Thanks, these are great links! Evette On Jul 13, 2012, at 7:39 PM, "Andrew Purkiss-Trew" <a.purk...@mail.cryst.bbk.ac.uk> wrote:
> Quoting Jacob Keller <j-kell...@fsm.northwestern.edu>: > >>> >>> 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? >> > > Not N2 poisoning, but lack of Oxygen in the blood. At altitude, the body > adjusts by breathing deeper and faster and people can become acclimatised (so > giving rise to altitude training for athletes). The really dangerous levels, > for a healthy adult, are a fair way below the 19.5%. The UK generally seems > to have O2 alarms set at 19% and maybe a second alarm at 17%. > > More details are given on the OHSA website > (http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_id=25743&p_table=INTERPRETATIONS > found with a quick google) and on one of the UK Liquid Nitrogen supplier's > websites (http://www.cryoservice.co.uk/oxygen_depletion.aspx) > > Hope this helps, > > Andrew Purkiss > > > ---------------------------------------------------------------- > This message was sent using IMP, the Internet Messaging Program.
