I have an assignment about deep sea diving and of course it involves some gas mixtures to be used. I just don't know what suitable gas mixtures do I have to use in order for this diving to be safe and successful. The scenario is this:

Question

1. A shipwreck is located at a depth of 220m.
2. Up to 5 dives will be needed (per diver) to bring valuable to the surface.
Note: You could you different gas mixtures for this. How much of the different gas mixtures do I need?
HELP PLEASE!

Answer 1

• The majority of gas used in most SCUBA tanks is compressed air. This air is composed of the same elements everywhere - 21% Oxygen 79% Nitrogen. Advanced SCUBA divers may use an "enhanced" mixture of 32% (up to about 40%) Oxygen with the balance being Nitrogen. The number of divers who use a mixture like this is about 2 to 5% of all certified divers. Less than 1% of all divers may use a special Tri-mix of some rather exotic gases to allow very deep dives - however, it takes years of instruction and training to use these exotic mixes.

http://www.worlddivingreview.com/scuba-diving-safety-know-your-breathing-gases

http://njscuba.net/gear/trng_12_calculators.html