Questions I. Calculate the depth a diver should not exceed if breathing Nitrox II to avoid oxygen toxicity. Show your working clearly, and state any assumptions that you make. II. Commercial divers working at extreme depths often use mixtures of helium and oxygen. If a diver working at 100m below sea level uses a mixture of 12% oxygen by volume, would this be a breathable mixture on the surface? Explain your answer.
Assumptions
* Density (p) of fluid in question is 1025 kg/m3, as is that of sea water. * A single atmosphere of pressure is equal to 101.325 kPa. * Acceleration due to gravity (g) is 9.8 m/s2.

Solutions I. Given molar fraction of O2 (Yi) as 36%, and partial pressure (PPO2) of 1.6 bar maximum, we can calculate a maximum pressure (Ptotal ) from Daltons law of partial pressures as,
PPO2Yi =Ptotal
1.60.36 =4.44 atm
Removing the single atmosphere of pressure at the surface we get,
Pdepth= Ptotal - Patm
Pdepth=3.44
Converting this pressure to pascals and then to a depth (h) in metres, Pdepth (Pa)p ×g=h 3.44 ×101.3251025×9.8=34.7 m II. No. Gas suitable for consumption at the surface is made up of oxygen and a mixture of inert gases, the function of which is to dilute the oxygen to an adequate concentration for human consumption. At sea level, or surface pressure, the partial pressure of oxygen in a 12% molar fraction mixture is simply 0.12 x 1atm of pressure, this partial pressure of 0.12 is far below the normal value of 0.21 and well into the range that will cause impaired activity, immediate exhaustion, and possibly health problems.
References
1. Michael Ange 2008, SCUBA Diving. Available from: http://www.scubadiving.com/training/basic-skills/practical-guide-nitrox. [6 April 2016] 2. Jonathan G. Fairman 1996, NASA. Available from:https://www.grc.nasa.gov/www/k-12/WindTunnel/Activities/fluid_pressure.html. [6 April 2016] 3. Richard E. Fairfax 2007, OSHA (USA). Available from:https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_id=25743&p_table=INTERPRETATIONS. [6 April 2016]