Report - Agence canadienne d'évaluation environnementale

Assessing the risks related to the project
Accident scenarios in the seaway and their consequences
The proponent assessed potential consequences of accident scenarios involving the
collision or grounding of an LNG tanker by taking into account the nature of the
accident which would result in a relatively large breach the LNG tanks aboard.
According to his calculations, risk levels would not change much when considering
larger ships like the Qflex type. The decreased rate of visits with larger-capacity
model would even be a positive factor as it would decrease the frequency of potential
accidents. According to the proponent, the increase in consequence extent was also
relatively small in view of the fact that the increase in LNG tanker size is due to their
larger width and the higher number of tanks, rather than due to an increase in the
height of their tanks. According to him, the tank height factor is the main parameter to
consider when calculating consequences accidents for different breach sizes
(DQ27.61).
Table 7 shows the main results obtained by the proponent for the various accident
scenarios retained, for both types of LNG tankers.
During the assessment process to establish the admissibility of the project’s impact
study, the MDDEP also compared the proponent’s results with those of the Sandia
study, and concluded that the scenarios used by the proponent were comparable to
those used in the Sandia study (Ms. Marie-Claude Théberge, DT4, p. 80).
The point of this exercise for the Panel (the size of the breaches retained, as well as
their consequences) was to establish the required security and emergency measures.
To the extent that the distances of the consequences of thermal radiation, and to the
dispersion of a natural gas cloud are comparable, then they would result in
comparable security and emergency measures.
136 Rabaska Project – Implementation of an LNG Terminal and Related Infrastructure