May 6, 2020

How to stop glasses fogging while wearing a face mask, according to science

The White House coronavirus taskforce has begun winding down but science has begun ramping up a “mask-force” of experts to dispel conspiracy theories on the vaccine to mask fog, like duct taping your face to create an air-tight seal.

From the annals of the Royal College of Surgeons of England medical journal, an existing research paper titled A simple method to prevent spectacle lenses misting up on wearing a face mask has found new popularity during the pandemic response.

Trauma doctors Sheraz Shafi Malik and Shahbaz Shafi Malik write that the misting effect is not just a nuisance, the annoying phenomenon could even incapacitate a person.

Their emergency room-tested, peer-reviewed method is as follows:

  • Step 1: Immediately before wearing a face mask, wash the spectacles with soapy water
  • Step 2: Shake off the excess
  • Step 3: Let the spectacles air dry, or gently dry off lenses with a soft tissue
  • Step 4: Put them back on

While the solution is seemingly simple enough, the misting scourge is anything but. In their paper, The misting characteristics of spectacle lenses, researchers Tom H Margrain and Chris Owen tested crown glass, CR39 and polycarbonate materials found not all spectacle lenses are created equal.

“Both the physical properties of the spectacle lens and a number of environmental factors determine how long spectacles take to demist,” they write.

“The polycarbonate lens demisted more rapidly than the CR39 lens which, in turn, demisted more rapidly than the glass lens. This indicates that polycarbonate spectacle lenses should be used in conditions where the adverse effects of spectacle misting need to be minimised.”

But as spectacles are only one part of the problem, they are only one part of the solution.

The researchers showed how face masks direct much of the exhaled air upwards towards the spectacle lenses, and the misting occurs from the warm water vapour condensing on the cooler surface of the lens.

As a result, tiny droplets form due to the surface tension between water molecules. The droplets scatter the light and reduce the ability of the lenses to transmit contrast.

The soapy water leaves behind a thin surfactant film that reduces this surface tension and causes the water molecules to evenly spread out into a transparent layer.

“This ‘surfactant effect’ is widely utilised to prevent misting of surfaces in many everyday situations,” the doctors Malik write.

But what if the misting process could be interrupted at the level of transmission?

In their paper Tying a surgical mask to prevent fogging, researchers DJ Jordan and R Pritchard-Jones argue that the problem of “fogging” results in reduced visual acuity.

While a standard method of tying a mask involves knotting two ties so they lie above and below the ear in a near parallel appearance, their method consists of looping the bottom tie above the ear and the top tie below the ear.

“This approach allows a closer seal over the nose and along the infraorbital ridge, stopping venting at the superior part of the facemask, and forms two lateral ‘vents’, allowing exhaled air to escape away,” they write.

“Multiple attempts have been made to solve this problem, including washing prior to application, adding tape, or the use of several masks, but we believe this to be the first description of a novel method that does not involve any further cost or instrumentation.”

The takeaway from today’s coronavirus mask-force briefing; experts advise people use polycarbonate lenses, wash them with soapy water, and double-cross tie face masks to avoid the loss of visual acuity and incapacitation from foggy goggles.

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