From: Monona Rossol <actsnyc**At_Symbol_Here**CS.COM>
Subject: Re: [DCHAS-L] Liquid nitrogen storage
Date: March 8, 2013 2:34:49 PM EST
Reply-To: DCHAS-L <DCHAS-L**At_Symbol_Here**MED.CORNELL.EDU>
Ralph. Lets assume the room is 10 x 10x 10 ft = 1000 ft2 The ASHAE 62-2001 standard is 20 cfm/person outside air just to stay healthy without any hazard in the room what ever. Let's put only one person in that room at a time so all we need is the 20cfm fresh air. And that 20 cfm is the fresh outside air. If the air is recirculating (as opposed to a displacement system), and the fresh air is 20% of the recirculated air, that means there is 100cfm of mixed air going into that room or 6000cfm/hour which is 6 room exchanges per hour already. Granted, this is ideal, and the final plans will chisel away at those numbers and we might use placement of supply and exhaust in better locations than at the ceiling to get better displacement, but that's the ball park.
So you are right. That 1 exchange/hour is way off. We would use 1 exchange/hour for some types of storage areas where people only enter briefly. If this room was a chemical darkroom with open baths (yes we still do that in art) the recommendations would be in the range of 10 room exchanges/hr just to deal with the small amounts of SO2 and HAc from the baths (unless we could do local exhaust).
For a room like this, I might consider a flush system. Determine the time you need to completely turn over the room in a worst case release and use an on-demand or sensor triggered exhaust/make up unit that can deliver this. Or enclose both the tank and the process and use local. These systems are better because you really can't afford to run a system that would provide safety from an asphyxiation hazard like this during all hours of use. You only need it that high when you REALLY NEED it because something went wrong.
Monona Rossol, M.S., M.F.A., Industrial Hygienist
President: Arts, Crafts & Theater Safety, Inc.
Safety Officer: Local USA829, IATSE
181 Thompson St., #23
New York, NY 10012 212-777-0062
From: Ralph B Stuart <rstuart**At_Symbol_Here**CORNELL.EDU>
To: DCHAS-L <DCHAS-L**At_Symbol_Here**MED.CORNELL.EDU>
Sent: Fri, Mar 8, 2013 10:44 am
Subject: [DCHAS-L] Liquid nitrogen storage
Does anyone have a rule of thumb for a ventilation rate in a room which is being
used to store liquid nitrogen containers? Several credible web sources recommend
a "well-ventilated area" without mentioning numbers. We have a room under
consideration for this purpose with about 1 air change per hour. This seems low
to me, but I thought I would sanity check it with DCHAS-L.
Thanks for any help with this.
Ralph Stuart CIH
Chemical Hygiene Officer
Department of Environmental Health and Safety
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