CARBON MONOXIDE: A FACT SHEET
Recently, public attention has focused on the risk of carbon monoxide (or CO) poisoning in the home. The National Fire Protection Association (NFPA) prepared this fact sheet to help people protect themselves and their families against CO poisoning.
What is carbon monoxide?
Carbon monoxide is an invisible, odorless, colorless gas created when fossil fuels (such as gasoline, wood, coal, propane, oil and methane) burn incompletely. In the home, heating and cooking equipment are possible sources of carbon monoxide. Vehicles running in an attached garage could also produce dangerous levels of carbon monoxide.
However, consumers can protect themselves against CO poisoning by maintaining, using, and venting heating and cooking equipment and by being cautious when using vehicles in attached garages.
What is the effect of exposure to CO?
CO replaces oxygen in the bloodstream, eventually causing suffocation. Mild CO poisoning feels like the flu, but more serious poisoning leads to difficulty breathing and even death.
Just how sick people get from CO exposure varies greatly from person to person, depending on age, overall health, the concentration of the exposure (measured in parts per million), and the length of exposure. Higher concentrations are dangerous even for a short time.
Table 1 shows typical symptoms, based on concentration and time of exposure.
When carbon monoxide replaces oxygen in the blood, a condition known as carboxyhemoglobin (COHb) saturation results. Carboxyhemoglobin levels do not consider the length of exposure. As more and more carbon monoxide accumulates in the blood, the percentage of COHb gets higher and higher - and people get sicker and sicker. Table 2 links symptoms of CO poisoning with percent of carboxyhemoglobin saturation.
What is your risk of CO poisoning?
Deaths from unintentional carbon monoxide poisoning - about 700 in 1993, according to the National Safety Council - are fairly rare. Three of every five of these deaths typically involve vehicles, one of every five typically involves heating or cooking equipment, and the other one of every five typically involves other or unspecified causes.*
In fact, deaths from unintentional carbon monoxide poisoning have dropped sharply in recent years, thanks to lower CO emissions from automobiles and safer heating and cooking appliances.* Deaths from "smoke inhalation" (largely carbon monoxide) in fires and suicides involving CO are far more common causes of gas-related suffocation deaths in homes. Published estimates on the role of CO in home fire deaths vary widely.
According to the NFPA, there were 242 CO-related non-fire deaths attributed to heating and cooking equipment in 1991.** The leading specific types of equipment were:
As with fire deaths, the risk of unintentional CO death is highest for the very young (ages 4 or younger) or the very old (ages 75 or above).
How can you protect yourself from CO poisoning?
The best defenses against CO poisoning are safe use of vehicles (particularly in attached garages) and proper installation, use and maintenance of household cooking and heating equipment.
You may also want to install CO detectors inside your home to provide early warning of accumulating carbon monoxide. However, a CO detector is no substitute for safe use and maintenance of heating and cooking equipment.
CO from a running vehicle inside an attached garage can get inside the house, even with the garage door open. Normal circulation does not provide enough fresh air to reliably prevent dangerous accumulations inside.
What are CO detectors?
Household carbon monoxide detectors measure how much CO has accumulated. Currently, CO detectors sound an alarm when the concentration of CO in the air corresponds to 10% carboxyhemoglobin level in the blood. Since 10% COHb is at the very low end of CO poisoning, the alarm may sound before people feel particularly sick.
What causes CO detector nuisance alarms?
Pollution and atmospheric conditions in some areas cause low levels of CO to be present for long periods of time. In fact, these "background" conditions may increase the COHb level to over 10%, causing CO detectors to alarm even though conditions inside the home are not truly hazardous.
If you buy CO detectors:
What to do if your CO detector alarms:
If anyone shows signs of CO poisoning: Have everyone leave the building right away. Leave doors open as you go.
If no one has symptoms of CO poisoning: Open windows and doors, shut down heating and cooking equipment, and call a qualified technician to inspect all equipment.
About the National Fire Protection Association and CO detectors.
The National Fire Protection Association (NFPA) prepared this fact sheet as a guide for consumers who are concerned about possible carbon monoxide poisoning at home. At this time, NFPA does not have a standard requiring the installation of household CO detectors. NFPA is currently developing NFPA 720 (proposed). This document is in the NFPA standards cycle and may be published as early as September 1997.
The National Fire Protection Research Foundation has initiated a research project to provide NFPA's technical committees with CO detector documentation.
* N. Cobb and R.A. Etzel, "Unintentional carbon monoxide-related deaths in the United States, 1979 through 1988, "Journal of the American Medical Association, Volume 266, #5, 1991, pp. 659-693, as reported in National Safety Council's Accident Facts.
** The latest year for which statistics are available at this level of detail.
Reprinted with permission from Fire News (Issue 809), Copyright
1995, National Fire Protection Association, Quincy, MA 02269
Concentration (parts per million) Symptoms
35 No adverse effects within 8 hours.
200 Mild headache after 2-3 hours of exposure.
400 Headache and nausea after 1-2 hours.
800 Headache, nausea and dizziness after 45 minutes; collapse after 2 hours.
1000 Loss of consciousness after 1 hour.
1600 Headache, nausea and dizziness after 20 minutes; unconsciousness after 30 minutes.
3200 Headache, nausea and dizziness after 5-10 minutes; unconsciousness after 30 minutes.
12,800 Immediate physiological effects; unconsciousness and danger of death after 1-3 minutes.
Source: U.S. Consumer Product Safety Commission
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Effects of Carboxyhemoglobin (COHb) Saturation COHb Saturation (%) Symptoms
10-20 Tension in forehead, dilation of skin vessels.
20-30 Headache and pulsating temples.
30-40 Severe headache, weariness, dizziness, weakened sight, nausea, vomiting, prostration.
40-50 Severe headache, plus increased breathing and pulse rates, asphyxiation and prostration.
50-60 Same as above, plus coma, convulsions, Cheyne-Stokes respiration.
60-70 Coma, convulsions, weak respiration and pulse. Death is possible.
70-80 Slowing and stopping of breathing, death within hours.
80-90 Death in less than 1 hour.
90-100 Death within a few minutes.
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