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Employers have been encouraged to remove sources of CO entirely from the working environment, where possible, or substitute engines or equipment with those that do not emit CO.
A new 'Guidance Notes' document has been launched by Hong Kong's Labour Department (LD) on 17 December 2025, advising employers and relevant duty holders on how to prevent carbon monoxide (CO) poisoning in workplaces.
CO is a colourless, odourless, and tasteless gas that is highly poisonous. Typically, what may lead to CO poisoning of workers is the use of fuel-powered equipment, engines or heating systems (such as diesel, petrol, and town gas) in poorly-ventilated workplaces.
The prevention strategies, LD stated, should include:
- Identifying all potential sources of CO;
- Eliminating or substituting harmful practices where possible;
- Ensuring adequate ventilation in workplaces,
- Using/installing CO detector for determining the extent of the hazard;
- Conducting regular air quality tests;
- Providing thorough training and awareness programmes; and
- Adhering to established exposure limits and safe work practices, etc.
These measures have been detailed below:
Elimination and substitution
The best way to prevent CO poisoning is to remove the sources of CO entirely from the working environment. Employers should substitute fuel-powered engines or equipment with electric, hydraulic or pneumatic equipment without emitting CO during operation, and eliminate using fuel powered engines or equipment in poorly ventilated or enclosed areas.
Engineering controls
Direct venting, local exhaust ventilation system, or portable exhaust device can be deployed to remove exhaust gas from work areas.
Employers should ensure that proper ventilation is in place in work areas when using any fuel-powered equipment. The following types of mechanical ventilation should be prioritised:
• Direct venting: Ensure all fuel-powered appliances (such as boilers, heaters) are properly installed with flues or chimneys that vent exhaust containing CO directly outdoors. Inspect and maintain these venting systems regularly to prevent blockages.
• Local exhaust ventilation (LEV): Capture CO at the source before it diffuses to the general workplace air. Examples include installing exhaust hoods over cooking appliances or industrial processes to capture exhaust directly. LEV systems must be properly designed, installed, used, and maintained.
• General ventilation: Increase the number of air changes in workplaces by using mechanical ventilation such as extraction fans, or air conditioning systems with fresh air intake supplemented by natural ventilation (e.g. through windows, doors, vents). Employers should ensure ventilation systems are functioning properly, well-maintained, with adequate airflow and sufficient fresh air supply.
• It is also important that there is a dedicated source of fresh air and a directional airflow from clean to dirty areas to improve the dilution efficiency. In general, appropriate air change rate should be determined if removing CO from indoor environment is required, depending on factors such as the dimension of workplaces and the number and condition of any fuel-powered equipment in use.
Caution: Natural ventilation by opening windows and doors is unlikely to be sufficient for removing exhausts with CO from workplaces, especially with significant emissions.
Caution: Natural ventilation by opening windows and doors is unlikely to be sufficient for removing exhausts with CO from workplaces, especially with significant emissions.
Administrative controls
Administrative controls can also minimise the risk of CO poisoning, including:
• Work practices: Prohibit idling engines indoors, maintain equipment properly, reduce workers’ exposure time, arrange workers to work in well-ventilated areas.
• Warning signs: Clearly mark potential CO sources/hazardous areas.
• Training: Provide training for employees on CO hazards, symptoms of CO poisoning, appropriate control measures, and emergency procedures.
• Monitoring programme: Implement a programme to regularly measure and monitor CO levels in workplaces.
Poorly maintained fuel-powered equipment produces more CO. Regular inspections and preventive maintenance of equipment (e.g. fork-lift trucks, heaters, backup generators, gas appliances etc.) that can produce CO is vital. Stop using malfunctioning equipment immediately. Replace or repair the equipment.
Regularly inspect and maintain ventilation systems to ensure that they are functioning properly. Further, employers should obtain user instructions from the equipment manufacturers or suppliers to understand the dangers of CO emission and when using such equipment indoors.
Fuel-powered generators, compressors, and other engine-driven equipment should be operated in well-ventilated outdoor areas, at least 5 metres away from any building openings (windows, doors, garages, etc.) and away from air intakes, to prevent exhaust contaminants from being drawn into the buildings.
It is recommended to provide personal CO detectors with both audible and visible alarms to workers in situations where potential high levels of CO exposure exist. Additionally, installing CO detectors in areas where internal combustion engines are operated (e.g. using fuel-powered fork-lift trucks in semi-enclosed loading bay) can offer early warning of accumulation of CO.
According to the Occupational Safety and Health Ordinance (Cap. 509) and the Factories and Industrial Undertakings Ordinance (Cap. 59) and their subsidiary regulations, employers and proprietors are obliged to provide or maintain a working environment that is, so far as reasonably practicable, safe and without risks to health.
Inhaled CO prevents blood from carrying oxygen to body tissues, consequently depriving vital organs like the heart and brain of this essential gas. Concentration of CO as little as 0.4% or 4,000 parts per million (ppm) in the air can cause unconsciousness and death in a few minutes.
The Guidance Notes on Prevention of Carbon Monoxide Poisoning in Workplaces can be downloaded here.
Lead image / Hong Kong LD
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