From: "Chainani, Edward Torres" <echaina2**At_Symbol_Here**ILLINOIS.EDU>
Subject: Re: [DCHAS-L] O2 Sensor Determination
Date: Tue, 17 Jul 2018 19:25:07 +0000
Reply-To: ACS Division of Chemical Health and Safety <DCHAS-L**At_Symbol_Here**PRINCETON.EDU>
Message-ID: 01323B76-B979-4C53-8ACD-7E263007B911**At_Symbol_Here**

Dear Jeffrey,

I have in the past pointed researchers to the following references and asked them to perform the calculation for oxygen depletion for their own labs. My understanding of the assumptions underlying the calculation was that of an instantaneous release and uniform distribution of the inert gas in the work space.

The first reference came from Cambridge, and while that document is publicly available, the online oxygen depletion calculator mentioned within is not.  However, the equations for the calculation are in the second reference. 

I must include the caveats communicated to me by the Cambridge Health and Safety person:

"I have absolutely no problem with ‘anyone' having any of my documents, all I would ask is that the logo and University address etc is removed if it is copied. You are quite welcome to copy any of it into your guidance, IFF you decide it is appropriate, but again I would ask reference to the University is limited to a ‘thanks' if you wish to acknowledge the source.
Basically we don't want anyone outside of the University of Cambridge potentially saying ‘I was following University of Cambridge Guidance' when it went horribly wrong.
If you are using a calculator, remember the caveats wrt ‘actual' room volume, that is, allowing for furniture/equipment, which reduces the air volume. Room height should allow for a room filling from the floor up with cold nitrogen (ex Liq N2), so we say the max height is 1.5 (to 1.8 metres), and this always assumes the person is standing! Clearly if they bend over or sit down to work the effective height is lower. It is critical as to where the monitoring point is (height and location if it is a fixed system. Obviously helium would rise, so its the height down from the ceiling to 1.8 m etc…. Nitrogen when it warms or is warm may rise with time. It all assumes perfect mixing and no ventilation (which can be allowed for, but we don't trust its reliability, (fatality in London in 2011 ). We always assume worst case scenario when selecting controls. Our biggest problems have been slow overnight or weekend  leaks into rooms (even buildings!), especially with the liq N2 and toxic CO2 gas supply from liquid tanks we have everywhere.
Don't forget dry ice , we had a potentially nasty incident with dry ice stored in an un ventilated cold room over the weekend."

Hope this helps.


Edward Chainani, Ph.D.

On Jul 17, 2018, at 1:53 PM, Jeffrey R. Cogswell <Jeffrey.R.Cogswell**At_Symbol_Here**DARTMOUTH.EDU> wrote:

Does anyone have a good reference for determining when a room needs an O2 sensor? I'm looking for an amount of liquid gas (nitrogen, argon, helium) vs cubic feet calculation. (We're assuming total catastrophe here: no ventilation and all the cryo-liquid escapes). Dartmouth is looking at doing an overhaul of all the O2 sensors on campus. Facilities will oversee maintain/scheduling of these sensors and require a "hard and fast" rule from EHS to justify their installation.
Jeffrey R. Cogswell, Ph.D.
Chemical Inventory and Laboratory Resource Center Technician, EHS
37 Dewey Field Road, HB 6216
Hanover, New Hampshire 03755
P: 603.359.0128  F: 603.646.2622
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