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Subject: Re: [DCHAS-L] singing and wind instruments indoors
Date: Sunday, July 26, 2020 at 8:03:10 AM
Author: Ralph Stuart <Ralph.Stuart**At_Symbol_Here**keene.edu> 		Next by Date:
Subject: Re: [DCHAS-L] singing and wind instruments indoors
Date: Sun, 26 Jul 2020 12:57:46 -0400
Author: Margaret Rakas

From: Monona Rossol <0000030664c37427-dmarc-request**At_Symbol_Here**LISTS.PRINCETON.EDU>
Subject: Re: [DCHAS-L] singing and wind instruments indoors
Date: Sun, 26 Jul 2020 13:32:58 +0000
Reply-To: Monona Rossol <actsnyc**At_Symbol_Here**CS.COM>
Message-ID: 553293058.6123115.1595770378085**At_Symbol_Here**mail.yahoo.com
In-Reply-To <4434094373557225.WA.ralph.stuartkeene.edu**At_Symbol_Here**lists.princeton.edu>


I hope EVERYONE reads your post below.  ASHRAE-compliant recirculating systems are prone to all kinds of serious air flow issues.  It is also why the ACH rates they calculate for 99% replacement are totally bogus on a practical level.  It all depends on where the diffusers and returns are located and how well balanced the system is.  And most of the people running building ventilation cannot balance the systems themselves so over time almost all systems become unbalanced.  Both time and changes to equipment, partitions, and the like, often leave rooms unbalanced.

I wish people could see what you have seen, the eddying and areas where not much air is being exchanged at all. 

If you REALLY are at risk from this virus as I am, you will stay OUT of any ordinary building environment unless you are wearing an N95 or better.  You cannot predict how good any ventilation system is by looking at it or feeling for air movement.  You just can't know.   And all the cloth masks and distancing are useless if the air you breath through that cloth mask is carrying significant droplets or aerosol in the area in which you are standing or sitting.

Monona 


-----Original Message-----
From: Ralph Stuart <ralph.stuart**At_Symbol_Here**KEENE.EDU>
To: DCHAS-L**At_Symbol_Here**Princeton.EDU
Sent: Sun, Jul 26, 2020 8:03 am
Subject: Re: [DCHAS-L] singing and wind instruments indoors

>The ACH is one thing, but the direction of air flow is also important to know.

To emphasize this observation,  I will add two points:
- The direction of air flow is not intuitive in many rooms; thanks to an IH smarter than I, I have learned to use theater fog generators to verify that air is moving, for example, towards fume hoods, rather than around them before measuring air flow rates in a lab. In the case I'm thinking of, the components of the ventilation control system had not aged well and the room was seriously out of balance.

- The direction of air flow in specific locations in a room can change with the Air Changes per Hour being pushed through the room. It is similar to a stream - there are lots of eddies and traps along the edges of a room that can grow and trap pollutants depending on the obstructions (furniture, people, equipment) it encounters as it moves faster.

Add to that the variation in types of airborne materials that could be carrying infectious virus and I'm reluctant to rely on ventilation as a Corona control measure

These comments are based on evaluating air flow in about 10 BSL 3 labs, which are very carefully designed to control particle movement. That's not the design approach in chemistry laboratories or other spaces which rely on dilution with fresh air to control exposures to chemical pollutants. That's not a good approach to biohazards.

- 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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