How low does O2 have to get to be dangerous? To reduce the oxygen concentration by a factor of two, you would have to mix equal volumes of air and nitrogen. Now since the nitrogen is coming off at about 70K, assuming equal heat capacity for N2 and 80% N2, the temperature of that mixture would be halfway between 4 C and 70 K, which would probably motivate one to leave the area already.
However when I brought this up I was told that a surprisingly small decrease in O2 pressure is enough to make you pass out- the 2-fold change I was considering might be way beyond fatal. I guess the problem is that it is increased CO2, and not decreased oxygen, that makes you feel breathless and start breathing hard. All that nitrogen would keep the CO2 way down and you would go on calmly working until you blacked out. Green, Todd wrote:
I've noticed that pretty much every time there is an autofill of the dewars in the hutches of SSRL or APS, the oxygen sensors go off. but that is a small space and many liters of liquid nitrogen. I've frozen routinely in a small cold room with a liter or 2 of liquid nitrogen with no issue. -----Original Message----- From: CCP4 bulletin board on behalf of Jacob Keller Sent: Fri 7/13/2012 4:42 PM To: CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] harvesting in cold room How frequently do the sensors go off? JPK On Fri, Jul 13, 2012 at 4:37 PM, David Schuller <dj...@cornell.edu> wrote: > On 07/13/12 17:29, Jacob Keller wrote: > > You probably already know this, but nitrogen is not at all > poisonous--about 78% of the air is nitrogen. I guess you were probably > worried about asphyxiation....? > > > We have oxygen sensors in our X-ray hutches for precisely that reason. > > -- > ======================================================================= > All Things Serve the Beam > ======================================================================= > David J. Schuller > modern man in a post-modern world > MacCHESS, Cornell University > schul...@cornell.edu > > -- ******************************************* Jacob Pearson Keller Northwestern University Medical Scientist Training Program email: j-kell...@northwestern.edu ******************************************* This email was scanned with Mcafee's Anti-Virus appliance, but this is no guarantee that no virus exists. You are asked to make sure you have virus protection and that it is up to date.
