> > The expansion ratio of liquid to gaseous nitrogen is approximately 1:700, > that is, 1 liter of liquid becomes 700 liters of gas (at room temperature). > When you are in a room that is 3 (~10ft) meters tall, 6 (~18ft) meters wide > and 10 (~30ft) meters long and you assume that it is poorly ventilated > (i.e. no gas replacement at all), then you will have 3x6x10 = 180m3 volume > of gas, which is 180,000 liters. Air consists of 21% oxygen and is > considered deficient if it goes down to 19.5%. OSHA recommends having > monitors present in the case you might, in worst case scenario, reach > 19.5%. Note: I don't know, but it seems unlikely that you are critically > injured at 19.5% >
How can this OSHA number be right? At fairly high altitude, say 2500 m, the partial pressure of O2 will be about 75% of that at sea level, and most are okay with it--so how can a drop from 21% to 19.5% have any importance? Is N2 competing with O2, perhaps? Never heard of that. Can N2 really be a poison, such that we are constantly poised at the cusp of suffocation? JPK > In this hypothetical case, you will have about 37800 liters of oxygen. If > you displace some of it with 700 liters of nitrogen (you spilled one liter > of liquid nitrogen), you will be down to 37100 liters, or approximately > 20.5%. So, no worry. > > If you have cryogenic storage for crystals (typically hundreds of liters) > or one of those large tanks to back-fill your cryo-system, the story > changes a lot. Large dewars or large tanks for filling do not normally > fail, but when they do, you will be at risk. Humans cannot sense the lack > of oxygen, you just feel sleepy and keel over. So in small rooms with large > amounts of liquid nitrogen, it makes sense to have a monitor (and it does > not make sense to be scared of the issue when you have a monitor). > > Educationally: > > For each safety risk in your environment you are supposed to do a > calculation like the one above and consider how likely (or not) it is that > this may happen to you and how bad it will be. Likelihood and severity > multiply: if it is very unlikely (that a large nitrogen tank will rupture) > but the consequence is severe (you die), then you need to think about how > you can make sure that it never happens (install sensor). > > Conclusion: if you only work with a small open dewar, then even in a small > room it is highly unlikely to run out of oxygen. > > It is an excellent idea to ask questions like you did. It should be > expected that your institution has experts who can answer such questions, > but some (like ours) do not and you have to figure it out yourself. It is a > good idea to document your concern, calculation and recommendation. > > Hope this helps. > > Mark > > PS: nirtogen vendors have excellent reference materials about these things. > > > -----Original Message----- > From: Radisky, Evette S., Ph.D., Ph.D. <radisky.eve...@mayo.edu> > To: CCP4BB <CCP4BB@JISCMAIL.AC.UK> > Sent: Fri, Jul 13, 2012 3:19 pm > Subject: Re: [ccp4bb] harvesting in cold room (was: cryo for high salt > crystal) > > Several have mentioned harvesting in the cold room to reduce > evaporation. I used to do this also as a postdoc, but I worried whether I > risked nitrogen gas poisoning from liquid N2 boil-off, since the cold room > did not seem very well-ventilated. I’ve also hesitated to recommend it to > trainees in my current lab for the same reason. Does anyone have solid > information on this? I would like to be convinced that such fears are > unfounded … > > Evette S. Radisky, Ph.D. > Assistant Professor > Mayo Clinic Cancer Center > Griffin Cancer Research Building, Rm 310 > 4500 San Pablo Road > Jacksonville, FL 32224 > (904) 953-6372 > *From:* CCP4 bulletin board > [mailto:CCP4BB@JISCMAIL.AC.UK<CCP4BB@JISCMAIL.AC.UK?>] > *On Behalf Of *Roger Rowlett > *Sent:* Thursday, July 12, 2012 2:11 PM > *To:* CCP4BB@JISCMAIL.AC.UK > *Subject:* Re: [ccp4bb] cryo for high salt crystal > > We frequently crystallize one of our proteins and variants of it in > 1.6-1.8 M ammonium sulfate solutions. Cryoprotection with 25-30% glycerol > or 25-30% glucose does not cause precipitation of salts. Both KCl (4.6 M) > and ammonium sulfate (5.6 M) have enormous solubilities in water, so I > would not expect cryoprotectant concentrations of glycerol or glucose to > cause precipitation (We can save cryoprotectant solutions of at least 2 M > ammonium sulfate indefinitely). How are you introducing cryprotectant? We > use one of two methods: > > 1. Fish the crystal out of the mother liquor and place into artificial > mother liquor with the same composition as the well solution + > cryoprotectant. For glycerol or other liquids, you have to make this from > scratch. For glucose, we just weigh out 300 mg of glucose in a > microcentrifuge tube and make to the 1.0 mL mark with well solution. (Mix > well of course before use. Gentle heating in a block or sonication will > help dissolve the glucose. > 2. Add 4 volumes of artificial mother liquor + 37.5% cryoprotectant to > the drop the crystals are in. You can do this all at once, or in stages, > keeping the drop hydrated by placing the hanging drop back in the well > between additions. > > If your drops are drying out during crystal harvesting (very possible in > dry conditions), you might try harvesting in the cold room, where > evaporation is slower. We often have problems with crystal cracking and > drop-drying in the winter months when the humidity is very low indoors. The > cold room is usually humid enough and cold enough to slow evaporation to > allow crystal harvesting. (I hate working in the meat locker, though.) > Cheers, > _______________________________________ > Roger S. Rowlett > Gordon & Dorothy Kline Professor > Department of Chemistry > Colgate University > 13 Oak Drive > Hamilton, NY 13346 > > tel: (315)-228-7245 > ofc: (315)-228-7395 > fax: (315)-228-7935 > email: rrowl...@colgate.edu > > On 7/12/2012 12:55 PM, m zhang wrote: > > Hi Jim, > > 25% is w/v. Thanks for the information. Will check the webinar. > > Thanks, > Min > ------------------------------ > From: jim.pflugr...@rigaku.com > To: mzhang...@hotmail.com; CCP4BB@JISCMAIL.AC.UK > > Subject: RE: [ccp4bb] cryo for high salt crystal > Date: Tue, 10 Jul 2012 17:39:56 +0000 > Sucrose, sorbitol, Splenda, trehalose, etc, but instead of 25% (is that > w/v or v/w?), try using 100% saturated in reservoir, 75% saturated in > reservoir, or 50% saturated in reservoir. You will have to TEST these. > See also this webinar on cryocrystallography which shows how to make these > solutions: http://www.rigaku.com/node/1388 > > You could also try high salt solutions with similar technique. > > Good luck! > > Jim > > > ------------------------------ > *From:* CCP4 bulletin board [CCP4BB@JISCMAIL.AC.UK] on behalf of m zhang > [mzhang...@hotmail.com] > > *Sent:* Tuesday, July 10, 2012 11:28 AM > *To:* CCP4BB@JISCMAIL.AC.UK > *Subject:* [ccp4bb] cryo for high salt crystal > regaentDear All, > > I am sure this question was discussed before. But I am wondering if > anyone got the same experience as I do. > I got a crystal out of condition with 1M KCl, 1.4M Ammonium sulfate at > pH7. I tried to use glycerol, ethylene glycol, 25% sucrose, paraton-N oil, > or ammonium sulfate itself: The problem is that all the cryo plus original > reagents in the reservoir precipitate the salts out. And more serious > problem is because of high salt in the condition, while I am trying to loop > the crystal, both the drop and cryoprotectant drop form salt crystals (not > sure it is KCl or ammonia sulfate) significantly and very quickly, that > cause my crystal dissolved. My crystal doesn't seem to survive paraton-N > oil. Does anyone here have similiar case? any suggestion will be > appreciated. > > Thanks, > Min > > > -- ******************************************* Jacob Pearson Keller Northwestern University Medical Scientist Training Program email: j-kell...@northwestern.edu *******************************************
