From: Ralph Stuart <ralph**At_Symbol_Here**>
Subject: Re: [DCHAS-L] Fume hood article of interest
Date: Tue, 31 Aug 2021 14:26:29 -0400
Reply-To: ACS Division of Chemical Health and Safety <DCHAS-L**At_Symbol_Here**Princeton.EDU>
Message-ID: DF699658-F42B-40B3-B84B-DE859F00B1CE**At_Symbol_Here**
In-Reply-To <009d01d79e77$ea9662a0$bfc327e0$**At_Symbol_Here**>

> >Remember though that NFPA 45 recommends you never let it go below 4 ACH even when unoccupied off hours.

Many teaching labs have a single ‰??waste‰?? hood which are kept on 24/7 to maintain some airflow through the room. They may not achieve 4 ACH that way, but teaching labs do have good control over when there is active chemical use in the lab. I suppose why this is an NFPA recommendation rather than a requirement.

- Ralph

Ralph Stuart, CIH, CCHO

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