What is the best indicator of ventilation?

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The Australian Health Protection Principal Committee (AHPPC) advises that improved ventilation may limit the spread of certain respiratory diseases, such as COVID-19 in indoor environments. Understanding and controlling building ventilation can help improve indoor air quality. In combination with other reasonably practicable control measures, improving indoor ventilation can be used to minimise the risks of COVID-19. 

Why indoor ventilation is important

Airborne transmission of COVID-19 can occur through dispersal of large respiratory droplets or smaller aerosols containing the virus. The COVID-19 virus can be transmitted in poorly ventilated indoor settings. Good ventilation is important to minimise build-up and stagnation of infectious aerosols indoors, including those containing the COVID-19 virus. Information on assessing the quality of indoor ventilation and practical ways to improve indoor ventilation is outlined below and in the resource on heating, ventilation and air conditioning (HVAC) systems.

It is important to ensure adequate air flow indoors and that HVAC systems are well‑maintained and operating properly to manage the risk of virus transmission in indoor workplaces. This includes any risks associated with the HVAC system being restarted after a period of shutdown, including potential risks caused by Legionella bacteria. 

Ventilation as part of a combination of control measures 

As an employer, you have a duty under the model Work Health and Safety (WHS) laws to eliminate, or if that is not reasonably practicable, minimise the risks of COVID-19 in the workplace, so far as is reasonably practicable. You also have a duty to consult workers regarding COVID-19 risks and how these risks are to be managed. 

To minimise  risks  of COVID-19 in the workplace, you must:

• undertake a risk assessment for the business (more information is available on the risk assessment page). Note in some jurisdictions, workplaces are required to develop COVID-19 safety plans under public health orders or directions  
• consider the effectiveness of available control measures and how they will help manage the  risks  of COVID-19, including ventilation
• consult with workers and  health and safety representatives about COVID-19 and relevant  control measures (more information on consultation obligations is available on the consultation page)
• consult, co-operate and co-ordinate, so far as is reasonably practicable, with any other duty holders 
• determine what  control measures  are reasonably practicable to implement in the workplace (more information on the meaning of reasonably practicable is available on the risk assessment page), and 
• continue to implement all reasonably practicable control measures to minimise the risks of COVID-19.

It is important to note that, under the hierarchy of controls, improving indoor ventilation is an engineering control and, on its own, will not eliminate or minimise the risks of COVID-19 at the workplace. 

As an employer, you must also continue to implement all reasonably practicable control measures to minimise the risks of COVID-19 in your workplace, such as:

• encouraging or ensuring vaccination, where applicable
• ensuring your workers do not come to work when unwell
• practising physical distancing and adhering to density limits (check occupancy limits for the type of building and building standards)
• relocating work tasks to different areas of the workplace, off-site or supporting workers to work from home
• practising good hygiene
• increasing cleaning and maintenance
• staggering your workers’ start, finish and break times
• reducing the number of situations where workers come into close contact, for example in lunchrooms and other shared spaces, and
• wearing face masks.

Some workplaces may already have adequate indoor ventilation or further improvements may be unable to be made. It is still important to consider ventilation in your risk assessment, monitor indoor air quality and regularly review the effectiveness of all control measures.

When determining whether a control measure is reasonably practicable under the model WHS laws, consideration must be given to several factors: 

• likelihood of risk occurring
• degree of harm that might result
• what person should reasonably have known
• availability of and suitability of ways to minimise risk, and 
• after assessing the extent of the risk and the available ways of eliminating or minimising the risk, the costs associated, including whether the cost of implementing a  control measure  is grossly disproportionate to the risk. 

Further information is available on the risk assessment page.

The COVID-19 situation is evolving and you must continue to assess the  risks and review the control measures to ensure they continue to be effective.

For information on applying the hierarchy of controls in healthcare and quarantine settings please refer to the Commonwealth Department of Health’s document Minimising the risk of infectious respiratory disease transmission in the context of COVID-19: The hierarchy of controls. 

For information on ventilation in hotel quarantine facilities please refer to the:

Consultation, cooperation and coordination

As an employer, the model WHS Act requires you to consult, cooperate and coordinate activities with all other persons who have a work health or safety duty in relation to the same matter, so far as is reasonably practicable. 

For example, in a large office building with multiple floors, with a complex HVAC system that is  shared by several businesses (tenant organisations), the building owner and/or facilities manager may obtain advice from a ventilation engineer or an occupational hygienist about monitoring and improving the indoor ventilation in the building. The building owner and/or facilities manager, and the tenant organisations should share information and work together in a cooperative and coordinated way so that risks associated with indoor air quality are eliminated or minimised, so far as is reasonably practicable.

Other hazards

Poor quality indoor and outdoor air can contain other hazards that can be harmful to your health. Work processes can release dusts, gases, fumes, vapours, mists and microorganisms into the air. Environmental pollutants, such as bush fire smoke, may also be present in outdoor air. You should consider both indoor and outdoor air quality and other potential hazards when you propose any changes to indoor ventilation.

Further information:

COVID-19 public health orders and directions

Some business operations are restricted under state or territory government public health orders and directions. For information about what COVID-19 public health orders and directions apply in your state or territory, go to your government website (links are available via the Fair Work Ombudsman website).

Assessing the quality of indoor ventilation

General information on assessing the quality of indoor ventilation and minimum ventilation rates in the context of COVID-19, can be found in the World Health Organization Roadmap to improve and ensure good indoor ventilation in the context of COVID-19 (the WHO Roadmap). The WHO Roadmap defines the key questions to consider when assessing whether indoor ventilation is adequate. It outlines steps to reach recommended ventilation rates through both natural and mechanical ventilation to reduce the risks of COVID-19.  Section 6.2 of the WHO Roadmap provides a helpful flow chart outlining these steps and strategies. The British Occupational Hygiene Society has also published a ventilation tool with helpful guidance for workplaces.

Many businesses have complex indoor spaces and/or complex ventilation systems which may make assessment of indoor ventilation and airflow difficult. In these cases, building owners and/or facilities managers or other businesses should consult with a mechanical or ventilation engineer and an occupational hygienist to assess the quality of indoor ventilation and get advice on maintaining or improving ventilation to minimise the risks of COVID-19. These experts may also advise on minimum ventilation rates per person and maximum building occupancy.

Monitoring the quality of indoor ventilation

Although carbon dioxide (CO2) levels are not a direct measure of possible exposure to the COVID-19 virus, checking levels using a CO2 monitor may help identify poorly ventilated areas.  However, CO2 levels will depend on the occupancy density and do not measure the effectiveness of other infection prevention and control measures put in place.

According to the UK Health and Safety Executive, a consistent indoor air concentration of less than 800 parts per million (ppm) CO2 is likely to indicate that a space is well ventilated.  

When CO2 concentration measurements average between 800-1500ppm over the occupied period this is an indicator to take action to improve indoor ventilation. An average of 1500ppm CO2 concentration over the occupied period in a space is likely an indicator of poor ventilation. You should particularly take action to improve ventilation where CO2 readings are consistently higher than 1500ppm. However, where there is continuous talking or singing, or high levels of physical activity (such as dancing, playing sport or exercising), a higher level of ventilation may be required to keep CO2 levels below 800ppm, given the higher risks of transmission. 

Measurements of CO2 should be taken at different times with different occupancies to get a better indication of how the ventilation system is working under different conditions. There are some situations where CO2 monitors may be less informative, such as areas that rely on air cleaning units, or large, open spaces with high ceilings (e.g. warehouses), or areas with very limited occupation density (e.g. large office areas with one or two occupants). There are many different types of CO2 monitors available and you should consult a ventilation engineer or occupational hygienist about whether CO2 monitoring is required, and which type is best for your circumstances.

Measures to improve indoor ventilation

This section provides general information about improving indoor ventilation through natural and mechanical ventilation. Improving ventilation using a combination of natural and mechanical ventilation is also possible, using the strategies outlined below. Further information can be found in the WHO Roadmap. You may need to consult with a mechanical or ventilation engineer, your building owner and/or facilities manager to adjust your systems to help minimise the risks of COVID-19. 

Natural ventilation (passive air flow)

Many buildings do not have mechanical ventilation systems. In these cases, improving ventilation will require you to consider passive air flow. You can consider ways to improve natural ventilation in your workplace such as opening windows, doors (but not fire doors), air vents and roof turrets/whirlybirds, where possible. Do not open windows and doors if doing so poses a security risk, safety risk (such as a risk of falling), or other health risk, such as triggering asthma or other respiratory diseases when pollen counts are high or bush fire smoke is present outside (refer to guidance on Managing the risks from air pollution: Advice for PCBUs for more information about air pollutants). If improvement to indoor air quality is needed in these situations, consider alternatives such as filtration (outlined in Table 2 in the section on Mechanical Ventilation below).

You should also consider whether objects such as furniture, pillars and screens prevent the flow of air and cause stale air to accumulate in parts of the workplace, noting that screens may be useful to protect workers. As mentioned above, using a CO2 monitor may help assess whether there is a need to improve air quality.

Where possible, you can open windows on opposite sides of the room to increase airflow through cross ventilation (air entering through one window, crossing the room and exiting via another window). When the room is occupied, the thermal comfort (heat and cold) of workers needs to be taken into consideration. 

You should consider still days and areas where airflow improvement is difficult (such as stairwells or elevators). Ceiling and portable fans can also be used to improve natural ventilation, but you should take care to ensure the air is not directly blowing from one person to another and that fresh air is available. Refer to Table 2 for more information about using mechanical ventilation options such as exhaust fans and air cleaners to improve indoor air quality.

Where possible, you should continue to leave doors and windows open even when the room is unoccupied to air the room. 

Table 1 lists some ways you can improve natural ventilation in the workplace.

Table 1: Measures to improve natural ventilation (adapted from the United States Centers for Disease Control and Prevention Ventilation in Buildings).

Mechanical ventilation

Mechanical ventilation is the active process of supplying air to or removing air from an indoor space by powered air movement components.

Ventilation can be improved by adjusting mechanical ventilation systems such as HVAC systems. Building mechanical ventilation systems can be complex and adjustments should be made by people familiar with the operation of your building’s systems. You may need to consult with a mechanical or ventilation engineer, your building owner and/or facilities manager to adjust your systems to help minimise the risks of COVID-19. 

For HVAC systems, it is preferable to maximise fresh air supply and not recirculate air. If you have exhaust fans in restrooms, kitchens and other facilities, check they are functional and operating continuously and at full capacity. Operating them when the space is not occupied will also improve overall ventilation. 

Kitchen exhausts in many fast-food shops and restaurants often deliver good ventilation outcomes providing there is a source of fresh air. To prevent contaminated air moving outside bathrooms, keep exhaust fans running in toilets provided the fan motors are suitable to be operated continuously. A mechanical engineer or electrician can check the fan motor’s capacity to operate continuously, or you may be able to download the fan specification. Do not operate fans continuously if they are not rated for this.

Exhausted air should be directed outdoors and away from windows and air intake systems of your building and that of any surrounding buildings. Your building owner and/or facilities manager can assist you with checking and adjusting air flow at your workplace. 

Air purifiers or cleaners such as those fitted with high-efficiency particulate air (HEPA) filters can lower the concentration of airborne contaminants (including viruses) in the air and are useful additions in areas with poor ventilation.  It is important to consider the filtration capacity required and to place in a location that does not interfere with existing HVAC airflow.  Air purifiers or cleaners should be operated and maintained in accordance with the manufacturer’s instructions. Businesses should consider consulting an occupational hygienist to assist in determining appropriate placement of these devices within the room to ensure maximum benefit is achieved. 

HVAC systems must always be maintained by a qualified mechanical or ventilation engineer in accordance with the manufacturer’s instructions to ensure ongoing compliance with building regulations, including during the COVID-19 pandemic. 

If you do not directly control or manage the HVAC unit or system, you will need to liaise with the building owner and/or facilities manager to ensure the system is regularly inspected and maintained. Before you allow your workers to resume work after a period of shutdown, you should confirm with the building owner and/or facilities manager that the correct start-up procedures and control settings have been followed. 

It is important that you do not open windows or doors to improve air quality in buildings with mechanical ventilation systems unless checked by a mechanical engineer. You should not operate fans outside their designed operation to avoid the risk of overheating fan motors. 

See our webpage on HVAC Systems for more details on maintenance.

Table 2 lists some ways you can improve mechanical ventilation in the workplace. 

Table 2: Measures to improve mechanical ventilation (adapted from the United States Centers for Disease Control and Prevention Ventilation in Buildings).