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><Answer (straight forward): He has a total volume of 200 * 10 l of air at >1 bar. In 20 m depth we have 4 bars, so the divers has 4 times less volume >to breathe than at the surface = (200 * 10)/4 l. As he consumes 20 l/minute >he can stay (200 * 10)/4/20 minutes = 25 minutes (we don't account for the fact >that he cannot empty the tank completely due to the pressure of 4 bars).> > >Try again---- the absolute pressure at 20m = 3 bar not 4 (1 bar >atmospheric and 2 bar from the depth of water) Be fair - he didn't say he was diving in water. :-) Assuming he was, let's re-run the calc including a safety margin this time (don't want these Yanks thinking we're a load of cowboys!). I have a 10L cylinder at 200bar. I want to keep a 50bar reserve, so I have 150bar usable, giving 10L*150bar = 1500L free air. If I consume 20L/min at the surface, that gives me 75mins surface use. My plan is to go to 20m, which is 20m / 10m/bar = 2bar (water), + 1bar (air) = 3bar absolute pressure, so I have 75mins/3bar = 25mins at 20m. The fact it's the same number is a coincidence. mike. ___________________________________________________________________________ Mike Salmon, Climatic Research Unit, | University of East Anglia, Norwich, UK | SCUBA diving in the United Kingdom m.salmon@ue*.ac*.uk* +44-1603-592875 | http://www.cru.uea.ac.uk/ukdiving/
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