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 or gaseous fuels. Appliances fueled with gas, oil, kerosene, wood or coal may produce CO. If such appliances are not installed, maintained, and used properly, CO may accumulate to dangerous levels. All fuel burning appliances have the potential to produce CO in varying concentrations.

How Does CO Affect The Human Body, What Are The Symptoms Of CO Poisoning And Why Are These Symptoms Particularly Dangerous?

After being inhaled, CO is absorbed into the bloodstream, taking the place of oxygen in the blood cells forming Carboxyhemoglobin. Tissues with the highest oxygen needs are most affected by CO including the brain, heart, and other large muscles. 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.

CO exposures especially affect pregnant woman, unborn babies, infants, elderly people, and people with anemia or a history of heart disease. Breathing low levels of CO can cause fatigue and increase chest pain in people with chronic heart disease. Remember even healthy people are at risk from this silent killer.

At What Concentration Level Is CO A Concern?

Health effects vary depending on age, sex, weight and overall state of health, the following therefore are approximate:
At 400 PPM, frontal headaches occur within 1 to 2 hours, life threatening after 3 hours.
At 800 PPM, nausea and convulsions occur within 20 minutes, death within 2 hours.
At 1600 PPM, nausea occurs within 20 minutes, death within 1 hour.
At 12800 PPM, death within 1 to 3 minutes.
New studies indicate that chronic, low level exposure can also have serious health consequences.
The EPA recommends 9 PPM CO or lower as an ambient air quality goal averaged over 8 hours and 35 PPM or lower over 1 hour.

How Many People Die From CO Poisoning Each Year?

During the 10-year period from 1979 to 1988, 56,133 death certificates contained codes addressing CO as a contributing cause. Of the unintentional deaths, 57% were due to automobile exhaust. The next leading identifiable cause was coal, wood or kerosene stoves and fireplaces; followed by combustion of natural gas from a pipeline; combustion of gasoline, acetylene or utility gas and industrial sources. The statistics for 1989 recorded there 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.

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

Elimination of carbon monoxide is through the lungs. The half-life of CO at room air is three to four hours. One hundred percent oxygen reduces the half-life to 30 to 90 minutes and hyperbaric oxygen at 2.5 atmospheres with 100% oxygen reduces it to 15-23 minutes, (this is a special chamber not widely available.)

Dangerous levels of CO can be prevented by proper appliance maintenance, installation and use.
Maintenance: A qualified service technician (or qualified home inspector) should check your home’s central and room heating appliances including water heaters and gas dryers annually. The technician should also 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 ensure proper operation. Installation:
* 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 ensure proper ventilation.

* Never use an unvented combustion heater overnight or in a room where you sleep.

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.

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 hot or warm moist air is detected around a fossil fueled heating system or hot water tank, this could be an indication of exhaust leakage. 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.

Yes, these are: Never use a gas or propane 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 a garage. Have your fossil fueled appliances and chimneys checked yearly. Have a home inspector check to make sure there is enough air supply for your fossil fueled appliances, (this includes fireplaces and wood or coal burning stoves.)


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 CO level in a person’s blood would become crippling.

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? If so, is a CO detector still needed? Vent safety shut off systems have been required on furnaces and vented heaters since the late 1980s. They protect against blocked chimneys or disconnected vents. Oxygen depletion sensors (ODS) have 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 are not a substitute for regular professional servicing, and many older, potentially CO-producing appliances may not have such devices. A CO detector is still important in any home as another line of defense.