DNV GL study on tankers at Westridge: a major spill is highly unlikely

By BCShippingNews
September 25 2015
Westridge Terminal (photo source: Trans Mountain)
DNV GL study calculates risks of an oil spill...
Modern ship construction and navigation technology, along with effective regulation and experienced, well-trained personnel make it highly unlikely that a tanker departing Westridge Marine Terminal will be involved in a spill.

As part of the Trans Mountain Expansion Project, however, a leading international marine consultant did an extensive study of the risks associated with increased tanker movement at Westridge.

Photo above: Westridge Terminal (photo source: Trans Mountain)

The consultant, DNV GL (formerly Det Norske Veritas), has been operating in the maritime sector for more than a century. DNV GL is a world-leading maritime ‘classification society,’ an independent organization relied upon by the marine industry to guide and certify construction, reliability and operation of large ships.

For Trans Mountain, DNV GL carried out a study to calculate the risks of an oil spill. It took into account all current and future marine traffic tracked in the Salish Sea study area by AIS, the Automatic Information System used around the world to track and monitor vessel movements.

This includes the approximately 550 tankers per year (about 60 attributed to Westridge) travelling into the region today. That number is expected to increase to about 1,000 tankers annually (408 attributed to Westridge) should TMEP receive permission to proceed.

The entire marine network was computer-modelled incorporating 12 consecutive months of weather and tested with the risk controls currently in place and additional measures that will be implemented as a result of the Project.

The conclusion — a major spill is highly unlikely.

Trans Mountain made the DNV GL research public in December 2013 as part of the Application for the pipeline Expansion Project and submission to TERMPOL, a Transport Canada process that reviews safety and technical aspects of the marine side of oil and gas projects.

After a thorough review that lasted almost 12 months, the additional risk controls proposed in the Trans Mountain/DNV work has been endorsed by organizations involved in the Canadian government’s TERMPOL Review Committee (TRC) process:

  • Transport Canada
  • Fisheries and Oceans Canada
  • Canadian Coast Guard
  • Environment Canada
  • Canadian Hydrographic Service
  • Pacific Pilotage Authority Canada
  • British Columbia Coast Pilots
  • Port Metro Vancouver

The TRC does not consider the overall increase in marine traffic levels arising from expanded operations at Westridge Marine Terminal to be an issue.

The proposal exceeds existing regulatory requirements — and many of Trans Mountain’s proposals have already been incorporated to guide movement of current tanker traffic and the NEB’s conditions for the Project. They include:

  • Expanded use of tethered and untethered tug escort across the entire shipping route
  • Extending the time/distance that local pilots remain aboard outbound ships
  • An enhanced spill response regime that compared with the current regime standard will be double the capacity and half the response time.

"The focus is not just on reducing the probability as low as possible, but to also focus on reducing the consequence, the impact on the environment. That’s why we added the proposal for the enhanced oil spill (mitigation) regime," said Captain Bikramjit Kanjilal, Marine Development Lead for TMEP. "The best case scenario is that you will exercise your prevention regime daily for every vessel and your response regime will be sitting idle every day."

Kanjilal noted DNV’s finding that for a spill of any size, the estimated frequency is 1 in 284 years. For a credible worst-case scenario cargo spill of 16,500 cubic metres of oil, it’s 1 in 2,841 years.

"Something to keep in mind is that a credible worst case is a hypothetical, theoretical spill. It is based on what has been researched through scientific means and tested using Monte Carlo simulation of more than 50,000 damage variations."

"It represents a scenario whose likelihood of occurrence is remote but not out of the realm of possibility, and which will, if the event were to occur, cause significant impact," Kanjilal said.

"This scenario assessment is then used to further develop mitigation measures that in Trans Mountain’s case include proposing additional navigation and operational risk controls and enhancing response requirements. A 90th percentile event causing uncontrolled spillage from a tanker’s cargo oil tanks was used as the Project’s credible worst case," he added.

As a more conservative case, Trans Mountain supported DNV GL’s selection of a side impact (vessel collision) scenario rather than a vessel grounding as the results showed a higher spill volume resulting from a collision. This spill volume is equivalent to the loss of entire cargo from two of the 12 to 14 separate individual tanks enclosed within the double hull of the oil tanker.

"Even if a collision occurs, the extent of damage is entirely dependent on several factors, primarily the energy of the collision. That will depend on the vessel speeds, the displacement (weight) of the ships involved, the angle of impact, etc. So not all incidents lead to an oil spill and not all oil spills would be that large," Kanjilal said.

In its recent Reply Evidence to the NEB, Trans Mountain asserted its confidence in its assessments of risk for increased oil transport. A marine risk assessment by some Intervenors in the TMEP Application, by contrast, contains inaccuracies and misrepresentations, including an assessment of DNV GL’s work that is based on an incorrect premise that greatly overstates the level of risk for a marine incident.

"I think people sometimes misplace their viewpoints based on thinking of consequences of very large spills which, probability-wise are very uncommon, very unlikely," Kanjilal said.

"To put that into some sort of perspective, there hasn’t been any large oil spill in Canada (including none involving a tanker departing Westridge Marine Terminal since operations began in 1953). When the tanker safety expert panel was doing its risk assessment, it went through all the records and couldn’t find any spill over 1,000 cubic metres, 1,000 tonnes in Canada for the past so many years."