Health Canada warns of cancer risk from fumes entering homes from attached garages

If your house has an attached garage, after you read this you'll be thinking twice about idling the car for long before you pull out on a winter morning. It appears you're increasing the chances of your family getting cancer.

The National Post reports Health Canada is preparing new guidelines for homeowners to improve the sealing and ventilation of their attached garages to reduce the migration of toxic vapours, especially benzene from car exhaust, into the home.

Your first reaction might be an eye-rolling "c'mon!" Isn't this a bit of unnecessary nanny-stateism, particularly from a government that downplays climate change and has muzzled federal scientists so they can't publicly contradict economic policies seen as bad for the environment?

But Health Canada has long played a role in setting guidelines for exposure to harmful substances. Its current Residential Indoor Air Quality Guidelines provide maximum exposure limits to a number of pollutants that can be found in the home environment.

The Canada Mortgage and Housing Corp. (CMHC) already provides a fact sheet on the risks of attached garages with recommendations on minimizing the transfer of garage air to the home. The problem can be especially acute for homes with living quarters above garage spaces that are not well sealed.

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Health Canada's latest worry is about benzene, which is in the family of volatile organic compounds and which has been linked to leukemia, the Post says. Though the risk is small, apparently it's not insignificant.

"The best advice is to lower exposure as much as possible," Deborah Schoen, head of Health Canada’s indoor-air section, told the Post. "It is recognized as a carcinogen … [And] attached garages are clearly a predictor of higher benzene levels, up to threefold on average."

Historically the main concern about benzene exposure has been in industry, where studies have found workers in certain facilities face increased risk of leukemia, the Post said.

As early as 1948, the Post noted, the American Petroleum Institute (API) declared "the only absolutely safe concentration of benzene is zero."

The API today offers an online benzene awareness training course to school plant managers and workers on safe practices.

According to a 2007 Natural Resources Canada survey, about 3.5 million Canadian homes have attached garages (my little townhouse condo included), the Post reported. The risk of benzene exposure is much lower than in industrial settings, Schoen said, but it does exist and it's worth addressing the issue.

Canadian homes might be at higher risk than their American counterparts, she said, because we heat our houses for longer over the year and that tends to suck in air from outside, including the garage.

The proposed new guidelines recommend things such as improving door seals, drywalling the garage walls if not done already, installing a garage-air exhaust fan, ensuring vehicles don't idle in the garage and not running gas-powered equipment in the garage.

It bears pointing out some of these things have already been suggested in the CMHC fact sheet, which is aimed mainly at prospective home buyers.

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But one cancer expert was skeptical homeowners need to race to their local DIY store to upgrade their garages.

"I suspect that the risk is somewhere between negligible and too small to detect," Jack Siemiatycki, an epidemiology professor at the University of Montreal, told the Post.

"But, since benzene exposure does nobody any good and there is a chance that it may do some harm, the guidelines would be valid if their implementation does not lead to large monetary expenses."

One advantage of this fresh attention on keeping benzene vapours out of homes is the impact on other garage-sourced toxic pollutants, such as carbon monoxide from car exhaust and vapours from stored lawnmower fuel, solvents and paints.

"By controlling benzene levels, you can control a lot of other pollutants," Schoen told the Post. "In general, if we can control infiltration from attached garages into the home … we’d generally be improving indoor air quality."