Why ventilation is important
Good ventilation reduces the concentration of the virus in the air and therefore reduces the risks from airborne transmission.
Coronavirus is spread through the air via large droplets and smaller particles that come out of the nose and mouth of an infected person as they breathe.
Coronavirus droplets are heavier and so fall out of the air quickly but there are lighter coronavirus particles that float in the air. They can linger in a room or any enclosed space and other people who can breathe them and become infected. Good ventilation takes away these smaller particles, so people don’t breathe them in.
Good ventilation cannot help with larger particles that land on surfaces or are projected from coughing or sneezing. These require the other common control measures e.g. cleaning, personal hygiene and other behaviors like catching sneezes in elbow, avoiding touch face.
Note: Application of social distancing principles will not eliminate the risk of these smaller airborne particles in a poorly ventilated space.
Identifying poorly ventilated areas
Carbon dioxide (CO2) is a by-product of human breathing and an elevated concentration of CO2 in a space is an indication that the air is ‘not fresh’ and therefore poorly ventilated.
The Chartered Institution of Building Services Engineers (CIBSE) have generated guidance that is supported by the Health & Safety Executive, this sets out several simple ways to identify poorly ventilated areas, one of which is to use CO2 monitors.
Establishing ‘poorly ventilated’ criteria
CIBSE recommend CO2 concentrations should be below 800PPM and have identified that a poorly ventilated space is above 1,500PPM.
For perspective the CO2 level in fresh air in the general environment is around 400PPM and the Health and Safety Executive state that 15,000PPM is the level at which health is placed at immediate risk to life through suffocation.
Using a gas detector in this case the X-am 5600 to check ventilation
The Draeger X-am 5600 with the appropriate sensors and calibrated as per CIBSE guidance can be used to quantify the standard of ventilation within a space. Below are the criteria which can be used:
- Place the device roughly in the middle of those expected to be in the room, so if it’s a meeting room, in the middle of a table.
- Place the device at roughly table height, do not position on floor, high up or in a corner as this is not representative of the breathing zone.
- Place the device at least 1 metre from individuals, as the CO2 expelled from them will directly influence the result and give elevated readings.
- Do not breathe directly onto the device as this can overexpose the sensor.
The device can is calibrated with CIBSE recommended two alarm settings:
|A1 (800PPM)||When the CO2 concentration reaches 800ppm, the device will sound an audible alarm to alert that action is required. The alarm can be acknowledged, which silences the audible alarm.|
|A2 (1500PPM)||When the CO2 concentration reaches 1500ppm, the device will sound an audible alarm to alert that action is required. The alarm will continue until the level drops below 800ppm – It cannot be silenced or switched off at this level. If you think about its design intent it is to inform the user that there is an immediate risk to their health, and they need to get to safety now.|
If the device goes into alarm this is a good early indication that action should be taken to improve the ventilation, in order to reduce the risk of airborne transmission.
It is important to highlight that when the device goes into alarm, it does not mean you are at an immediate risk of being infected with coronavirus. It is to be used as an early warning that action needs to be considered to improve ventilation. Actions to be taken are:
- Improve ventilation (Opening windows & doors)
- Reduce the number of people in the room (Rule of six or less)
- Longer term
- Does the meeting need to take place face to face, can those present be reduced in number, is the ventilation strategy suitable for long term occupation?