Scientist Brett Singer is a vegetarian. So why has he been frying up hamburgers? Singer and his team of Lawrence Berkeley National Laboratory (Berkeley Lab) indoor air researchers have found hazardous levels of nitrogen dioxide and carbon monoxide in a surprisingly large portion of California home kitchens. What’s more, their studies have shown that the most common device for mitigating this indoor air problem--range hoods--vary widely in performance.
In a small nondescript building in a parking lot on the Berkeley Lab site, Singer’s group has set up a test kitchen to conduct a battery of cooking trials. By frying up burgers and green beans with a variety of range hoods operating at different settings, the researchers are collecting important data on the impacts to air quality as well as developing a standard test for range hoods that could eventually allow consumers to evaluate and compare their effectiveness.
In a study of southern California homes to be published soon in Environmental Health Perspectives, Singer’s group found that a significant portion of residences exceed outdoor air quality standards for several pollutants on a weekly basis as a result of cooking with gas burners. "If these were conditions that were outdoors the EPA [Environmental Protection Agency] would be cracking down. But since it’s in people’s homes, there’s no regulation requiring anyone to fix it," Singer said. "Reducing people’s exposure to pollutants from gas stoves should be a public health priority."
Berkeley Lab’s team of indoor air quality researchers is the oldest and most comprehensive in the country and has contributed to many of the standards and building codes now in place for both homes and industrial buildings, such as schools and offices. In recent years, as more attention has been paid to making buildings more energy efficient--which often means making them "tighter," or less leaky, to reduce heating and cooling costs--ventilation has become increasingly important.
Dangers of Poor Ventilation
Without appropriate ventilation, indoor air quality can suffer and cause serious health problems. A previous Berkeley Lab study , which Singer co-authored with Berkeley Lab scientist Jennifer Logue, found that the aggregate health consequences of poor indoor air quality--of which cooking is the major but not sole source--are as significant as those from all traffic accidents or infectious diseases in the United States.
In a recent study led by Logue, the team analyzed extensive data from several sources to understand how common it is for California homes to experience indoor air pollution at hazardous levels. They estimated that 60 percent of homes in the state that cook at least once a week with a gas stove can reach pollutant levels that would be illegal if found outdoors. That equates to 12 million Californians routinely exposed to nitrogen dioxide levels that exceed federal outdoor standards, 10 million exposed to formaldehyde exceeding federal standards and 1.7 million exposed to carbon monoxide exceeding ambient air standards in a typical week in winter.
Berkeley Lab’s Tips for Buying and Using Range Hoods
- Turn on the hood every time you cook, and set the fan to the highest setting that the noise is tolerable.
- Make sure it vents to the outdoors. If it doesn’t, the hood will simply recirculate air in the kitchen.
- If your range hood does not extend over the front burners, cooking on the back burners could make the hood up to twice as effective at removing pollutants.
- If buying a new hood, it should cover your front burners and have a setting that moves at least 200 cubic feet of air per minute.
- If having a range hood is not possible, opening a window while cooking does help.
These pollutants can come both from the cooking burners--especially gas burners but to a lesser extent electric burners also--as well as from cooking itself. The primary health effect of nitrogen dioxide, which is also found in the fumes of any type of combustion, is an increased likelihood of respiratory problems. Exposure to carbon monoxide is most serious for those who suffer from cardiovascular disease as it can enter the bloodstream and reduce oxygen delivery to the body’s organs and tissues.
The indoor pollutant that scientists believe may be most harmful to human health is particles, including fine particles, which are less than 2.5 micrometers in diameter, and ultrafine particles, which are smaller than 1 micrometer. They are produced by both gas and electric burners and by cooking. They are potentially very harmful because they can enter the lungs and, for the smaller particles, enter the bloodstream or other tissues.
"Electric burners produce ultrafine particles essentially by volatilizing dust," Singer explained. "It’s the same process with your toaster, resistance heater or radiator if you haven’t used it for awhile. After you turn it on, you can smell it--it smells terrible. You’re smelling the chemicals that have been volatilized. Once they’re in the air, they recondense into these ultrafine particles. This is the chemistry lab in your kitchen."
Range Hoods Can Help--Or Can They?
Singer recommends the use of range hoods while cooking. "If every one one of those homes were to use a range hood that exhausts to the outside and is even moderately effective, the number of homes exceeding the standards would drop by more than half," he said.
Still, Singer’s previous studies have found that range hoods vary widely in their capture efficiency, or effectiveness at removing pollutants. In a laboratory study of seven models ranging from $40 to $650, he and colleague Woody Delp found capture efficiencies ranging from 15 to 98 percent, and also found that a higher price did not guarantee better performance.
Another study of 15 range hoods installed in homes found that airflows often fell below advertised values and that less than half of the pollutants emitted by gas burners are removed in many instances. What’s worse, there’s no rating system that will tell consumers which products are better at removing pollutants.
A Rating System for Range Hoods
This is where the burgers come in. In the test kitchen Singer and his team are measuring the pollutants emitted by cooking foods at different temperatures and then evaluating how effective different range hoods used in different configurations are in capturing the pollutants.
Delp is in charge of making sure that every burger and every batch of green beans is cooked in precisely the same way each time--whether operating at low or high setting, whether on the front or back burner, repeated three times each. He is also making a "simulated pie," which consists of a spoonful of corn syrup on a pan to simulate drippings--the main source of emissions from the oven--to gather the same data for baking.
The aim of these experiments is to develop a reliable test methodology that manufacturers of range hoods can use to give a rating to their product. Currently, range hoods are rated only for energy efficiency and noise level but not for pollutant capture efficiency.
"There are some relatively effective and quiet range hoods on the market at affordable prices," Delp said. "Still, while consumers can get information about sound levels and airflow ratings for some models, there is currently no standard rating for effectiveness. "
The Berkeley Lab researchers are working toward an ASTM International test standard that manufacturers could voluntarily use to rate their products.
Further down the road, Singer’s team would like to see quieter hoods that come on automatically. The research involves finding a robust control algorithm for turning the fan on and off. "We want systems that don’t require people to turn things on," Singer said. "When your water heater comes on, the exhaust gases go outside, and you don’t have to flip a switch. It should be the same in the kitchen."
The research described here was funded by the Department of Energy (DOE), the California Energy Commission, the Department of Housing and Urban Development (HUD) and the Environmental Protection Agency (EPA).