From:
CRAIG MERLIC <merlic**At_Symbol_Here**G.UCLA.EDU>
Subject:
Re: [DCHAS-L] Use of Fume Hood "Max Height"stickers with alarms vs just alarms
Date:
Jul 2, 2025 13:15 UTC
Reply-To:
ACS Division of Chemical Health and Safety <DCHAS-L**At_Symbol_Here**Princeton.EDU>
Message-ID:
<CADK3QwZrHXtx4vxSQb5dikWeuhp7FL=cbWB0UUUpczEx0M9Duw**At_Symbol_Here**mail.gmail.com>
In-Reply-To:
<A83976B7-56A9-4A49-B00E-94B58E4F684C**At_Symbol_Here**ilpi.com>
Morning!
My organic and inorganic chemistry colleagues and I moved into our building at UCLA in 1993. As a building designed for wet chemistry it has about 275 fume hoods on five floors. All are equipped with Phoenix controls with air flow alarms and the mechanical stops. The stops are about 3"x3" and can be slipped aside with a finger. The alarms also have an override button to turn off the alarm which can be pushed each time the alarm goes off. Most hoods also have proper height stickers from years of EH&S testing of the air flows.
In my experience and opinion the mechanical stops have true value. Yes, the stickers show the proper height, but when a researcher is raising a hood sash while focused on their chemistry they do not look at the sticker. In contrast the mechanical stop provides a simple and effective way of stopping at the correct height. I have not seen the problem that Margaret described, but the mechanical stops bump the sash at the opening while the cables are in the back of the hood. So a connection between the stops and frayed cables is not clear.
Craig
Craig A. Merlic
Professor of
Chemistry, UCLA Department of
Chemistry and Biochemistry
Executive
Director, UC Center for
Laboratory Safety
http://cls.ucla.edu
Can’t comment on the hood stops, but cut a piece of scrap wood or cardboard 18” long and you have an instant install template.
Rob Toreki
Good morning,
When we moved into our 'wet lab' building about 15 years ago, each fume hood was equipped with a mechanical stop placed at 18 inches, as well as an alarm system governed by Phoenix controls. In this time, we have only had a malfunction with an alarm (didn't go off) in one hood. The mechanical stop is on one side of the hood, and can be manually released to raise the hood above the stop point in order to set up apparatus, etc.
Because the mechanical stop is easy to 'hit', even though students are generally careful, over 15 years we have recently seen two incidents of the sash cable becoming frayed and as a result, the sash is difficult to open/shut. Repairs are costly plus a large inconvenience as the hood and solvent cabinets underneath must be emptied and deconned.
Apparently these 18" mechanical sash stops are rare in other institutions per our vendor; and we are planning to remove them. We were thinking of placing labels denoting the 18 inch mark after the stops were removed, but this would mean installing about 70-80 labels pretty quickly. Not a difficult task, but enough time spent with a tape measure that I wanted to ask...
Does your institution rely on just the alarm going off if the sash is raised above the setpoint, or do you also have a visual guide to the maximum set point on the side of each fume hood? We would confirm the alarms were working at the beginning of each semester as well as the beginning of the summer research period.
thank you!
Margaret
-- Margaret A. Rakas, Ph.D.
Lab Safety & Compliance Director
Clark Science Center
Smith College
413-585-3877 (p)
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