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This guidance will apply in most workplaces – it will help you and your workers:

• Understand what is defined as poor air quality

• Identify poorly ventilated areas

• decide on the steps you can take to improve ventilation

Signs of poor indoor air quality

Symptoms related to poor workplace air quality vary depending on the type of contaminant. They can easily be mistaken for symptoms of other illnesses such as allergies, stress, colds and influenza.

The usual clue is that people feel ill or find it hard to concentrate while inside the building, and the symptoms go away shortly after leaving the building, or when away from the building for a period of time 

What potential pollutants need to be monitored:

Particulates (dust):

Dust within a workplace can be generated from a number of sources (outdoor pollution, manufacturing processes etc), elevated levels can lead to the development of asthma and other chronic respiratory illnesses. A well designed and maintained HVAC system should adequately control this pollutant. A guidance level would be <12 ug/m3 for PM 2.5 and <150 ug/m3 for PM 10

Significance of CO2 Levels

Carbon Dioxide levels in fresh air (atmospheric) are 400ppm (parts per million), as we breathe we generate excess carbon dioxide which increases the overall concentration of this gas in the indoor environment. A poorly ventilated workplace with very little fresh air can easily see levels in excess of 2000ppm as the working day progresses. Good indoor air quality managed with an efficient HVAC system using the correct ratio of fresh to recirculated air should be achieving carbon dioxide levels <1000 ppm.

Identifying poorly ventilated areas

You should identify areas of your workplace that are usually occupied and are poorly ventilated. There are some simple ways to identify poorly ventilated areas:

• Look for areas where people work and there is no mechanical or natural ventilation such as open windows, doors or vents etc

• Check that mechanical systems provide outdoor air. If a system only recirculates air and has no outdoor air supply, the area is likely to be poorly ventilated.

• Identify areas that feel stuffy or smell bad

• You may wish to use carbon dioxide (CO2) monitors. Checking CO2 levels will help you decide if ventilation is poor.

There are a number of factors to consider when deciding on the ventilation needed in your workplace:

How do you provide fresh air (ventilation) to your workplace?

Adequate ventilation is key to improving indoor air quality. Your workplace may have different means of providing ventilation for different areas.

Remember to include changing rooms and areas used for breaks, such as canteens. If you are not able to easily tell how an area is ventilated, it may be because it is poorly ventilated.

How many people use or occupy the area?

The more people who use or occupy an area the greater the impact on air quality and therefore in high occupancy areas you may need to increase the level of ventilation.

How much time do people spend in the area?

The longer people use or occupy an area is worth considering in your assessment. Rooms such as kitchens or toilets that are only occupied for short periods may need very little ventilation.

How large is the area?

The larger the area, the lower the risk. This is because larger areas:

• have more air to help dilute the virus

• tend to be designed with higher ventilation rates

• mean it takes longer for pollutants to build up

What tasks or activities take place in the area?

Activities that make you breathe deeper, for example physical exertion or shouting, will increase carbon dioxide levels and bio-aerosols.

How to improve natural ventilation

You can improve natural ventilation by fully or partially opening windows, air vents and doors. Buildings are designed to provide an adequate amount of ventilation and, where this is through windows and air vents, you should be able to open them. If they cannot be opened whilst occupied, the ventilation in that area will be affected. 

Purging of unoccupied rooms (in-between shifts or on breaks) by opening all windows and doors fully can improve ventilation levels.

How to improve mechanical ventilation

Mechanical ventilation brings fresh air from outside into a building. You should speak to the people who manage the day-to-day operations of your workplace ventilation systems to:

• understand how they operate

• make sure they’re supplying fresh air into an area and how much

• make sure they’re maintained in line with manufacturers’ instructions

You should base ventilation rates on the maximum ‘normal’ occupancy of an area.

These mechanical systems will provide adequate ventilation if they are set to maximise fresh air and minimise recirculation. 

If your system draws in fresh air, it can continue to operate. You need to know how much fresh air it draws in and if this provides adequate ventilation. You may need to increase the rate or supplement with natural ventilation (opening doors, windows and air vents) where possible. 

You can also consider extending the operating times of mechanical ventilation systems to before and after people use work areas.

Recirculating air

It is preferable not to recirculate air from one space to another. Recirculation units for heating and cooling that do not draw in a supply of fresh air can remain in operation provided there is a supply of outdoor air, for example windows and doors left open.

Recirculation units (including air conditioning) can mask poor ventilation as they only make an area feel more thermally comfortable.

Air cleaning and filtration units

You can use local air cleaning and filtration units to improve air quality. You should prioritise any areas identified as poorly ventilated for improvement in other ways before you think about using an air cleaning device. These devices have very limited capabilities when it comes to removing pollutants and improving air quality. The majority are based on particulate filtering and will only reduce levels of dust and bio-aerosols. Very few of these devices are capable of improving levels of formaldehyde, VOC's and carbon dioxide.