×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Liquid Nitrogen store ventilation

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.

RE: Liquid Nitrogen store ventilation

First thing is to check for existence of local codes. Nitrogen asphyxiation is very dangerous and it causes fatality, sometimes, without indication.

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

(OP)
thank you imok & quark - as always, information that is relevant.

RE: Liquid Nitrogen store ventilation

ad77, imok & quark,
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

As Quark stated, “Oxygen monitor is a must IMHO.”  I don’t know too much about the construction of a small Dewar; however, many large cryogenic storage vessels rely on maintaining a vacuum in the interstitial space.  If there is a vacuum leak the evaporation rate will be much higher.  Also, a oxygen sensor could monitor the area in case of a spill.  One source that will have a lot of safety standards for this is the CGA (Compressed Gas Association.)

RE: Liquid Nitrogen store ventilation

Lilliput,

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,

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources