Attached Garages Create Many Carbon Monoxide Hazards

There are many carbon monoxide hazards of having an attached garage, including leaving a car running, using lawn and power tools. Powerful suction forces will drive CO indoors.

By Rebecca Martin

One factor which does not always come to mind when considering the source of carbon monoxide poisonings is the carbon monoxide hazard of the familiar attached garage which has become a staple in American homes.

carbon monoxide hazards

Attached garages come with many carbon monoxide hazards, which include leaving your car running, putting a portable electric generator in the garage and many other yard and other power tools.

In the 1920s, the increasing use of cars prompted the building of garages. Early garages were generally constructed of wood and set away from the home due to the danger of gasoline explosions.  Gas was often stored in garages prior to the appearance of gas stations. Carriage houses were often converted to auto storage. A detached garage creates few carbon monoxide hazards.

Eventually it became more common to build garages out of noncombustible materials like brick. But in the 1940s, attached garages began to appear and by the 1950s, attached garages were integrated into the design of new homes as America’s reliance on cars increased. The convenience of attached garages has been part of American architecture ever since.,pressed%20tin%2C%20rather%20than%20wood.

An Attached Garage is not Outdoor Space

The carbon monoxide hazard with attached garages is that we tend to think of them as part of the outdoor living of a home rather than an integrated part of the living space. In addition to garages we too typically store all the fuel-burning tools needed for outdoor maintenance. The large doors give us a false sense of safety when open because of the mistaken assumption that if the door is open there is plenty of fresh air and the danger from carbon monoxide is diminished. But even with the house door firmly closed, an open or closed garage can create a deadly hazard.

Your home creates negative air pressure, perhaps easier to think of as a suction. This sucrion increases with the use of dryer vents, hood vents, and bathroom vents.

Ways in Which Carbon Monoxide Hazards Get Into House

There are multiple ways this negative pressure/suction can result in pulling the air from the attached garage inside, even if the door between the house and garage appears firmly sealed.  Very small amount of wind blowing into an open garage can cause emissions from vehicles or machinery in the garage to enter the house. Anytime the positive air flow is greater in the garage, air can be sucked into the home through even the most minute entry points. This of this as a river of air. That air has to flow somewhere. If the wind is forcing it into the garage, it will ultimately find a pathway into the house.

Another way the toxic air in the garage can get inside the house is called the stack effect. Warm air rises and can carry toxic fumes with it. For garages that have living space above them, this means that rising warm air can carry the fumes into the rooms above.

A third way is based on the operations of the machinery of the house. Your furnace is drawing air from outside and that air is heated and rises to the highest points and fumes can be carried in that airflow due to the negative pressure created between home and garage.

Garages Can’t Be Sealed from Other Indoor Space

There is virtually no way to create a completely airtight barrier between a garage and a house. Studies have shown that even drywall is not an adequate air barrier.

“In laboratory tests, carbon monoxide gas infused through drywall reached fatal indoor concentrations in as little as 17 minutes. While sheets of painted drywall slowed the infiltration process—as did double sheets of drywall—CO gas was still able to infiltrate the home. “,able%20to%20infiltrate%20the%20home.

Extreme Weather Increases Carbon Monoxide Hazards

During extreme weather we are more tempted to leave vehicles running in the attached garage which creates a concentration of carbon monoxide. Due to the negative pressure in the home, these fumes are drawn into the home whether or not the garage door is open or closed. Whether warming up a car due to frigid weather conditions or to charge a cell phone during a weather emergency, these activities should always be performed outside of the garage and ideally with a buffer zone in between the garage and the home. Cold engines produce more carbon monoxide than in the summer.

“According to research completed by Iowa State University, just pulling the car into the garage emits enough carbon monoxide to trigger most detectors! Warming a car for just two minutes raises the CO level to a dangerous 500 ppm. Measurable concentrations may linger for as much as 10 hours. People working in the garage as much as 10 hours later remain in danger.”

Additionally, “A Minnesota study found that as much as 85% of the air leaking into your house comes from the garage. The carbon monoxide flowing from the garage may build up inside your home but be too diluted to trigger the alarm on your family’s indoor CO detector.”

A carbon monoxide detector in your garage is not the ultimate way to eliminate the carbon monoxide hazard. Carbon monoxide detectors are not designed for conditions created within a garage.  Instead, carbon monoxide detectors need to be placed where anyone sleeps in the home and ANY WHERE ELSE THAT SOMEONE BREATHS INDOOR AIR.

In November 2023, a family of four in Ogden, Utah, were poisoned by carbon monoxide after a vehicle was left running in their garage. Fire fighters discovered the car was producing a slow leak into the home and that luckily the outcome was not fatal for the family.

A family in Kitchener, Ontario was not as fortunate. In December 2023, seven people were transported to the hospital where one was later pronounced dead due to a vehicle left running in a garage.

Another deadly source of carbon monoxide in the home is the use of a portable generator during power outages. Just like a car, running a portable generator in an attached garage creates the same hazards. These hazards are also not alleviated by leaving the garage door open or by having a carbon monoxide detector in place. It is also important to repeat that the dangerous accumulation of carbon monoxide in a garage is not easily dispersed just by opening the door. It is more likely that due to the negative air pressure in the house, carbon monoxide will travel inward.

While January is coming to an end, there is still plenty of weather to be prepared for. It is extremely important to understand the dynamics of airflow in the home, particularly when that home has an attached garage. The same diligence should be used in apartment complexes in which the garages are located on a lower level.

There are more and more sources for carbon monoxide detectors in communities across the country. Contact your local fire department for more information.

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