Engineering firm protects staff with evidence-based Covid risk-reduction strategy


BPP-TECH, the parent company of BonaCaeli, provides engineering consultancy and risk advisory services to blue chip clients in the energy, insurance, utilities, and transport sectors. BPP-Tech’s Health and Safety Officer, Mr Philip Thomas, wanted to ensure the company was taking all reasonable measures to protect office staff from Covid infection – and tasked the BonaCaeli team with conducting an AirRISK assessment at its head offices at City Tower, in the City of London.


BPP-Tech’s Health and Safety Officer wanted to ensure its office, at level 10, City Tower, in the City of London, was a safe as possible for employees. As Covid-19 is primarily transmitted by airborne particles, the risk of infection from Covid-positive people in any given venue is primarily governed by four factors: the frequency of occupation, the circulation of people, ventilation rates and local community infection rates. He, therefore, asked the BonaCaeli team to assess BPP-Tech’s offices based on those factors and to provide recommendations for reducing the risk.


BonaCaeli began by collecting all relevant data for the risk assessment. This included:

  • A plan of the BPP-Tech offices showing the location of desks and other points of interest.
  • Analysis of the typical behaviour patterns of BPP-Tech’s workers.
  • Assessment of ventilation rates and the locations of air inlets and exhausts.
  • Analysis of average user occupancy and attendance times.
  • Research into ONS data on local community infection rates.

Having collected the data, the BonaCaeli team used the Markov chain circulation model (which helps to describes a sequence of interdependent possible events) to represent user movements between the desks, kitchen/coffee area and other locations such as at printers and photocopiers. The team simulated 20,000 days based on an average 15 venue users per day to cover all possible permutations of the circulation of employees – a total of 300,000 permutations. The team repeated this analysis 25 times to test a series of risk reduction strategies.

BonaCaeli then presented the full results of its risk assessment to Phil Thomas at BPP-Tech. The analysis gave a clear picture of the company’s current risk, putting it into context with other familiar scenarios – from relatively high risks such as catching a train that is delayed by 5 minutes to low risks such as being injured when walking one mile. BonaCaeli also presented BPP-Tech with a detailed risk reduction strategy, along with a clear and fully quantified explanation of the predicted effectiveness of each recommendation.

“The AirRISK assessment has taken the guesswork out of our Covid risk strategy – enabling us to easily identify the most cost-effective ways to keep our staff safe. The analysis also really helps staff to understand for themselves the risks of coming into the office – and compare those with other common activities. And it has given us all reassurance that we’re making informed decisions in these uncertain times.” said Phil Thomas BPP-Tech’s Health and Safety Officer.


Following its assessment in July 2021, BonaCaeli summarised the risk of infection at BPP’s offices in the City of London as follows:

  • Based on the community infection rate of 500 per 100,000, a person infected with COVID-19 would be likely to enter the office on approximately 6.5% of working days.
  • For an unvaccinated employee, the risk of catching COVID during an office visit was 1 in 70.
  • For a fully vaccinated employee the risk falls to 1 in 470.
  • The risk for a fully vaccinated office user is lower than that of injury from playing tennis for two hours or horse riding for one hour, but significantly higher than that from cycling for 10 miles or driving for 100 miles.
  • These figures will vary as the community infection rates varies from week to week. Graphs provided with the AirRISK assessment show how these risks change.

BonaCaeli’s chief recommendations were:

  1. Reduce the occupancy rate of hotspot areas, including the coffee machine, the kitchen, and colleague’s desks, by encouraging staff to maintain social distancing and to replace face-to-face conversations at each other’s desks with Teams chats as often as possible.
  2. Increase the air exchange rate (both replacement and recirculation) as much as possible. According to the analysis, doubling of the air exchange rate would reduce virus transmission risk by 10%.
  3. Introduce occupancy limits at peak times by encouraging employees to work from home where possible. The analysis showed limiting occupancy to 50% of pre-pandemic occupancy levels would reduce transmission by 47%.
  4. Install a viral inactivation device such as the BonaCaeli AirVSAFE 2000 in the general open plan office area. The analysis showed that this could reduce the transmission rate by more than 99%
  5. Monitor ONS data on local community infection rates weekly to track infection risks levels.
  6. Request staff to take a weekly lateral flow COVID-19 test and, self-isolate if positive. This precaution alone would reduce the risk of infection by 29%.
  7. Staff should get fully vaccinated as soon as they have the opportunity – reducing individual risk from around 1.4% to 0.2% (or from 1 in 70 to 1 in 470).


  • BPP-Tech now fully understands the risk to employees of infection from Covid in its offices, and how these vary with local community infection rates. More importantly, the employees themselves understood the basis of this science-led analysis and its results.
  • The company and its employees understand what the main risk factors are and have a clear, evidence-based strategy to mitigate them.
  • A detailed breakdown of the analysis enables BPP-Tech to identify which strategies will be most cost-effective in reducing virus transmission.
  • Employees are more confident coming into the office, knowing what the risks are and that BPP-Tech has taken all reasonable measures to reduce them.
  • BPP-Tech can continue to operate productively, with minimal disruption from Covid.


BonaCaeli’s AirRISK assessment gave BPP-Tech and its employees a clear understanding of the risk of infection from Covid in its offices, along with an evidence-based risk reduction strategy. The breakdown of the benefits of each reduction strategy enabled BPP-Tech and its employees to determine how best to direct their efforts to reduce the risk. The clear understanding of the risk involved reassured staff and enabled BPP-Tech’s Health and Safety Manager to make informed decisions on remote working.