Smaller droplets a threat to some PPE

Small aerosol droplets could penetrate some personal protective equipment (PPE) used to shield people from infections like coronavirus, scientists have warned.

A team of researchers from Heriot-watt University and Edinburgh University created a mathematical model that separated how small, medium and large aerosol droplets were dispersed through the air.

The study, published in the journal Physics of Fluids yesterday, found that both large and small droplets travelled further than medium-sized ones.

The authors said that while PPE such as masks and face shields were an “effective barrier” against larger droplets it may be less effective against small ones.

Felicity Mehendale, co-author and academic surgeon at Edinburgh University, added: “Our study shows there isn’t a linear relation between droplet size and displacement – with both small and large droplets travelling further than mediumsized ones.

“We can’t afford to be complacent about small droplets.

“PPE is an effective barrier to large droplets but may be less effective for small ones.”

The team is creating an aerosol extractor device to keep clinicians safe during a wide range of aerosol-generating procedures routinely performed in medicine and dentistry.

Extraction units placed near the droplet sources can effectively trap droplets if their diameters fall below that of a human hair, the authors said.

Cathal Cummins, of Heriotwatt University, added: “This has important implications for the Covid-19 pandemic.

“Larger droplets would be easily captured by PPE, such as masks and face shields.

“But smaller droplets may penetrate some forms of PPE, so an extractor could help reduce the weakness in our current defence against Covid-19 and future pandemics.”

The authors said that if the spread of coronavirus by aerosol droplets is confirmed to be “significant” then it will require a reconsideration of guidelines on social distancing, ventilation systems and shared spaces.