Report - Agence canadienne d'évaluation environnementale

Assessing the risks related to the project
spread after the LNG spill’s gravitational pull, known as an initial spill pool, could not
support the initial combustion rate for long. Once the balance is established between
the combustion rate and the pool’s supply rate, the pool shrinks to reach the
decreased dimensions of a smaller pool, known as a steady-state spill pool. While the
combustion of the initial spill pool produces more heat during a short period of time,
the combustion of the steady-state pool produces relatively less heat for a longer
period of time (PR3.3.2, F-2, p. 102). In that regard, the MDDEP stated that the
description given by the proponent for this physical phenomenon was satisfactory
(Ms. Marie-Claude Théberge, DT2, p. 13).
Spills on land
As for spills which occur over water, natural gas is dispersed by wind, and the cold
vapours of the LNG appear in the shape of a white cloud, stemming from the water
condensation phenomenon in the air. In such circumstances, an ignition source could
result in a localized fire.
The risk-analysis process
In this section, the Panel briefly examines the risk-analysis process, including the two
main approaches used as well as risk assessment methods. It also covers the
methodology used by the proponent, as well as reservations expressed by a number
of participants in the hearing in this respect.
The probabilistic and deterministic approaches
The proponent used two approaches when assessing risks. The exclusion areas of
the proposed land facilities were established according to a deterministic approach
based on predetermined consequence scenarios. On the other hand, the probabilistic
approach, based on the occurrence probability of events and accidents, was used to
establish the acceptability of the risks deemed to be the greatest for this project.
The ministère de la Sécurité publique specified to the Panel that the probabilistic
approach was appropriate to establish the acceptability of risks associated with a
given industrial project (Mr. Romain St-Cyr, DT8, p. 75). As for the MDDEP, it
believed that the consequences of accident scenarios, as well as their respective
occurrence, must be considered in a complementary fashion to determine the
acceptability of a given project (DQ61.1, p. 1).
118 Rabaska Project – Implementation of an LNG Terminal and Related Infrastructure