Carbon Monoxide Headquarters

CO & Motor Vehicles

CO Exposure in Motor Vehicles:

Mr. Albert Donnay wrote to me recently, expressing the following thoughts about CO exposure in automobiles.

"Several commentators have questioned the validity of carbon monoxide levels over 100 ppm measured inside vehicles in traffic, based on their experience with the much lower CO levels they've measured alongside busy highways and in buildings and commercial parking garages.

What these people overlook are the DILUTION and DISPERSION of CO sources in outdoor air and large indoor spaces (like office buildings and commercial garages). In comparison, the inside of a vehicle is a relatively TINY CONFINED SPACE, measuring only a few dozen cubic feet.

The level of CO in vehicle exhaust is usually under 100 ppm if the catalytic is warmed up and working properly, but if it's not, the level is 50,000 - 150,000 ppm. If your car stops close behind an idling vehicle with such a non-working catalytic converter while you have your air intake fan on, much of this CO will be sucked into your passenger compartment, which will quickly cause a much higher level of CO to CONCENTRATE inside than you could measure outside the car even if standing right next to it. Each time you get close to such a vehicle, more CO will enter yours, further increasing the CO concentration inside relative to outside.

If you keep your windows closed or only slightly open (as is common in winter when exhaust CO levels are highest), the CO you have just entrained will NOT dissipate quickly unless and until you open more than one window and start to drive again. Just opening the windows doesn't work if you don't also start moving to induce some air exchange. (You can also accumulate high levels inside your car if you have a cracked manifold, which would cause your own exhaust to accumulate in your engine compartment from whence it is easily sucked into the passenger compartment).

The proof that very high levels can accumulate--much higher than even 100 ppm-- is that many people die every year of CO poisoning while sleeping in their cars with the motor running, even outdoors with the windows open! In 1998, the last year for which US data are available, 68 people died of CO poisoning while they were driving!

Using an electrochemical CO sensor (the AIM 450 model, as well as other models from Bacharach, Zellweger and KED Eng.), I regularly record levels in the 20-50 ppm range inside my ten-year old Subaru station wagon while driving in heavy traffic around Baltimore. I once got a spike over 50 ppm on a virtually empty rural interstate after passing an old pickup truck at high speed. Imagine how much more CO would have accumulated in my car had I been tailgating this pickup in a traffic jam.

I urge the skeptics to put a CO detector in their own vehicle and see what happens. There is no way to predict levels inside vehicles based solely on monitoring the outdoor air around them."

........ Mr. Albert Donnay, MHS, November, 2002

Deaths from CO in Motor Vehicles

CO in Automobile Exhaust

Problems with the Air Pressure Relief Valve?

...... last changed 12/16/02

Back to the COHQ Main Index