United States Government Accountability Office

Why GAO Did This Study

Highlights

Accountability Integrity Reliability

February 2007

MARITIME SECURITY

Public Safety Consequences of a 

Terrorist Attack on a Tanker Carrying 

Liquefied Natural Gas Need Clarification 

Highlights of GAO-07-316, a report to 

congressional requesters 

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 Recommends

GAO recommends that the

Secretary of Energy ensure that 

DOE incorporates into its LNG

study the key issues identified by

the expert panel.

In reviewing our draft report, DOE 

agreed with our recommendation. 

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. 

LNG Tanker Passing Downtown Boston on Its Way to Port

Source: GAO.

www.gao.gov/cgi-bin/getrpt?GAO-07-316.

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. 
Contents 

Letter 1

Results in Brief 7

Background 8

Studies Identified Different Distances for the Heat Effects of an

LNG Fire 11 

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 17 

Conclusions 22

Recommendation for Executive Action 23 

Agency Comments and Our Evaluation 23 

Appendix I Scope and Methodology 24 

Appendix II Names and Affiliations of Members of GAO’s 

Expert Panel on LNG Hazards 26 

Appendix III Summary of Expert Panel Results 27 

Appendix IV GAO Contact and Staff Acknowledgments 41 

Tables 

Table 1: Key Assumptions and Results of the LNG Spill 

Consequence Studies 13 

Table 2: Expert Panel’s Ranking of Need for Research on LNG 21 

Figures 

Figure 1: Existing, Approved, and Proposed LNG Terminals in the 

United States, as of October 2006 3 

Figure 2: LNG Membrane Tanker 11 

Page i GAO-07-316 Maritime Security
Abbreviations 

BLEVE boiling liquid expanding vapor explosion 

DOE Department of Energy 

DOT Department of Transportation 

FERC Federal Energy Regulatory Commission 

kW/m2 kilowatts per square meter 

LNG liquefied natural gas 

LPG liquefied petroleum gas 

m2

 square meters 

m3

 cubic meters

m/s meters per second 

RPT rapid phase transition 

WSA Waterway Suitability Assessment 

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. 

Page ii GAO-07-316 Maritime Security
United States Government Accountability Office

Washington, DC 20548 

February 22, 2007 

The Honorable John D. Dingell 

Chairman 

The Honorable Joe Barton 

Ranking Member 

Committee on Energy and Commerce 

House of Representatives 

The Honorable John D. Dingell 

Chairman 

The Honorable Joe Barton 

Ranking Member 

Committee on Energy and Commerce 

House of Representatives 

The Honorable Bennie G. Thompson

Chairman 

The Honorable Peter King 

Ranking Member 

Committee on Homeland Security 

House of Representatives 

The Honorable Bennie G. Thompson

Chairman 

The Honorable Peter King 

Ranking Member 

Committee on Homeland Security 

House of Representatives 

The Honorable Edward J. Markey 

House of Representatives 

Worldwide, over 40,000 tanker cargos of liquefied natural gas (LNG) have

been shipped since 1959, and imports of LNG are projected to increase 

over the next 10 years. LNG is a supercooled liquid form of natural gas—a 

crucial source of energy for the United States. Natural gas is used in 

homes for cooking and heating and as fuel for generating electricity, and it 

accounts for about one-fourth of all energy consumed in the United States 

each year. Prices for natural gas in the United States have risen over the 

past 5 years as demand for natural gas has increased faster than domestic 

production. To make up for the domestic shortfall, the United States 

imports some natural gas in pipelines from Canada. However, most 

reserves of natural gas are overseas and cannot be transported through 

pipelines. Natural gas from these reserves has to be transported to the 

United States as LNG in tankers. Because of the projected increase in LNG 

tankers arriving at U.S. ports, concerns have been raised about whether 

the tankers could become terrorist targets. 

Worldwide, over 40,000 tanker cargos of liquefied natural gas (LNG) have

been shipped since 1959, and imports of LNG are projected to increase 

over the next 10 years. LNG is a supercooled liquid form of natural gas—a 

crucial source of energy for the United States. Natural gas is used in 

homes for cooking and heating and as fuel for generating electricity, and it 

accounts for about one-fourth of all energy consumed in the United States 

each year. Prices for natural gas in the United States have risen over the 

past 5 years as demand for natural gas has increased faster than domestic 

production. To make up for the domestic shortfall, the United States 

imports some natural gas in pipelines from Canada. However, most 

reserves of natural gas are overseas and cannot be transported through 

pipelines. Natural gas from these reserves has to be transported to the 

United States as LNG in tankers. Because of the projected increase in LNG 

tankers arriving at U.S. ports, concerns have been raised about whether 

the tankers could become terrorist targets. 

LNG—primarily composed of methane—is odorless and nontoxic. It is 

produced by supercooling natural gas to minus 260 degrees Fahrenheit at 

atmospheric pressure, thus reducing its volume by more than 600 times. 

This process makes transport by tankers feasible. The tankers are doublehulled, with each tanker containing between four and six adjacent tanks 

heavily insulated to maintain the LNG’s supercool temperature. Generally, 

LNG—primarily composed of methane—is odorless and nontoxic. It is 

produced by supercooling natural gas to minus 260 degrees Fahrenheit at 

atmospheric pressure, thus reducing its volume by more than 600 times. 

This process makes transport by tankers feasible. The tankers are doublehulled, with each tanker containing between four and six adjacent tanks 

heavily insulated to maintain the LNG’s supercool temperature. Generally, 

Page 1 GAO-07-316 Maritime Security
these ships can carry enough LNG to supply the daily energy needs of over 

10 million homes. Importing LNG requires specialized facilities—called 

regasification terminals—at ports of entry. At these terminals, the liquid is

reconverted into natural gas and then injected into the pipeline system for 

consumers. Currently, the United States has a total of five LNG import 

terminals—four are considered onshore terminals, that is, they are located 

within 3 miles of the shore; one is an offshore terminal located 116 miles 

off the Louisiana coast in the Gulf of Mexico.1

The United States imports about 3 percent of its total natural gas supply as 

LNG in recent years, but by 2030, LNG imports are projected to account

for about 17 percent of the U.S. natural gas supply, according to the 

Department of Energy’s (DOE) Energy Information Administration. To 

meet this increased demand, energy companies have submitted 32 

applications to build new terminals for importing LNG in 10 states and five 

offshore areas. Figure 1 shows the locations of LNG terminals that are 

operational, approved, and proposed. 

 1

The onshore facilities are near Boston, Massachusetts; Cove Point, Maryland; Savannah, 

Georgia; and Lake Charles, Louisiana. The United States also has one LNG export facility in 

Kenai, Alaska, that ships LNG to Japan.

Page 2 GAO-07-316 Maritime Security
Figure 1: Existing, Approved, and Proposed LNG Terminals in the United States, as of October 2006

Sources: FERC and GAO.

Approved by FERC

Proposed to FERC

Proposed to Maritime Administration/Coast Guard

Existing LNG import terminals

Approved by Maritime Administration/Coast Guard

Everett, MA

Cove Point, MD

Lake Charles, LA Elba Island, GA

Page 3 GAO-07-316 Maritime Security
As of October 2006, the Federal Energy Regulatory Commission 

(FERC)2

—responsible for approving onshore LNG terminal siting 

applications—and the U.S. Coast Guard3

—responsible for approving 

offshore LNG terminal siting applications—had together approved 13 of 

these applications. In addition, the Coast Guard contributes to FERC’s 

review of onshore LNG facilities by reviewing and validating an applicant’s 

Waterway Suitability Assessment (WSA) and reaching a preliminary 

conclusion as to whether the waterway is suitable for LNG operations with 

regard to navigational safety and security considerations. The WSA 

includes a security risk assessment to evaluate the public safety risk of an 

LNG spill from a tanker following an attack. The security risk assessment 

analyzes potential types of attacks, their probability, and the potential 

consequences. The WSA also identifies appropriate strategies that can be

used to reduce the risk posed by a terrorist attack on an LNG tanker, 

either by reducing the probability of an attack, or by reducing its 

consequences. If the WSA deems the waterway suitable for LNG tanker 

traffic, the Coast Guard provides FERC with a “Letter of 

Recommendation,” which describes the overall risk reduction strategies 

that will be used on LNG tankers traveling to the proposed terminal. The 

Coast Guard is the lead federal agency for ensuring the security of active 

LNG import terminals and tankers traveling within U.S. ports. 

As figure 1 shows, six new facilities have been proposed for the 

northeastern United States, a region that faces gas supply challenges. The 

Northeast has limited indigenous supplies of natural gas, and receives 

most of its natural gas either through pipelines from the U.S. Gulf Coast or 

Canada, or from overseas via tanker as LNG. The pipelines into the 

Northeast currently run at or near capacity for much of the winter, and 

demand is projected to significantly increase over the next 5 years, 

exceeding available supply by 2010. To meet the increasing demand, new 

supplies of natural gas must reach the Northeast by expanding existing 

pipeline capacity, constructing new pipelines, or constructing new LNG 

terminals—all of which have risk associated with them. Difficulties siting

LNG facilities in the Northeast could lead to higher natural gas prices 

 2

Under the Natural Gas Act, as amended, FERC has exclusive authority to approve or deny 

an application for the siting, construction, or operation of onshore LNG terminals, 

including pipelines, and offshore facilities in state waters—that is, generally within 3 miles 

of shore. 

3

The Coast Guard, along with the Department of Transportation’s Maritime Administration,

has jurisdiction under the Deep Water Port Act of 1974, as amended, to approve the siting 

and operation of offshore LNG facilities in federal waters. 

Page 4 GAO-07-316 Maritime Security
unless additional supply can be brought into the region via new, or 

expansion of old, pipelines. 

Scientists and the public have raised concerns about the potential hazards 

that an LNG spill could pose. When LNG is spilled from a tanker, it forms a 

pool of liquid on the water. Individuals who come into contact with LNG 

could experience freeze burns. 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.

4

 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. 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 multiple tanks on the ship to fail 

in sequence—called 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. 

Although LNG tankers have carried over 40,000 shipments worldwide 

since 1959, there have been no LNG spills resulting from a cargo tank 

rupture. Some safety incidents, such as groundings or collisions, have 

resulted in small LNG spills that did not affect public safety. In the 1970s 

and 1980s, experiments to determine the consequences of a spill examined 

small LNG spills of up to 35 meters in diameter. Following the terrorist 

attacks of September 11, 2001, however, many experts recognized that an

attack on an LNG tanker could result in a large spill—a volume of LNG up 

to 100 times greater than studied in past experiments. Since then, a 

number of studies have reevaluated safety hazards of LNG tankers in light 

of a potential terrorist threat. Because a major LNG spill has never 

occurred, studies examining LNG hazards rely on computer models to 

 4

LNG vapors only ignite when they are in a 5 percent to 15 percent concentration in the air. 

If the LNG concentration is higher, there is not enough oxygen available for fire. If the

concentration is lower, there is likewise not enough fuel for fire. 

Page 5 GAO-07-316 Maritime Security
predict the effects of hypothetical accidents, often focusing on the 

properties of LNG vapor fires. The Coast Guard uses one of these studies, 

conducted in 2004 by Sandia National Laboratories,5

 as a basis for 

conducting the security risk assessment required in the WSA for proposed 

onshore LNG facilities.6

 Access to accurate information about the 

consequences of LNG spills is crucial for developing accurate risk 

assessments for LNG siting decisions. While an underestimation of the 

consequences could expose the public to additional risk in the event of an 

LNG spill, an overestimation of consequences could result in the use of 

inappropriate and costly risk mitigation strategies. DOE recently funded a 

new study—to be completed by Sandia National Laboratories in 2008—

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

validate existing models (such as the one used by Sandia National 

Laboratories in their 2004 study) that calculate the heat hazards of large 

LNG fires. 

In this context, you asked us to (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 the first objective, we identified eight unclassified, completed 

studies of LNG hazards and reviewed the six studies that included new, 

original research (either experimental or modeling) and clearly described 

the methodology used. While we have not verified the scientific modeling 

or results of these studies, the methods used seem appropriate for the 

work conducted. We also interviewed agencies responsible for LNG 

regulations and visited all four onshore LNG import facilities and one 

export facility. To address the second objective, we identified 19 

recognized experts in LNG hazard analysis and convened a Web-based 

expert panel to obtain their views on LNG hazards and to get agreement 

on as many issues as possible. In selecting experts for the panel, we 

sought individuals who are widely recognized as having experience with 

one or more key aspects of LNG hazard analysis. We sought to achieve 

balance in representation from government, academia, consulting, 

 5

Sandia National Laboratories. Guidance on Risk Analysis and Safety Implications of a

Large Liquefied Natural Gas (LNG) Spill Over Water. Albuquerque: 2004.

6

DOE is also sponsoring additional research that applies the 2004 Sandia National 

Laboratories’ methodology to LNG tankers larger than those previously studied, which is

expected to be completed in July 2007. 

Page 6 GAO-07-316 Maritime Security
research organizations, and industry. Additionally, we ensured that our 

expert panel included at least one author from each of the six unclassified

studies of LNG hazards. Because some of the studies conducted are 

classified, this public version of our findings supplements a more 

comprehensive classified report produced under separate cover. A more 

detailed description of our scope and methodology is presented in 

appendix I. We conducted our work from January 2006 through January 

2007 in accordance with generally accepted government auditing 

standards. 

The six unclassified studies we reviewed all examined the heat impact of

an LNG pool 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 ranged from about 500 meters (less than 1/3 of a 

mile) to more than 2,000 meters (about 1-1/4 miles). The Sandia National 

Laboratories’ study concluded that the most likely distance for a burn is 

about 1,600 meters (1 mile). These variations occurred because 

researchers had to make numerous modeling assumptions to scale-up the 

existing experimental data for large LNG spills since there are no large 

spill data from actual events. 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 cascading failure. All three studies considered LNG vapor explosions 

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

National Laboratories’ study examined asphyxiation, and it concluded that 

asphyxiation did not pose a hazard to the general public. Finally, only the 

Sandia National Laboratories’ 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. 

Results in Brief 

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

LNG spill, disagreed with a few conclusions reached by the Sandia 

National Laboratories’ study, and suggested priorities for research to 

clarify the impact of heat and cascading tank failures. Experts agreed that 

(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 

Page 7 GAO-07-316 Maritime Security
as freeze burns and asphyxiation, do not pose a hazard to the public. 

Experts disagreed with the heat impact and cascading tank failure 

conclusions reached by the Sandia National Laboratories’ study, which the 

Coast Guard uses to prepare WSAs. Specifically, all experts did not agree 

with the heat impact distance of 1,600 meters. Seven of 15 experts thought 

Sandia’s distance was “about right,” and the remaining eight experts were 

evenly split as to whether the distance was “too conservative” or “not 

conservative enough” (the other 4 experts 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 

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 identified by the 

expert panel.

We are recommending that DOE incorporate into its current LNG study 

the key issues identified by the expert panel. We particularly recommend 

that DOE examine the potential for cascading failure of LNG tanks. 

Natural gas is primarily composed of methane, with small percentages of 

other hydrocarbons, including propane and butane. When natural gas is 

cooled to minus 260 degrees Fahrenheit at atmospheric pressure, the gas 

becomes a liquid, known as LNG, and it occupies only about 1/600th of the 

volume of its gaseous state. Since LNG is maintained in an extremely 

cooled state—reducing its volume—there is no need to store it under 

pressure. This liquefaction process allows natural gas to be transported by 

trucks or tanker vessels. LNG is not explosive or flammable in its liquid 

state. When LNG is warmed, either at a regasification terminal or from 

exposure to air as a result of a spill, it becomes a gas. As this gas mixes 

with the surrounding air, a visible, low-lying vapor cloud results. This 

vapor cloud can be ignited and burned only within a minimum and 

maximum concentration of air and vapor (percentage by volume). For 

methane, the dominant component of this vapor cloud, this flammability 

range is between 5 percent and 15 percent by volume. When fuel 

concentrations exceed the cloud’s upper flammability limit, the cloud 

cannot burn because too little oxygen is present. When fuel concentrations 

are below the lower flammability limit, the cloud cannot burn because too

little methane is present. As the cloud vapors continue to warm, above 

Background 

Page 8 GAO-07-316 Maritime Security
minus 160 degrees Fahrenheit, they become lighter than air and will rise 

and disperse rather than collect near the ground.

If the cloud vapors ignite, the resulting fire will burn back through the 

vapor cloud toward the initial spill and will continue to burn above the 

LNG that has pooled on the surface. This fire burns at an extremely high 

temperature—hotter than oil fires of the same size. LNG fires burn hotter 

because the flame burns very cleanly and with little smoke. In oil fires, the 

smoke emitted by the fire absorbs some of the heat from the fire and 

reduces the amount of heat emitted. Scientists measure the amount of heat

given off by a fire by looking at the amount of heat energy emitted per unit 

area as a function of time. This is called the surface emissive power of a 

fire and is measured in kilowatts per square meter (kW/m2

). Generally, the 

heat given off by an LNG fire is reported to be more than 200 kW/m2

. By 

comparison, the surface emissive power of a very smoky oil fire can be as

little as 20 kW/m2

. The heat from fire can be felt far away from the fire 

itself. Scientists use heat flux—also measured in kW/m2

—to quantify the 

amount of heat felt at a distance from a fire. For instance, a heat flux of 5 

kW/m2

 can cause second degree burns after about 30 seconds of exposure 

to bare skin. This heat flux can be compared with the heat from a candle—

if a hand is held about 8 to 9 inches above the candle, second degree burns

could result in about 30 seconds. A heat flux of about 12.5 kW/m2

, over an

exposure time of 10 minutes, will ignite wood, and a heat flux of about 

37.5 kW/m2

 can damage steel structures. 

Four types of explosions could potentially occur after an LNG spill: rapid 

phase transitions (RPT), deflagrations, detonations, and boiling-liquidexpanding-vapor-explosions (BLEVE).7

 More specifically: 

• An RPT occurs when LNG is warmed and changes into natural gas nearly

instantaneously. An RPT generates a pressure wave that can range from 

very small to large enough to damage lightweight structures. RPTs strong

enough to damage test equipment have occurred in past LNG spill 

experiments on water, although their effects have been localized at the site 

of the RPT.

• Deflagrations and detonations are explosions that involve combustion 

(fire). They differ on the basis of the speed and strength of the pressure 

 7

Generally, an explosion is an energy release associated with a pressure wave. Some 

explosions are large enough that the pressure wave can break windows or damage 

structures, while others are much smaller. 

Page 9 GAO-07-316 Maritime Security
wave generated: deflagrations move at subsonic velocities and can result 

in pressures (overpressures) up to 8 times higher than the original 

pressure; detonations travel faster—at supersonic velocities—and can 

result in larger overpressures—up to 20 times the original pressure. 

Methane does not detonate as readily as other hydrocarbons; it requires a 

larger explosion to initiate a detonation in a methane cloud. 

• A BLEVE occurs when a liquefied gas is heated to above its boiling point 

while contained within a tank. For instance, if a hot fire outside an LNG 

tanker sufficiently heated the liquid inside, a percentage of the LNG within 

the tank could “flash” into a vapor state virtually instantaneously, causing

the pressure within the tank to increase. LNG tanks do have pressure relief 

valves, but if these were inadequate or failed, the pressure inside the tank 

could rupture the tank. The escaping gas would be ignited by the fire 

burning outside the tank, and a fireball would ensue. The rupture of the 

tank could create an explosion and flying debris (portions of the tank). 

World natural gas reserves are abundant, estimated at about 6,300 trillion 

cubic feet, or 65 times the volume of natural gas used in 2005. Much of this

gas is considered “stranded” because it is located in regions far from 

consuming markets. Russia, Iran, and Qatar combined hold natural gas 

reserves that represent more than half of the world total. Many countries

have imported LNG for years. 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. In 2005, LNG imports to 

the United States originated primarily in Trinidad and Tobago (70 

percent), Algeria (15 percent), and Egypt (11 percent). The remaining 4 

percent of U.S. LNG imports came from Oman, Malaysia, Nigeria, and 

Qatar. 

LNG tankers primarily have two basic designs, called membrane or Moss 

(see fig. 2). Both designs consist of an outer hull, inner hull, and cargo

containment system. In membrane tank designs, the cargo is contained by

an Invar, or stainless steel double-walled liner, that is structurally 

supported by the vessel’s inner hull. The Moss tank design uses 

structurally independent spherical or prismatic shaped tanks. These tanks, 

usually five located one behind the other, are constructed of either 

stainless steel or an aluminum alloy. LNG tankers ships are required to 

meet international maritime construction and operating standards, as well 

as U.S. Coast Guard safety and security regulations. 

Page 10 GAO-07-316 Maritime Security
Figure 2: LNG Membrane 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’ 

variations in heat effects result from the assumptions made in the studies’ 

models. Some studies also examined other potential hazards such as LNG 

vapor explosions, other types of explosions, and asphyxiation, and 

identified their potential impacts on public safety. 

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. Key assumptions 

made included the following: 

Source: GAO.

Studies Identified 

Different Distances 

for the Heat Effects of 

an LNG Fire 

Studies Identified Various 

Distances That the Heat 

Effects of an LNG Fire 

Could Be Hazardous to 

People because of 

Assumptions Made 

• Hole size and cascading failure. Hole size is an important parameter for 

modeling LNG spills because of its relationship to the duration of the 

event—larger holes allow LNG to spill from the tanker more quickly,

resulting in larger LNG pools and shorter duration fires. Conversely, small 

holes could create longer-duration fires. Cascading failure is important 

because it increases the overall spill volume and the duration of the spill.

Page 11 GAO-07-316 Maritime Security
• Waves and wind. These conditions can affect the size of both the LNG 

pool and the heat hazard zone. One study indicated that waves can inhibit

the spread of an LNG pool, keeping the pool size much smaller than it 

would be on a smooth surface, and thereby reducing the size of the LNG 

pool fire. Wind will tend to tilt the fire downwind (like a candle flame 

blowing in the wind), increasing the heat hazard zone in that direction 

(and decreasing it upwind). 

• Volume of LNG spilled. The amount of LNG spilled is one of the factors 

that can affect the size of the pool. 

• Surface emissive power of the fire. While the amount of heat given off by 

a large LNG fire is unknown, assumptions about it directly affect the 

results for the heat hazard zone. It is expected that the surface emissive 

power of LNG fires will be lower for large fires because oxygen will not 

circulate efficiently within a very large fire. Lack of oxygen in the middle 

of a large fire would lead to more smoke production, which would block 

some of the heat from the fire. 

The LNG spill consequence studies’ key assumptions and results are 

shown in table 1. 

Page 12 GAO-07-316 Maritime Security
Table 1: Key Assumptions and Results of the LNG Spill Consequence Studies 

Key assumptions Key results 

Environmental 

conditions modeled:

Hole 

size (m2

) 

Number of 

tanks that 

rupture

(cascading

failure 

Wind

speed

and its

effect on

waves

(m/s)

Wind

speed

and its

effect on

fire (m/s)

Spill

volume 

(m3)

Fire 

surface 

emissive

power

(kW/m2)

Pool 

diameter 

(meters) 

Distance to

the 5kw/m2

heat level 

(meters)

Duration

(minutes)

19.6 1 1.5 1.5 12,500 b156 497 14.3

19.6 1 5.0 5.0 12,500 b146 531 16.6

Quest 

Consultants 

Inc. (Quest)a

19.6 1 9.0 9.0 12,500 b110 493 28.6

2 3 c c37,500 220 209 784 20

5 3 c c37,500 220 572 2,118 8.1

5 1 c c12,500 350 330 1,652 8.1

5d1 c c12,500 220 330-405 1,305-1,579 5.4-8.1

Sandia 

National 

Laboratories 

(Sandia) 

12 1 c c

12,500 220 512 1,920 3.4

Pitblado, et 

al. 

(Pitblado)e

1.77 1 c

3.0 17,250 b171 750 32

0.79 1 c8.9 12,500 265 200gABS 650 51

Consulting

(ABSC)f

19.6 1 c

8.9 12,500 265 620g1,500 4.2

Fay (Fay)h20 1 c c14,300 b b1,900 3.3

Lehr and 

SimecekBeatty (Lehr)i b b c c

500 200 b500 2-3

Source: GAO analysis of spill consequence studies. 

a

“Modeling LNG Spills in Boston Harbor.” Copyright© 2003 Quest Consultants, Inc., Norman, OK 

73609; Letter from Quest Consultants to DOE (October 2, 2001); Letter from Quest Consultants to 

DOE (October 3, 2001). 

b

Information not available. 

c

Not included in the model. 

d

The study examined multiple scenarios of 5m2. The ranges listed summarize the highest and lowest 

values for those scenarios. 

e

R. M. Pitblado, J. Baik, G. J. Hughes, C. Ferro, and S. J. Shaw. “Consequences of Liquefied Natural

Gas Marine Incidents.” Process Safety Progress 24 no. 2 (June 2005). 

f

ABS Consulting Inc. Consequence Assessment Methods for Incidents Involving Releases from 

Liquefied Natural Gas Carriers. May 13, 2004. FERC “Staff’s Responses to Comments on the 

Consequence Assessment Methods for Incidents Involving Releases from Liquefied Natural Gas 

Carriers,” June 18, 2004. 

Page 13 GAO-07-316 Maritime Security
g

ABS Consulting modeled pool size as a semicircle and reported the radius of that semicircle in the 

study. The reported radii were used to calculate the diameter of the semicircle so the study results 

could be compared with the other studies. 

h

J.A. Fay. “Model of Spills and Fires from LNG and Oil tankers.” Journal of Hazardous Materials B96 

(2003): 171-188.

I

William Lehr and Debra Simecek-Beatty. “Comparison of Hypothetical LNG and Fuel Oil Fires on 

Water.” Journal of Hazardous Materials 107 (2004): 3-9. 

In terms of the studies’ results, we identified the following three key 

results: 

• Pool size describes the extent of the burning pool—and can help people 

understand how large the LNG fire itself will be. 

• Heat hazard distance describes the distance at which 30 seconds of 

exposure could cause second degree burns. 

• Fire duration of the incident describes how long people and 

infrastructure will be exposed to the heat from the fire. The longer the fire, 

the greater potential for damage to the tanker and for cascading failure. 

Although all the studies considered the consequences of an LNG spill, they 

were conducted for different purposes. Three of the six studies—Quest, 

Sandia, and Pitblado—specifically addressed the consequences of LNG 

spills caused by terrorist attacks. Two of these three studies—Quest and 

Sandia—were commissioned by DOE. The Quest study, begun in response 

to the September 11, 2001, attacks, was designed to quantify the heat 

hazard zones for LNG tanker spills in Boston Harbor. Only the Quest study 

examined how wind and waves would affect the spreading of the LNG on 

the water and the size of the resulting LNG pool. The Quest study based its 

wind and wave assumptions on weather data from buoys near Boston 

Harbor. The Quest study found that, while the waves would help reduce 

the size of the LNG pool, the winds that created the waves would tend to 

increase the heat hazard distance downwind. To simplify the modeling of 

the waves, the Quest study considered “standing” waves (rather than 

moving waves) of various heights and, therefore, did not consider the 

impact of wave movement on LNG pool spreading. The ABSC study 

expressed concern that Quest’s standing wave assumption resulted in pool 

sizes that were too small because wave movement might help spread the

LNG. 

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 

Page 14 GAO-07-316 Maritime Security
could be used to mitigate the consequences of an LNG spill. The 

assumptions and results in table 1 for the Sandia study refer to the 

scenarios Sandia examined that had terrorist causes. According to Sandia, 

the study used available intelligence and historical data to develop 

credible and possible scenarios for the kinds of attacks that could breach 

an LNG tanker. Sandia then modeled how large a hole each of the weapon

scenarios could create in an LNG tanker.8

 Two of these intentional breach 

scenarios included cascading failure of three tanks on an LNG tanker. 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. After considering all

of its scenarios, Sandia concluded that, as a rule-of-thumb, 1,600 meters is

a good approximation of the heat hazard distance for terrorist-induced 

spills. However, as the table shows, one of Sandia’s scenarios—for a large 

spill with cascading failure of three LNG tanks—found that the distance 

could exceed more than 2,000 meters and that the cascading failure would 

increase the duration of the incident.

Finally, the stated purpose of industry’s Pitblado study was to develop

credible threat scenarios for attacks on LNG tankers and predict hazard 

zones for LNG spills from those types of attacks. The study identified a 

hole size smaller than the other studies that specifically considered 

terrorist attacks. 

The other studies we reviewed examined LNG spills regardless of cause. 

FERC commissioned the ABS Consulting study to develop appropriate 

methods for estimating heat hazard zones from LNG spills. FERC uses 

these methods, in conjunction with the Sandia study, to examine the 

public safety consequences of tankers traveling to proposed onshore LNG 

facilities before granting siting approval. The two scenarios in the ABSC 

study illustrate how small holes could result in longer fires, which have a 

higher potential to damage the tanker itself. One scenario used a hole size

of 0.79 square meters and the other a hole size of about 20 square meters. 

The difference in duration is striking—it takes 51 minutes and 4.2 minutes, 

respectively, for the fire to consume all the spilled LNG. 

Finally, the Lehr and Fay studies compared the fire consequences of LNG 

spills with known information about oil spills and fires. Although most 

 8

Please note that the information used to develop Sandia’s terrorist scenarios is classified 

and will be discussed in GAO’s classified report.

Page 15 GAO-07-316 Maritime Security
studies made similar assumptions about the volume of LNG spilled from 

any single LNG tank, Lehr examined a much smaller spill volume—just 500 

cubic meters of LNG, compared with a range of 12,500 to 17,250 cubic 

meters. 

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

including LNG vapor explosions, other types of explosions, and 

asphyxiation. 

LNG vapor explosions. Three studies—Sandia, ABSC, and Pitblado—

examined LNG vapor explosions, and all agreed that it is unlikely that LNG 

vapors could explode and create a pressure wave if the vapors are in an

unconfined space. Although the three studies agreed that LNG vapors 

could explode only in confined areas, they did not conduct modeling or 

describe the likelihood of such confinement after an LNG spill from a 

tanker. The Sandia study stated that fire will generally progress through 

the vapor cloud slowly and without producing an explosion with damaging

pressure waves. The study did suggest, however, that if the LNG vapor 

cloud is confined (e.g., between the inner and outer hull of an LNG 

carrier), it could explode but would only affect the immediate surrounding 

area. The ABSC study and the Pitblado study agreed that a confined LNG 

vapor cloud could result in an explosion. 

Other types of explosions. Three studies—Sandia, ABSC, and Pitblado—

examined the potential for RPTs. The Sandia study concluded that, while 

RPTs have generated energy releases equivalent to several pounds of 

explosives, RPT impacts will be localized near the spill. Sandia also noted 

that RPTs are not likely to cause structural damage to the vessel. The 

ABSC study noted that their literature search suggested that damage from

RPT overpressures would be limited to the immediate vicinity, though it

noted that the literature did not include large spills like those that could be 

caused by a terrorist attack. Only one study, Pitblado, discussed the 

possibility of a BLEVE. According to our discussions with Dr. Pitblado, an 

LNG ship with membrane tanks could not result in a BLEVE, but he said 

that Moss spherical tanks could potentially result in a BLEVE. A BLEVE 

could result because it is possible for pressure to build up in a Moss 

tanker. A 2002 LNG tanker truck incident in Spain resulted in an explosion 

that some scientists have characterized as a BLEVE of an LNG truck. 

Portions of the tanker truck were found 250 meters from the accident 

itself, propelled by the strength of the blast. 

Asphyxiation. Only the Sandia study examined the potential for 

asphyxiation following an LNG spill if the vapors displace the oxygen in 

Some Studies Examined 

Other Potential Hazards 

and Identified Their 

Impact on Public Safety 

Page 16 GAO-07-316 Maritime Security
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.

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.9

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. 

Experts discussed two types of fires: vapor cloud fires and pool fires. 

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. While the initial vapor cloud fire would be of short duration as

the flames burned back toward the LNG carrier, any flammable object

enveloped by the vapor cloud fire could ignite nearby objects, creating 

secondary fires that present hazards to the public. Three experts 

emphasized in their comments that the vapor cloud is unlikely to penetrate 

very far into a populated area before igniting. Expanding on this point, one 

expert noted that any injuries from a vapor cloud fire would occur only at 

the edges of a populated area, for example, along beaches. One expert 

disagreed, arguing that a vapor cloud fire is unlikely to cause significant 

secondary fires because it would not last long enough to ignite other 

materials. 

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 

Experts Agreed That the 

Heat from an LNG Fire 

Was Most Likely to Affect 

Public Safety, but That 

Explosions from an LNG 

Spill Are Unlikely 

 9

We considered experts “in agreement” if more than 75 percent of experts indicated that

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

commented on every issue discussed. 

Page 17 GAO-07-316 Maritime Security
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 and scenario-specific factors. Furthermore, a large, 

unconfined pool fire is very difficult to extinguish; generally almost all the 

LNG must be consumed before the fire goes out. Experts agreed that three 

of the main factors that affect the amount of heat from an LNG fire are the 

following: 

• Site-specific weather conditions. Weather conditions, such as wind and 

humidity, can influence the heat hazard distances. For example, more 

humid conditions allow heat to be absorbed by the moisture in the air, 

reducing heat hazard distances. 

• Composition of the LNG. The composition of the LNG can also affect the 

distance at which heat from the fire is felt by the public. In small fires, 

methane, which comprises between 84 percent and 97 percent of LNG, 

burns cleanly, with little smoke. Other LNG components—propane and

butane—produce more smoke when burned, absorbing some of the fire’s 

heat and reducing the hazard distance. As the fire grows larger, the 

influence of the composition of LNG is hypothesized to be less

pronounced because large fires do not burn efficiently. 

• Size of the fire. The size of the fire has a major impact on its surface 

emissive power; the heat hazard distance increases with pool size up to a 

point but is expected to decrease for very large pools, like those caused by 

a terrorist attack. 

Experts also discussed the following hazards related to an LNG spill: 

• RPTs. Experts agreed that RPTs could occur after an LNG spill but that the 

overpressures generated would be unlikely to directly affect the public. 

• Detonations and deflagrations. Experts made a key distinction between 

these types of explosions in confined spaces as opposed to unconfined 

spaces. For confined spaces, they agreed that it is possible, under 

controlled experimental conditions, to induce both types of explosions of 

LNG vapors; however, a detonation of confined LNG vapors is unlikely 

following an LNG spill caused by a terrorist attack. Experts were split on 

the likelihood of a confined deflagration occurring after a terrorist attack: 

eight thought it was unlikely, four thought it likely, and five thought 

neither likely nor unlikely.10 For unconfined spaces, experts were split on 

 10Two experts did not comment. 

Page 18 GAO-07-316 Maritime Security
whether it is possible to induce such explosions; however, even experts 

who thought such explosions were possible agreed that deflagrations and

detonations in unconfined spaces are unlikely to occur following an LNG 

spill caused by a terrorist attack. 

• BLEVE. Experts were split on whether a BLEVE is theoretically possible 

in an LNG tanker. Of the ten experts who agreed it was theoretically

possible, six thought that a BLEVE is unlikely to occur following an LNG 

spill caused by a terrorist attack on a tanker.11

• Freeze burns and asphyxiation. Experts agreed that freeze burns do not 

present a hazard to the public because only people in close proximity to 

LNG spill, such as personnel on the tanker or nearby vessels, might come 

into contact with LNG or very cold LNG vapor. For asphyxiation, experts 

agreed that it is unlikely that an LNG vapor cloud could reach a populated 

area while still sufficiently concentrated to pose an asphyxiation threat. 

Experts disagreed with heat hazard and cascading failure conclusions of 

the Sandia study. Specifically, 7 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). Experts who thought the distance was too 

conservative generally listed one of two reasons. First, the assumptions 

about the surface emissive power of large fires were incorrect because the 

surface emissive power of large fires would be lower than Sandia 

assumed. Second, Sandia’s hazard distances are based on the maximum 

size of a pool fire. However, these experts pointed out that once a pool fire 

ignites, its diameter will begin to shrink, which will also reduce the heat 

hazard distance. Experts who thought Sandia’s heat hazard distance was 

not conservative enough listed a number of concerns. For example, 

Sandia’s distances do not take into consideration the effects of cascading 

failure. One expert suggested that a 1-meter hole in the center tank of an 

LNG tanker that resulted in a pool fire could cause the near simultaneous 

failure of the other four tanks, leading to a larger heat hazard zone. 

Experts Disagreed with a 

Few Key Conclusions of 

the Sandia National 

Laboratories Study 

 11Three experts said that BLEVEs were “neither likely nor unlikely,” and one expert thought

that BLEVEs were likely. 

Page 19 GAO-07-316 Maritime Security
Officials at Sandia National Laboratories and our panel of experts 

cautioned that the hazard distances presented cannot be applied to all 

sites. According to the Sandia study authors, their goal was to provide 

guidance to federal agencies on the order of magnitude of the hazards of 

an LNG spill on water. As they pointed out in interviews and in their 

original study, further analysis for specific sites is needed to understand 

hazards in a particular location. Six experts on our panel also emphasized 

the importance of site-specific and scenario-specific factors. For instance, 

one expert explained that the 5kW/m2

 hazard distance depends on the size 

of the tanker and the spill scenario, including factors such as wind speed, 

timing of ignition, and the location of the hole. Other experts suggested 

that key factors are spill volume and the impact of waves. 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.” 

Only 9 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. Three experts said 

that an LNG spill and subsequent fire could potentially result in the loss of 

all tanks on board the tanker. 

Twelve of 16 experts agreed, however, with Sandia’s conclusion that 

cascading failure events are not likely to greatly increase (by more than 20 

to 30 percent) the overall fire size or heat hazard ranges. The four experts 

who disagreed with Sandia’s conclusion about the public safety impact of

cascading failure cited two main reasons: (1) Sandia did not clearly 

explain how it reached that conclusion and (2) the impact of cascading 

failure will partly depend on how the incident unfolds. For instance, one 

expert suggested that cascading failure could include a tank rupture, 

fireball, or BLEVE, any of which could have direct impacts on the public 

(from the explosive force) and which would change the heat hazard zones 

that Sandia identified. 

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 20 GAO-07-316 Maritime Security
In the second iteration of the Web-based panel, we asked the experts to 

identify the five areas related to the consequences of LNG spills that need

further research. Then, in the final iteration of the Web-based panel, we 

provided the experts with a list of 19 areas—generated by their 

suggestions and comments from the second iteration—and asked them to 

rank these in order of importance. Table 2 presents the results of that 

ranking for the top 10 areas identified and indicates those areas that are 

funded in the DOE study discussed earlier. 

Table 2: Expert Panel’s Ranking of Need for Research on LNG

Experts Suggest Future 

Research Priorities to 

Determine the Public 

Safety Impact of an LNG 

Spill 

Rank Research area

Funded in 

DOE’s study

1 Large fire phenomena √

2 Cascading failure

3 Large-scale spill testing on water √

4 Large-scale fire testing √

5 Comprehensive modeling: interaction of physical processes 

6 Risk tolerability assessments 

7 Vulnerability of containment systems (hole size) 

8 Mitigation techniques

9 Effect of sea water coming in as LNG flows out 

10 Impact of wind, weather, and waves 

Source: GAO.

Note: A rank of 1 is the highest rank, and a rank of 10 is the lowest. Panel members ranked 19 areas 

of research from 1 to 19; a score was calculated for each area based on this ranking. Only the 10 

areas with the highest scores are presented in this table. 

As the table shows, two of the top five research areas identified are related 

to large LNG fires—large fire phenomena and large-scale fire testing. 

Experts believe this research is needed to establish the relationship 

between large pool fires and the surface emissive power of the fire. 

Experts recommended new LNG tests for fires between 15 meters and 

1,000 meters. The median suggested test size was 100 meters. Some 

experts also raised the issue of whether large LNG fires will stop behaving 

like one single flame but instead break up into several smaller, shorter 

flames. Sandia noted in its study that this behavior could reduce heat 

hazard distances by a factor of two to three. 

Experts also ranked research into cascading failure of LNG tanks second 

in the list of priorities. Concerning cascading failure, one expert noted 

that, although the consequences could be serious, there are virtually no 

Page 21 GAO-07-316 Maritime Security
data looking at the hull damage caused by exposure to extreme cold or 

heat. 

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. For DOE, Sandia National Laboratories 

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. The goal of this fire testing is to document the 

impact of smoke on large LNG pool fires. Sandia suggests that these tests 

will create a higher degree of knowledge of large-scale pool fire behavior 

and significantly lower the current uncertainty in predicting heat hazard 

distances. 

According to researchers at Sandia National Laboratories, some of the 

research our panel of experts suggested may not be appropriate. Sandia 

indicated that comprehensive modeling, which allows various complex 

processes to interact, would be very difficult to do because of the 

uncertainty surrounding each individual process of the model. One expert

on our panel agreed, noting that while comprehensive modeling of all LNG 

phenomena is important, combining those phenomena into one model 

should wait for experiments that lead to better understanding of each 

individual phenomenon.

It is likely that the United States will increasingly depend on the 

importation of LNG to meet the nation’s demand for natural gas. 

Understanding and resolving the uncertainties surrounding LNG spills is 

critical, especially in deciding on where to locate LNG facilities. Because 

there have been no large-scale LNG spills or spill experiments, past studies 

have developed modeling assumptions based on small-scale spill data. 

While there is general agreement on the types of effects from an LNG spill, 

the results of these models have created what appears to be conflicting

assessments of the specific consequences of an LNG spill, creating 

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. Although DOE has 

recently funded a study that will address large-scale LNG fires, this study 

will address only 3 of the top 10 issues—and not the second-highest 

Conclusions 

Page 22 GAO-07-316 Maritime Security
ranked issue—that our panel of experts identified as potentially affecting 

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 recommend that the Secretary of Energy ensure that 

DOE incorporates the key issues identified by the expert panel into its 

current LNG study. We particularly recommend that DOE examine the 

potential for cascading failure of LNG tanks in order to understand the 

damage to the hull that could be caused by exposure to extreme cold or 

heat. 

We requested comments on a draft of this report from the Secretary of 

Energy (DOE). DOE agreed with our findings and recommendation. In 

addition, DOE included technical and clarifying comments, which we 

included in our report as appropriate. 

As agreed with your offices, unless you publicly announce the contents of

this report earlier, we plan no further distribution until 30 days from the 

report date. At that time, we will send copies to interested congressional 

committees, the Secretary of Energy, and other interested parties. We also 

will make copies available to others upon request. In addition, the report 

will be available at no charge on the GAO Web site at http://www.gao.gov. 

If you or your staff have any questions regarding this report, please 

contact me at (202) 512-3841 or wellsj@gao.gov. Contact points for our 

Offices of Congressional Relations and Public Affairs may be found on the 

last page of this report. Key contributors to this report are listed in 

appendix IV.

Jim Wells 

Director, Natural Resources 

 and Environment 

Recommendation for 

Executive Action 

Agency Comments 

and Our Evaluation 

Page 23 GAO-07-316 Maritime Security
Appendix I: Scope and Methodology 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. While we have not verified the 

scientific modeling or results of these studies, the methods used seem 

appropriate for the work conducted based on conversations with experts 

in the field and our assessment. We also discussed these studies with their 

authors and visited all four onshore LNG import facilities and one export 

facility. We attended a presentation on LNG safety and received specific 

training on LNG properties and safety. We also conducted interviews with 

officials from Sandia National Laboratories, Federal Energy Regulatory 

Commission, Department of Transportation, Department of Energy, and 

the U. S. Coast Guard. During our interviews, we asked officials to provide 

information on past LNG studies and plans for future LNG spill 

consequences work. 

To obtain information on experts’ opinions of the public safety 

consequences of an LNG spill from a tanker, we conducted a three-phase, 

Web-based survey of 19 experts on LNG spill consequences. We identified 

these experts from a list of 51 individuals who had expertise in one or 

more key aspects of LNG spill consequence analysis. In compiling this 

initial list, we sought to achieve balance in terms of area of expertise (i.e.,

LNG experiments, modeling LNG dispersion, LNG vaporization, fire 

modeling, and explosion modeling). In addition, we included at least one 

author of each of the six major LNG studies we reviewed, that is, studies 

by Sandia National Laboratories; ABS Consulting; Quest Consultants Inc.; 

Pitblado, et al.; James Fay (MIT); and William Lehr (National Oceanic and

Atmospheric Administration). We gathered resumes, publication lists, and 

major LNG-related publications from the experts identified on the initial 

list. 

We selected 19 individuals for the panel. One or more of the following 

selection criteria were used: (1) has broad experience in all facets of LNG 

spill consequence modeling (LNG spill from hole, LNG dispersion, 

vaporization and pool formation, vapor cloud modeling, fire modeling, and 

explosion modeling); (2) has conducted physical LNG experiments; or (3) 

has specific experience with areas of particular importance, such as LNG 

explosion research. In addition, we included: (1) at least one author from 

each of the major LNG studies and (2) representatives from private 

industry, consulting, academia, and government. All 19 experts selected 

for the panel agreed to participate. The names and affiliations of panel 

members are included in appendix II. 

Page 24 GAO-07-316 Maritime Security
Appendix I: Scope and Methodology 

To obtain consensus concerning public safety issues, we used an iterative 

Web-based process. We used this method, in part, to eliminate the 

potential bias associated with group discussions. These biasing effects 

include the potential dominance of individuals and group pressure for 

conformity. Moreover, by creating a virtual panel, we were able to include

more experts than possible with a live panel. 

For each phase in the process, we posted a questionnaire on GAO’s survey 

Web site. Panel members were notified of the availability of the 

questionnaire with an e-mail message. The e-mail message contained a 

unique user name and password that allowed each respondent to log on 

and fill out a questionnaire but did not allow respondents access to the 

questionnaires of others. 

In the questionnaires, we asked the experts to agree or disagree with a set

of statements about LNG hazards derived from GAO’s synthesis of major 

LNG spill consequence studies. Prior to the first iteration, we had an LNG 

spill consequence expert who was not a part of the panel review each 

statement and provide comments about technical accuracy and tone. 

Experts were asked to indicate agreement on a 3-point scale (completely 

agree, generally agree, do not agree) and to provide comments about how 

the statements could be changed to better reflect their understanding of 

the consequences of LNG spills. 

If most experts agreed with a statement during the first iteration, we did 

not include it in the second iteration. If there was not agreement, we used

the experts’ comments to revise the statements for the second iteration. 

The second iteration was posted on the Web site, using the same protocol 

as used for the first. Again, panel members were asked to agree or 

disagree and provide narrative comments. We revised the statements 

where there was disagreement and posted them on the Web site again for 

the third iteration. At the end of the third iteration, at least 75 percent of 

the experts agreed or generally agreed with most of the ideas presented. 

Because some of the studies conducted are classified, this public version

of our findings supplements a more comprehensive classified report 

produced under separate cover. We conducted our work from January 

2006 through January 2007 in accordance with generally accepted 

government auditing standards. 

Page 25 GAO-07-316 Maritime Security
Appendix II: Names and Affiliations of 

Members of GAO’s Expert Panel on LNG Appendix II: Names and Affiliations of Hazards 

Members of GAO’s Expert Panel on LNG 

Hazards 

Myron Casada ABS Consulting 

T.Y. Chu Sandia National Laboratories 

Philip Cleaver Advantica 

Bob Corbin U.S. Department of Energy 

John Cornwell Quest Consultants, Inc.

James Fay Massachusetts Institute of Technology 

Louis Gritzo FM Global 

Jerry Havens University of Arkansas 

Benedict Ho BP 

Greg Jackson University of Maryland 

Ron Koopman Hazard Analysis Consulting 

Bill Lehr National Oceanic and Atmospheric Administration 

Georges Melhem ioMosaic Corporation 

Gordon Milne Lloyd’s Register 

Robin Pitblado Det Norske Veritas 

Phani Raj Technology and Management Systems, Inc. 

Velisa Vesovic Imperial College 

Harry West Texas A&M University 

John Woodward Baker Engineering and Risk Consultants, Inc. 

Page 26 GAO-07-316 Maritime Security
Appendix III: S

Results 

ummary of Expert Panel 

Page 27 GAO-07-316

Appendix III: Summary of Expert Panel 

Results 

For each question below, we show only those responses that were 

selected by at least one expert. The number of responses adds up to 19—

the total number of experts on the panel. Percentages may not add to 100% 

due to rounding. 

Large LNG spills from a vessel could be caused by an accident, such as 

collision or grounding, or by an intentional attack. While large accidental 

LNG spills are highly unlikely given current LNG carrier designs and 

operational safety policies and practices, these spills do pose a hazard to 

the public if they occur in or near a populated area. What is your level of

agreement with this paragraph? (Finalized in the second iteration.) 

Count Percentage Label

8 42.11% Completely agree

11 57.89% Generally agree

LNG is a cryogenic liquid composed primarily of methane with low 

concentrations of heavier hydrocarbons, such as ethane, propane, and 

butane. LNG is colorless, odorless, and nontoxic. When LNG is spilled, it 

boils and forms LNG vapor (natural gas). The LNG vapor is initially denser 

than ambient air and visible; LNG vapor will stay close to the surface as it 

mixes with air and disperses. LNG and LNG vapor pose four possible 

hazards: freeze burns, asphyxiation, fire hazard, and explosions. What is 

your level of agreement with this paragraph? (Finalized in the second

iteration.) 

Introduction 

LNG Hazards 

Overall Hazards 

Count Percentage Label

5 26.32% Completely agree

12 63.16% Generally agree

2 10.53% Do not agree 

Maritime Security
Appendix III: Summary of Expert Panel 

Results 

LNG poses a threat of freeze burns to people who come into contact with 

the liquid or with very cold LNG vapor. Since LNG boils immediately and 

vaporizes after it leaves an LNG tank and LNG vapor warms as it mixes 

with air, only people in close proximity to the release, such as personnel 

on the tanker or nearby escort vessels, might come into contact with LNG 

or LNG vapor while it is still cold enough to result in freeze burns. Freeze 

burns do not present a direct hazard to the public. What is your level of 

agreement with this paragraph? (Finalized in the second iteration.) 

LNG Hazards-Freeze Burns 

Count Percentage Label

14 73.68% Completely agree

5 26.32% Generally agree

After an LNG spill, LNG vapor forms a dense, visible vapor cloud that is 

initially heavier than air and remains close to the surface. The cloud 

warms as it mixes with air and as portions of the cloud reach ambient air 

temperatures, they begin to rise and disperse. Asphyxiation occurs when 

LNG vapor displaces oxygen in the air. Asphyxiation is a threat primarily 

to personnel on the LNG tanker or to people aboard vessels escorting the 

tanker at close range. An LNG vapor cloud could move away from the 

tanker as it mixes with air and begins to disperse. However, it is unlikely 

that the vapor cloud could reach a populated area while still sufficiently 

concentrated to pose an asphyxiation threat to the public. What is your 

level of agreement with this paragraph? (Finalized in the second 

iteration.) 

LNG Hazards-Asphyxiation 

Count Percentage Label

8 42.11% Completely agree

10 52.63% Generally agree

1 5.26% Do not agree 

The effect of wind on an LNG vapor cloud varies with wind speed. The 

most hazardous wind conditions, however, are low winds, which can push 

a vapor cloud downwind without accelerating the LNG vapor dispersion 

into the atmosphere. Low wind conditions have the highest potential of 

allowing an LNG vapor cloud to move a significant distance downwind. 

LNG Hazards-Vapor Cloud: 

Wind Effect 

Page 28 GAO-07-316 Maritime Security
Appendix III: Summary of Expert Panel 

Results 

What is your level of agreement with this paragraph? (Finalized in 

the third iteration.) 

Count Percentage Label

8 42.11% Completely agree

10 52.63% Generally agree

1 5.26% Do not agree 

Because LNG vapor in an approximately 5 to 15 percent mixture with air is 

flammable, LNG vapor within this flammability range is likely to ignite if it 

encounters a sufficiently strong ignition source such as a cigarette lighter 

or strong static charge. What is your level of agreement with this 

paragraph? (Finalized in the third iteration.) 

LNG Hazards-Fire Hazard 

Count Percentage Label 

13 68.42% Completely agree

6 31.58% Generally agree

The main hazard to the public from a pool fire is the thermal radiation, or 

heat, that is generated by the fire rather than the flames themselves. Often 

this heat is felt at considerable distance from the fire. Scientific papers 

have used two different thresholds as end points to describe the impact of 

thermal radiation on the public: 5 kilowatts per square meter and 1.6 

kilowatts per square meter. 

Which level do you think is the appropriate end point to use to 

define thermal hazard zones in order to protect the public? 

(Please indicate your response, then provide an explanation in the 

textbox below your answer.) 

LNG Hazards-Fire Hazard: 

Thermal Hazard End Point 

Count Percentage Label

8 42.11% 5 kilowatts per square meter 

2 10.53% 1.6 kilowatts per square meter 

6 31.58% Other

3 15.79% I do not have the expertise necessary to 

respond to this question. 

Page 29 GAO-07-316 Maritime Security
Appendix III: Summary of Expert Panel 

Results 

Of the six experts who answered “other,” two experts indicated that 

5kW/m2

 is a useful or appropriate level for measuring the impact on 

people. One expert suggested that dosage (a measure that combines 

thermal radiation and duration of exposure) is most appropriate. Another

expert suggested that both thresholds are appropriate, depending on the 

circumstances of the analysis. (Finalized in the first iteration.) 

A pool fire could form in the wake of a vapor cloud fire burning back to 

the source or just after an LNG spill, if there is immediate ignition of the 

LNG vapor. A pool fire burns the vapor above a liquid LNG pool as the 

liquid boils from the pool. A large, unconfined pool fire is very difficult to

extinguish; generally almost all the LNG must be consumed before the fire

goes out. What is your level of agreement with this paragraph?

(Finalized in the second iteration.) 

LNG Hazards-Fire Hazard: Pool 

Fire 

Count Percentage Label

13 68.42% Completely agree 

5 26.32% Generally agree 

1 5.26% Do not agree 

The main hazard to the public from a pool fire is the thermal radiation, or 

heat, from the fire. This heat can be felt at a considerable distance from 

the flames themselves. Numerous factors can impact the amount of 

thermal radiation that could affect the public: site-specific weather 

conditions, including humidity and wind speed and direction, the 

composition of the LNG, and the size of the fire. What is your level of 

agreement with this paragraph? (Finalized in the second iteration.) 

Count Percentage Label

13 68.42% Completely agree

6 31.58% Generally agree

The wind speed and direction also affect the distance at which thermal 

radiation from the fire is felt by the public. In high winds, the flames will 

tilt downwind, increasing the amount of heat felt downwind of the fire and 

decreasing the amount of heat felt upwind. More humid conditions allow 

heat to be absorbed by the moisture in the air reducing the heat felt by the 

public. What is your level of agreement with the above paragraph?

(Finalized in the second iteration.) 

Page 30 GAO-07-316 Maritime Security
Appendix III: Summary of Expert Panel 

Results 

Count Percentage Label

6 31.58% Completely agree 

11 57.89% Generally agree but suggest the following 

clarification. 

2 10.53% I do not have the expertise necessary to respond to 

this section. 

The composition of the LNG can also affect the distance at which thermal 

radiation from the fire is felt by the public. In small fires, methane, which 

comprises between 84 percent and 97 percent of LNG, burns cleanly, with 

little smoke. Cleaner-burning LNG fires, particularly those burning LNG 

with higher methane content, result in higher levels of thermal radiation 

than oil or gasoline fires of the same size because the smoke generated by

oil and gasoline fires acts as a shield, reducing the amount of thermal 

radiation emitted by the fire. While LNG composition can have a large 

impact on the thermal radiation from small LNG fires, as LNG fires get 

larger, these effects are hypothesized to be less pronounced. What is 

your level of agreement with this paragraph? (Finalized in the third 

iteration.) 

Count Percentage Label

5 26.32% Completely agree 

10 52.63% Generally agree

3 15.79% Do not agree 

1 5.26% I do not have the expertise necessary to respond to this 

section. 

The size of the fire has a major impact on the thermal radiation from an 

LNG pool fire. Thermal radiation increases with pool size up to a point but

is expected to decrease for very large pools, like those caused by a 

terrorist attack. What is your level of agreement with this paragraph?

(Finalized in the second iteration.) 

Page 31 GAO-07-316 Maritime Security
Appendix III: Summary of Expert Panel 

Results 

Count Percentage Label

4 21.05% Completely agree 

10 52.63% Generally agree 

4 21.05% Do not agree 

1 5.26% I do not have the expertise necessary to respond to this 

section. 

If an LNG vapor cloud formed in the wake of an LNG spill and drifted 

away from the tanker as it warmed and dispersed, the vapor cloud could

enter a populated area while areas of the cloud had LNG vapor/air 

mixtures within the flammability range. Since populated areas have 

numerous ignition sources, those portions of the cloud would likely ignite. 

The fire would then burn back through the cloud toward the tanker and 

continue to burn as a pool fire near the ship, assuming that liquid LNG still 

remains in the spill area. Ignition of a vapor cloud over a populated area 

could burn people and property in the immediate vicinity of the fire. While 

the initial fire would be of short duration as the flames burned back

toward the LNG carrier, secondary fires could continue to present a 

hazard to the public. What is your level of agreement with the above

paragraph? (Finalized in the second iteration.) 

LNG Hazards–Vapor Cloud Fire 

Count Percentage Label

7 36.84% Completely agree 

11 57.89% Generally agree but suggest the following 

clarification 

1 5.26% Do not agree 

After ignition of a vapor cloud that drifted away from an LNG 

tanker spill, how fast could the flame front travel back toward the 

spill site if it was unconfined or confined? (Finalized in the second 

iteration.) 

LNG Hazards–Vapor Cloud 

Fire: Burn Back Speed 

Page 32 GAO-07-316 Maritime Security
Appendix III: Summary of Expert Panel 

Results 

Count Percentage Label

15 78.95% Not checked 

2 10.53% I do not have the expertise necessary to respond to 

this section. 

2 10.53% No answer 

Experts did not agree on the speed of a flame front traveling through an 

LNG vapor cloud in either a confined or unconfined state. Responses 

varied from less than 5 meters per second up to 50 meters per second in 

unconfined settings and from 0 meters per second to 2,000 meters per 

second in confined settings. 

A rapid phase transition (RPT) can occur when LNG spilled onto water 

changes from liquid to gas virtually instantaneously due to the rapid 

absorption of ambient environmental heat. While the rapid expansion from 

a liquid to vapor state can cause locally large overpressures, an RPT does 

not involve combustion. RPTs have been observed during LNG test spills 

onto water. In some cases, the overpressures generated were strong 

enough to damage test equipment in the immediate vicinity. Overpressures 

generated from RPTs would be very unlikely to have a direct affect on the

public. What is your level of agreement with this paragraph?

(Finalized in the second iteration.) 

Explosions-RPT 

Count Percentage Label

15 78.95% Completely agree 

4 21.05% Generally agree 

Deflagrations and detonations are rapid combustion processes that move 

through an unburned fuel-air mixture. Deflagrations move at subsonic 

velocities and can result in overpressures up to eight times the original 

pressure, particularly in congested/confined areas. Detonations move at 

supersonic velocities and can result in overpressures up to 20 times the 

original pressure. What is your level of agreement with this 

paragraph? (Finalized in the third iteration.) 

Explosions-Deflagrations and 

Detonations 

Page 33 GAO-07-316 Maritime Security
Appendix III: Summary of Expert Panel 

Results 

Count Percentage Label

1 5.26% Not checked 

7 36.84% Completely agree 

10 52.63% Generally agree 

1 5.26% Do not agree 

Please choose the response that best describes your opinion about each 

type of explosion of LNG vapors in each setting described. (Finalized in 

the third iteration.) 

Explosions—Deflagrations, 

Detonations, and BLEVEs 

Answer 

Deflagration with

overpressure in an

unconfined setting

Deflagration with

overpressure in a 

confined setting

Detonation in an

unconfined

setting

Detonation in a

confined setting 

Boiling-liquidexpandingvapor-explosion

(BLEVE)

Under controlled

experimental conditions, it is 

possible to induce this type of

explosion in this type of 

setting. 7 18 4 15 11

This type of setting cannot 

support this type of explosion. 8 0 11 2 7

More research is necessary 

to answer this question. 3 0 3 0 0

I don’t have the expertise

necessary to answer this 

question. 0 0 0 1 0

No answer/not checked 1 1 1 1 1

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? (Finalized in the third iteration.) 

Page 34 GAO-07-316 Maritime Security
Appendix III: Summary of Expert Panel 

Results 

Answer 

Deflagration with

overpressure in an

unconfined setting 

Deflagration with

overpressure in a 

confined setting

Detonation in an

unconfined

setting

Detonation in a

confined setting

Boiling-liquidexpandingvapor-explosion

(BLEVE)

Highly unlikely 3 6 1 7 4

Unlikely 2 2 3 3 2

Neither likely nor unlikely 1 5 0 3 3

Likely 1 4 0 2 1

Highly likely 0 0 0 0 0

No answer/ not checked 0 1 0 0 1

A BLEVE is the worst potential hazard of an LNG spill. It would result in 

the rupture of one or more LNG tanks, perhaps simultaneously, on the 

ship, with potential rocketing debris and damaging pressure waves. What 

is your level of agreement with the above paragraph? (Finalized in 

the first iteration.) 

LNG Hazards–Is BLEVE the 

Worst? 

Count Percentage Label

2 10.53% Completely agree 

16 84.21% Do not agree (Please explain in the textbox 

below.) 

1 5.26% No answer 

The Sandia report concluded that the most significant impacts to public 

safety exist within 500 meters of a spill, with much lower impacts at 

distances beyond 1,600 meters even for very large spills. Please choose 

the response that best describes your opinion about these hazard

distances. (Finalized in the third iteration.) 

Questions About the 2004 

Sandia National 

Laboratories Study1

 1

Since two of the experts were authors of the Sandia study, their responses to ALL the 

questions related to the study below have been excluded. For the questions related to the

Sandia study, there are 17 experts responding. 

Page 35 GAO-07-316 Maritime Security
Appendix III: Summary of Expert Panel 

Results 

Count Percentage Label

4 23.54% They are too conservative (i.e., should be 

smaller) 

7 41.18% They are about right 

4 23.53% They are not conservative enough (i.e., 

should be larger) 

2 11.76% No answer 

The Sandia report concluded that large, unignited LNG vapor clouds could 

spread over distances greater than 1,600 meters from a spill. For a nominal 

intentional spill, the hazard range could extend to 2,500 meters. The actual 

hazard distances will depend on breach and spill size, site-specific 

conditions, and environmental conditions. Please choose the response 

that best describes your opinion about these hazard distances. 

(Finalized in the third iteration.) 

Count Percentage Label

4 23.53% They are too conservative (i.e., should be 

smaller) 

6 35.29% They are about right 

4 23.53% They are not conservative enough (i.e., should 

be larger) 

1 5.88% Do not have the expertise to answer 

2 11.76% No answer 

The Sandia report concluded that cascading damage (multiple cargo tank

failure) due to brittle fracture from exposure to cryogenic liquid or fireinduced damage to foam insulation is possible under certain conditions

but is not likely to involve more than two or three cargo tanks for any 

single incident. What is your level of agreement with this paragraph? 

(Finalized in the third iteration.) 

Count Percentage Label

3 17.65% Completely agree 

6 35.29% Generally agree 

6 35.29% Do not agree 

2 11.76% I do not have the expertise necessary to respond to 

this section. 

Page 36 GAO-07-316 Maritime Security
Appendix III: Summary of Expert Panel 

Results 

The Sandia report concluded that cascading events are not expected to 

greatly increase (not more than 20-30 percent) the overall fire size or 

hazard ranges (500 meters for severe impacts, much lower impacts beyond

1,600 meters) but will increase the expected fire duration. What is your 

level of agreement with this paragraph? (Finalized in the third 

iteration.) 

Count Percentage Label

7 41.18% Completely agree 

5 29.41% Generally agree 

4 23.53% Do not agree 

1 5.88% No answer 

The Sandia report suggested that consequence studies should be used to 

support comprehensive, risk-based management and planning approaches 

for identifying, preventing, and mitigating hazards to public safety and 

property from potential LNG spills. What is your level of agreement 

with this paragraph? (Finalized in the third iteration.) 

Count Percentage Label

8 47.06% Completely agree 

8 47.06% Generally agree 

1 5.88% Do not agree 

In your opinion, what is the risk to public safety posed by an attack on 

tankers carrying each of the following energy commodities? (Finalized in 

the first iteration.) 

Commodity Comparison 

Answer 

Liquefied

natural gas

Crude

oil Diesel Gasoline 

Heating

oil 

Jet 

fuel

Liquefied

petroleum 

gas

Little to 

None 1 2 1 0 1 1 0

Little 3 10 11 5 11 6 1

Medium 6 3 3 8 3 6 4

Page 37 GAO-07-316 Maritime Security
Appendix III: Summary of Expert Panel 

Results 

Answer 

Liquefied

natural gas

Crude

oil Diesel Gasoline 

Heating

oil 

Jet 

fuel

Liquefied

petroleum 

gas

Large 3 0 0 2 0 2 5

Very Large 2 0 0 0 0 0 5

No expertise 

to answer 1 1 1 1 1 1 1

No answer 3 3 3 3 3 3 3

In the first and second survey iterations, you noted areas related to LNG 

spill consequences that need further research. We are interested in your 

thoughts on the relative level of need for research in these areas, and also 

the five areas you think should be of highest priority in future research. 

Please indicate the degree to which further research is needed in 

each of the areas listed below. (Finalized in the third iteration.) 

Responses to each part of this question are in the table below, which is 

sorted by mean score so that the highest-ranked research priorities appear 

first. 

Future Research 

Type of research

Very great 

need 

(1) 

Great 

need 

(2) 

Moderate 

need

(3)

Some 

need

 (4) 

Little to 

no need

(5)

Do not have 

the expertise 

to answer 

(6) 

No 

answer

 (7) 

Mean

score

Large fire phenomena

(impact of smoke 

shielding, large flame 

versus smaller 

flamelets) 9 5 3 0 1 1 0 4.17

Cascading failure 5 9 4 1 0 0 0 3.95

Large-scale LNG spill 

testing on water

a

7 7 2 1 2 0 0 3.84

Large-scale fire testingb7 6 3 2 1 0 0 3.84

Comprehensive 

modeling allowing 

different physical 

processes to interact 2 10 3 4 0 0 0 3.53

Risk tolerability 

assessments 5 4 3 1 3 1 2 3.44

Page 38 GAO-07-316 Maritime Security
Appendix III: Summary of Expert Panel 

Results 

Type of research

Very great 

need 

(1) 

Great 

need 

(2) 

Moderate 

need

(3)

Some 

need

 (4) 

Little to 

no need

(5)

Do not have 

the expertise 

to answer 

(6) 

No 

answer

 (7) 

Mean

score

Vulnerability of LNG

containment systems, 

including validating hole 

size predictions for the 

double hull ship

structure 5 4 3 5 2 0 0 3.26

Mitigation techniques 3 5 6 3 2 0 0 3.21

Effect of sea water 

pouring into a hole as 

LNG flows out 2 6 5 3 2 0 1 3.17

Impact of wind, weather, 

and waves (on pool 

spread size, evaporation 

rate, pool formation, 

etc.) 3 4 6 3 3 0 0 3.05

Improvements to 3-D 

computational fluid 

dynamics dispersion 

modeling 0 4 6 6 2 1 0 2.67

Effects of different LNG

compositions (on 

vaporization rates, 

thermal radiation, 

explosive behavior, etc.) 2 2 4 8 3 0 0 2.58

Whether an explosive 

attack will result in 

immediate vapor cloud 

ignition 0 5 4 5 4 1 0 2.56

Rapid phase transitions: 

likelihood in various 

scenarios and impact 1 2 6 6 4 0 0 2.47

Effects of igniting LNG

vapors in containment 

or ballast tanks 0 5 3 5 6 0 0 2.37

BLEVE properties of 

tanks on LNG ships 1 4 3 4 7 0 0 2.37

Deflagration/detonation 

of LNG 1 0 5 8 5 0 0 2.16

Effects of a large, 

unignited vapor cloud 

drifting from the incident 

site 0 0 7 5 7 0 0 2.00

Page 39 GAO-07-316 Maritime Security
Appendix III: Summary of Expert Panel 

Results 

Type of research

Very great 

need 

(1) 

Great 

need 

(2) 

Moderate 

need

(3)

Some 

need

 (4) 

Little to 

no need

(5)

Do not have 

the expertise 

to answer 

(6) 

No 

answer

 (7) 

Mean

score

Effect of clothing and 

obstructions on the 

radiant heat level 

received by the public 1 1 2 6 9 0 0 1.89

Otherc12 2 0 0 0 0 5 d

a

Experts suggested pool sizes of 15 meters up to 1,000 meters, though the median response was 100 

meters. 

b

Experts suggested pool sizes of 15 meters up to 1,000 meters, though the median response was 100 

meters. 

c

Experts suggested frequency modeling, determination of acceptable risk to society, analysis of foam 

on LNG tankers, risk analysis for larger LNG tankers, CFD modeling for pool spreading and 

evaporation, and improvement to existing techniques used for fighting LNG fires. 

d

Not applicable. 

Page 40 GAO-07-316 Maritime Security
Appendix IV: 

A

GAO Contact and Staff 

cknowledgments 

Page 41 GAO-07-316

Appendix IV: GAO Contact and Staff 

Acknowledgments 

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

In addition to the individual named above, Mark Gaffigan, Amy Higgins, 

Lynn Musser, Janice Poling, Rebecca Shea, Carol Herrnstadt Shulman, and

James W. Turkett made key contributions to this report. 

GAO Contact 

Staff 

Acknowledgments 

(360675) Maritime Security
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