Industry representatives have assured local government that these tanker transits are done in "total safety," citing the move towards double-hulled vessels as a rationale. However, even double-hulled vessels are not structurally designed to withstand supporting the weight of a loaded tanker on a portion of the hull.

Aframax tankers now making these dangerous transits can hold 40 times as much diluted bitumen as spilled into the Kalamazoo River. There are plans to move to larger Suezmax tankers that carry 80 times the Kalamazoo spill amount. A spill of that magnitude might make large parts of the Lower Mainland uninhabitable for weeks.

Chemicals in diluted bitumen kept secret

Oil sands operators have considered the composition of diluted bitumen blends a trade secret and regulators are often not provided detailed information on the types of chemicals they might have to respond to in the event of a spill and subsequent public health emergency. What information is available is not reassuring. The Material Safety Data Sheet (MSDS) for one common variety of diluted bitumen warns:

"High vapour concentrations are irritating to the eyes, nose, throat and lungs; may cause headaches and dizziness; may be anesthetic and may cause other central nervous system effects, including death. Hydrogen sulphide gas may be released. Hydrogen sulphide may cause irritation, breathing failure, coma and death, without necessarily any warning odour being sensed. Avoid breathing vapours or mists."

Expert testimony last year to the U.S. Congress also flagged the possibility of off-gassing bitumen solvents "exploding with catastrophic results." The MSDS sheet from Imperial Oil states "Extremely flammable; material will readily ignite at normal temperatures... may release vapours that form flammable mixtures at or above the flash point."

Cuts to response preparation

The lead oil spill response agency is the federal government, but it seems little has been done to prepare for the air quality emergency created if a tanker accident happened in the Lower Mainland. A recent auditor general's report on spill preparedness revealed that the Canadian Coast Guard has not done a national risk assessment of oil spills from ships since 2000 -- long before Alberta started scaling up deliveries of diluted bitumen to the B.C. coast.

Rather than increasing capacity to respond to potential spills, the Harper government is slashing front line staff. More than 760 jobs are slated to be lost from the Coast Guard. The B.C. command centre for emergency oil spills is being closed and moved to Quebec. Almost all of the Fisheries and Oceans scientists involved in pollution monitoring learned recently that they are being fired.

So why has Vancouver become the major Pacific outflow for unrefined bitumen? Squeezing loaded tankers through the Second Narrows channel is far from the safest route for this dangerous cargo to access international markets. However, it may merely be the easiest for the oil industry to scale up.

There has been strong public opposition to proposed pipelines to the north B.C. coast and through the U.S. Midwest. However, the pipeline right-of-way owned by Kinder Morgan from Alberta to Burnaby was approved almost 60 years ago, originally to supply modest amounts of conventional crude to refineries in Burrard Inlet.

Kinder Morgan can upgrade this existing pipeline without triggering significant regulatory approvals, even if this results in tanker transits almost on a daily basis through the largest metropolitan area in Western Canada.

There is an added potential benefit for oil companies to scale up shipments of bitumen to Asian markets. So much diluent is now needed that thousands of barrels per day are being imported into Alberta from elsewhere in the world. If foreign chemicals are used to dilute bitumen for delivery to U.S. markets it could result in millions of dollars in duties under NAFTA since it might be considered a "non NAFTA good."

The increased risk of a tanker spill in Vancouver's harbour posed by Kinder Morgan's plans to greatly increase the bitumen it pumps from Alberta has sparked concern and alarm among local politicians, but little has been said about the toxic cloud leaked bitumen likely would send drifting over one of Canada's most densely populated regions -- and the evacuation nightmare that could create.

Any debate over whether the pipeline upgrade should proceed needs to include the real possibility of the scenario outlined here, based as it is on available facts, views of experts, and the three-week evacuation prescribed when a smaller spill of diluted bitumen changed life for thousands near Kalamazoo, Michigan.