In the last two decades we have been confronted with three Coronavirus disease outbreaks, SARS, MERS and now COVID-19. With the current pandemic affecting how we use building and it’s likely impact on how we design buildings in the future, Hilson Moran has gathered together existing advice and looked at ways in which diseases can be transmitted, to help advise building owners, occupiers and investors on how to manage their assets.
Infectious diseases can be transmitted in a number of ways including; contact from person to person or surface to person; via droplets in the air by sneezing or coughing; and via faecal to oral through the movement of contaminated water droplets from WC’s or wastewater. In the workplace, contact and airborne are by far the most likely methods of viral transmission.
It’s difficult to predict at this time what the long term impact the current guidelines on social distancing will have on office design. Occupancy densities have increased over the last 10 years or so, with desks becoming smaller and more densely packed, resulting in workers sitting closer together. Desk sharing, with different workers using the same facilities such as desks, seats, monitors and keyboards are likely to require more frequent and intense cleaning routines to sanitise workstations before a new user takes over. Occupancy density, typically 8 m2 per person, may reduce over time, and the trend to share desks may be at least partially reversed, with more desks being individually allocated to particular users.
However, social distancing will only prevail for relatively short periods in the total lifetime of an office, so good office design should allow for occupation densities to be flexible and controlled by the Building Managers, to allow temporary reductions to be enforced quickly and easily. It is recognised that in multi-let properties the responsibility for implementing these measures will generally fall to the tenants ensuring that the measures fit into and are compatible with a building-wide strategy.
So what factors need to be considered to ensure a safe building of the future? We’ve identified a number of important areas to consider.
Understandably, internal air quality is under considerable focus. The requirements for good indoor air quality (IAQ) is well established in many design standards. Indoor air quality will be impacted by both the quality and quantity of outside air introduced to the occupied space and pollutants within the space. Recommended external outside air rates in Building Regulations and BCO Guidance are based on dilution levels that will reduce pollutants to recommended levels. However, with an increased focus on occupant wellbeing in working environments there is an increasing focus of the potential benefits of increasing fresh air rates above current regulations (World Green Building Council – Health, Wellbeing and Productivity in Offices), although this needs to be reconciled with the potential increased energy consumption this could cause.
Outdoor air is not seen as a high risk source of Coronavirus viral particles and therefore very high efficiency filters in outside air ventilation plant will not materially reduce the risk of transmission, but good quality air filtration does have health benefits.
Central air handling plant is commonly provided with Pre-filters and F7 Grade bag filtration. An F7 grade filter only just meets the requirements to block the density of coronaviral particulates. WHO and NHS England identify the virus to be measuring around 0.080 to 0.16 µm and an F7 Grade filter will protect up to 80% efficient in particulate up to 0.070µm. Increasing this filtration to F9 Grade filters typically increases the filter pressure drop by 35-45% which will have a long term negative impact on energy consumption and higher maintenance costs due to more frequent replacement. Therefore, it is recommended that building ventilation systems employ a minimum of F7 Grade filtration as standard, but consider replacing filters with Grade F9 during pandemics.
HEPA filters are generally made of pleated glass fibre paper and can be more efficient at collecting bacteria down to 0.3µm. Typical applications are in clean rooms, medical applications and they are now quite common place in the domestic market against allergies. HEPA filters are typically 40-70% higher pressure drop than Grade F7 filters and will require more frequent replacement. It is not considered necessary for HEPA filters to be utilised in outside air ventilation plant, due to the levels of filtration that can be achieved with F7 and F9 Grade filtration. HEPA filters should be considered for any centralised ventilation systems that employ recirculation.
Terminal units such as fan coil units recirculate room air continuously and do not typically employ high levels of filtration, with EU 2 filtration being common. The grade of filter necessary to capture coronaviral particulates would not be viable in terminal units due to their pressure drop and there is no evidence to suggest that providing higher levels of filtration in terminal units will have any discernible impact on the transmission of viruses. However, incorporating the highest level of filtration available from the manufacturers of the terminal units is a sensible precaution and will give some comfort to occupiers.
During times of a pandemic, introducing portable room air purifiers which incorporate HEPA filters would likely offer greater benefit and would be more ‘visible’ to occupants, although these type of units can only serve a relatively small area whilst still being effective. This approach also has no long term detrimental impact on the energy consumption of the base building systems.
Typical Internal temperatures should also be maintained, although during times of a pandemic, it is suggested internal temperatures should not exceed 23 °C.
Research has concluded that the range of room relative humidity’s suitable for occupant comfort has negligible impact on the behaviour or lifespan of viral outbreaks so no changes to accepted practice is required, although low humidity’s lower than 40% should be avoided.
The separation of ventilation intake and discharge points should be in accordance with CIBSE and ASHRAE guidance which recommends 4m for standard ventilation systems, however prevailing winds can pose a risk to contamination of intake air paths. It has also been found that galvanised sheet steel can harbour nuclei for up to 3 hours in an external environment, therefore caution should be taken in evaluating the points of intake adjacent to exhaust.
Whilst a pandemic is at a peak it is necessary to prevent potentially contaminated exhaust air from re-entering the intake. It has been proven the virus cannot withstand a temperature of 60 °C for more than 30 seconds. Where the relative locations of intake and discharge gives any cause for concern, one recommendation is to fit electric or LTHW coils on points of discharge to ensure off coil temperatures of 65°C, but the need for this should be avoided by good design.