Sources of Carbon Monoxide Poisoning

Auto exhaust is thought to be the number # 1 cause of accidental CO poisoning in North America and has been reported to be the cause of around 60% of carbon monoxide alarm responses.

Just notice how many people let their automobiles warm up inside garages with the door open and for how long before they back out and close the door with their automatic door control.  Typically, any gasoline engine produces the highest CO levels during a cold start.

CO gets trapped inside the garage and can easily disperse into the rest of the building through unseen but loose fitting construction connections (like wiring penetrations, framing joints, ductwork seams, door jambs and other areas).

Building pressure and temperature variations work as siphon points and air exchange locations.

Carbon monoxide in homes does not always come from traditional sources.  The service and HVAC industry has been targeting cracked heat exchangers as the leading source of CO poisoning (almost exclusively without test instrument verification until about 1985).

Recent, more thorough testing for CO suggests that unvented, poorly installed, unmaintained and misused gas and oil appliances are the 2^nd leading cause of CO alarm response, and may constitute as much as 20% of CO alarm call sources.

The 3^rd leading cause of CO exposure appears to be due to vented atmospheric, natural drafting appliances which backdraft into the structure and may account for 19% of the CO alarms going off. 

Intermittent backdrafting of CO laden flue gases complicates source investigations. Improperly sized and installed vent systems, old vents in need of repair, and competing building pressures contribute to this affect. 

Even if no significant levels of CO are measured in the flue gases, keep your eyes open to indications that spillage is occurring during other periods of time.  Soot or rust on draft hood surfaces or above the burner areas are common examples.

It should be noted that cracked heat exchangers make up one of the smallest percentages of CO alarm response causes (less than 1%).

Frequently, a furnace with a cracked heat exchanger is condemned by a technician or utility personnel, red tagged and shut off only to be returned to operation by a homeowner.

A furnace left in operation while a known crack exists represents a tremendous health, safety and liability concern and should be thoroughly tested for CO production.  Test results can then be presented to the homeowner emphasizing a very real and present danger.