Ellen,

After the incident at the Georgia Sperm Bank, our PD asked us to assess any spaces where a possible deficiency may occur. We basically made some assumptions involving complete dead air (we have had a number of campus-wide power outages), calculated the volume of the laboratory (or other space), and then the size of the Dewar. If the calculations showed that a 120 or 160L Dewar could displace enough oxygen to result in a low oxygen atmosphere, we installed local monitoring. This included the NMR facility, a few labs using Dewars to act as a nitrogen gas source (we do not have house nitrogen), various storage rooms, and, last but not least - the room that houses SMU Athletics' cryotherapy unit.

Frankly, as alluded to, much of this is overkill. We have had storage rooms drop down to about 19.4% when Dewars are venting as part of their pressure relief systems. We recently had an NMR quench (that is a whole other story and involves a compressed air cylinder transported too close to the magnet). Even then, during quenching, the oxygen in the NMR room never dropped below about 20%.

Regards,

Brandon S. Chance, MS, CCHO

Director of Environmental Health and Safety

Southern Methodist University

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