Hi Ralph!

I liked the study you cited:

https://pubs.acs.org/doi/10.1021/acs.chas.8b21106

I realize how much the "accepted" rate of air changes has changed over the last two decades and also know that 6 ACH has gained traction. One quotation from "Sweet and Stuart" I particularly liked was:

"The first challenge is that, by definition, laboratory operations use a wide variety of chemicals in changing amounts and concentrations on an irregular basis. Therefore, the risks associated with airborne chemicals in the laboratory change irregularly. With this in mind, it is tempting to try to organize ventilation of laboratories based on their design intent (e.g., wet or dry labs) or a generic description of the science conducted there (e.g., biochemistry, engineering or molecular biology). Unfortunately, we have found that laboratory work within these classifications is not organized around the chemical hazards associated with the scientific work. Rather, laboratory work is more likely to be organized around the personnel of specific lab groups, their fields of research interest, and the processes involved in conducting their science rather than around the chemical hazards associated with this work. Additionally, scientific work is becoming increasingly multi-disciplin!
ary, which means that the use of hazardous chemicals can show up in unexpected places. For these reasons, we have found that it is not uncommon to find a small, but significant, number of laboratories in specific departments that use chemicals more intensely than the rest of the department"

This statement implies that it is less likely that increased ventilation needs will "average out" because groups of shared mutual interests (and resources) will be working together. Control banding in such cases does not require searching out high ACH labs as much as using lower sash openings, assuring good room throughput, and staggering heavy-use experiments within such labs.Particular in current University research labs, this approach in my opinion has the best practical chance of achieving lab safety.

Again, thanks for the article reference, I appreciated it.

Dr. Bob Haugen
Director of Product and Technology Development
Flow Sciences, Inc.

910 332 4878

www.flowsciences.com
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-----Original Message-----
From: ACS Division of Chemical Health and Safety On Behalf Of Stuart, Ralph
Sent: Tuesday, February 23, 2021 2:42 PM
To: DCHAS-L**At_Symbol_Here**Princeton.EDU
Subject: Re: [DCHAS-L] Lab Ventilation

> Regardless of what you are doing, you should accommodate existing lab practices based upon what ACH lab is operating at because you cannot easily adjust ACH without domino-like repercussions.

Despite the prudence of this engineering recommendation, I have very seldom seen it followed in the academic environment. In my experience, space assignments are made for administrative reasons rather than ventilation capabilities of specific spaces.

>Maximum sash opening, storage of flammables, policing lab door openings ,etc, etc is best way to maximize containment for more dangerous chemicals using whatever ACH you have. 6 ACH is very low and should never be used, although many education labsare now sized this way to ‰??save energy‰??.
>
I‰??m not sure what ‰??very low‰?? means in this context. Based on a review of the chemistry being used in about 80% of the spaces I visited on a research campus, 6 ACH is appropriate, as long as the system is true lab exhaust in the sense that it is not recirculated into occupied spaces. This is not always the case in buildings which have been repurposed several times. The criteria I used to make these determinations is described at Identifying General Laboratory Ventilation Requirements Using A Control Banding Strategy by Ellen Sweet and Ralph Stuart at
https://pubs.acs.org/doi/10.1021/acs.chas.8b21106

>For new labs, one should always devise a system assuming usages may change. I personally believe minimum 10 ACH is better, but you may have trouble establishing this for new labs.
>
The data reported in Laboratory Air Quality And Room Ventilation Rates: An Update by Robert C. Klein, Cathleen King, and Anthony Kosior at https://pubs.acs.org/doi/10.1021/acs.chas.8b18208 suggests that there is marginal value added by going as high as 10 ACH.

> >Follow up ‰?? what criteria do you use to classify high risk vs low risk research labs?

See above.
>
> > ‰?¢ Has anyone done Computational Fluid Dynamic (CFD) analysis of their typical labs to validate that the air flow rates and directions are sufficient?

I have seen CFD models that address these concerns. They can be helpful before lab workers move into the spaces in assessing air movement patterns, but the human element often confuses the CFD model results.

- 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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