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Speed and distance of Covid-19 droplets tracked by Mater researchers

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The speed and distance which droplets carrying the Covid-19 virus travel and the impact face coverings have on its spread have been demonstrated by a team of mechanical engineers and doctors working out of the Mater hospital in Dublin.

Using a combination of old and new technologies based around light, mirrors and lasers, Dr Kevin Nolan, a UCD engineer, and Ronan Cahill, the Mater’s professor of surgery, have displayed how droplets can travel more than two metres from a starting point and linger in the air for more than an hour.

The research has also illustrated the ease with which aerosols carrying the virus can exit the abdomen during keyhole surgery and highlighted the need for medical staff to take enhanced protection measures when performing laparoscopic surgeries on patients with the illness.

Dr Nolan used two different methods to prove the effectiveness of masks. He first deployed Schlieren technology – a physics principle dating back more than a century which relies on high-spec mirrors and light to show the density of fluids and gases and the speed and distance they can move when people breathe, cough and sneeze.

“We can see that large droplets fall quickly to the ground while smaller particles which can contain the virus linger in the atmosphere,” Dr Nolan said. “When someone with Covid-19 coughs or sneezes some of the particles carry the virus and others don’t, which is why I refer to it as Russian roulette.”

Wearing masks

He said his research had shown that wearing masks had a dramatic impact on how far droplets could travel.

“Conspiracy theorists will have you believe masks can’t work because they virus is so small and can travel through material but that is to misunderstand the science. Yes, you can liken the virus to a minnow which can easily pass through a fishing net but the reality is that every minnow is travelling not in isolation but in a droplet of liquid and that is what the masks can catch.”

One of the core objectives of Dr Nolan’s research was to capture the manner in which gases escape from the abdomen during keyhole surgery, which he described as “an aerosol-generating event” and how they can quickly spread in an operating theatre, potentially putting entire teams of medical professionals at risk.

The Schlieren technology has limitations and does not cover great distances so over the summer the academic based at the Mater hospital devised an experiment using high-powered lasers to show just how the far droplets can travel and how long they can stay airborne.

Fluid mechanics

Dr Nolan told The Irish Times that “when you study fluid mechanics you rely on cold, hard numbers, very precise numbers and what this research has been able to do has been to bring physics to a medical procedure – and we have been able to show, using a laser sheet, the risks associated with aerosol-generating events.”

Prof Cahill hailed the research for again displaying in an easy to understand manner why mask wearing was important but also for “moving the research into the operating theatre”.

He said it was difficult to illustrate the spread of virus-carrying aerosols when it is “based on an abstract idea so what we are trying to show is what the spread actually looks like. You can think you know your environment and you can get very comfortable with it but when you can see exactly what is happening using this technology it is very shocking – and now we have a different way of looking at that.”

He said the knowledge gleaned from the research would allow hospitals and surgical teams to modify some of their practices, including the ventilation and how people move around the theatre, and what masks need to be worn where.

Prof Cahill also said it would help medical engineers develop comparatively simple devices which would lessen the spread of potentially harmfully aerosols during keyhole surgery.

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