Gavelli_edit.qxp 1/7/09 3:32 pm Page 83
LNG
Liquefied Natural Gas Explosion Hazards – Are They Real?
a report by
Filippo Gavelli
Senior Manager, Exponent
Recent years have seen a rapid increase in the number of projects to depends on the design, construction and layout of a facility as well as
build and operate liquefied natural gas (LNG) facilities around the world. its surrounding environment. In the case of terrorist or other intentional
These projects have been met with varying degrees of acceptance by the acts, the risk analysis requires access to intelligence about credible
respective local populations. In some areas, such as the Gulf of Mexico, regional and local threats to the energy infrastructure.
public opinion has been predominantly in favour of LNG terminals,
although some projects in the area have been opposed based primarily In practical terms, the main difference between a hazard-based and a
on environmental impact arguments. In other areas, such as California risk-based assessment of the potential impact of an LNG terminal on
and some European countries, public opposition to LNG terminals has the population is simple: when hazards alone are considered, the most
been relentless and the range of arguments brought against the severe impact will most likely come from large-scale, possibly
proposed facilities has spanned a broad spectrum of issues – from catastrophic accidents; when the probability of occurrence of any given
environmental to economic to safety. scenario is factored in, the greater risks tend to come from smaller
consequence but more likely accidents. In general, the benefits of
This article focuses on the safety debate and, in particular, on the the LNG terminal from a socioeconomic standpoint must outweigh the
debate around the explosion hazards of LNG facilities. The purpose is combined risk of low- and high-probability hazards and their
to synthesise the arguments most frequently presented to demonstrate subsequent consequences.
the possibility of catastrophic explosion scenarios and to examine the
validity of their supporting evidence. The author recognises that LNG Postulated Explosion Hazard Scenarios
does present hazards that must be carefully evaluated before an LNG- This review of LNG hazards is limited to explosion hazards; other types
handling facility is constructed. The motivation for this article is to of LNG hazard, such as radiant heat flux from pool fires, flash fires, etc.,
review and – where appropriate – correct some of the misinformation are not considered.
that surrounds the LNG safety debate. For example, in a recent book by
Piero Angela, a well-known Italian journalist who has been authoring The most common large-scale LNG explosion scenarios debated in
science education books and television shows for almost 40 years, the public can be grouped into the following four categories, which will be
scenario resulting from a large-scale LNG release from a vessel near reviewed individually in this article:
shore is described as “the most catastrophic foreseeable accident
among all energy sources”, with an explosive power potential “close to • vapour cloud explosion (VCE) scenarios;
one megaton”.
1
These kinds of statement often have no demonstrable • floating bomb scenarios;
scientific basis, but have become ‘facts’ in many people’s minds as they • rapid phase transition (RPT) scenarios; and
are propagated through interviews, blogs, newspaper articles and so • boiling liquid expanding vapour explosion (BLEVE) scenarios.
on. The goal of this article is thus to separate the myths from the actual
LNG hazards based on the current status of our scientific knowledge Vapour Cloud Explosion Scenarios
and LNG industry operating experience. Perhaps the most frequently used argument against LNG facilities is the
possibility of catastrophic damage from the explosion of a flammable
Hazard versus Risk vapour cloud caused by the vaporisation of a large-scale LNG spill. VCEs
A common trait of the ‘LNG explosion’ arguments is the focus on the are commonly categorised according to the degree of obstruction that
hazards associated with the postulated scenarios: it is assumed that the expanding flame front encounters: confined VCEs occur when the
the scenario being discussed will occur and, when it does, the ignited vapour cloud is affected by the presence of obstacles, such as
consequences will be catastrophic. As such, hazard-based arguments
neglect to account for the likelihood that a postulated scenario will
Filippo Gavelli is a Senior Manager at Exponent, an
actually happen – they simply assume that it will. The more sensible
engineering and scientific consulting firm. His liquefied
approach would be to evaluate the ‘risks’ of an activity instead of its
natural gas (LNG) project experience includes risk
assessment and LNG hazard analysis for onshore and
worst-case hazards, and to weigh those risks against the benefits from
offshore LNG receiving terminals. He has extensive
the same activity. This is, after all, what often drives people’s decision-
experience with the analysis of LNG vapour dispersion and
fires to determine the potential consequences to the
making in everyday life.
public and public property from large-scale LNG releases,
and is the author of several LNG safety-related papers. Dr
The risk-based approach factors in the hazard (i.e. consequences) from
Gavelli is a member of the technical committee responsible for NFPA 59A, the Standard for
the Production, Storage and Handling of LNG, as well as a member of several expert panels
an accident with the probability that an accident will occur. When
on LNG safety. He is also a Certified Fire and Explosion Investigator in the US.
considering LNG terminals, the risk associated with these facilities can
E: Fgavelli@exponent.com
be evaluated only on a case-specific basis (i.e. facility by facility) as risk
© TOUCH BRIEFINGS 2009
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