Liquid Nitrogen store ventilation
Liquid Nitrogen store ventilation
(OP)
what is a typical ventilation arrangement for a store room housing liquid nitrogen vessels (small vessels associated with a laboratory)?
any assiatnce will be appreciated.
any assiatnce will be appreciated.





RE: Liquid Nitrogen store ventilation
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RE: Liquid Nitrogen store ventilation
You should check with Dewar manufacturers about liquid N2evaporation rates. 1 liter of liquid N2 evaporates into 24.6 ft3 of gas.
Generally. oxygen level should not be less than 18%. If I consider a typical evaporation rate of 0.095l/day/dewar then N2gas released into the room will be 0.095*700 = 66.5 liters or 2.35 cu.ft/day. Suppose if your room size is 1000 cubic feet then oxygen content should be 209.5 cu.ft and nitrogen will be 790.5 cu.ft. But, due to asphyxiation N2 increases to 790.5+2.35 = 792.5 cu.ft and O2 will be 207.5 cu.ft or 20.75%. There is a reduction of 0.2% approximately. This type of calculation can be used to get required no. of fresh air changes in the absence of codes.
Oxygen monitor is a must IMHO. The following links will be useful to you.
http://www.gla.ac.uk/seps/01-024.html
http://www.onc.ed.ac.uk/liquidnitrogen.htm
Regards,
RE: Liquid Nitrogen store ventilation
RE: Liquid Nitrogen store ventilation
I have made ventilation calculations using excel spreadsheet but it should be verified. The Liquid N2 freezer manufacturer rep never got back to me to let me know the evaporation rate. Also I am not sure if my procedure - calculating the critical concentration is correct. If you guys can give me your email address I can email you the spreadsheet & you can let me know what you think.
lilliput1
RE: Liquid Nitrogen store ventilation
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RE: Liquid Nitrogen store ventilation
RE: Liquid Nitrogen store ventilation
If the transfer of liquid nitrogen is automatic by level control or temperature control inside the freezer then you have to only deal with evaporation rates resulting from temperature difference. But our application(storage of master cell banks) includes opening of cryocan lids. I never did the detailed calculation for evaporation when the lid is open because this includes evaporation of liquid nitrogen and superheating of gaseous nitrogen. We only take care of evaporation when the lid is closed and don't have much problems. O2 is in control.
I want to have a look at your spreadsheet. My id is builblock1@yahoo.com
PS: OSHA recommends oxygen level of 19.5%
Regards,