>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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