From: "Chance, Brandon" <bchance**At_Symbol_Here**MAIL.SMU.EDU>
Subject: Re: [DCHAS-L] Liquid nitrogen storage
Date: Fri, 19 Jan 2018 22:07:45 +0000
Reply-To: ACS Division of Chemical Health and Safety <DCHAS-L**At_Symbol_Here**PRINCETON.EDU>
Message-ID: C4C9FA59-1230-44DE-B271-555BB7847CCC**At_Symbol_Here**


After a police officer line of duty death last year, the question was raised here.  We ended up looking at all of the rooms that had large Dewars and calculated the air volume of the space.  If the calculations dictated that there was a risk of an oxygen deficient atmosphere, we placed sensors in the room.  The standard places were storage rooms, the NMR facility, and an interior loading dock area where the vendor drops them and leaves them.  We did have a couple of labs that met our thresholds as well.   

Because we are in the process of switching over to an outside vendor running our controls shop, central plant, and BMS systems, I had them install the units and wire them in with the BMS system. They are also on a preventative maintenance schedule for calibration and sensor changes. If a deficient atmosphere is recorded, EHS and PD are notified.  We have signage on doors regarding entry when the alarm is sounding. The storage areas routinely go into alarm briefly when they vent (the alarm threshold is currently 19.5% and they drop to the 19% range).

Our most recent addition was Athletics.  We have a cryogenic treatment unit that was installed in a very small training room - which definitely warranted sensor installation. We found that athletics was storing 2 large dewars at a time to serve the unit. 

Brandon S. Chance, MS, CCHO
Associate Director of Environmental Health and Safety
Sustainability Committee Chair
Office of Risk Management
Southern Methodist University 
PO Box 750231 | Dallas, TX  75275-0231
T) 214.768.2430 | M) 469-978-8664

"… our job in safety is to make the task happen, SAFELY; not to interfere with the work…" Neal Langerman

From: ACS Division of Chemical Health and Safety on behalf of James Saccardo
Reply-To: ACS Division of Chemical Health and Safety
Date: Friday, January 19, 2018 at 3:40 PM
To: "DCHAS-L**At_Symbol_Here**PRINCETON.EDU"
Subject: Re: [DCHAS-L] Liquid nitrogen storage

Hi Paul,

It depends on the volume in use/stored. Once you are over 55 gallons (~200L) it spurs the requirement to have atmospheric monitoring in my jurisdiction.


One dewar is about 200L and is constantly evaporating, one large dewer per/ lab unit is okay without the need to have oxygen sensors. Be sure there is a secondary egress and that aisles are not locked by the dewar.

If you store a second, as a backup, we risk exceeding this limit per control area. We use Administrative controls (policy and signs) so that two dewers are never in a single lab unit at the same time, therefore, never more that 200L per control area.


We did put a hard wired O2 detection system in our main gas cylinder storage area where we can have more than 1 dewer of LN2 at a given time interval.

Most Fire departments refer to NFPA 55 - there is also guidance from the Compressed Gas Association  (CGA p-18).


More than 200L - I say yes. If you have a pressurized cryogen system, yes again. Do what is right and then ask "am I meeting the minimum requirements of the law".


Be Well,



From: ACS Division of Chemical Health and Safety [mailto:DCHAS-L**At_Symbol_Here**PRINCETON.EDU] On Behalf Of Battles, Paul
Sent: Friday, January 19, 2018 3:36 PM
Subject: [DCHAS-L] Liquid nitrogen storage


Hello All,


We are in the process of building a new biology building and one of the labs will regularly contain a liquid nitrogen tank. Are oxygen depletion sensors required? The only thing I have come across said "recommended if room doesn't have adequate ventilation."



Paul Battles


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