Maritime Security
Opportunities Exist to Further Clarify the Consequences of a Liquefied Natural Gas Tanker Spill Gao ID: GAO-07-840T May 7, 2007Liquefied natural gas (LNG) is a supercooled liquid form of natural gas. U.S. LNG imports are projected to increase to about 17 percent of natural gas supplies by 2030, from about 3 percent today. To meet this increase, energy companies have submitted 32 applications for new terminals. If a terrorist attack on an LNG tanker caused a spill, potential hazards, such as fire, asphyxiation, and explosions, could result. The Department of Energy (DOE) recently funded a study to conduct small- and large-scale experiments to refine and validate models that calculate how heat from large LNG fires would affect the public. This testimony is based on GAO's report, Maritime Security: Public Safety Consequences of a Terrorist Attack on a Tanker Carrying Liquefied Natural Gas Need Clarification (GAO-07-316). To prepare this report, GAO examined the results of six recent studies on the effects of an LNG spill and convened a panel of 19 experts to identify areas of agreement on the consequences of a terrorist attack on an LNG tanker.
The six studies GAO reviewed examining the potential effect of a fire resulting from an LNG spill produced varying results; some studies also examined other potential hazards of a large LNG spill and reached consistent conclusions on explosions. Specifically, the studies' conclusions about the distance at which 30 seconds of exposure to the heat (heat hazard) could burn people ranged from less than 1/3 of a mile to about 1-1/4 miles. Sandia National Laboratories (Sandia) conducted one of the studies and concluded, based on its analysis of multiple attack scenarios, that a good estimate of the heat hazard distance would be about 1 mile. Federal agencies use this conclusion to assess proposals for new LNG import terminals. The variations among the studies occurred because, with no data on large spills from actual events, researchers had to make numerous modeling assumptions to scale up the existing experimental data for large LNG spills. Three studies considered LNG vapor explosions and concluded that such explosions are unlikely unless the vapors were in a confined space. Only the Sandia study examined the potential for the sequential failure of multiple tanks on the LNG vessel (cascading failure) and concluded that only three of the five tanks in a typical tanker would potentially be affected, and that such failure would increase the duration of the LNG fire. GAO's expert panel generally agreed on the public safety impact of an LNG spill caused by a terrorist attack, disagreed on specific conclusions of the Sandia study, and suggested future research priorities. Experts agreed that the most likely public safety impact of an LNG spill is the heat impact of a fire and that explosions are not likely to occur unless LNG vapors are in confined spaces. However, the experts did not all agree with the heat hazard and cascading failure conclusions reached by the Sandia study. Finally, they suggested priorities to guide future research aimed at clarifying uncertainties about heat impact distances and cascading failure. DOE's recently funded study involving large-scale LNG fire experiments addresses only some of the research priorities the expert panel identified.
GAO-07-840T, Maritime Security: Opportunities Exist to Further Clarify the Consequences of a Liquefied Natural Gas Tanker Spill
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Testimony:
Before the Subcommittee on Coast Guard and Maritime Transportation,
Committee on Transportation and Infrastructure, House of
Representatives:
United States Government Accountability Office:
GAO:
For Release on Delivery:
Expected at 10:00 a.m. EDT:
Monday, May 7, 2007:
Maritime Security:
Opportunities Exist to Further Clarify the Consequences of a Liquefied
Natural Gas Tanker Spill:
Statement of Mark Gaffigan, Acting Director:
Natural Resources and Environment:
GAO-07-840T:
GAO Highlights:
Highlights of GAO-07-840T, testimony before the Subcommittee on Coast
Guard and Maritime Transportation, Committee on Transportation and
Infrastructure, House of Representatives
Why GAO Did This Study:
Liquefied natural gas (LNG) is a supercooled liquid form of natural
gas. U.S. LNG imports are projected to increase to about 17 percent of
natural gas supplies by 2030, from about 3 percent today. To meet this
increase, energy companies have submitted 32 applications for new
terminals. If a terrorist attack on an LNG tanker caused a spill,
potential hazards, such as fire, asphyxiation, and explosions, could
result. The Department of Energy (DOE) recently funded a study to
conduct small- and large-scale experiments to refine and validate
models that calculate how heat from large LNG fires would affect the
public.
This testimony is based on GAO‘s report, Maritime Security: Public
Safety Consequences of a Terrorist Attack on a Tanker Carrying
Liquefied Natural Gas Need Clarification (GAO-07-316). To prepare this
report, GAO examined the results of six recent studies on the effects
of an LNG spill and convened a panel of 19 experts to identify areas of
agreement on the consequences of a terrorist attack on an LNG tanker.
What GAO Found:
The six studies GAO reviewed examining the potential effect of a fire
resulting from an LNG spill produced varying results; some studies also
examined other potential hazards of a large LNG spill and reached
consistent conclusions on explosions. Specifically, the studies‘
conclusions about the distance at which 30 seconds of exposure to the
heat (heat hazard) could burn people ranged from less than 1/3 of a
mile to about 1-1/4 miles. Sandia National Laboratories (Sandia)
conducted one of the studies and concluded, based on its analysis of
multiple attack scenarios, that a good estimate of the heat hazard
distance would be about 1 mile. Federal agencies use this conclusion to
assess proposals for new LNG import terminals. The variations among the
studies occurred because, with no data on large spills from actual
events, researchers had to make numerous modeling assumptions to scale
up the existing experimental data for large LNG spills. Three studies
considered LNG vapor explosions and concluded that such explosions are
unlikely unless the vapors were in a confined space. Only the Sandia
study examined the potential for the sequential failure of multiple
tanks on the LNG vessel (cascading failure) and concluded that only
three of the five tanks in a typical tanker would potentially be
affected, and that such failure would increase the duration of the LNG
fire.
GAO‘s expert panel generally agreed on the public safety impact of an
LNG spill caused by a terrorist attack, disagreed on specific
conclusions of the Sandia study, and suggested future research
priorities. Experts agreed that the most likely public safety impact of
an LNG spill is the heat impact of a fire and that explosions are not
likely to occur unless LNG vapors are in confined spaces. However, the
experts did not all agree with the heat hazard and cascading failure
conclusions reached by the Sandia study. Finally, they suggested
priorities to guide future research aimed at clarifying uncertainties
about heat impact distances and cascading failure. DOE‘s recently
funded study involving large-scale LNG fire experiments addresses only
some of the research priorities the expert panel identified.
Figure: LNG Tanker Passing Downtown Boston on Its Way to port:
[See PDF for Image]
Source: GAO.
[End of figure]
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.
[Hyperlink, http://www.gao.gov/cgi-bin/getrpt?GAO-07-840T].
To view the full product, including the scope and methodology, click on
the link above. For more information, contact Mark Gaffigan at (202)
512-3841 or gaffiganm@gao.gov.
[End of section]
United States Government Accountability Office:
Washington, DC 20548:
Mr. Chairman and Members of the Subcommittee:
I am pleased to be here to discuss the results of our report on the
public safety consequences of a terrorist attack on a tanker carrying
liquefied natural gas (LNG).[Footnote 1] As you know, LNG is a
supercooled liquid form of natural gas, which, if spilled, poses
potential hazards, such as fire, asphyxiation, and explosions. U.S.
imports of LNG, now about 3 percent of total U.S. natural gas supplies,
are projected to be about 17 percent of U.S. supplies by 2030. To meet
this increased demand, energy companies have submitted 32 applications
to federal regulators to build new terminals for importing LNG in 10
states and 5 offshore areas. Because of the projected increase in
tankers carrying LNG to these terminals, public safety concerns have
been raised, including the consequences of a terrorist attack. In light
of these concerns, access to accurate information about the
consequences of LNG spills is crucial for developing risk assessments
for LNG siting decisions. Despite several recent modeling studies of
the consequences of potential LNG spills, uncertainties remain about
the risks such spills would pose to the public. One of these studies,
conducted by Sandia National Laboratories (Sandia) in 2004, is used by
the Coast Guard to assess the suitability of waterways for LNG tankers
traveling to proposed LNG facilities. In this context, DOE has recently
funded a new study that will conduct small-and large-scale LNG fire
experiments to refine and validate existing models that calculate how
heat from large LNG fires would affect the public.
My testimony today summarizes the results of our report. Specifically,
I will (1) describe the results of recent studies on the consequences
of an LNG spill and (2) identify the areas of agreement and
disagreement among experts concerning the consequences of a terrorist
attack on an LNG tanker. To address these issues, we examined six
studies of the consequences of LNG spills. We also convened a Web-based
panel of 19 experts to identify areas of agreement and disagreement on
LNG spill consequence issues, including consideration of a terrorist
attack.
Summary:
The six studies we reviewed all examined the heat impact of an LNG fire
but produced varying results; some studies also examined other
potential hazards of a large LNG spill and reached consistent
conclusions on explosions. Specifically, the studies' conclusions about
the distance at which 30 seconds of exposure to the heat could burn
people--also termed the heat impact distance--ranged from less than 1/
3 of a mile to about 1-1/4 miles. These variations occurred because,
with no data on large spills from actual events, researchers had to
make numerous modeling assumptions to scale up the existing
experimental data for large LNG spills. These assumptions involved the
size of the hole in the tanker, the number of tanks that fail, the
volume of LNG spilled, key LNG fire properties, and environmental
conditions, such as wind and waves. Three of the studies also examined
other potential hazards of an LNG spill, including LNG vapor
explosions, asphyxiation, and the sequential failure of multiple tanks
on the LNG vessel (cascading failure). All three studies considered LNG
vapor explosions unlikely unless the vapors were in a confined space.
Only the Sandia study examined asphyxiation and concluded that
asphyxiation did not pose a hazard to the general public. Finally, only
the Sandia study examined the potential for cascading failure of LNG
tanks and concluded that only three of the five tanks on a typical LNG
vessel would be involved in such an event and that this number of tanks
would increase the duration of the LNG fire.
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 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.
Background:
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.
Studies Identified Different Distances for the Heat Effects of an LNG
Fire, but Agreed on Other LNG Hazards:
The six studies we examined identified various distances at which the
heat effects of an LNG fire could be hazardous to people. The studies'
results about the distance at which 30 seconds of exposure to the heat
could burn people ranged from less than 1/3 of a mile (about 500
meters) to about 1-1/4 miles (more than 2,000 meters). The studies'
variations in heat effects occurred because (1) different assumptions
were made in the studies' models about key parameters of LNG spills and
(2) the studies were designed and conducted for different purposes.
Since no large-scale data are available for LNG spills, researchers
made numerous modeling assumptions to scale up the existing
experimental data for large spills. Key assumptions made included hole
size and cascading failure, waves and wind, the volume of LNG spilled,
and the amount of heat radiated from the fire. For example, studies
made assumptions for the size of the hole in the LNG tanker that varied
from less than 1 square meter up to 20 square meters. Additionally, the
studies were conducted for different purposes. Two studies were
academic analyses of the differences between LNG and oil spills; three
specifically addressed spills caused by terrorist attacks, which was a
concern in the wake of the September 11 attacks; and the final study
developed appropriate methods for regulators to use to estimate heat
hazards from LNG fires. Results of these studies can be found in our
report.
Some studies also examined other potential hazards, such as explosions,
asphyxiation, and cascading failure, and identified their potential
impacts on public safety. Three studies examined the potential for LNG
vapor explosions, and all agreed that it is unlikely that LNG vapors
could explode if the vapors are in an unconfined space. Only one study
examined the potential for asphyxiation following an LNG spill if the
vapors displace the oxygen in the air. It concluded that fire hazards
would be the greatest problem in most locations, but that asphyxiation
could threaten the ship's crew, pilot boat crews, and emergency
response personnel. Finally, only the Sandia study examined the
potential for cascading failure of LNG tanks and concluded that only
three of the five tanks would be involved in such an event and that
this number of tanks would increase the duration of the LNG fire.
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:
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.[Footnote 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.
* 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.
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.
Conclusions:
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.
Contacts and Acknowledgments:
For further information about this testimony, please contact me at
(202) 512-3841 or gaffiganm@gao.gov. James W. Turkett, Janice M.
Poling, and Carol Herrnstadt Shulman also made key contributions to
this statement.
FOOTNOTES
[1] GAO, Maritime Security: Public Safety Consequences of a Terrorist
Attack on a Tanker Carrying Liquefied Natural Gas Need Clarification,
GAO-07-316 (Washington, D.C.: Feb. 22, 2007). This report was prepared
at the request of the House Committee on Homeland Security, the House
Committee on Energy and Commerce, and Representative Edward J. Markey.
[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.
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