Coronavirus (COVID-19): ventilation guidance

Workplace and commercial settings

This guidance is for employers, building managers and those who are responsible for workplace, non-domestic or commercial settings, especially where people work with or close to other people.

It explains the role of effective ventilation in helping to reduce the spread of COVID-19 in these settings. A range of experts/stakeholders have contributed to this guidance.

There is government funding available to help businesses improve their ventilation.

In this guide:

• summary - how to reduce the spread of coronavirus
• ventilation as part of a risk controls approach
• assessing ventilation requirements
• natural ventilation
• mechanical ventilation 
• supporting staff
• legal requirements, specialist support and advice
• useful tips

Summary - how to reduce the spread of coronavirus

To reduce the spread of coronavirus: 

• let in as much fresh air as possible – open windows, doors (excluding fire doors), and vents in your workplace, the canteen and changing rooms. This will dilute any infected particles and reduce the risk of infection
• avoid recirculating air – avoid using ventilation systems which only recycle used air. Make sure that fresh air is introduced to all spaces
• be aware of the relevant occupancy level – more people together means more particles, and needs more ventilation
• air rooms between users or regularly throughout the day. If you share a space with others, you should open the windows regularly, especially between users, to help reduce the risk
• ensure adequate ventilation. It is important to avoid gathering with colleagues in poorly ventilated rooms. Opening the windows a little is the easiest way to keep the fresh air flowing. If rooms cannot be adequately ventilated, consider how they are used and whether you can avoid using them. 
• if ventilation makes it feel cold, consider relaxing uniform requirements, so employees can continue to work comfortably
• understand your building’s ventilation system. Do not adjust mechanical settings without expert advice. It is important to make sure that ventilation systems and/or extractor fans are used correctly

A poster providing good ventilation advice that can be printed out and displayed in the workplace is available.

There are a range of other COVID-19 control measures to consider including:

• adopting a hybrid approach to working or retaining some home working to reduce office or building capacity
• staggering working patterns or shift start and finish times
• increasing surface cleaning regimes

This guidance provides general good practice and guiding principles. Appropriate risk assessments must be carried out for each specific indoor environment.

Employers must, by law, ensure an adequate supply of fresh air in the workplace.

Good ventilation can help reduce the risk of spreading coronavirus, so a focus on improving general air flow, preferably through fresh air or effective mechanical systems, will help keep staff and other building users safe when planning a return to work. Building managers should consider ways to maintain and increase the supply of fresh air - for example by opening windows and doors.

Areas of stagnant air or poorer ventilation can be improved by using desk or ceiling fans. However, these should only be considered if there is good ventilation elsewhere in the premises through the provision of fresh, outdoor air.

The risk of air conditioning spreading COVID-19 in the workplace is extremely low, as long as there is an adequate supply of fresh air and ventilation. Most types of air conditioning system can continue to be used as normal. However this becomes more complex when centralised ventilation systems are in operation. You should turn off the recirculation of air and use a fresh air supply where possible.

If you are unsure, seek the advice of your heating ventilation and air conditioning (HVAC) engineer or adviser.

Ventilation as part of a risk controls approach

Ventilation should be considered as part of a hierarchy of risk controls. These include:

• effective fresh air ventilation, working alongside face coverings where required and enhanced hygiene regimes
• restricting or reducing duration of activities indoors
• room layout
• using rooms with good ventilation and avoiding the use of those without
• factoring in the use of suitable air cleaning and purifying devices to enhance indoor air quality. As explained in the HSE guidance, these units are not a substitute for ventilation. You should prioritise any poorly ventialted areas for improvement in other ways before you think about using an air cleaning device

Transmission depends on the interaction of multiple factors including the viral emission rate, the ventilation rate, the duration of exposure and the number of occupants. Providing the ventilation rate remains the same, increasing the number of people or the time spent in the environment increases the probability of airborne transmission.

In many situations a ventilation assessment will need to be carried out by someone with appropriate engineering expertise. The proposed solutions are likely to be specific to each building and situation depending on the number of people, how long they spend there, what they are doing, and the type of ventilation. 

The safe use of office (or indoor) environments - risk assessment

When preparing for staff using an office or other indoor environment, employers must protect people from harm. This includes taking reasonable precautions to protect those using these environments from COVID-19. A risk assessment should be carried out to consider work activities or situations which might increase the risk of transmission of the virus (such as working for 15 minutes or more in close proximity to others).

A risk assessment should be carried out to consider work activities or situations which might increase the risk of transmission of the virus, such as working for long periods of time - 15 minutes or more - in close proximity to others.

This risk assessment should follow the same principles as any other workplace risk assessment, including having a clearly defined hierarchy of controls that looks at all the workplace risks, not just COVID-19 in isolation.

While intended for wider use, the Health and Safety Executive has produced helpful guidance on Covid-19 risk assessments.

Assessing your ventilation requirements

It is important to speak to staff and building users for their views on the working environment as this can support the identification of poorer ventilation.

For example, you may encounter:

• a rising number of fatigue or headache complaints
• flu-like symptoms out of season
• dizzy spells and nausea
• complaints of smell or stale air
• stuffy environments.

Increasing the flow of fresh air should help to reduce these problems.

If you are not able to increase the flow of fresh air by either natural or mechanical means, then you should consider how spaces are used and avoid using these spaces until this can be rectified.

For small-medium businesses, the Business Ventilation Fund may be able to help you with costs for this.

Monitoring air quality

It is important to regularly monitor the quality of air within an enclosed environment, as this highlights the need to take action to reduce the risk of transmitting COVID-19.

Where your workplace (or parts of it) are poorly ventilated, you will need to improve ventilation in those areas to reduce the risk of airborne transmission.

There are some simple ways to identify poorly ventilated areas:

• look for areas where there is no mechanical ventilation or no natural ventilation, such as opening windows and vents, unless doors are opened very frequently
• check that mechanical systems provide outdoor air, temperature control or both. If a system (eg a local air conditioner) is recirculating only and doesn’t have an outdoor air supply, or a separate source of outdoor air, the area is likely to be poorly ventilated
• identify areas that feel stuffy or smell badly
• use NDIR carbon dioxide (CO2) monitors to identify the CO2 levels to help decide if ventilation is poor. These monitors measure carbon dioxide concentration using light absorption of the CO2 molecules.You should seek specialist advice on the use of these. For further information, please see the Health and Safety Executive (HSE) guidance

If you work in an environment with a complex ventilation system, for example supplying multiple floors and rooms, or old buildings, there is more guidance from the Chartered Institution of Building Services Engineers (CIBSE).

Natural ventilation

For naturally ventilated spaces, windows, doors and vents are often the mechanism for providing outside air.

In the colder months, the natural forces that drive air through these openings, wind and indoor/outdoor temperature difference are greater, so they do not need to be opened as wide.

Opening vents can enable more mixing of the outside air with air in the space and also warms the incoming air before it reaches the occupied zone. This allows colder outside air to be introduced to the space without affecting thermal comfort.

It is better to open all the windows or vents a small amount to aid mixing and warming. If natural ventilation openings are the only mechanism for delivering outside air into a space it is important not to close these entirely.

A well ventilated space reduces the concentration of viral load in the air, reducing the risk of transmission of the virus.

Evidence to date suggests that poorly ventilated spaces pose the highest risk, so it is recommended that mitigation measures focus on those spaces where ventilation is absent or inadequate.

There is some research into the benefit of air cleaning devices and some types may be more beneficial than others. It is important to note that air cleaning / purifying / filtration devices do not provide additional fresh air into a space, and should only be used where there are no ventilation options available. Specialist ventilation engineering advice should be sought prior to investment/installation of these devices.

Those spaces where there are several people in close proximity for a prolonged period, for example social spaces, schools and meeting rooms or where an infectious person is more likely to be present, for example in pharmacies, should be prioritised for mitigation measures.

Practical steps to improve natural ventilation

A good supply of fresh, clean air can mitigate the risk of coronavirus transmission, whether this be through mechanical means, or through the opening of windows and doors that don’t need to remain closed for other purposes (for example, internal fire doors).

Any actions taken must also comply with broader health, safety and welfare regulations, which in most cases would take priority over the ventilation requirements for coronavirus.

To increase natural ventilation, you may wish to consider:

• opening more than one window or door, if possible. Do not open windows and doors if doing so poses a safety or health risk to staff or customers. For example, opening doors can invalidated fire risk assessments so that would constitute an unacceptable increase in risk
• opening windows (or doors) at opposite sides of a building and keeping internal doors open to allow a cross flow of ventilation
• where there are both high level and low level openable windows in a room then it is recommended to open the high level windows during cooler weather in the first instance, as incoming air will be warmed as it flows down into the room thereby reducing cold draughts. This also improves mixing of the outside air with air in the room before reaching the occupied zone. To maximise airflow when draughts are not a concern, both high and low windows should be opened. This does not just increase the opening area but creates a more efficient flow, thereby increasing the dilution of pollutants
• using indoor fans in combination with open doors or windows to further increase air movement. In addition to specialised window fans, box fans or tower fans can be placed in front of a window. Fans can face toward the window (blowing air out of the window) or away from the window (blowing air into the room)
• using multiple fans, for additional ventilation, to push air out of one window and draw it in from another. Note: if a single fan is used, it should be facing (and blowing air) in the same direction the air is naturally moving
• directing the airflow of any fan so that is does not blow directly from one person to another

Mechanical ventilation

Mechanical ventilation systems should be operated at the maximum design flow rate, even if a space has a lower occupancy than the maximum permitted.

As set out in CIBSE guidance it is recommended that ventilation systems are set to run on full fresh air as far as possible. However, where systems incorporate the heating of incoming air in to their design this could significantly increase the carbon footprint for that unit and could be uneconomical for a smaller than normal occupancy. It is recommended that 8-10 litres of fresh air per person (minimum) would be a better guide to fresh air demand.

Practical steps to improve mechanical ventilation

Optimal approaches for mechanical ventilation systems will vary depending on the nature of the system in operation, however it may be useful to consider the following as part of a wider discussion with engineers, who are experts in utilising such systems:

• understand where you may have poorly ventilated spaces or areas - increase the ventilation rate as much as reasonably possible. This may require changes to CO2 set points (for both mechanical ventilation and automated windows)
• measurements of elevated CO2 levels in indoor air are an effective method of identifying poor ventilation in multi-occupant spaces.
• avoid recirculation/transfer of air from one room to another unless this is the only way of providing a sufficient airflow to all occupied rooms
• recirculation of air within a single room where this is complemented by an outside air supply is acceptable as this helps to provide more outside air to occupants, and can help to maintain thermal comfort
• where thermal (or enthalpy) wheels are installed to recover heat, then a competent engineer should check that the configuration and operating conditions are such that any leakage across the device is from the supply side to the extract side, to minimise the risk of transferring contaminated air into the supply

Where practical, spaces where there is potential for long duration exposure over several hours within the same group (e.g. offices, schools) should ensure occupants have regular breaks, ideally with purge ventilation/airing of the room, to reduce the potential for viral exposure. This may mean alterations to the work pattern or teaching or office areas.

Supporting staff to understand the importance of ventilation

Improving the dilution of aerosols is not just about better levels of fresh air entering a building, it’s about how it then travels and eventually leaves the building.

The effectiveness of ventilation in many environments is strongly influenced by user behaviour and an understanding of what measures are introduced. This could be as straightforward as individuals opening windows, which others then close, increasing the number of touchpoints (which should be cleaned regularly to reduce the risk of transmission) within an office environment. 

Clear instructions to building users is required on how ventilation systems should be used, particularly throughout winter. There is an increased risk of user interference with systems, which could affect the measures taken to improve ventilation in buildings. This can be complex due to the variety of ventilation systems available, and as such employers should consult manufacturers’ instructions and with engineers with expertise in such equipment, as required.

Raising awareness of the potential for airborne transmission and the importance of ventilation is the key to ensuring that guidance is followed. The focus in the shorter term is to support businesses to improve the standard of ventilation and that working from home should be continued to at least some extent, where this is possible.

Thermal comfort

Environmental factors (such as humidity and sources of heat in the workplace) combine with personal factors (such as the clothing a worker is wearing and how physically demanding their work is) to influence what is known as thermal comfort.

Individual personal preference makes it difficult to specify a thermal environment which satisfies everyone. For workplaces where the activity is mainly sedentary, for example offices, the temperature should normally be at least 16 °C. If work involves physical effort it should be at least 13 °C (unless other laws require lower temperatures). In practice, offices are typically set to 21 °C.

When altering the ventilation of premises, employers may also wish to consider relaxation of uniform/dress code requirements during the winter months, as rooms are likely to have increased ventilation during these months to prevent the spread of the virus. This is likely to affect thermal comfort in some situations.

Legal requirements, specialist support and advice

Compliance with health and safety, fire regulations and building regulations regarding ventilation

You must continue to comply with existing health and safety, fire safety and building regulations alongside this guidance. 

Achieving optimum airflow by the opening of windows or doors must not contravene duties in the above regulations and put staff or customers at increased risk.

Equally, with increased ventilation, thermal comfort of building users must also be considered, and advice should be sought on the appropriate ambient temperatures for different environments.

Links to relevant regulations and guidance can be found at:

• Health and Safety at Work etc. Act, 1974
• The Fire Safety (Scotland) Regulations 2006
• Building Regulations: Ventilation

Specialist support and advice

Employers can access general advice and guidance on risk assessment, prepared by the Health and Safety Executive (HSE).

In support of this, The British Occupational Hygiene Society created a risk matrix for employers.

There is also sector specific guidance available for ventilation in schools that can apply equally to many offices and workplaces.

The Chartered Institution of Building Services Engineers (CIBSE), in recognising the challenges the cold season brings for building managers trying to minimise the risk of COVID-19 transmission, have developed guidance, including the optimum use of HVAC strategies for buildings.

The above guidance illustrates the importance of increasing the flow of outside air and preventing any pockets of stagnant air. Recirculation of air within buildings should be avoided to reduce the risk of transmission. This may lead to an increase in energy bills.

HSE and CIBSE have provided detailed guidance, underpinned by expert advice, on working safely during the coronavirus outbreak. This guidance is updated frequently as new evidence emerges on the transmission of coronavirus and should be regularly reviewed to support the safe conducting of business.

In particular, the second link to the CIBSE guidance allows a building user or manager to access information on the form of ventilation present in their building and build a relatively straightforward operation model for ventilating the building spaces, offices and other populated areas. In most of the cases, CIBSE are suggesting increasing ventilation using, as far as possible outside air as part of the control strategy for coronavirus airborne transmission.

It does suggest that where an understanding of how to best achieve this is not immediately apparent, specialist help may be required to tackle the calculations and estimates necessary to achieve these improvements. Such help could be in the form of a ventilation engineer, an Occupational Hygienist with a specialisation in indoor air quality, an architect with a similar background or a similarly knowledgeable professional.

Read the SAGE report on the role of ventilation in controlling SARS-CoV-2 transmission.

It reminds us that at the very least it is important that adequate ventilation is provided year-round, as poor indoor air quality also negatively impacts health, wellbeing and productivity. This is not something to consider just because of COVID-19, but something to improve for general wellbeing in indoor spaces.

Useful tips

Opening windows for a short period of time

The opening of windows frequently, even for a short period, will ensure the replacing of air within enclosed environments. This can be effective in the winter months where colder temperatures could affect how comfortable staff or customers are within your premises.

Wedging doors open

Only wedge doors open if they serve no other purpose such as fire containment or security for vulnerable people.

If unable to open windows

If you are unable to open windows in your premises, check to see if air quality is already acceptable by measuring CO2. Mechanical ventilation may be providing fresh air or hidden vents may be doing what they were designed to do. 

Monitoring air quality in the workplace

You would not usually need to monitor air quality in the workplace, taking basic steps to improve fresh air coming in will normally be enough and monitoring air quality parameters will be the exception rather than the rule. Only monitor if there is a risk that the basic steps have not been effective.

Areas identified as poorly ventilated

If a risk assessment or air quality monitoring shows a specific space is poorly ventilated, prioritise this for the introduction of fresh air through natural or mechanical means.

If this is not possible, or is not sufficient to resolve the issues, then consider changing the use of the space or avoid using the space until actions are put in place to make it adequately ventilated.

If customers or staff comment on windows or doors being opened

It may be beneficial to explain to staff/customers that this is a protective measure put in place to reduce the risk of transmitting coronavirus.

You could alter the layout of premises to avoid very cold areas because of proximity to open windows or doors. You should display the poster to help people understand the need for good ventilation.

Opening windows for a short period of time

The opening of windows, even for a short period, will ensure the replacing of air within enclosed environments. This may be effective in the winter months where colder temperatures could affect how comfortable staff or customers are within your premises.

Examples of improving ventilation in different workplace settings

HSE have produced useful examples of practical steps which can be taken to improve ventilation in different types of workplace settings, which will reduce the risk of transmission of the virus.