Mater research puts masks in sharp focus

Image Credit: Sinéad Mohan

Aela O’Flynn explores the impact of new research from the Mater Hospital highlighting the importance of face masks in our defence against COVID-19

They may steam up your glasses and give you "mask-ne", but face coverings are one of the most powerful tools in our anti-COVID arsenal. New images from a UCD research collaboration with the Mater Hospital have provided powerful visual proof of the effectiveness of face masks against COVID-19. The more we learn about face masks, the more important they become in our defence against the virus. International health governance is increasingly adamant about the need for universal use of face masks. The WHO states that "masks are a key measure to suppress transmission and save lives" and should be used in combination with physical distancing, avoidance of crowded or enclosed settings, maximisation of ventilation, hand washing, and respiratory etiquette. CDC Director, Dr. Robert R Redfield, similarly says, "cloth face coverings are one of the most powerful weapons we have to slow and stop the spread of the virus".

Dr. Kevin Nolan of the UCD School of Mechanical and Materials Engineering and Professor Ronan Cahill of the UCD School of Medicine and the Mater Hospital have collaborated to demonstrate the speed and distance of COVID-19 droplets in the air, and how they are affected by face masks, using Schlieren imaging. Schlieren is a "flow visualisation technique" that uses a high-speed camera to record and photograph the flow of gas through the air, with SARS-CoV-2 droplets affecting the flow of gas in this case. Smaller droplets are difficult to visualise with Schlieren alone, so it was paired with laser scattering to improve the resolution and widen the field of view.

Droplet airflow was initially recorded when breathing and coughing without any form of face covering. Dr Nolan explains that droplet speed from normal exhalation and coughing can range from 1 to 5 m/s. Smaller droplets "follow this airflow faithfully", while larger droplets "rapidly slow and fall to the ground". Smaller droplets and aerosols can therefore remain suspended in the air for up to an hour.

Droplet air flow was then recorded when breathing or coughing while wearing a visor, a surgical mask, and a cloth face covering. Surgical masks, when worn correctly, greatly reduce the speed and distance of droplet flow from the nose and mouth. Cloth coverings are similarly effective. Visors, however, are "of limited use in isolation", but Dr Nolan says they can "protect from direct spray in conjunction with a mask". 

There has been concern expressed on how a seemingly insubstantial piece of cloth can protect us, or anyone else from a virus. Fluid mechanics and Schlieren here have shown that face coverings limit the speed and distance that SARS-CoV-2 particles can travel through the air, and thus limit their infectious potential. COVID-19 is particularly dangerous because it has an extremely efficient person-to-person transmission. If droplets, as the primary source of transmission, can be diminished, we then begin to control the spread of infection.

The primary intention of this research was to investigate aerosol generation in keyhole surgery and other procedures. Dr Nolan says "surgeons have known for some time of the dangers that CO2 and smoke leaks present, but the SARS-CoV2 pandemic has brought these risks into sharp focus". "Aerosol-generating events" in COVID-positive patients can be extremely dangerous for exposed hospital staff. A prime example is high flow nasal oxygen therapy which is as an intervention is "very beneficial for treatment of critical Covid patients", but generates a huge volume of aerosols. Additional precautions must therefore be put in place to protect healthcare workers involved in this procedure.

As infections began to rise again in August, the research team saw an opportunity to use Schlieren to demonstrate the "invisible threat" of COVID-19 aerosols. "I wanted to show people what is hidden there, not to fear-monger but to educate and inform" says Dr Nolan. While the efficacy of face masks was well documented prior to this project, Schlieren is different because it is "entirely passive" and "simply sees the air you breathe in real-time" without the need for additional influences, such as dye or smoke.

Schlieren imaging has been around since the 1850s, but this novel use of the technique has generated highly practical outputs. First, it has identified important aerosol-generating events, the risk that they pose in healthcare, and the need for additional protective measures with these procedures. Secondly, it has demonstrated that the transmission of COVID-19 droplets can be diminished by face masks, thus highlighting their importance. Finally, this research has endorsed the power of physician-physicist/engineer collaboration in a medical context. This has been recognised by the European Commission who have provided further funding to the team, part of which, Dr Nolan explains, will be used "to develop a new type of Schlieren system that can be easily deployed and have a much larger field of view." This will not be the last we hear of Schlieren in medicine and healthcare.

So what can we do to protect ourselves and those around us? Environment is an important consideration, and Dr Nolan recommends that we "avoid enclosed and crowded spaces" where aerosols tend to stall in the air for longer. But among the most useful measures is to "wear a well-fitting mask". Dr Nolan emphasises the importance of a good fit "around the edges and especially at the nose" for best results, as "concavity here can result in air leaks, it's why your glasses fog up."

Put simply - wear a mask to save a life.

There are many great Irish businesses selling face masks. You can add to your reusable mask wardrobe while supporting some of these local suppliers - just make sure it fits!