What is carbon monoxide?

Carbon monoxide (CO) is a poisonous gas that you cannot see or smell. It can form when carbon-containing fuels do not burn completely. Your senses cannot tell you that the air is safe.

Where can it come from?

Fuel-burning furnaces, boilers, water heaters and fireplaces can produce CO. Portable generators and vehicle engines are also sources. Combustion problems can increase CO production. Blocked vents, disconnected venting or improper draft can prevent combustion gases from leaving the building as intended.

Never run a generator indoors or in a garage. CDC advises using generators outdoors, more than 20 feet from windows, doors and vents. Never run a vehicle in an attached garage, even with the garage door open.

Why does CO affect the body?

CO interferes with the blood’s ability to carry oxygen to organs including the brain and heart. Headache, dizziness, nausea, weakness and confusion can occur. These symptoms overlap with other conditions and cannot diagnose or rule out exposure. Infants, older adults and people with certain heart, blood or breathing conditions may be more vulnerable. A clinician must evaluate suspected poisoning.

CO is different from CO₂

CO has one oxygen atom per carbon atom; carbon dioxide (CO₂) has two. Both can result from fuel combustion, but they are different gases with different hazards. CO₂ is also produced by breathing. A CO₂ indoor-air monitor is not a substitute for a CO alarm, and a CO alarm does not measure CO₂ unless the device explicitly includes a separate sensor.

Prevention and testing work together

Maintain fuel-burning equipment and venting with qualified professional service. Install and maintain appropriate CO alarms according to their instructions and applicable requirements. Alarms supplement proper installation and maintenance; they do not correct a combustion or venting problem. Do not attempt to reproduce a suspected unsafe condition yourself.