Carbon Monoxide Fact Sheet

The Hazard

What is carbon monoxide (CO) and how is it produced in the home?

CO is a colorless, odorless, toxic gas. It is produced by the incomplete combustion of solid, liquid and gaseous fuels. Appliances fueled with gas, oil, kerosene, or wood may produce CO. If such appliances ar not installed, maintained, and used properly, CO may accumulate to dangerous levels.

What are the symptoms of CO poisoning and why are these symptoms particularly dangerous?

Breathing CO causes symptoms such as headaches, dizziness, and weakness in healthy people. CO also causes sleepiness, nausea, vomiting, confusion and disorientation. At very high levels, it causes loss of consciousness and death.

This is particularly dangerous because CO effects often are not recognized. CO is odorless and some of the symptoms of CO poisoning are similar to the flu or other common illnesses.

Are some people more affected by exposure to CO than others?

CO exposures especially affect unborn babies, infants, and people with anemia or a history of heart disease. Breathing low levels of the chemical can cause fatigue and increase chest pain in people with chronic heart disease.

The Data

How many people die from CO poisoning each year?

In 1989, the most recent year for which statistics are available, thee were about 220 deaths from CO poisoning associated with gas-fired appliances, about 30 CO deaths associated with solid-fueled appliances (including charcoal grills), and about 45 CO deaths associated with liquid- fueled heaters.

How many people are poisoned from CO each year?

Nearly 5,000 people in the United States are treated in hospital emergency rooms for CO poisoning; this number is believed to be an underestimate because many people with CO symptoms mistake the symptoms for the flu or are misdiagnosed and never get treated.

CO Prevention

How can production of dangerous levels of CO be prevented?

Dangerous levels of CO can be prevented by proper appliance maintenance, installation, and use.


A qualified service technician should check your home’s central and room heating appliances (including water heaters and gas dryers) annually. The technician should look at the electrical and mechanical components of appliances, such as thermostat controls and automatic safety devices.

  • Chimneys and flues should be checked for blockages, corrosion, and loose connections.
  • Individual appliances should be serviced regularly. Kerosene and gas space heaters (vented and unvented) should be cleaned and inspected to insure proper operation.
  • CPSC recommends finding a reputable service company in the phone book or asking your utility company to suggest a qualified service technician.


Proper installation is critical to the safe operation of combustion appliances. All new appliances have installation instructions that should be followed exactly. Local building codes should be followed as well.

  • Vented appliances should be vented properly, according to manufacturer’s instructions.
  • Adequate combustion air should be provided to assure complete combustion.
  • All combustion appliances should be installed by professionals.

Appliance Use

Follow manufacturer’s directions for safe operation.

  • Make sure the room where an unvented gas or kerosene space heater is used is well ventilated; doors leading to another room should be open to insure proper ventilation.
  • Never use an unvented combustion heater overnight or in a room where you are sleeping.

Are there signs that might indicate improper appliance operation?

Yes, these are:

  • Decreasing hot water supply
  • Furnace unable to heat house or runs constantly
  • Sooting, especially on appliances
  • Unfamiliar or burning odor
  • Increased condensation inside windows

Are there visible signs that might indicate a CO problem?

Yes, these are:

  • Improper connections on vents and chimneys
  • Visible rust or stains on vents and chimneys
  • An appliance that makes unusual sounds or emits an unusual smell
  • An appliance that keeps shutting off (Many new appliances have safety components attached that prevent operation if an unsafe condition exists. If an appliance stops operating, it may be because a safety device is preventing a dangerous condition. Therefore, don’t try to operate an appliance that keeps shutting off; call a service person instead.)

Are there other ways to prevent CO poisoning?

Yes, these are:

  • Never use a range or oven to heat the living areas of the home
  • Never use a charcoal grill or hibachi in the home
  • Never keep a car running in an attached garage

CO Detection

Can CO be detected?

Yes, CO can be detected with CO detectors that meet the requirements of Underwriters Laboratories (UL) standard 2034.

Since the toxic effect of CO is dependent upon both CO concentration and length of exposure, long-term exposure to a low concentration can produce effects similar to short term exposure to a high concentration.

Detectors that meet the UL standard measure both high CO concentrations over short periods of time and low CO concentrations over long periods of time. The effects of CO can be cumulative over time

Detectors sound an alarm before the level of CO in a person’s blood would become crippling

Detectors that meet the UL 2034 standard currently cost between $35 and $80.

Where should the detector be installed?

CO gases distribute evenly and fairly quickly throughout the house; therefore, a CO detector should be installed on the wall or ceiling in sleeping area/s but outside individual bedrooms to alert occupants who are sleeping.

Aren’t there safety devices already on some appliances? And if so, why is a CO detector needed?

Vent safety shutoff systems have been required on furnaces and vented heaters sine the late 1980s. They protect against blocked or disconnected vents or chimneys.

Oxygen depletion sensors (ODS) have also been installed on unvented gas space heaters since the 1980s. ODS protect against the production of CO caused by insufficient oxygen for proper combustion.

These devices (ODSs and vent safety shutoff systems) are not a substitute for regular professional servicing, and many older, potentially CO-producing appliances may not have such devices. Therefore, a CO detector is still important in any home as another line of defense.

Are there other CO detectors that are less expensive?

There are inexpensive cardboard or plastic detectors that change color and do not sound an alarm and have a limited useful life. They require the occupant to look at the device to determine if CO is present. CO concentrations can build up rapidly while occupants are asleep, and these devices would not sound an alarm to wake them.

Consumer Protection Safety Commission’s Role

  • CPSC worked closely with UL to develop a safety standard for CO detectors (UL 2034).
  • CPSC embarked on an extensive public awareness campaign in 1993 to reach consumers and educate them about CO through the media. Activities included a message from President Clinton declaring the last week of September “CO Safety Awareness Week.” CPSC also developed stories for television, radio, and newspapers, as well as brochures and posters for consumers.
  • CPSC is proposing that the national model building code organizations include a provision for the installation of state of the art CO detectors in all new residential construction. The proposal calls for installation in sleeping areas, but outside individual bedrooms.
  • Under CPSC’s proposal, battery-operated units would be allowed only in existing homes, not new construction. Even homes with no permanently-installed fuel-burning appliances would have to install them because CO deaths have been associated with the use of portable kerosene heaters, wood-burning stoves, charcoal grills wrongly used indoors, and auto fumes from an attached garage.
  • CPSC staff is working with state and local code jurisdictions to incorporate CO detector requirements into state and local legislation.
  • CPSC is working with the National Fire Protection Association to develop a national installation standard.

CO Detector Requirements in the U.S.

  • On September 15, 1993, Chicago, IL became one of the first cities in the nation to adopt an ordinance requiring the installation of CO detectors that bear the mark of a nationally-recognized testing laboratory in all new single-family homes and in existing single-family residences that are being equipped with new oil or gas combustion furnaces.
  • Kingston, NY has approved a code to require the installation of CO detectors in multiple dwellings with four or more dwelling units.
  • Bel Air, TX requires CO detectors in some single-family dwellings.
  • The Recreational Vehicle Industry Association (RVIA) requires CO detectors in motor homes made after September 1, 1993. RVIA requires CO detectors in all recreational vehicles that are motorized and in towable recreational vehicles that have a generator or are prepped for a generator. RVIA’s membership includes approximately 90% of all U.S. recreational vehicle manufacturers.