Introduction
In the UK, as specified in Section 6 of the 1992 Workplace Health, Safety and Welfare Regulations, companies have a legal obligation to ensure that workplaces have efficient ventilation and availability of fresh or purified air for the workforce1.
Chronic exposure to high levels of atmospheric carbon dioxide (CO2) can have a wide range of health effects such as inflammation, bones and kidney composition changes, respiratory acidosis as well as behavioural and physiological changes2. Normal outdoor CO2 levels range between 350-450 ppm (parts per million) and complaints of stuffiness and less comfortable breathing indoors occur when levels range between 600-1000 ppm3. General drowsiness can occur between 1000-2500 ppm and adverse health effects happen when concentrations reach 2500. Levels above 2500 can occur in certain circumstances but in general, ventilation strategies should be used to keep CO2 levels below 1000ppm which is acceptable to most humans.
Average CO2 concentrations in offices typically range from 600-1000 parts per million (ppm) but can often exceed 2000 ppm with increased room occupancies and reduced building ventilation rates impacting on employee’s wellbeing and productivity. Workforce productivity, the amount of goods or services that workers produce in a given amount of time in the workplace, in the UK is lagging behind other G7 countries. Recently, the Whole Life Performance Plus (WLP+) project provided significant findings on how worker performance declines when CO2 and temperature levels become too high4. Key findings from the study were: high CO2 levels and temperatures are rarely monitored; higher CO2 levels cause increased tiredness, slower reaction times and poor decision making and; lower CO2 concentrations can yield 60% higher work rate.
Another important finding from the WLP+ study was that in older buildings with limited building management system capability, simple monitoring of the indoor environment linked to supplementary ventilation can lower CO2 from >2000 ppm to <1000 ppm. This demonstrated that the addition of supplementary systems to office space can be more effective and less costly than upgrades to an existing system or where no system exists. Finally, both humidity and temperature extremes within an office can impact human wellbeing where relative humidity (Rh) in the range of 40 to 70% are recommended5 and an acceptable temperature for most types of work being between 16oC to 24OC with 20oC optimal for an office6.
Case study
Interestingly, most studies on indoor air quality within the workplace have been carried out within larger office space in newer builds despite a large percentage of office based staff in small offices in old buildings with only windows for ventilation. Therefore, using a portable continuous monitor, we assessed CO2, temperature and humidity in a small office environment supporting three staff in a brick 40-year old building a town centre with no building management system. The office space was 5m length x 5m width x 3m height rising to 7m at a ceiling apex. A single door to the office was left permanently open and the only other ventilation was a single ceiling Velux window. CO2, temperature and humidity were measured using an Elsys ERS CO2 Lite LoRaWAN enabled internal sensor placed centrally at desk level in the room. Data were retrieved each minute over a three week period to a ThinkAir cloud database via a Kerlink Wirnet iFemtoCell LoRaWAN gateway. Up to 3 members of staff occupied the office at desks each working day between the hours of 6.00am and 6.00pm. Maximum occupancy was generally between 9.00am and 5.00pm.
Internal CO2 levels
Hourly averaged CO2 data were analysed for a total of 15 working days during the study period CO2 levels (Figure 1). Eleven of the 15 study days showed levels to have exceeded 1000ppm during working occupancy. Times were noted by staff when the Velux roof window was opened for an hour on some days due to a feeling of ‘stuffiness’ which coincided with a drop in CO2 levels over the next hour to between 500 and 750 ppm. These times are apparent as troughs in the line graph in Figure 1. CO2 levels exceeded 1500 ppm on two working days.
Figure 1. Line graph showing hourly averaged CO2 concentration (ppm) data for the small office space over a 3 week period. Red line = CO2 levels. Grey bars show office occupied hours each day by staff.
Generally, CO2 levels peaked at around midday as the office was at full occupancy on most mornings (Figure 2). Occupancy varied during the afternoons due to work patterns and CO2 levels gradually decreased to a median value of 600 ppm by 5.00pm.
Figure 2. Boxplot showing hourly averaged CO2 concentration (ppm) data by each hour.
Peaks exceeding 1000 ppm all occurred between 9.00am and 4.00pm with the highest median level occurring at 10.00am and highest observed levels at 11.00am following full occupancy from 9.00am (Figure 3). Staff stated that they were likely to open a window around midday which aided ventilation and decreased CO2 concentration. The staff also claimed that the ‘uncomfortable’ air in the mornings led them to open the Velux window for improved ventilation.
Figure 3. Boxplot showing hourly averaged CO2 concentration (ppm) data by each hour when levels exceeded 1000 ppm.
Internal Humidity and Temperature levels
Relative humidity and temperature levels over the study period generally showed an expected inverse relationship where a lower temperature was often associated with higher humidity (Figure 4). In 9 of the working days, relative humidity fell below the acceptable lower limit value of 40% and this was pretty much sustained 7 working days of the study. During 7 of these days, the observed temperature increased to above the maximum acceptable limit of 24oC. Whereas humidity did not show an observable pattern linked to occupancy and daily working patterns, temperature often did particularly when humidity levels were low. We observed no association between increased CO2 concentration levels and humidity or temperature extremes.
Figure 4. Line graphs showing hourly averaged relative humidity (Rh) concentration (red line) and temperature (oC) data for the small office space over a 3 week period. Grey bars show office occupied hours each day by staff.
Conclusion
Our case study reveals how temporal patterns of CO2 change throughout the day in a small, 3-person office environment with no ventilation management system to aid air circulation part from a roof Velux window. Our data shows how, despite only a small number of staff occupying the office, CO2 levels can quickly increase during the first few hours of occupancy to above a recommended comfortable level of 1000 ppm. It was clear that staff were aware of the reduced air quality complaining of ‘stuffiness’ and the need to open a window. Staff also felt that the ‘uncomfortable’ air impacted on their concentration. Furthermore, humidity and temperature levels fell outside acceptable limits. Despite a short study period our data show how a small office with just 3 employees can lead to environmental conditions that exceed acceptable levels. As the WLP+ study showed4, environmental factors such as CO2 and temperature are rarely monitored. Simple monitoring of the indoor environment, as demonstrated by an IoT solution such as the low-cost and portable ThinkAir indoor monitoring system, can however empower employers and employees with data and knowledge of the air around them enabling them to rapidly adjust ventilation and working conditions.
References
2Jacobson, T.A., Kler, J.S., Hernke, M.T. et al. Direct human health risks of increased atmospheric carbon dioxide. Nat Sustain 2, 691–701 (2019). https://doi.org/10.1038/s41893-019-0323-1
3https://www.engineeringtoolbox.com/co2-comfort-level-d_1024.html
4Rajat Gupta, John O’Brien, Alastair Howard and Tom Cudmore (2018). Improving productivity in the workplace: lessons learnt and insights from the Whole Life Performance Plus project, Oxford Brookes University and LCMB Building Performance Ltd, Oxford.
5https://www.hse.gov.uk/foi/internalops/ocs/300-399/oc311_2.htm
