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 National 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.
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:
- nausea or vomiting
- 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.
PCBUs and their workers can take several actions to ensure that symptoms of CO poisoning do not occur.
In order to prevent the build-up of hazardous CO levels, all possible sources of chemical 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.
Other appropriate methods:
- Internal combustion engine powered forklift trucks (including LPG) must not be 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.
- Motor vehicles must be designed and maintained so that exhaust gases cannot enter the cabin and affect occupants. Hazards frequently arise from damaged or worn-out exhaust systems, from modification of vehicles and when specialised bodywork is fitted to a commercial vehicle chassis.
- Where motor vehicles are operated in enclosed areas, such as workshops, the potential for CO build-up must be assessed and preventative measures implemented. Flexible exhaust ducting for motor vehicle exhausts will be necessary for many workshops to ensure safety.
- 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.
The Workplace exposure standards for airborne contaminants guide lists exposure standards and contains key information about the way they are applied, while being interpreted under work health and safety laws.
The Guidance on the interpretation of workplace exposure standards for airborne contaminants guide provides help with interpreting exposure standards.