Asked to name the last major oil tanker spill, most British Columbians can at least summon the Exxon Valdez.

That spill in Prince William Sound, Alaska in 1989 – 10.8 million gallons – was small compared to other spills around the world. It does not rank among the top 10, or even top 30 worst oil spills.

Even so, the Exxon Valdez was considered the worst oil spill in U.S. history until 2010, when the Deepwater Horizon disaster pumped 210 million gallons into the Gulf of Mexico.

The Exxon Valdez spill coated 1,300 miles of Alaskan shoreline with oil, killed an estimated 30,000 seabirds, as many as 5,000 sea otters, 300 harbour seals and wiped out nearly half of a resident killer whale pod.

To this day, oil is found just below the surface on many Alaskan beaches. It cost the company an estimated US$4 billion in cleanup costs and fines.

With the approval of the Trans Mountain pipeline expansion, it’s expected that oil tanker traffic moving up Burrard Inlet to the Westridge Marine Terminal in Burnaby will rise from five to 34 vessels per month.

Of all the negative environmental consequences associated with pipelines and fossil fuels in general, the threat of an oil spill along the B.C. coast is the one that worries opponents, like the City of Vancouver, the most.

In May 2015, the city produced economic modelling that estimated the economic costs of a spill. It concluded a spill in May would do the most damage.

“In the event of a May spill, Vancouver’s ocean-dependent economy could suffer total losses in the range of $380 million to $1.2 billion,” the study concluded.

That’s just the economic impact to local tourism, fisheries and other businesses connected with the marine environment – it doesn’t include the cleanup costs.

A group of Vancouver business people called Conversations for Responsible Economic Development (CRED) studied the pros and cons of the project and concluded the benefits are not worth the risks.

“The likelihood of a major tanker spill is very low, but the impacts if it did happen would be catastrophic,” said CRED director Liz McDowell.

If there was anything positive to come out of the Exxon Valdez, it was that it has reduced the chance of an oil tanker spill happening again on the Pacific Coast, because it prompted both the U.S. and Canadian governments to adopt stringent new regulations for oil tankers.

In recommending the Trans Mountain pipeline expansion be approved, the National Energy Board (NEB) concluded there is “a very low probability of a large oil spill.” Some in the industry say the risk is practically nil.

“The probability of something going wrong with the tankers has been minimized significantly – in fact, close to zero,” said Brian Young, director of marine operations for the Pacific Pilotage Authority. “And that’s primarily because of the consequence side of the equation.”

In other words, it is acknowledged that a major oil spill in B.C. coastal waters could be catastrophic, so there is considerable emphasis on preventing one from ever happening.

There is a far greater risk of a bunker fuel spill from any number of container ships, or a pipeline rupture on land, close to water, like the one in Burnaby in 2007 that pumped 224,000 litres of heavy synthetic crude into Burrard Inlet.

Following the Exxon Valdez disaster, the U.S. government enacted rules – adopted later by Canada – requiring all oil tankers coming into North American waters to be double-hulled and compartmentalized.

That’s still no guarantee, however, as even double-hulled tankers can be ruptured in a collision with another vessel, as was the case in 2010 when the Eagle Otome oil tanker was sliced open in a collision with a barge, spilling 450,000 gallons of crude in Port Arthur, Texas.

The biggest risk for an oil tanker is colliding with another vessel or losing power in stormy weather and being driven onto rocks. There are therefore strict regulations on all large ships entering Vancouver’s port.

All vessels over 400 gross tonnes coming into Vancouver must be brought in by Transport Canada-certified pilots through Pacific Pilotage Authority Canada.

The vessels enter via shipping lanes that generally straddle the U.S.-Canada border. Near Victoria, they are boarded by a Canadian pilot, who then assumes control of the vessel.

The Pacific Pilotage Authority has more than 100 coastal mariners and eight Fraser River pilots, all of whom are experienced mariners who know local waters.

“To the best of my knowledge, over the last 50 to 60 years since these tankers have been coming and going, I don’t believe there has been an incident on an oil tanker,” Young said.

If an oil tanker were to rupture and start leaking crude oil or diluted bitumen, the Western Canada Marine Response Corp. (WCMRC) would respond with special vessels equipped with booms and sweepers to contain the spill.

The WCMRC owns 33 vessels and operates manned facilities in Burnaby, Duncan and Prince Rupert. It has 65 full-time staff.

When the Trans Mountain project proceeds, the WCMRC – which is industry funded by major oil companies and shippers – will spend close to $200 million expanding its capacity. That includes adding several new bases, another 26 new vessels and 115 additional full-time staff.

“These enhancements are only focused on the southern shipping lane,” said Michael Lowry, communications manager for WCMRC.

On a recent certification exercise for Transport Canada, Lowry explained what would happen in the event of an oil spill in Vancouver harbour.

The WCMRC is mandated to get oil or fuel off the water within 10 days. The first action is to contain the oil or fuel with booms. Special vessels called skimmers then begin essentially scooping up the oil or fuel.

Once the oil is off the water, shoreline cleanup assessments are done to determine what areas might have been contaminated. The WCMRC can also take preventative measures to protect environmentally sensitive areas.

“We’ve mapped the entire southern shipping lane for sensitivities, like seal haul-outs or eelgrass beds,” Lowry said. “We can go out and pre-boom those.”

Since its creation four decades ago, the WCMRC has never responded to an oil spill from an oil tanker. The biggest oil spill was the 2007 one, when a work crew ruptured a Trans Mountain pipeline, spilling synthetic crude into Burrard Inlet.

“Certainly tankers are not what keep us up at night, just because of all the safety measures,” Lowry said. “We’re more concerned about all the other types of vessels that have bunker fuel on them. Some of those large grain carriers you see out in English Bay, some of them have 10,000 tonnes of bunker on them.”