There has been a wealth of scientific evidence worldwide that confirms the current SARS-2 Coronavirus that causes Covid-19, primarily infects by airborne transmission.

This infection route should not come as a surprise, given that other deadly coronaviruses, SARS, and MERS, were airborne too. The world’s leading institution in disease control and prevention, the CDC in the USA, has finally begun to recognise the evidence and align with other institutions and governments worldwide.

We know that people infected with Covid-19 are the source of the viral hazard to others. From the moment they exhale breath, talk, sing or shout, tiny particles in their breath are emitted into the air. 

Some bigger particles (droplets) may fall to the ground quickly but not always, and the smallest particles (aerosols) usually remain airborne for a few hours. They can travel several metres, especially inside due to air currents. If ventilation is inadequate, the risk of infection is accelerated. 

Other risk accelerators occur when many people use the same space indoors, or there is a risk of overcrowding. Environmental conditions have an effect too, such as working inside chilled food factories. 

However, it is important to note that ventilation, alone, is not the “silver bullet”. Indeed, some types of ventilation can make infection risks even worse, so we need to consider what ventilation can do to suppress or accelerate the spread of Covid-19.

What have we learnt about how Covid-19 spreads?

Numerous “super-spreader” events worldwide have confirmed the airborne transmission route. 

One such event was the incident on The Diamond Princess cruise ship in 2020 and, in early 2021, the Perth Sheraton “Quarantine Hotel” incident.   

The former had – what one would classify pre-Covid – an excellent fresh air ventilation system. In terms of management processes, people were confined to cabins when Covid infection broke and yet, several hundred more still contracted Covid-19. Infection rates accelerated and sending passengers to their rooms proved ineffective. 

So, what went wrong? 

A large percentage of the ship’s ventilation was recirculated air, extracted from inside rooms and cabins via ceiling grills, collected into the ventilation ducts and then, re-distributed again via the shared ship’s ventilation system.

The incident in February 2021 at The Sheraton Hotel in Perth, Western Australia – a “quarantine hotel” – is perhaps the most worrying infection event yet.

A traveller isolating in his hotel room was a Covid infected individual, whose isolation room was approximately three metres from guard working security. In a matter of days, the guard had become infected., Yet there was no physical contact between them, the infected person was locked in their room, the guard was wearing a mask and he had also followed procedure.

Investigators confirmed that despite the hotel being equipped with an air ventilation system, and government guidance being followed, the infection had still been able to spread.

The virus escaped the room because drafts can occur below doors. The hotel room door also had to open occasionally to allow food and drink to be passed to the quarantined traveller. The infected air also escaped into the corridor air space.

Interior air currents arise from ventilation systems and, naturally, from occupants’ body heat, light bulbs, and the atmospheric pressure differences between interior spaces. We should also be aware of inside to outside pressure differentials that are commonplace, such as when we hear doors slamming at the other end of the house.

Our buildings’ air or transport modes are not static. Air moves, and so do particles within those numerous air streams indoors, including those air currents that are potentially carrying coronavirus from infected people.    

What does this mean for indoor transmission risk?

We spoke to experts at PPL-Biosafety, which is made up of chartered engineers, professional scientists, and medics. The team at PPL-Biosafety has come together to help in the fight against the virus by looking at how pathogens travel. 

Dr Rhys Thomas, Chief Medical Officer, confirmed that research data varies on the airborne transmission of coronavirus.

“It is sensible to get a balanced view and not get overly hung up on the percentages, nor on splitting them down or being too quantitative,” says Dr Thomas.

“It is reasonable to look at an 80:20 rule when considering how coronavirus travels, with air transmission accounting for 80 per cent of transmission risk, and surface transmission making up the remaining 20 per cent.

“Non-vaccine interventions such as checking your temperature as you walk into your workplace are still helpful, to a degree. Similarly, Lateral Flow testing is beneficial. 

“However, some of the newer variants are not picked up on the Lateral Flow tests so their effectiveness may decrease in future.

“We also shouldn’t ignore the importance of that 20 per cent for surface transmission of the virus. It is crucial to keep surfaces clean, hands clean and to comply with the government’s guidance. It is all about applying layers of risk management.”

However, even when complying with the two-metre rule, there is still a risk of infection from airborne particles, says Dr Thomas. 

“Most of the guidance on the two-metre rule is inadequate, because exhaled breath can swiftly become airborne, travelling much further than the arbitrary guidance of two-metres.

“In fact, the guidance on social distancing was established as a result of what was learnt about human airborne illnesses in 1934; surely in 2021 we can do better than that?”

The new normal

The UK economy is once again opening in the wake of the latest lockdown, but Professor Chris Whitty is warning that we will see Covid cases rise again. 

Despite the tremendous success of the vaccines, at a No. 10 briefing with the Prime Minister on 5th April 2021, Professor Whitty said: “I don’t think that it’s any surprise that it is still with us now, nor is this going to magically disappear over the next few months. This virus will be with us for the foreseeable future.”

Research has confirmed that wearing a good quality mask helps to reduce the spread of Covid, however the mask-wearer does not benefit from significantly reduced risk. Current guidance states that in most spaces if we are sitting down at a desk or table other than on public transport, it is okay not to wear a mask. 

However, PPL warns against this advice and advises that other engineered infection mitigations are in place.

Dr Thomas explains the magnitude of this risk: “As soon as the air currents in a room or building take hold of the bigger and smaller particles from an infected person’s breath, there is a largely uncontrolled hazard moving around in the air we share in that room.- just like the Perth and Diamond Princess incidents.” 

So, where does that leave us if the virus can be transported at random through the air?

PPL’s Chief Technical Officer, Paul Waldeck, a chartered engineer with a career in safety critical environments, echoed Dr Thomas’ position.

“We can simplify the jargon and think about the practical basics of what we are dealing with so that we can destroy this virus or remove its route to infecting us in the first place,” says Paul.

“We have the hazard; coronavirus and its source (infected). We know its pathway; air and surfaces (the 80:20 rule), and we know its target – humanity.

“In simple terms, if we remove any one of these three fundamentals, there is no risk of getting ill from Covid. We can destroy the hazard and its pathway at the same time by using hand sanitiser. 

“The bleaching and cleaning of surfaces is cheap and easy for surface contamination; chemical fumigation and ozone will work for air contamination but are very costly and present serious health risks, in themselves.

“Filters in buildings, ships and trains are pretty much a waste of time against small bacteria or viruses, unless they are medical grade filters, known as HEPA. (Even HEPA will not work entirely effective against the virus that causes Covid-19). 

“When dealing with one of nature’s hazards, we should also look to nature to help us intervene against it. We at PPL focus on the power of nature’s two most potent elements – air and light.”

Air 

Our first line of attack against this airborne virus must be improving the ventilation for each room in a building to enable us to take control of its movements via those interior air currents. 

“Introducing more fresh air into the building will dilute the risk but does not necessarily remove the virus unless we can get the air extracted,” Paul continues. 

“Previous Tuberculosis and SARS infections were suppressed at a level of ten air changes per hour (ACH). Opening windows will help with dilution and so reduce risk to a modest degree, but unless one can get many ACH’s, approaching the 10+ air changes per hour, the risk is still there. Indeed, some spaces may need to be higher than that, depending on the risk. Some experts would recommend 20+ ACH on the underground, for example, to better suppress the risk of infection. 

 “Operating theatres should be at least 16 ACH’s per hour, and these have worked pretty well through this Covid-19 pandemic, but general hospital wards, corridors and toilets and other spaces sub-10 ACH, have not.” 

“Existing buildings were not designed to be biosafe, so inadequate ventilation will prevail in most buildings, unable to combat this new viral hazard. One may consider an upgrade to the HVAC system, if one exists, and upgrade filtration, which will also perversely decrease air-flow rates because the higher-grade filters are far more restrictive to the air passing. 

“The level of filtration, flow rate, plant and power needed to mitigate Covid in buildings by relying on HVAC systems will be cost-prohibitive and impractical in most cases. We need to look at what can be optimised and add supplementary mitigations.”

“The other issue is that air distribution in buildings can be pretty inconsistent, and often, even in well-designed systems, there can be dead air zones. So, as the Perth Quarantine Hotel incident confirms, unless one considers quite specialist building physics and fluid dynamics modelling to prove good distribution, and air flows, there are risks.”  

Light

One solution, says Paul, is to install Germicidal Ultraviolet Filters into the existing building ventilation systems. Either in HVAC, if a system exists, and/or as fan assisted-ceiling or wall-mounted UVGI air disinfection devices. 

“Short-wavelength Ultraviolet light (UV-C) is germicidal at specific wavelengths and is commonly known as UVGI,” Paul continues. 

“Using this is one of the most potent interventions that one can undertake to inactivate any microbe. When designed, engineered, specified, and deployed correctly for air infection interventions, it is perfectly safe for people to go about their day at the same time.” 

Dr Thomas adds: “UVGI destroys all known bacteria and viruses because it re-configures the RNA and DNA proteins of microbes, rendering them utterly inactive in milliseconds. 

“Coronavirus is a straightforward, simple, single-strand RNA virus, and it doesn’t take very much UV light energy or exposure time to destroy it. The coronavirus is deadly and has taken over the world, but it does have this irresistible Achilles Heel that it cannot fight.”

UVGI filters have been extensively deployed in high microbial hazard settings for almost a century. 

Finsen won the Nobel Prize for Medicine in 1908 for his use of UV against tuberculosis. Now, this lifesaving “old-tech” is essential to protect more conventional occupied spaces which, because of Covid-19, are all potentially bio-hazardous.

The tech has moved on over the century and now has almost limitless applications to deal with this latest Coronavirus biohazard. Today’s UVGI devices are specified to ensure negligible impact on air flow, are safe, chemical-free, low energy, low maintenance (anti-static coating) and are relatively low cost to buy. 

Local source control

 Paul also advises that a risk-managed and layered approach is necessary.

“We need the total building ventilation infection risk mitigation but also a second intervention, which is a local source control approach where we treat each area as a single environment,” he says. 

“At PPL-Biosafety, we can advise upon and engineer many types of mitigation solutions depending on the primary ventilation system and the particular spaces’ occupancy, temperature, humidity, and many other factors. 

“The local higher risk environments, once identified, can often be protected best with a range of UVGI upper room air disinfection devices. The more significant infection intervention devices are fan assisted units, and we can deploy these for industrial scales. These UVGI devices are so powerful that they have been proven to sterilise the air, not just in the laboratories but also in real-life applications such as meat processing facilities. 

 “As part of the targeted local infection mitigation approach, one also has to consider air distribution and potential pathways from a given hazard source, which is primarily dictated by the direction of air currents. 

“For complex or higher risk spaces a specialist engineering methodology called computational fluid dynamics (CFD) may be needed to model air flows and currents.

“In most cases though, it’s usually fairly obvious to professional engineers; the industry has a huge part to play in beating Covid-19 because it can deploy know-how on ventilation systems along with UVGI technology to remove the hazard and, indeed, destroy the virus before it gets the chance to infect and harm people.”

Conclusion

These two approaches of the whole building and local space infection intervention, when layered together, create this new level of biosafety infrastructure that is essential to protect people adequately against Covid-19.

Still, such bio-risk solutions should always be applied with good management practices, not instead of them. 

The HSE has confirmed they will be enforcing their new Covid-secure workplace standards, which have been updated to reflect better ventilation and the use of mitigations in lieu, such as UVGI.

Paul concludes: “While the guidance given by the HSE is right, the issue is the lack of definition on what good ventilation actually means. 

“There are plenty of sources around the world to assemble a viable specification for different types of spaces, but one needs to know where to look and then apply that specification correctly. It would be of great benefit to society if the leading Institutions could set that best practice down much more definitively.”

Chancellor Rishi Sunak announced his “super-deductions scheme” at the March 2021 Budget, meaning that most ventilation improvements and UVGI technologies are eligible as integral features. 

Under the new rules for annual capital allowances, businesses can claim 130% of the cost back with no limit, meaning these sorts of biosafety interventions to make businesses safer and more resilient and ready for the future, are eventually free. 

The government has effectively introduced a “stick and carrot” dynamic here, placing the onus on businesses to future-proof and make their premises safer.

ENDS

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