A 67-year-old man with a history of stroke was shoveling snow while warming his car. He decided to rest for a few minutes inside the car and was found unconscious one hour later. The man regained consciousness the day after his hospital admission. After six days he was discharged from the hospital with a walker.

A five-year-old girl was playing while her father shoveled snow from around their car. He started the engine while the rear of the vehicle was still encased in a snowbank and allowed the child to sit in the car for warmth. She was noticed to be unresponsive within five minutes. She was removed from the car and awoke shortly thereafter.Carbon monoxide (CO) is the most common cause of accidental death by poisoning in the United States. CO exposure has happened in a variety of settings including homes, engine-powered vehicles, recreational boats and indoor ice-skating rinks. The main source of CO in the air we breathe is automobile exhaust.

It's important to prevent CO exposures. The public needs to know about the risks of remaining in a stationary vehicle during heavy snowfall if the engine is left running.

In some cases, leaving a car window or door partially open does not prevent CO exposure. Public service announcements should include the warning that opening a window may be insufficient protection against CO exposure.

The smell of engine exhaust has also been reported to relate with CO poisoning. Although CO itself is colorless and odorless, it is found in high concentration in exhaust gases, which have an identifiable odor.

Drivers should know:

- to visually inspect the vehicle's exhaust system before starting the engine.

- the importance of an unobstructed tailpipe for vehicles caught in snowdrifts.

- that recognition of unusual odors or fumes in the car may indicate possible CO exposure (even though you cannot smell CO).