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A local Seaspan tugboat assists a Seattle-based tug towing a double-hulled fuel barge carrying a full load across English Bay into the harbour, in Vancouver, B.C., on Sunday September 18, 2016.DARRYL DYCK

During the National Energy Board hearings into the proposed expansion of the Trans Mountain pipeline, fears were raised about the risks of oil-tanker accidents.

The City of Vancouver warned that a major oil spill would cause up to $3-billion in damages by crippling tourism and destroying its brand as a green paradise. The difficulty of cleaning up a bitumen spill, which could take years if the heavy oil sinks only to wash ashore later, and the damage to fish, birds and marine mammals were also concerns.

But Trans Mountain won the support of the NEB panel, which granted conditional approval last May, by promising a safety plan "well above globally accepted shipping standards." A federal panel is now reviewing the $6.8-billion proposal and Ottawa is expected to make a final decision in December.

One key factor in the Trans Mountain safety plan is that oil tankers will be continually escorted by tugs as they make the 300-kilometre journey between the open Pacific and Vancouver harbour.

Tugs are a common sight on the coast, and the skill of the crews is apparent as they gently shunt freighters into docks, or deftly manoeuvre massive barges through recreational boat traffic. It is comforting to know that such dependable workhorses will be escorting oil tankers, because with a tug on the bow and another on the stern, what could go wrong?

According to the NEB panel – not much, even though the project would increase tanker traffic to 34 a month from five.

"Trans Mountain said that with the implementation of its proposed mitigation of additional dedicated tug escort and other risk-reduction measures, the return period for a spill of any size from project-related tanker traffic would be 1 in 284 years," states the NEB report. "The Board accepts the evidence filed by Trans Mountain regarding marine shipping navigation and safety."

Double-hulled tankers, modern navigation aids, and the use of B.C. pilots were all part of the safety plan, but the promise of tugs seemed to seal the deal, assuring an additional layer of protection.

But while tugs project an image of power and dependability, they are not infallible.

Marine investigation reports by the Transportation Safety Board of Canada show nationally there have been 46 accidents involving tugs over the past 22 years. Of those, 25 tug mishaps occurred on the West Coast, the vast majority in the waters the oil tankers will ply. Equipment failures, human error, sudden weather changers and just plain bad luck were all factors.

The tug Manson, towing two barges in Georgia Strait in 2004, vanished with its two-man crew shortly after reporting steering problems. Rescuers found the barges drifting free and a small oil slick on the surface, but the tug and those aboard were gone. Investigators think that when the crew went below to investigate mechanical problems, the drifting barges violently snapped the tow line tight, sinking the tug.

The bulk carrier Pacific Dolphin was being escorted by two tugs, Seaspan Falcon and Seaspan Hawk, when it ran aground in the harbour near Port Moody in 1998. Under the guidance of a B.C. Coast Pilot, the ship was being moved to a terminal when it began to swing with the tide. The Seaspan Falcon couldn't stop it and the tug was driven aground. Then, the Pacific Dolphin shuddered. The ship's double hull was "indented and the associated frames, stiffeners and floors were distorted," but there was no leakage. So it was a close call, but not an oil spill.

In 2009, the tug North Arm Venture was pulling a barge loaded with 370,156 litres of diesel and gasoline when the tow veered to starboard in Sechelt Inlet. TSB investigators said the skipper tried to control the barge, but it overtook the vessel and forced it to capsize. The crew escaped. The drifting, oil-laden barge was saved from the rocks only because a second tug was nearby and raced to the rescue.

U.S. accidents aren't in the TSB investigation records, but you don't have to go far to find one. In 1988, the oil barge Nestucca, accompanied by the tug Ocean Service, ran aground in Washington State's Grays Harbor after a tow line snapped. By the time a second tug arrived, the barge had spilled 231,000 gallons of heavy oil, killing 2,000 birds and fouling beaches. Three months later, the Exxon Valdez ran aground in Alaska and the Nestucca incident was largely forgotten.

Tugs assist in thousands of vessel movements annually on the West Coast, and most of the time they perform flawlessly. But tugs can't always overcome nature, make up for bad decisions, or counter sudden equipment failures.

With the movement of oil, comes risk. It is now up to the federal cabinet to decide if the risk is acceptable.

Editor's note: A previous version of this story incorrectly said the Exxon Valdez sank in Alaska. In fact, the Exxon Valdez ran aground and was later refloated.

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