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Part C: Factsheets (continued)

Carbon monoxide

Substance name:	Carbon monoxide
CASR number:	630-08-0
Molecular formula:	CO
Synonyms:	Carbonic oxide, monoxide, carbon oxide

Physical and chemical properties

Carbon monoxide is a colourless, odourless gas.

Melting point:-205.05°C
Boiling point: -191.5°C
Vapour density: 0.967
Flashpoint: -191°C

Carbon monoxide is formed when carbon in fuels (petrol, wood, coal, natural gas, etc) is not burned completely. It is highly flammable.

Common uses

Carbon monoxide is used as a chemical intermediate in some chemical processes (production of formaldehyde and methanol).

Sources of emissions

Point sources

Industrial plant exhaust to air (large emitters are steel plants, foundries, oil refining, and chemical manufacturing).

Diffuse sources, and point sources included in aggregated emissions data

Incomplete combustion of carbon-containing fuels, smoking cigarettes, burning of waste, defective heaters, defective stoves and ovens all cause emission of carbon monoxide to air.

Natural sources

Volcanoes, marsh gases, natural gases in coal mines, forest fires. Carbon monoxide is produced by lightning. Some marine algae or kelp will also produce carbon monoxide, as do some seed-germinating processes.

Mobile sources

Vehicle exhaust.

Consumer products that may contain carbon monoxide

No consumer products contain carbon monoxide; however, many consumer products will emit carbon monoxide when burned or operated. Consumer products that emit carbon monoxide are automobiles (exhaust), tobacco (smoke), internal combustion engines (chainsaws, lawnmowers, leaf blowers, etc) heaters (non-electric), charcoal grills, woodstoves, etc.

Health effects

How might I be exposed to carbon monoxide?

Most exposure is in the home, by smoking, using unflued gas heaters, malfunctioning equipment (gas water heaters, fuel fired heaters, fireplaces and woodstoves, gas stoves, gas dryers) and using charcoal grills. Exposure may also occur in poorly vented automobiles with defective exhaust systems. Workers in industries that use or produce carbon monoxide are also at risk of exposure.

By what pathways might carbon monoxide enter my body?

Carbon monoxide will enter the body if we breathe in contaminated air. Carbon monoxide is quickly absorbed into the bloodstream from the lungs.

Health guidelines

National Occupational Health and Safety Commission (NOHSC):

• TWA (eight-hour time weighted average) exposure limit in the workplace: 30 ppm (34 mg/m³).

There is not a conventional short-term (15 minutes) exposure limit (STEL) for carbon monoxide. However, guidelines for the control of short-term excursions for carbon monoxide have been established by the NOHSC. They are:

• 200 ppm (15 minutes);
• 100 ppm (30 minutes); and
• 60 ppm (60 minutes).

What effect might carbon monoxide have on my health?

Carbon monoxide quickly enters the blood when inhaled into the lungs. Levels normally present in the atmosphere are unlikely to cause ill effects. Carbon monoxide concentration may reach harmful levels in poorly ventilated rooms during operation of unflued gas heaters or defective non-electric heating appliances, or in the passenger compartment of vehicles with defective exhaust systems. At low levels it may cause poor concentration, memory and vision problems, and loss of muscle coordination. At higher levels (200 ppm for 2–3 hours), it may cause headaches, fatigue and nausea. At very high levels (400 ppm) the symptoms intensify and will be life-threatening after three hours. Exposure to levels of 1200 ppm or greater are immediately dangerous to life. Carbon monoxide combines with haemoglobin to form carboxyhaemoglobin, reducing the oxygen-carrying ability of the blood. Long-term (chronic) exposure to low levels of carbon monoxide may produce heart disease and damage the nervous system. Exposure of pregnant women to carbon monoxide may cause low birthweight, increased foetal mortality and nervous system damage to the offspring. Carbon monoxide is classified by the NOHSC as a Category 1 reproductive toxicant (substance known to cause developmental toxicity to humans).

Environmental effects

Environmental fate

Although carbon monoxide is not considered a greenhouse gas, it is a precursor to greenhouse gases. Carbon monoxide elevates the concentrations of methane (a greenhouse gas) and ozone in the atmosphere. It eventually oxidises into carbon dioxide.

Environmental transport

Industrial emissions of carbon monoxide can produce elevated, but still low-level, concentrations in the atmosphere around the source. Volcanic eruptions, while sporadic, are significant contributors to carbon monoxide in their local area. Fires of all types will also contribute to carbon monoxide in the atmosphere.

Environmental guidelines

Ambient Air Quality NEPM Standards and Goals:

• 9.0 ppm averaged over eight hours, with an allowable exceedance once a year.

What effect might carbon monoxide have on the environment?

Carbon monoxide increases the amount of other greenhouse gases (methane), and eventually oxidises into carbon dioxide. Greenhouse gases are linked to global warming. Very high levels of carbon monoxide will cause the same problems to birds and animals that are experienced by people, although these levels are very unlikely to be encountered in the environment except during extreme events like bushfires. At high levels, carbon monoxide will cause illness (fatigue, gastric upset). At very high levels, carbon monoxide will be life-threatening. Long-term (chronic) exposure to low levels of carbon monoxide may produce heart disease and damage to the nervous system. Exposure of pregnant animals to carbon monoxide may cause low birthweight, increased foetal mortality and nervous system damage to the offspring.

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