Iowa State University Extension



AMES, Iowa -- In cold weather do you open the overhead garage door and start the car to let it warm up for a minute or two before driving away? Thomas Greiner, an extension agricultural engineer from Iowa State University, has this warning. "Don't ever warm-up a car in a garage, even with the garage door open. In less than two minutes gas fumes build to lethal concentrations in the garage." In an attached garage, fumes can quickly spread to the house.

Deadly fumes from vehicle exhaust include carbon monoxide (CO), a colorless, odorless, tasteless, and non-irritating byproduct of incomplete combustion. Greiner has consulted on and investigated several cases of poisoning from car fumes, some resulting in death.

"When cold engines first start, they run rich," Greiner said. The catalytic converter is cold and not converting deadly carbon monoxide (CO) to carbon dioxide (CO2). Concentrations in the exhaust can be more than 80,000 parts per million. Concentrations so large fill the garage with carbon monoxide in a very short time even with the door open. Once the car is backed out of the garage and the garage door closed, large concentrations of gas still remain trapped in the garage. In a house built with an attached garage, part of the gas then seeps into the house where it remains for hours.

Carbon monoxide reduces the oxygen supply to the brain, causing carbon monoxide intoxication. At high concentrations, such as produced in the exhaust of a cold engine, carbon monoxide intoxication occurs in only a few minutes, leaving those poisoned incapable of realizing they are poisoned, and unable to protect themselves. Carbon monoxide poisoning can happen to anyone, although children, the elderly and those with health concerns are especially susceptible.

Greiner conducted an investigation at a central Iowa home where the family was diagnosed with carbon monoxide poisoning and treated with oxygen. The husband typically opened the overhead garage door in the attached garage, started his small pick-up, let it warm for one or two minutes, drove out, shut the garage door, and left for work. His wife, who works in a home office, often developed late morning headaches. The family installed a carbon monoxide alarm. It sounded an alarm several hours after the truck was driven from the garage. Repeating the sequence of events, Greiner found that after only two minutes of warm-up in the opened garage, carbon monoxide concentrations rose to a lethal 575 parts per million. Within one minute, measurable levels of CO seeped into the house and after only 45 minutes the level in the house rose to 23 parts per million. Eight hours later carbon monoxide concentrations still remained above the allowable 9 ppm.

To prevent carbon monoxide poisoning from vehicles:

  • NEVER run engines in a garage, even if the garage door is open.
  • Make certain all vehicles are tuned up and running clean.
  • Check and repair exhaust system leaks.

When starting a car and leaving from the garage:

  • Make certain everyone is in the car and ready to leave.
  • Open the overhead garage door before starting the car.
  • Start the car and immediately back out.
  • Shut the garage door.
  • Immediately drive away. Consult the owner's manual for recommendations when driving with a cold engine.

Finally, buy UL listed carbon monoxide alarms and install them near sleeping areas and on every level of your home. "Carbon monoxide is a sneaky killer, a silent killer. Protect your home and family by being alert to its dangers," Greiner said.


This story was published 1/10/97.

Return to Carbon Monoxide Information from ISU Extension.

Page last updated October 16, 2000