Helium is used as the inert gas in diving gas mixture because of the problems connected with nitrogen narcosis, not so much because of carbon dioxide. In most SCUBA systems, the exhaled air is expelled into the water (all those bubbles), and where it isn't, the rebreathing systems are there to recover O2 from the CO2.

Peter Zavon, CIH
Penfield, NY

PZAVON**At_Symbol_Here**Rochester.rr.com

From: ACS Division of Chemical Health and Safety <DCHAS-L**At_Symbol_Here**Princeton.EDU> On Behalf Of Sambor, Andrew:(Exelon Nuclear)
Sent: Friday, June 26, 2020 4:01 PM
To: DCHAS-L**At_Symbol_Here**Princeton.EDU
Subject: Re: [DCHAS-L] Sars-CoV2 infectivity

Thank you, I was unaware of the impacts under those conditions. Is that why helium is utilized as the inert portion of breathing air for deep diving operations?

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From: ACS Division of Chemical Health and Safety <DCHAS-L**At_Symbol_Here**Princeton.EDU> on behalf of Osprey, James <ospreyj**At_Symbol_Here**NOVATECH.CA>
Sent: Friday, June 26, 2020 1:19:42 PM
To: DCHAS-L**At_Symbol_Here**Princeton.EDU <DCHAS-L**At_Symbol_Here**Princeton.EDU>
Subject: [EXTERNAL] Re: [DCHAS-L] Sars-CoV2 infectivity

EXTERNAL MAIL. Do not click links or open attachments from unknown senders or unexpected Email.

I have enjoyed following this email train.

My last 40 odd years have been spent amongst other things in the development of techniques for the measurement of gases (including CO2) in controlled atmospheres and process conditions.

I am more than happy to concur with Monona's arithmetic.

I would point out that the toxicity of CO2 is related to the partial pressure, which at atmospheric pressure becomes quite significant at 5% leading to unconsciousness greater than 10%. As such, most alarm conditions in confined spaces are set at 5,000 ppm (0.5% v/v) at normal atmospheric pressure. However in hyperbaric environments (say 600ft, depth in diving bell) the operating pressure is around 20bar and the alarm condition must be set at 250ppm or less). There are additional risk factors associated with stratification and increased concentration at low lying locations in the diving bell.

It's important to note that the much vaunted statement that CO2 is a simple asphyxiant is profoundly untrue as exposure to such low levels (at pressure) which can hardly be considered as oxygen displacers, has resulted in immediate collapse and death.

James Osprey

UK 07393 426915

Canada

514 339 5374, 208

905 569 9824, 208

1 800 465 5347, 208

Sent from my iPhone

On 26 Jun 2020, at 18:11, Monona Rossol <0000030664c37427-dmarc-request**At_Symbol_Here**lists.princeton.edu> wrote:

=EF=BB=BF

Ooops. 4-5% = 40,000 - 50,000 ppm. lungs are REALLY good at exchanging gases apparently. Monona

-----Original Message-----
From: Monona Rossol <0000030664c37427-dmarc-request**At_Symbol_Here**LISTS.PRINCETON.EDU>
To: DCHAS-L**At_Symbol_Here**Princeton.EDU
Sent: Fri, Jun 26, 2020 12:25 pm
Subject: Re: [DCHAS-L] Sars-CoV2 infectivity

Hmm. 0.04% = 400 ppm (world average now) and 4-5% is 4000-5000 ppm, soooo, when they exhale 3500 ppm CO2 that's about right. Monona

-----Original Message-----
From: Backus, Bruce <backusb**At_Symbol_Here**WUSTL.EDU>
To: DCHAS-L**At_Symbol_Here**Princeton.EDU
Sent: Fri, Jun 26, 2020 11:39 am
Subject: Re: [DCHAS-L] Sars-CoV2 infectivity

Hi Ralph,

Is that breathing directly into a CO2 meter, or analyzing the air in the breathing zone under a mask? The air we breathe in contains about 0.04% CO2, but we exhale air that contains about 4 to 5% CO2.

Thanks,
Bruce

_____________________________________
Bruce Backus
Assistant Vice Chancellor | Environmental Health and Safety | Washington University in St. Louis
4533 Clayton Ave.| Campus Box 8229 | Saint Louis, MO 63110
S: 314.362.8976 | Cell C: 314.302.0466 | : backusb**At_Symbol_Here**wustl.edu

-----Original Message-----
From: ACS Division of Chemical Health and Safety <DCHAS-L**At_Symbol_Here**Princeton.EDU> On Behalf Of Stuart, Ralph
Sent: Friday, June 26, 2020 9:55 AM
To: DCHAS-L**At_Symbol_Here**Princeton.EDU
Subject: Re: [DCHAS-L] Sars-CoV2 infectivity

> 900 to 1000 ppm CO2 is also where documented effects on mental acuity can be shown. It's a nice number.

Is there a reference for this? I just had one of our librarians who had been wearing a cloth mask for an hour exhale into a CO2 meter and he hit 3500 ppm. After wearing a cloth mask for 20 minutes, I max out around 1500, so I suspect that the longer wearing periods could become productivty problem.

- Ralph

Ralph Stuart, CIH, CCHO
Environmental Safety Manager
Keene State College
603 358-2859

ralph.stuart**At_Symbol_Here**keene.edu

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