A Spill Risk Assessment of the Enbridge Northern Gateway Project

(Brandsæter and Hoffman 2010 p. 5-­‐49). This lack of transparency raises concerns
related to the number and types of tanker incidents included in the data set and
whether the analysts altered any of the LRFP data based on undisclosed
assumptions. Further, LRFP data likely reflects jurisdictions where marine safety
measures such as those announced by the Canadian government and mitigation
measures such as escort tugs are already enforced. Thus incident frequencies
potentially double count the use of escort tugs that DNV incorporates into LRFP
data to reduce the likelihood of tanker spills although it is impossible to determine
without access to the proprietary data (potential double-­‐counting of mitigation
measures discussed on p. 33).
Second, DNV fails to support assumptions used in the development of tanker
incident frequencies. DNV claims that assumptions used in the development of
base incident frequencies per nm are based on information from tanker operators
and captains, as well as studies of vessel operating patterns (Brandsæter and
Hoffman 2010 p. 5-­‐50) yet there is no evidence provided to support these
assumptions. Two of the four assumptions used to estimate the average distance
travelled by a tanker per year are supported with reference to a study completed
for the liquefied natural gas terminal Rabaska (Rabaska 2004 as cited in
Brandsæter and Hoffman 2010 p. 5-­‐51). However, detailed information or
discussion comparing the similarities and differences between Rabaska and the
ENGP is absent from the report and the Rabaska study is not appended to DNV’s
study nor is it found in the project’s public registry database on the NEB website.
Furthermore, assumptions related to the amount of time tankers sail in areas
where a grounding could occur and the amount of time tankers sail in open water
where foundering can occur are not supported with any evidence or references nor
are any of the assumptions calibrated with historical data or expert opinion.
Incident frequencies are the basis for estimating spill return periods in the ENGP
application. Since return periods are the product of incident frequencies,
conditional probabilities, the distribution of tanker routes travelled, the length of
each tanker route, and mitigation measures, any uncertainty or errors in incident
frequencies will carry through to the final result. Thus, given the importance of
incident frequencies as a critical data input, DNV must effectively disclose all
adjustments, assumptions, and uncertainties in a transparent manner. The lack of
evidence in the ENGP regulatory application makes it impossible to assess the
validity of these values.
2. Insufficient evidence supporting conditional probabilities for tanker spills
The consequence assessment portion of the marine shipping QRA fails to
adequately disclose any supporting information used to estimate conditional
probabilities that an incident will result in a spill. DNV uses two different methods
to estimate conditional spill probabilities: the first method determines conditional
spill probabilities based on LFRP data; the second method estimates spill
quantities for bottom and side damages for groundings and collisions based on the
International Marine Organization International Convention for the Prevention of
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