I have maintain a quiet presence but now must speak up.

First, it is well known that exhaled air contains a higher concentration of CO2 than ambient air. This is basic physiology.

Second, (no pun intended) this is the second time I have commented on the use of a direct reading instrument not intended for human use to demonstrate a problem. There is a U-tube video of a man using a 4 gas monitor to prove oxygen deficiency inside the mask. Yes, the unit pumps the air past sensors and he put it inside the cloth face covering and yes it alarmed (as they all will when you restrict flow). And another yes to expired air containing less oxygen which is another well-known fact.

Third, N95 respirators and surgical masks and others are worn and have been worn for very long period of time by many workers for decades without any evidence of serious physical harm from lower oxygen levels or higher CO2 levels. Yes, they can increase breathing resistance so are problematic for working hard or those with Asthma like my colleague Monona. If the CO2 levels increase, the breathing rate increases-normal physiology.

Fourth and final. If you think there is an issue, purchase an oxygen monitor (Oximeter) for your finger tip and then see if you oxygen level drops in your blood (also a sign of COVID19).

I will sign off before I become fodder for those who are convinced that gases are restricted by these devices.

Zack

--- For more information about the DCHAS-L e-mail list, contact the Divisional membership chair at membership**At_Symbol_Here**dchas.org Follow us on Twitter **At_Symbol_Here**acsdchas