Carbon monoxide (CO) gas is an ever-present fact of life these days. It’s found anywhere combustion occurs. It presents no threat in small amounts. But in large amounts, it can be very dangerous—even deadly. Because of the danger, it’s important to know some basics about CO.

Where does CO come from?
CO is a colorless, odorless gas. It is a byproduct of fuel combustion. Pieces of equipment, machinery or heaters that burn coal, wood, charcoal, oil, kerosene, gasoline, propane or natural gas produce small amounts of CO. Equipment or machinery powered by an internal combustion engine—cars, lawn mowers and power generators--—also produce it.

Is CO poisoning you right now?
It is impossible for humans to detect CO, which makes this gas especially dangerous. People do not know when they are being exposed to it. At low levels, the symptoms resemble the flu but without the fever:

• Headache
• Fatigue
• Shortness of breath
• Nausea
• Dizziness

As the concentration of CO increases, so does the severity of symptoms:
• Confusion
• Vomiting
• Loss of coordination
• Loss of consciousness

Ultimately, exposure leads to death.

How long before the symptoms appear?
CO poisoning depends on concentration and the length of exposure. At low concentrations, the symptoms develop gradually and are often misdiagnosed as the flu. However, even at low concentrations, the longer the exposure, the more severe the symptoms will become. At high CO concentrations, e.g., when using a gas-powered generator indoors, victims will typically develop more serious symptoms quickly (possibly in less than an hour) without the mild symptoms.

How can I prevent CO poisoning?
The best way to limit your exposure to CO is to avoid operating internal combustion engines indoors. Unfortunately, that cannot always be avoided. The amount of CO produced by machinery and equipment can be minimized through frequent maintenance and engine tune-ups. A safe, effective option may be to replace CO-producing equipment and machinery with adequate electrical counterparts.

In some situations, using a combustion engine is unavoidable. In these instances, maintain ventilation and ensure fresh air circulation throughout the area. These strategies will help decrease the CO concentrations but cannot prevent CO poisoning. CO detectors should be used whenever using CO producers.

What CO levels are dangerous?
The Occupational Safety and Health Administration (OSHA) has specified certain concentrations that are of note.

35 parts per million (ppm) and below
• OSHA’s 8-hour permissible limit
• No effects in healthy adults

200 ppm
• OSHA’s short-term exposure limit
• Individuals display the previously listed symptoms

400 ppm
• Severe headache, fatigue
• Nausea, dizziness, confusion
• Life-threatening after three hours of exposure

800 ppm and above
• Convulsions, collapse
• Death

How reliable are CO detectors?
CO detectors are designed to sound before an area reaches potentially life-threatening CO levels. Safety standards for CO alarms are continually improving, and current models are not as likely to sound nuisance alarms as earlier models. However, like smoke detectors, having them in place can save lives.

What if a CO alarm sounds?
Never ignore a CO alarm; it is a warning of a potentially deadly situation. Also, don’t go looking for the source of the CO. Get out of the area.

Once outside, call 911 or the emergency services/fire department. Once 911 is called, ensure everyone is accounted for. Don’t re-enter until emergency services has cleared the area.

When you have been allowed back in, if the alarm reactivates within a 24-hour period, repeat the above steps and call a qualified technician to locate the source or sources of the CO. All fuel-burning equipment and machinery should be inspected. Once the source is located, have it serviced immediately.

Is it necessary to have a CO detector?
The answer depends on where you live and work. Many states and local municipalities have begun to require CO detectors/alarms in residences. Check state and local building codes for the requirements that apply to your area. Remember, even if it isn’t required, the detector could save lives.


KELLY is a safety and health specialist with Intec, a safety consulting, training and publishing firm that offers on-site assistance and produces manuals, training videos and software for contractors. She can be reached at 800.745.4818 and dkelly@intecweb.com. Joe O’Connor edited this article.