CIBSE COVID-19 VENTILATION GUIDANCE
Getting back to work safely is a main concern for many employers. Is it too soon? Is there enough space in between desks? A key aspect that is often overlooked however is the question of “is there enough ventilation?”
On 15th July 2020 CIBSE published new COVID-19 ventilation guidance:
This CIBSE COVID-19 ventilation guidance is intended to give business owners and managers an outline of ventilation systems commonly encountered in buildings to assist in the preparation to re-open workplaces. This guidance will inform considerations of safe working practices and the provision of ventilation in buildings.
The guidance document describes the many variations of building ventilation systems including natural ventilation scenarios. Each system is examined and measures described to increase ventilation rates.
Building ventilation has always been an important part of a healthy building environment as it ensures that a steady stream of outside air is brought into the building whilst stale air is exhausted. Stale air includes bioeffluents (body odours and exhaled breath), airborne pollutants (such as smells from cleaning products and furniture), amongst others.
Ventilation is also a very important way of diluting any airborne pathogens and there is good evidence that demonstrates room occupants are more at risk of catching an illness in a poorly ventilated room than in a well-ventilated room. This is because in a poorly ventilated room occupants are exposed to a higher concentration of airborne pathogens, and the risk will increase with a greater amount of time spent in such an environment.
Risk = exposure x time
The risk of airborne infection to the individual can therefore be reduced by:
– Reducing time spent in the location
– Reducing airborne exposure concentration of infectious material
– Reducing risk of contact spread through regular handwashing, surface cleaning and reducing deposition of infectious particles.
Ventilation rate and effectiveness play a role in both airborne exposure and deposition rates.
The risk for COVID-19 transmission will be from asymptomatic or pre-symptomatic individuals who occupy a building without knowledge that they are shedding viral particles. Current government advice should be consulted with regards to reducing risks posed by symptomatic individuals.
To minimise the risks of airborne transmission of SARS-CoV2 the general advice is to increase the air supply and exhaust ventilation, supplying as much outside air as is reasonably possible. The underlying principle is to dilute and remove airborne pathogens as much as possible, exhausting them to the outside air and reducing the chance that they can become deposited on surfaces or inhaled by room users. Recirculation/transfer of air from one room to another should be avoided unless this is the only way of providing adequately high ventilation to all occupied rooms.
In rooms and zones where there is no direct supply of outside air then consideration should be given to prohibiting access to these spaces by building users, especially where it is likely that they would be occupying such a space for considerable lengths of time (longer than 30 minutes). This may include basement rooms or storage areas which rely on infiltration of air from other spaces.
The key actions are:
– Understand your ventilation system
– Run your ventilation at higher volume flow rate; this may require changes to CO2 set points (for both mechanical ventilation and automated windows)
– Avoid recirculation/transfer of air from one room to another unless this is the only way of providing adequately high ventilation to all occupied rooms
– Recirculation of air within a single room where this is complemented by an outdoor air supply is acceptable.
– If applicable enthalpy (thermal) wheels should be switched off, but the pressure difference will need to be maintained between supply and extract to minimise any leakage flow from the extract to supply side
Recently, Kinetic Engineers Ltd have been commissioned to undertake ventilation studies in various environments to provide a ‘back to work’ safely path for workers. We survey the building and its various services, perform detailed calculations and provide the client with a feasibility study that will determine the requirements to bring back employees into the working environment safely.
Contact us to find out how we can help your workplace get back to normal.