In our previous article, we have looked at how buildings can support the fight against Covid-19 and future pandemics. In this article, we are taking a closer look at how we can measure whether an office is safe to occupy with respect to infection risk for Covid-19.
The Covid-19 restrictions will get partially or fully lifted as vaccination rates increase in Kuala Lumpur and in other population centers. This will require the Standard Operating Procedures (SOPs) concerning maximum workplace occupancy to be adjusted for offices, manufacturing etc. A similar “return to normal” is observed around the region where high vaccination rates are found. However, according to The Economists, Global Normalcy Index, the office usage for Malaysia is still well below the global average with a score of around 65 out of 100, where 100 represents the pre-pandemic levels of activity. In contrast, Singapore is currently around the global average with a score of around 85/100.
The Economist, Global Normalcy Index, Office Usage - Average, Malaysia and Singapore
The new normal and increased office occupancy will undoubtedly make people ask the question: Is it safe to go back to the office? And, how can we measure the virus infection risk in the space? Questions that real-time building operational and measured data can help to answer.
Standards and certification programs, such as The RESET Air standard, a sensor-based and performance-driven indoor air quality building standard and certification scheme, has the goal of standardising indoor air quality data and setting daily targets for the IAQ performance of a space. The standard provides owners and operators with transparency and the ability to provide public awareness about the current performance of the Indoor Air Quality. In addition to the conventional measurements of Relative Humidity and Temperature are TVOC, CO2 and PM2.5 used to calculate daily averages, which are compared against the international health standard thresholds for occupational health and reflected in the RESET Air Index. 
A new index from RESET draws on these same measurements (excluding TVOC) to give a risk assessment of virus infection potentials. This new index is called RESET Viral Index.
RESET Viral Index
The RESET Viral Index will be able to indicate the Viral Infection Potential. The index will provide occupants and operators with an understanding of how likely airborne virus infections are at the current moment within the space on a scale from 0 - 100%. A high score close to 100% means that the risk of viral infection is high, and vice versa.
RESET Viral Index (Illustration by RESET)
The index uses real-time operational measured data for Relative Humidity, Temperature, PM2.5 and CO2. Scientific papers have been referenced to estimate the relationship between the measured data and three key parameters, namely the Virus Health (survivability), Immune System Health and Dosage as quantity over time to calculate the viral infection potential. Based on the latest research, RESET has developed the following formula to predict the infection potential:
RESET Viral Index equation
The Virus Health is estimated from the Temperature and Relative Humidity measurements. RESET is estimating the Virus Health index from previous studies, which have found how healthy a virus is based on the surrounding environmental conditions of temperature and relative humidity. A value of 0 - 1 represents a 0 - 100% healthy virus.
RESET Viral Index, Virus Survivability
Immune System Health is likewise estimated from previous studies and the relationship between measured Temperature, Relative Humidity and PM2.5. A value of 0 - 1 represents a 0 - 100% healthy immune system.
RESET Viral Index, Immune System Health
Dosage uses CO2, occupancy and air changes to estimate the viral load within the space. A value of 0 - 1 represents a 0 - 100% minimum infective dose.
RESET Viral Index, Infection Potential
The relationship between the three variables is given by the equation. As seen, too low temperatures and relative humidity will affect the immune system health, weakening the occupant's immune system and therefore increasing the overall infection potential. Similarly, high virus survivability can increase the infection potential. Areas with high concentrations of outdoor air pollution can also see an increased infection potential, if the air filtration is not sufficient, as the immune system health will be affected by the increased PM2.5 concentrations.
Animation by IEN Consultants, information and data shown in the animation from RESET, presentation on The Viral Index: RESET Index - Open Webinar on August 20th (2020).
The RESET Viral Index will therefore become a useful tool to indicate the overall virus infection potential within a space. However, as the RESET Viral Index algorithm is not publicly available yet, we will have to look for other sources to gain an understanding of the measures which can be considered when evaluating whether an office is safely occupied.
While we wait for the Viral Index to Become public
Multiple organisations and agencies, including the World Health Organisation (WHO), have come with recommendations and measures to be considered concerning Covid and ventilation. The WHO released their guidelines on indoor ventilation (WHO Roadmap to improve and ensure good indoor ventilation in the context of COVID-19) back in March 2021. The document provides a step by step guide to both natural ventilated and mechanical ventilated spaces for non-residential and residential buildings as well as healthcare facilities.
The guideline recommends a minimum ventilation rate of 10L/s*person referencing the EN 16798-1 standard (Category I, non-adapted person l/s with an occupancy of 10m2/person). This requirement is slightly higher than the outdoor air requirements found in ASHRAE 62.1, which is commonly used in this region. ASHRAE 62.1 gives a combined outdoor air rate per person of 8.5 for offices with a default occupancy density of 20m2/person. With a lower occupancy density (typically around 10m2, pre-covid and as per EN 16798-1, adapted persons), the provided outdoor air will only be around 55% of the recommended 10L/s*person. Hence, the occupancy needs to be reduced by around half, unless the outdoor air (OA) provided by the HVAC system can be increased as shown for the graphs with 30% and 60% increased OA. The graph below shows the relationship between the occupancy and the provided outdoor air calculated according to ASHRAE 62.1.
Graph showing the relationship between calculated outdoor air vs occupancy density. The ASHRAE calculated outdoor air is based on per person plus area. The EN 16798 graphs are based on 10l/s /person, as this is the recommended value given in the WHO - Roadmap to improve and ensure good indoor ventilation in the context of COVID-19.
Here is a checklist of items to keep in view, when evaluating if a space is safely occupied:
Occupancy Density: Identify the outdoor air volume supplied to the space, designed or actual measured. Divide this number by 10l/s /person to get the recommended occupancy density.
Relative Humidity: Keep the RH between 50% to 70% to ensure occupants immune system health.
Dry Bulb Temperature: Keep the temperature between 23͒C to 26͒C to ensure occupant thermal comfort and immune system health.
Filters: Install ePM1 70% (MERV 14 / F8) or higher grade air filters
Exhaust: Run the exhaust fans continuously to ensure a negative pressure within the space/building.
Air Purifier: Additional portable air cleaners/purifiers can be considered if the provided outdoor air volume is less than required or further improvements of the air quality are desired.
Check our previous article, for a general introduction to the subject: How Buildings can Support the Fight against Covid-19 & Future Pandemics.
1. The Economist. The global normalcy index. [online]. [Accessed 20 October 2021]. Available at: https://www.economist.com/graphic-detail/tracking-the-return-to-normalcy-after-covid-19
2. RESET. RESET Air. [online]. [Accessed 20 October 2021]. Available at: https://reset.build/standard/air
3. RESET. RESET Viral Index. [online]. [Accessed 20 October 2021]. Available at: https://reset.build/resources/indexes/viral
4. RESET. 2020. RESET Index - Open Webinar on August 20th. [Online]. [Accessed 20 October 2021]. Available at: https://www.youtube.com/watch?v=u2rNX2T2Hew
5. World Health Organization. Roadmap to improve and ensure good indoor ventilation in the context of COVID-19. [online]. [Accessed 20 October 2021]. Available at: https://www.who.int/publications/i/item/9789240021280x