CARBON MONOXIDE

Carbon monoxide
(Carbonic oxide, monoxide)
CAS 630-08-0

CO

Colorless gas
bp -191.5 °C, mp -205 °C
Slightly soluble in water (0.004 g/100 mL at 20 °C)

Odorless gas

0.97 (air = 1.0)

>760 mmHg at 20 °C

< -191 °C

609 °C

LC₅₀ inhal (rat) 1807 ppm (2065 mg/m³; 4 h)

LC_LO inhal (man) 4000 ppm (4570 mg/m³; 30 min)

PEL (OSHA) 50 ppm (55 mg/m³)

TLV-TWA (ACGIH) 25 ppm (29 mg/m³)

Moderately toxic gas with no warning properties; decreases the ability of the blood to carry oxygen to the tissues.

The acute toxicity of carbon monoxide by inhalation is moderate. Carbon monoxide is a chemical asphyxiant that exerts its effects by combining preferentially with hemoglobin, the oxygen-transport pigment of the blood, thereby excluding oxygen. Symptoms of exposure to CO at 500 to 1000 ppm include headache, palpitations, dizziness, weakness, confusion, and nausea. Loss of consciousness and death may result from exposure to concentrations of 4000 ppm and higher; high concentrations may be rapidly fatal without producing significant warning symptoms. Exposure to this gas may aggravate heart and artery disease and may cause chest pain in individuals with preexisting heart disease. Pregnant women are more susceptible to the effects of carbon monoxide exposure. Since carbon monoxide is odorless, colorless, and tasteless, it has no warning properties, and unanticipated overexposure to this highly dangerous gas can readily occur.

Carbon monoxide has not been found to be carcinogenic in humans. This substance has shown developmental toxicity in animal tests. Chronic exposures to carbon monoxide at levels around 50 ppm are thought by some investigators to have a negative impact on the results of behavioral tests such as time discrimination, visual vigilance, choice response tests, visual evoked responses, and visual discrimination thresholds.

Carbon monoxide is a flammable gas. It forms explosive mixtures with air in the range of 12.5 to 74% by volume.

Carbon monoxide is a reducing agent; it reacts violently with strong oxidizers. It undergoes violent reactions with many interhalogen compounds such as ClF₃, BrF₃, and BrF₅. CO reacts with many metals to form metal carbonyls, some of which may explode on heating, and reduces many metal oxides exothermically. Carbon monoxide reacts with sodium and with potassium to form explosive products that are sensitive to shock, heat, and contact with water.

Because of its toxic, flammable, and gaseous nature, carbon monoxide should be handled using the "basic prudent practices" of Chapter 5.C, supplemented by the additional precautions for work with flammable compounds (Chapter 5.F) and for work at high pressure (Chapter 5.H). In particular, cylinders of carbon monoxide should be stored and used in a continuously ventilated gas cabinet or fume hood. Local fire codes should be reviewed for limitations on quantity and storage requirements.

In the event of a release of carbon monoxide, evacuate the area immediately. Rescue of an affected individual requires appropriate respiratory protection. Remove exposed individual to an uncontaminated area and seek immediate emergency help. Keep victim warm, quiet, and at rest and provide assisted respiration if breathing has stopped.

To respond to a release, use appropriate protective equipment and clothing. Positive pressure air-supplied respiratory protection is required. Close cylinder valve and ventilate area. Remove cylinder to a fume hood or remote area if it cannot be shut off.

Excess carbon monoxide should be returned to the manufacturer, according to your institution's waste disposal guidelines.

The information in this LCSS has been compiled by a committee of the National Research Council from literature sources and Material Safety Data Sheets and is believed to be accurate as of July 1994. This summary is intended for use by trained laboratory personnel in conjunction with the NRC report Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. This LCSS presents a concise summary of safety information that should be adequate for most laboratory uses of the title substance, but in some cases it may be advisable to consult more comprehensive references. This information should not be used as a guide to the nonlaboratory use of this chemical.

Copyright 1995 National Academy of Sciences. All rights reserved.