From: Richard Palluzi <000006c59248530b-dmarc-request**At_Symbol_Here**LISTS.PRINCETON.EDU>
Subject: Re: [DCHAS-L] Lab Ventilation
Date: Wed, 24 Feb 2021 07:29:05 -0500
Reply-To: ACS Division of Chemical Health and Safety <DCHAS-L**At_Symbol_Here**Princeton.EDU>
Message-ID: 002c01d70aa8$a47232d0$ed569870$**At_Symbol_Here**

If you accept the premise that work involving hazardous materials in a laboratory should take place in a properly designed fume hood then I believe that he fume hood exhaust should set the laboratory ACH not an arbitrary figure. I will acknowledge that if this hood based ACH is not at least 6 ACH I provide general exhaust. The trouble with using ACH as the primary protection is that any release is very likely to contact personnel before adequate dilution. How much exposure is possible and how serious are both difficult to impossible to determine. So to me, the key safety factor is to provide enough properly functioning hoods, teach personnel how to use them properly (yes there is some training required), enforce the annual maintenance and certification programs to keep the hoods working properly, and - most importantly - rigorously enforce the rules that all operations involving hazardous materials take place in a hood.

The last point is probably one of the hardest, particularly in an academic environment. When hood space is limited (it always is) or where facilities are over crowded (not terribly uncommon) then there is a tendency to do more work on the bench. Trying to mitigate exposure using ventilated enclosures and local exhaust is possible but requires careful design, hazard analysis, and enforcement. Three items that I find sadly lacking in many laboratories.

For more discussion on this are you might want to look at:

The Ten Most Common Laboratory Ventilation Mistakes at
Ventilation Dilution: A Safe Way to Avoid A Fire or Explosion or a Placebo? At
Ventilated Enclosures: Why Do They Often Fail to Work Properly at
Limiting Hood Openings: A Bad Idea at
‰??Why Can‰??t We Put It In the Hood?‰?? at

Richard Palluzi

72 Summit Drive
Basking Ridge, NJ 07920

-----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

>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 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


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