Carbon Monoxide (CO) is produced whenever carbon-based material such as wood, paper, oil, petrol, gas or other carbonaceous material is burned in a limited supply of air or oxygen, resulting in incomplete combustion. It is commonly found in the exhaust gases from petrol, diesel or LPG internal combustion engines, and accounts for the majority of man-made emissions and the resultant workplace hazards.

Other industrial sources of CO include:

  • combustion-based heating equipment
  • cupolas in iron and steel foundries
  • catalytic cracking units in petroleum refineries
  • sintering of blast furnace feed in sintering plants.

Incorrectly installed and malfunctioning combustion-based heating appliances have frequently caused poisoning in domestic settings.

If ventilation is reduced, or the rate or duration of CO production increases, a normally safe environment can suddenly become extremely hazardous.

CO is also a major hazard for fire fighting services. The daily, 8-hour time-weighted average exposure standard for CO is currently 30 parts per million (ppm). Short-term higher exposures may be permitted provided the average does not exceed 30 ppm. However, exposure controls should aim to keep the carboxyhemoglobin (COHb) levels below 5%.

Exposure examples, further detailed in the Workplace Exposure Standards, are a total permitted exposure time of:

  • 15 minutes at 200 ppm
  • 30 minutes at 100 ppm, and
  • 60 minutes at 60 ppm.

400ppm should NEVER be exceeded.

Health effects

Early symptoms of CO poisoning, such as headaches and nausea, are non-specific, and therefore episodes of significant exposure to the chemical can occur without the problem being recognised.

CO has long been known to combine with the oxygen-carrying component in the blood known as haemoglobin (Hb) to create carboxyhemoglobin (COHb). This combination decreases the capacity of blood to carry oxygen to the tissues.

Symptoms of CO exposure to be aware of, with increasing severity of poisoning, are:

  • headache
  • nausea or vomiting
  • weakness
  • breathlessness
  • drowsiness, irritability and impaired judgement
  • collapse, coma and death.

If the lack of oxygenation of tissues associated with CO poisoning is prolonged, the chance of developing severe and permanent pathological changes, such as brain damage may occur.

There is also considerable evidence to suggest that both acute and chronic exposure to low levels of CO can affect the heart and blood vessels. This may be an important cause for the association between cigarette smoking and heart disease.

Managing the risks of exposure

PCBUs must manage the risks of exposure to Carbon Monoxide to ensure workers are not exposed to levels which exceed the exposure standard.

In order to prevent the build-up of hazardous CO levels, all possible sources of chemical exposure inside any building or partially enclosed structure must be identified. This includes combustion-based heating equipment as well as industrial processes that may produce carbon monoxide.

To reduce the risk of exposure to carbon monoxide, a PCBU should:

  • where possible, substitute fuelled equipment with electric or manual equipment (e.g. electric forklifts or manual pallet jacks)
  • engage a competent person, such as an occupational hygienist, to undertake an assessment of the workplace, including air monitoring, to assist in identifying appropriate control measures
  • increase ventilation in enclosed or poorly ventilated areas
  • ensure internal combustion engine powered forklift trucks (including LPG) are not used in areas where adequate ventilation cannot be guaranteed under all possible operating conditions, such as when doors and windows are closed in winter or if ventilation is decreased for any reason
  • ensure that a risk assessment is conducted for motor vehicles operating in enclosed areas, such as workshops, and control measures are implemented. Flexible exhaust ducting for motor vehicle exhausts will be necessary for many workshops to ensure safety.
  • ensure all motor vehicles including internal combustion engine powered forklift trucks, are designed and maintained so that exhaust gases cannot enter the cabin and affect occupants.
  • install carbon monoxide alarms/detectors in indoor workplaces in which fuelled equipment is used
  • ensure alarms are maintained and calibrated as per the manufacturer’s recommendations
  • ensure fuelled equipment is maintained appropriately, including regular servicing and inspections/assessments of exhaust systems.
  • when respiratory protection is needed, air-supplied respirators must be used. Commonly available air-purifying respirators are not effective against CO.

There are a range of devices available to monitor CO levels and to warn, by way of audible and visible alarms, if potentially hazardous levels are approached. These should only be used to confirm that safe conditions have been achieved.

If there is any significant possibility of unsafe levels, corrective measures to prevent CO build-up must be implemented.

This assessment can be done by an occupational hygienist.

Additional Information

Respiratory Protection Equipment (REP) - SafeWork SA

Workplace exposure standards for airborne contaminants guide

Guidance on the interpretation of workplace exposure standards for airborne contaminants