Skip Content

Please Upgrade Your Browser Grainger will no longer support Internet Explorer 8 as of 07/2018. Please upgrade your browser or contact your System Administrator for support.



Carbon Monoxide Facts

Quick Tips #236

Basic Carbon Monoxide Facts

Carbon monoxide (CO) is an odorless, colorless, tasteless gas that is slightly lighter than air. It is sometimes called carbonic oxide, exhaust gas or flue gas. It becomes a liquid under high pressure. It can also kill within minutes in high concentrations.

Carbon monoxide is produced by the incomplete combustion of any fuel that contains carbon. This includes gasoline, natural gas, oil and propane, as well as coal and wood products. At home, sources of carbon monoxide include gas- and oil-burning appliances such as furnaces, dryers, water heaters, ovens, wood-burning stoves, charcoal grills and automobiles.

At work, carbon monoxide buildups can occur in operations near furnaces, ovens, generators, forges and kilns when they are fired up to operating temperatures. Other workplace exposure points include:

  • Organic chemical synthesis, including some petroleum-product processes
  • Gasoline-powered tools such as high-pressure washers, welders and pumps
  • As a reducing agent in metallurgical processes
  • When air is supplied from reciprocating oil-lubricated compressors

Because many of these sources are only used in cold weather, carbon monoxide poisoning is considered by many to be a "seasonal" risk. However, carbon monoxide gas can build up in any enclosed or semi-enclosed space at any time. Exposure can occur through inhalation of the gas and eye or skin contact with the liquid.

Carbon Monoxide Facts: Symptoms

Carbon monoxide is a chemical asphyxiant. When inhaled, it bonds with the hemoglobin in the blood, which is responsible for carrying oxygen throughout the body. The carbon monoxide replaces the oxygen molecules in hemoglobin, and deprives the heart, brain and body of the oxygen it needs to function. High concentrations will displace enough oxygen in your body to cause oxygen starvation.

The symptoms of low-level carbon monoxide poisoning include headaches, nausea, weakness, dizziness and confusion. Exposure causes a victim's blood pressure to rise in an attempt to get more oxygen to the body. As a result, the skin might take on a reddish color. The symptoms at low levels are very similar to what a person might exhibit if affected by the flu or other common illnesses. Therefore, carbon monoxide is sometimes referred to as the "great imitator."

As carbon monoxide exposure increases, more serious symptoms develop, including a lack of coordination, chest pain, vomiting and loss of consciousness. If exposed to carbon monoxide long enough, coma and death can occur. A concentration of 1200 ppm carbon monoxide is considered immediately dangerous to life or health. This table lists common symptoms and effects on healthy adults at various carbon monoxide concentrations.

Carbon Monoxide Level in ppm
(Parts per Million)
Resulting Conditions / Effects on Humans
Permissible exposure limit (PEL) for eight hours (OSHA)
Possible mild frontal headache in two to three hours
Frontal headache and nausea after one to two hours; occipital headache (back of head) after two to three hours
Headache, dizziness and nausea in 45 minutes; collapse and possible death in two hours
Headache, dizziness, and nausea in 20 minutes; collapse and possible death in one hour
Headache and dizziness in five to 10 minutes; unconsciousness and danger of death in 30 minutes
Headache and dizziness in one to two minutes; unconsciousness and danger of death in 10 to 15 minutes
Immediate unconsciousness; danger of death in one to three minutes

Typically, upon removal from exposure to carbon monoxide, symptoms usually resolve themselves, unless there has been an episode of severe acute poisoning.

Carbon Monoxide Detectors

Detection is crucial because of the common sources of carbon monoxide and its inherent dangers. Common methods of indoor air-quality testing include using detector tubes, diffusion tubes, color badges, portable gas monitors and household or industrial fixed-gas monitors.

Detector tubes determine the instantaneous CO concentration in the air at any point in time. A pump pulls a volume of air through the detection media. When CO is present within the detection limits of the tube, the media changes color indicating the concentration. Diffusion tubes and badges also use color to reveal the concentration of CO but are designed to determine the dose (concentration over time).

Portable carbon monoxide detectors monitor carbon monoxide levels. Most of these monitors have a digital readout as well as visible and audible alarms. When carbon monoxide concentration reaches a preset level, the instrument's alarm will activate. Portable alarms are commonly used in industrial settings where ongoing carbon monoxide exposures are tracked as well as for monitoring air quality before and during confined-space entries. When monitoring confined-space entries, a multi-gas detector with an oxygen sensor, a combustible sensor and the appropriate toxic-gas sensors should be used. For more information on confined-space entry, see Quick Tips #115: Confined Spaces, 29 CFR 1910.146.

Fixed-location detectors are commonly used in industrial settings to monitor the ongoing concentration at a fixed point or source. They are mounted in one location and are equipped with visible and audible alarms. These devices can be set up to read the concentration at the control box or be used in conjunction with transmitters to detect carbon monoxide in remote areas. Another common feature of fixed detectors is a relay device that is designed to signal certain events during an alarm condition, such as opening a door or turning on an exhaust fan.

Several organizations recommend that people have a carbon monoxide alarm on every level of their home or apartment. While they are usually less sophisticated than their industrial cousins, a home carbon monoxide detector should also be equipped with a visible and audible alarm. The Consumer Product Safety Commission (CPSC) recommends installing at least one alarm with an audible warning signal near the sleeping areas in your home.

Carbon Monoxide Facts: Exposure Levels and OSHA Air Quality

The Occupational Safety and Health Administration (OSHA) permissible exposure limit for carbon monoxide is 50 ppm of air, or 55 milligrams per cubic meter (mg/m3) as an eight-hour time-weighted average concentration. The National Institute for Occupational Safety and Health (NIOSH) recommends exposure levels (REL) below the OSHA air-quality numbers. They recommend keeping exposure to less than 35ppm, or 40 mg/m3 in eight hours. The ACGIH has assigned a carbon monoxide threshold-limit value (TLV) of 25 ppm or 28.6 mg/m3 for eight hours.

Carbon Monoxide Facts: Poisoning-Prevention Measures

Regardless of what your application is, it is important to be aware of the dangers of carbon monoxide and how to protect yourself. The following are a few suggestions to help protect you from carbon monoxide effects:

  • Install a carbon monoxide detector in your business and your home
  • Educate yourself and your family on the effects of carbon monoxide poisoning
  • Check gas appliances periodically for proper operation and venting
  • Ensure that chimneys, flues and vents are free and clear of debris
  • Do not use unvented gas and wood stoves or charcoal grills indoors
  • Do not permit automobiles or other gas-powered equipment to run indoors without proper ventilation
  • Ventilate areas to dilute or reduce the concentration of carbon monoxide


American Industrial Hygiene Association (AIHA)

Occupational Safety and Health Administration (OSHA)

ACGIH [1991]. Documentation of the threshold-limit values and biological exposure indices. 6th ed. Cincinnati, OH: American Conference of Governmental Industrial Hygienists.

ACGIH [1986]. Documentation of the threshold-limit values and biological exposure indices. 5th ed. Cincinnati, OH: American Conference of Governmental Industrial Hygienists.

Related Articles

Quick Tips #145: Fume Extraction: Engineering Controls for Reducing Employee Chemical Exposure

Quick Tips #230: Indoor Air Quality

Quick Tips #231: Air Monitoring Equipment

(Rev. 1/2015)

Find even more information you can use to help make informed decisions about the regulatory issues you face in your workplace every day. View all Quick Tips Technical Resources at

Think Safety. Think Grainger.®
Grainger has the products, services and resources to help keep employees safe and healthy while operating safer facilities. You’ll also find a network of safety resources that help you stay in compliance and protect employees from hazardous situations. Count on Grainger for lockout tagout, fall protection equipment, confined space products, safety signs, personal protective equipment (PPE), emergency response and so much more!

Please Note:
The information contained in this publication is intended for general information purposes only and is based on information available as of the initial date of publication. No representation is made that the information or references are complete or remain current. This publication is not a substitute for review of the current applicable government regulations and standards specific to your location and business activity, and should not be construed as legal advice or opinion. Readers with specific questions should refer to the applicable standards or consult with an attorney.

©2018 W.W. Grainger, Inc.