Report - Agence canadienne d'évaluation environnementale

Assessing the risks related to the project
Modelling and breach sizes
The analyses to assess consequences performed by Det Norske Veritas (DNV) for
the proponent were done with the help of the PHAST model that was developed by
DNV to simulate the consequences of events and accidents. This model has been
validated by the experiences of close to 600 users and clients over more than
15 years 1 . The task of calculating risks attributable to LNG leaks and dispersions on
the basis of their probability was done with the help of the Safeti software program, a
model which was also developed by DNV, whose usage requires the results of the
PHAST model analysis. In this respect, Environment Canada and the MDDEP
specified that the software programs used by the proponent to estimate the
consequences and frequency of accident scenarios were recognized and commonly
used in this field (DB5; Mr. Pierre Michon, DT12, p. 54).
LNG spills over water that could result in pool fires may be a consequence of
breaches made by a collision with an LNG tanker, its grounding or through a
deliberate act. When modelling such events, the size of breaches assumed for the
analysis is a determining factor when assessing consequences. According to the
impact study, breach size selection was specifically based on past events, and after
discussions with experts on this subject. Consequently, a 25-cm breach was deemed
plausible for a tank puncture, a 75-cm breach as the maximum plausible size for an
accident and a 1.5-m breach as the maximum plausible size for the consequence of
an intentional act (PR3.3.2, F-2, p. 106 and 107).
Several hearing participants questioned that choice and referred to other studies
which used larger breaches, quoting in this respect the study of Sandia National
Laboratories (Sandia 2 ), conducted for the United States Department of Energy’s, a
study done by the American Bureau of Shipping (ABS) for the Federal Energy
Regulatory Commission (FERC 3 ), as well as the risk assessment of the Cacouna
Energy LNG terminal project. It should be noted that the latter was carried out by
DNV, the same consulting firm which conducted the study of the Rabaska project.
The Sandia study used diameters of 1.1 m and 1.6 m for accidental breaches, and
2.5 m for intentional breaches. The ABS study used diameters of 1 m for relatively
long-lasting leaks, and 5 m for shorter-lasting leaks. However, as was specified in that
study’s summary, the study assessed the potential consequences of large spills
1. Robin Pitblado, John Baik and Vijay Raghunathan, “LNG decision making approaches compared”, Journal of
Hazardous Materials 130, DNV Report, Project no. 700041972006, p. 148 to 154.
2. Sandia National Laboratories, Guidance on Risk Analysis and Safety Implications of a Large Liquefied Natural
Gas Spill Over Water, 2004, 167 p.
3.. Federal Energy Regulatory Commission, Consequence assessment methods for incidents involving releases
from liquefied natural gas carriers, ABS Consulting Inc., 2004, 59 p. and Appendices.
124 Rabaska Project – Implementation of an LNG Terminal and Related Infrastructure