(222f) Uncertainties in Modelling the Physical Behaviour of Large LNG Releases upon Sea-Water

A
detailed investigation of the recently applied modelling approaches and used methodologies
for LNG fire and dispersion modelling after an accidental or intentional
release has shown that the currently applied computer models still contain many
assumptions. Some of these modelling assumptions are due to the unknown
physical behaviour of LNG after releases in such large amounts, others due to
the limited validity range of the applied physical effects models, the
so-called model limitations. Most of these modelling assumptions will have a
large influence upon the final results of e.g. a quantitative risk assessment
for an LNG terminal.

In
this paper an overview will be given of the applied assumptions after an LNG
release categorized after the unknown physical behaviour or model limitations. The
assumptions are made throughout the complete chain of subsequent models after a
release of LNG.

A
typical LNG release scenario includes:

·         
LNG
outflow from a hole in one side of a vessel after e.g. a collision,

·         
Evaporation
of a violently boiling and quickly spreading LNG pool upon sea-water,

·         
A
possible LNG pool fire upon sea-water close to the LNG carrier,

·         
Dispersing
of the cold LNG vapour evolving from the evaporating pool, which initially is denser
than air,

·         
A
possible explosion (after late ignition) of the dispersing LNG vapour from the
evaporating pool.

In
a sensitivity analysis the consequences of the applied modelling assumptions will
be made explicit in some typical LNG example calculation scenarios. Finally
some recommendations will be given to achieve (in the near future) a more
realistic way of modelling LNG releases from LNG carriers.

References

1.     ABS Consulting
Inc., 2004. Consequence assessment methods for incidents involving releases
from liquefied natural gas carriers. Report prepared for Federal Energy
Regulatory Commission, contract FERC04C40196. May 13, 2004.

2.     Sandia National
Laboratories, 2004. Guidance on Risk Analysis and Safety Implications of a
Large Liquefied Natural Gas (LNG) Spill Over Water. Sandia Report
SAND2004-6258. December 2004.