Carbon Monoxide · Canairy

What it is

Carbon monoxide (CO) is a colorless, odorless, tasteless gas formed when carbon-based fuels burn incompletely. It is the same molecule whether it comes from a car engine, a charcoal grill, or a malfunctioning furnace.

CO is dangerous because it binds to hemoglobin in your blood about 200 times more tightly than oxygen does. Once attached, it blocks oxygen delivery to the heart, brain, and other tissues. Severe exposures can kill within minutes.

Where it comes from

Outdoors, vehicle exhaust dominates, especially in heavy traffic and near tunnels, parking garages, and idling trucks. Wildfires, wood stoves, and industrial combustion add to the mix.

The bigger health threat is usually indoors. Common sources are gas furnaces with cracked heat exchangers, blocked chimneys, water heaters, gas stoves and ovens (especially when used to heat a room), portable generators, charcoal grills used indoors, kerosene heaters, idling cars in attached garages, and tobacco smoke. Generators used during power outages cause hundreds of US poisoning deaths each year.

Health effects

Mild exposure feels like the flu: headache, fatigue, dizziness, nausea, and confusion. Many CO poisonings are misdiagnosed as viral illness, especially when whole families get sick at the same time in winter.

Higher concentrations cause chest pain in people with heart disease (CO can trigger heart attacks at relatively low levels), impaired coordination and vision, loss of consciousness, and death. Pregnant people, infants, older adults, and anyone with cardiovascular or respiratory disease are most vulnerable. Survivors of severe poisoning can have lasting brain damage, including memory loss and movement disorders.

How it's measured and typical levels

CO is measured in parts per million (ppm) for indoor and ambient air, or as carboxyhemoglobin (COHb) percent in the blood for medical assessment.

Key benchmarks:

WHO 24-hour guideline: 4 mg/m³ (about 3.5 ppm)
US EPA NAAQS, 8-hour: 9 ppm
US EPA NAAQS, 1-hour: 35 ppm
OSHA workplace 8-hour limit: 50 ppm
NIOSH ceiling: 200 ppm
Immediately Dangerous to Life or Health (IDLH): 1,200 ppm

Indoor background in homes without gas appliances runs 0.5 to 5 ppm. Near a properly adjusted gas stove, 5 to 15 ppm. A poorly adjusted stove can produce 30 ppm or more. A running generator in an attached garage can push levels above 500 ppm in minutes.

What you can do

Install UL-listed CO alarms on every floor, including outside sleeping areas, and replace them every 5 to 7 years per the manufacturer. Test them monthly. If an alarm sounds, get everyone outside and call 911 from outside.

Have gas furnaces, water heaters, and chimneys inspected annually by a qualified technician. Never run a generator, grill, or unvented combustion heater indoors or in an attached garage, even with a door open. Do not warm up a car in a garage. Make sure your range hood vents outside, not just into the kitchen.

If you suspect CO poisoning (headache, nausea, dizziness that improves when you leave the building), get fresh air and call 911 or poison control (1-800-222-1222 in the US).

Sources

This article is for educational purposes only. Canairy does not provide medical advice, diagnosis, or treatment. Talk to a qualified health professional about your specific situation.