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Cooking up a storm

Did you know that cooking is one of the largest sources of air pollution in your home? Every time you turn on that stove, particles may be released into the air, which could cause health issues in the long run. The solution is not to stop cooking entirely and eat out every day! Instead, just ventilate when you cook. Turn your kitchen exhaust fan on when you start cooking and leave it on for about 5 to 15 minutes after you finish cooking, or open a window, to help improve the air quality in your home.

To develop this advice, Health Canada researchers Liu Sun (Sunny), M.Sc., and Nina Dobbin, M.Sc., studied whether kitchen exhaust fans were efficient in reducing cooking pollutants, and how long we should leave them on. “When we cook, we can be exposed to pollutants in the form of tiny particles. When we use a gas stove, we are also exposed to pollutants like nitrogen dioxide (NO2), and carbon monoxide (CO), ” explains Sunny. As the government looks for ways to reduce Canadians’ exposure to pollutants indoors, this air health research study provides the foundational data to inform science-based decision making.

Sunny and Nina were looking for pollutants known as fine particulate matter (PM2.5) and ultrafine particles (UFP) that can come from both gas and electric burners, as well as from the food as it is being cooked. Due to their small size, these particles can easily be inhaled, get into the lungs and cause health problems. In fact, cooking was found to be the most important source particles in non-smoking homes. The team tested three different kitchen exhaust fans, at various speeds, in the Canadian Centre for Housing Technology’s twin research houses located in Ottawa, Ontario.

“We were surprised to see that exposures to pollutants are actually largest in the hour following cooking, rather than during the relatively short cooking period, because pollutants linger in the air long after you turn the stove off,” says Sunny. That is usually when everyone is gathered close to the kitchen and are more likely to breathe in the air. “Because we get used to the nice smells from cooking, we don’t think of cooking as a source of air pollution,” says Sunny. “We have to get into the habit of using the fan the entire time we are cooking, not just when there is smoke or food burning.”

Currently, fan flow rate and noise level are used to determine the fan’s performance. “Fan flow rate is important. Our experiments show that running an exhaust fan on high speed can reduce exposure to cooking pollutants by about 80% when compared to slower speeds,” explains Sunny. But even at the same airflow rate, different hoods could have very different performances in capturing pollutants. Other factors, such as the shape of the hood and how much of your cooktop burners are covered by the hood, really make a difference in its efficiency. If your range hood only covers part of the front burners, it might be best to use the back burners for things that generate more pollutants, like frying or sautéing.

Nina and Sunny collaborated closely with experts from the Lawrence Berkeley National Laboratory in the United States to build on their existing knowledge base. The U.S. has done a lot of leading work in this area, but not much has been done in Canada. But this is just the beginning! Recently, a nationwide online survey on kitchen ventilation use was conducted. “This survey of 4,500 homes can help us understand what type of kitchen exhaust fans Canadians have in their homes and how frequently they were used during various types of cooking. This will help Health Canada to prepare better campaigns to encourage good kitchen ventilation during cooking.” The analysis of the survey is expected to be completed by the end of 2020.

Next, Sunny will be looking at the efficiency of recirculating kitchen fans. Outdoor venting fans, such as the ones tested by Sunny and Nina, are required by most building codes for new homes because they are the most efficient at removing pollutants from the air inside the home. However, some older homes or apartments may have recirculating fans. “There is no evidence as to their efficiency in removing cooking pollutants. We think they are less efficient, but we don’t really know,” says Sunny. The results from this indoor air research will be used to support government policy, mitigation and decision making as well as identify best practices.

Especially now as Canadians cook more at home than ever while practicing physical distancing, we should remember to turn on our fans to make our homes as healthy as possible!

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