The reason to wear a cloth mask is to capture each wearer's droplets when they speak or cough to keep them out of the air for others to inhale.
The shield will only change the direction of the droplets as they exit out the sides and bottom of the shield. The droplets then enter the lab unfiltered which totally defeats the purpose of masks.
To make the point, in training I show slides 1) of the both freely expelled by a man sneezing; and 2) by someone wearing a surgical cloth mask which captures most (not all) of the droplets.
And since no one was dumb enough to make a Tyndall light picture of a sneeze behind a shield, I commissioned a cartoonist to do this. He wisely showed the effect on people standing to the left and right of the shield sneezer. The term "gob smacked" comes to mind.
The cartoon makes the point for anyone with the least bit of common sense.
Even more important, think about the droplets expelled during talking or just breathing. There is nothing on the shield to absorb or capture them. They are going freely into your lab air.
Monona
-----Original Message-----
From: Burgmeier, Sally <sallyburgmeier**At_Symbol_Here**AUGUSTANA.EDU>
To: DCHAS-L**At_Symbol_Here**Princeton.EDU
Sent: Tue, Jun 23, 2020 4:10 pm
Subject: [DCHAS-L] Cloth face masks trapping fumes
My teaching colleagues are concerned that cloth or surgical face masks worn by students or faculty in a chemistry lab setting where volatile chemicals are used, for example organic lab, could trap fumes within the masks and therefore be harmful to the user? They are wondering if face shields should be worn in labs instead of cloth face masks to prevent covid19 spreading, but mot allow chemical fume buildup.
We do have fume hoods for every student to use. Any guidance on this issue?
Thank you,
Sally Burgmeier
Chemistry Safety Officer
Augustana College
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