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Building use: measures to reduce disease transmission

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.

Ultra Violet Irradiation

It has been known for a considerable time that providing Ultraviolet Germicidal Irradiation, (often referred to as UVC), in centralised HVAC systems has the potential to deliver benefits in improved health & wellbeing, together with energy savings from improved heat transference in the heating and cooling coils. Physical trials have been undertaken in some hospital installations but this technology has not gained popularity in commercial installations to-date.

Other potential benefits of introducing UVC are:

  • Destroys mould and bio-film on coil surfaces
  • Destroys 99% of viruses and bacteria passing through the coil
  • Reduction in staff absence levels and improvement of patient care
  • Eliminates cooling coil maintenance, saving labour and associated material costs
  • Non-mechanical duct cleaning – Reduces mould in ducts, by destroying the food source
  • Increases the life of the coil by removing invasive cleaning methods
  • Extends the life of high performance (HEPA) filters downstream of the UVC

There are also examples where UVC light is being used to disinfect surfaces directly. In China, whole buses are being lit up by the blue UVC light each night, while UVC-emitting robots have been cleaning floors in hospitals. Banks have even been using the UVC light to disinfect their money.

However, these are specific applications being done under controlled conditions, so this direct application of UVC is not considered appropriate for use in commercial office applications.

However, the use of UVC in centralised air handling equipment, where the process can be better controlled, is likely to gain popularity in the future. Further research into the true benefits, cost and maintenance is required before this technology would be recommended for common use in commercial buildings, but the potential is worthy of further consideration.

Retro-fitting into existing installations will be subject to physical space limitations, equipment configurations and characteristics.  It should be noted that UV lamps generally have a rated life of circa 9,000 hours and therefore will require changing annually assuming constant operation.  The efficacy of the lamps is known to be affected by temperature, humidity and air flow and deterioration of light output over time can be quite rapid.  UV light will degrade plastics and similar materials and therefore could lead to the early breakdown of AHU and filter media components, glues, seals, gaskets etc. if these products have not been originally designed with the use of UV light in mind.


We are aware of suggestions that greater use of PAPA (Positive Air Pressure Attenuator) devices should be considered in drainage systems to mitigate the effects of positive air fluctuations in the drainage pipework system. Whilst such devices may have a useful application in specific instances, (such as high rise buildings) there is no evidence to suggest that increased usage will provide any tangible benefits in reducing the risk of Faecal transmission.

We are also aware there has been suggestions that waterless traps, commonly referred to as HepvO traps, which don’t rely on water to create a seal should be utilised, as traditional water traps can sometimes lose their seal due to evaporation, siphonage, leaking or movement. There is no evidence to suggest that increased usage will provide any tangible benefits in reducing the risk of faecal transmission so general good design and correct installation of P-traps are still considered the preferred solution and require less ongoing maintenance than waterless traps. Waterless traps may continue to be considered for very intermittently occupied areas.

Low energy hand dryers have become commonplace in recent years. Some sources are suggesting the air movement created could increase the spread of airborne contaminated droplets and are promoting a return to paper towels, ignoring the long term environmental impacts of paper use. There is no research or evidence as yet to determine the impact that hand dryers have, so this should be kept under review, but we do not anticipate a move away from hand dryers at the current time. The use of paper towels could be considered during the times of a pandemic only.

This document acknowledges the current advice provided by;

  • The World Health Organisation (WHO)
  • Imperial College London COVID-19 Infection modelling
  • Oxford University COVID-19 Behavioural Analysis
  • COVID-19 Guidance (REHVA – Federation of European Heating, Ventilating and Air Conditioning Systems, 2020)
  • British Council for Offices (BCO) Thoughts on Office design and operation after Covid-19
  • CIBSE TM40 COVID-19 Guidance Update
  • CIBSE Guidance documents, Covid Ventilation Guidance_v09.1, Recommissioning of Lifts and Escalators Post Lockdown, Emerging from Lockdown_ver1
  • HM Government advice – Working Safely during Covid-19 in Offices and Contact Centres
  • Scientific research into the airborne transmittal of COVID-19 and similar COVID related viruses

For more detail please contact Nigel Clark,


This document is based on the best available evidence and knowledge of dealing with general viral infection outbreaks. The authors exclude any liability for any direct, indirect or incidental damages or any other damages resulting from, or be connected with, the use of the information presented in this document. Specific advice should always be sought from an appropriately qualified professional for individual cases.



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