What is carbon monoxide?

Carbon monoxide (CO), known as the silent killer, is an odorless, colorless, and tasteless gas produced by the incomplete combustion of carbon in fossil fuels such as wood, propane, charcoal, oil, gas, coal, or other fuel.

A 2015 study in The American Journal of Emergency Medicine determined that CO poisoning was the second most frequent non-medicinal poisoning death in the United States between 1999 and 2012.¹

CO poisoning occurs when a gas appliance has been incorrectly fitted, badly repaired or poorly maintained, or when flues, chimneys or vents are blocked, cutting off airflow.

Where does it come from?

Carbon monoxide is produced by the burning of fossil fuels. Any appliance that burns fossil fuels is a potential carbon monoxide source.
Sources may include:

• gas appliances, such as furnaces, ovens, ranges, water heaters, and clothes dryers
• electric generators
• water heaters
• fireplaces (gas/woodburning)
• wood stoves
• space heaters
• coal or oil furnaces
• car exhaust fumes
• power tools
• tobacco smoke
• charcoal grills and camp stoves
• gas-powered lawn mowers and power tools^2,3

Carbon monoxide is associated with improper operation or poor ventilation of appliances. Due to the many potential sources of CO, people should be cautious of potential exposure when camping, sailing, ice fishing, or in garages. The outdoor air can also have high concentrations of CO near roads and highways.

Smoke inhalation can also lead to carbon monoxide poisoning.

How does it affect your health?

Everyone is at risk for carbon monoxide poisoning, though unborn babies, children, older adults, and people with chronic heart disease, anemia, or breathing problems are more susceptible to adverse effects.

In the United States, 400 people die each year from accidental carbon monoxide poisoning unrelated to fires.⁴ An additional 20,000 are admitted to the emergency room, while 4,000 victims are hospitalized for symptoms.

When carbon monoxide enters the bloodstream, it prevents blood cells from carrying oxygen. CO attaches to the red blood cell hemoglobins that carry oxygen throughout your body.

This causes an onset of symptoms similar to that of oxygen deprivation, including:

• headaches
• dizziness
• weakness
• upset stomach
• vomiting
• chest pain
• blurred vision
• confusion

Because CO poisoning symptoms are flu-like in nature, they’re often ignored or misdiagnosed as being the flu, allergies, stroke, or migraine headache. Though the symptoms can be subtle, it is a life-threatening condition. If you’re experiencing CO poisoning, you should immediately seek both fresh, outdoor air and emergency medical attention.⁵

How do you prevent carbon monoxide poisoning?

Large amounts of carbon monoxide can cause people to pass out. Without proper attention, recovery can be difficult. There are a number of steps you can take to reduce your risk of carbon monoxide poisoning.

Carbon monoxide poisoning can be prevented by ensuring proper use and maintenance of all devices running on fossil fuels and by supplying a constant flow of fresh air into your indoor spaces.

Keep an eye out for these warning signs of CO poisoning:

• battery-operated detectors detect carbon monoxide spikes
• soot streaks near appliances
• rusting flue pipes
• excess moisture
• pilot lights that burn orange or yellow, as opposed to blue
• chimney has no upward draft⁶

CO alarms should be installed near bedrooms, indoor walls shared with garages, and near appliances and fuel-burning equipment. Batteries should be regularly replaced and the alarms themselves replaced every 5 to 7 years.

Appliances should always be fully vented to the outdoors.

When using portable generators, they should be kept at least 25 feet from homes and away from doors and windows.

Fireplaces and flues should be cleaned annually. However, homeowners with fireplaces should be aware that any fireplace use can create dangerous indoor air quality.

Don’t run cars or mowers in attached garages. If the garage is detached, the car should only be run with the door open.⁷

What should you do if you hear the CO alarm?

If you have a CO alarm installed in your home and the alarm has sounded take the following steps:

• go outside and get fresh air
• make sure everyone is accounted for
• call emergency services
• don’t go back inside until emergency responders indicate it’s safe

Air pollution carries a tremendous human and financial cost. Check out our Cost of Air Pollution counter to learn how the health and economic costs of air pollution poses a far greater challenge to humanity than the cost of reduction.