How air hygiene can protect schools and workplaces from COVID-19

The COVID-19 pandemic almost overnight changed the working practices of millions of people around the world. For many people with office jobs, working from home has become routine, while those who have continued in their workplace have had to follow new working practices and procedures aimed at preventing the transmission of infection.

Everyone returning to offices, schools, universities and public areas such as hotels, restaurants and shops will be nervous about becoming infected when they come into closer contact with other people in public areas.

Keeping a minimum distance apart, however, is not enough to prevent contaminated respiratory particles transferring from infected people to others. There is now overwhelming evidence that infection by airborne particles is more important than was thought at the beginning of the pandemic. Research on aerosols has shown that respiratory particles can travel farther and remain airborne for much longer than previously thought.

This means air hygiene is a crucial factor in protecting people indoors and should be included in the package of measures businesses take to prevent transmission of COVID-19 – air, surface and hand hygiene. This includes ensuring there is adequate ventilation and the use of air purifiers with HEPA filters.

It is also important for employees’ wellbeing to see that their air quality is being improved. In an international survey of office workers commissioned by Rentokil Initial in March 2020, over two-thirds of survey respondents said they would feel cared for by their employer if indoor air quality was being monitored or regulated.

How airborne particles can spread disease

Respiratory infections such as COVID-19 and tuberculosis are mainly transmitted by virus-containing respiratory particles. These have often been classified by researchers into droplets (>5–15μm) and aerosols (<5–15μm) – arbitrary and overlapping classifications used to differentiate particles that quickly fall to the ground and the lighter ones that can float in the air for long periods.

The majority of droplets fall out of the air in seconds within 1–2m from the infected person. They are sprayed like tiny pellets onto surfaces and people. Guidelines from WHO and governments still recommend keeping these distances in places where people interact and that social distancing, surface and hand hygiene are required to help prevent cross-contamination from these larger droplets.

The recommendations for social distancing, however, are based on a 1930s model of droplet transmission and the distance the droplets travel. Scientists who study and model gas clouds have shown that a large proportion of the transmission of COVID-19 is caused by airborne transmission via aerosols. Particles in a continuum of sizes are exhaled from infected people during breathing, talking, coughing, sneezing, singing and shouting.

The traditional size classifications are now known to be erroneous. Particles up to 100μm can remain suspended in the air for hours and be inhaled, which makes this size a better distinction between droplets and aerosols. The smaller particles (<10μm) can be inhaled deep into the lungs.

Both the droplets (>100 μm) and aerosol particles are composed of mucus and saliva made airborne by the air passing over infected tissues throughout the respiratory system, from the inner lungs up to the nose and mouth. Virus particles are carried in these droplets and aerosol particles.

A study of the stability of SARS-CoV-2 virus particles in aerosols found that they remain viable for several hours. This makes it essential that businesses consider this means of transmission when implementing safety measures in their workplace. But how can businesses offer their staff protection from the lighter aerosols that are floating in the air and can build up in a room with poor ventilation?

How turbulent gas clouds can transmit viruses over long distances

The social distancing guidelines also don’t consider the physics of aerosols that are exhaled as turbulent gas clouds and have a complex behaviour. A gas cloud traps and carries with it clusters of droplets and aerosol particles with a continuum of sizes. The warm and moist conditions in the cloud, together with the turbulence, allow the droplets of all sizes to remain airborne for longer and travel several metres farther (7–8m) than the social distancing guidelines.

A proportion fall out as the cloud travels, while others shrink as they evaporate and can float in the air for hours, following the air flow in the room. The faster and more turbulent the cloud – such as from a cough or sneeze – the farther all the particles travel.

In many work environments, there’s no way to bring in fresh air, so the most practical way for businesses to remove aerosols from the air is with air purification using filters.

Indoor transmission of COVID-19

Aside from the scientific basis for viral transmission, there are real-life examples that demonstrate the critical part airflow and aerosols play in air hygiene. A study of infections in China found several people were infected by airborne transmission while in a restaurant.

An infected person sitting at a table in a room infected five other people on two adjacent tables. The three tables were at one end of the room in the air flow from an air conditioning unit on the wall. None of the customers at tables in the other part of the room in different air flows, nor restaurant staff, was infected.

A follow-up study that measured dispersion of tracer gas in the same part of the restaurant and made computer simulations of the spread of aerosols, concluded that the infection was “consistent with a spread pattern of virus-laden aerosols”.

There have been numerous mass-spreading events in choir practices, care homes, funerals, gym classes, family gatherings, restaurants, bus, airplanes and even a quarantine hotel, where infection can only be explained by airborne transmission.

This means air hygiene in spaces where people are together for long periods is an essential component of air safety measures in indoor spaces such as offices, shops, restaurants, classrooms and public transport.

People are looking for reassurances that it is safe to return to an enclosed environment for long periods. Employers should, therefore, make sure their indoor air quality (IAQ) is hygienic and of a high standard to prevent transmission of airborne infections via aerosols and respiratory droplets to maintain people’s health and wellbeing.

Strategies for improving air quality

The WELL Building Standard from the International WELL Building Institute provides several strategies for facilities managers to improve health and wellbeing in buildings by planning infection prevention, preparedness, resilience and recovery. The primary factors for infection prevention are good cleaning protocols, supporting and promoting hand hygiene and improving air quality by providing adequate ventilation and filtration.

The strategy for air quality includes the following measures.

• Ventilation: Bring in fresh air from outdoors to dilute human and product-generated air pollutants. Provide demand-control ventilation, displacement ventilation and advanced air distribution
• Air filtration: Implement a suitable air filtration system and maintain filters properly
• Openable windows: Provide windows that can open and encourage staff to open them when outdoor air quality is acceptable
• Microbe and mould control: Treat the air with ultraviolet light to kill microorganisms
• Moisture management: Limit moisture accumulation and mould growth by preventing water infiltration and condensation by using suitable design strategies
• Humidity control: Maintain humidity at levels that limit the growth of pathogens and are conducive to health and wellbeing

The strategies listed above for improving air quality are largely influenced by building design and maintenance. Many modern buildings don’t have windows that can open or they’re kept shut to maintain temperature and humidity. HVAC systems are not effective at filtering pollution generated in the indoor environment. Therefore a filtered HVAC system combined with air purifiers placed in the room can be the most practical solution for businesses to ensure air hygiene.

ASHRAE (the American Society of Heating, Refrigerating and Air-Conditioning Engineers) recommend air filters are MERV 13 and the CDC recommend the more efficient HEPA filters for air filtration and in portable air cleaners to remove infectious particles. The capacity of the filtration system also has to be adequate for the room size, which is to be able to achieve 5 or more total air changes per hour (ACH).

Why air hygiene matters

As the spread of COVID-19 begins with infected respiratory particles, filtering pathogens from the air will be seen by employers and staff as a reassuring and necessary first step to prevent infection, reduce ill-health and absenteeism and keep them safe at work.

Indoor air quality (IAQ) can be quickly improved by installing mobile air purifier devices in the workplace. These can be placed in strategic positions in a wide range of indoor spaces in offices, schools, hotels, care homes and healthcare institutions to yield optimal results for cleaner ‘local’ air. They’re also a visual and reassuring indicator for staff that their employer considers air quality important for their protection while providing peace of mind from the monitoring and display of the IAQ around them.

The air purification devices not only provide businesses with a flexible option for filtering over 99.95% of harmful airborne particulates, including aerosols contaminated with bacteria and viruses from people’s respiratory systems. HEPA 13 and carbon filters also capture gaseous pollutants, mould spores, allergens, smoke particles and VOCs.

In choosing an air purifier for the work environment, there are five critical issues that businesses should consider.

•       How efficient are the devices’ filters?
•       Does it have a high clean air delivery rate (CADR)?
•       Is there an option for a service to maintain the filters safely?
•       Is it cost-effective?

A badly maintained filter can cause additional health problems, so it’s important to choose an air purifier carefully. You can find out more about the dangers of poor air quality and how to maintain air hygiene in the workplace during the COVID-19 crisis in our whitepaper or by talking to us today.

Read more about air purifiers in our blog: What you need to know about air purifiers to help protect yourself from airborne diseases.