Can Old Scuba tanks be used for CO2?

Attention SCUBA divers! Crush depth of scuba tanks? NOT burst strength of tanks from internal pressure, but?

• how much external pressure can tanks withstand before rupture? (please read rest of details! ) I KNOW it will be far deeper than a person could actually dive with scuba tanks. I am not looking for the maximum depth a person could reach. Go to the deepest part of the ocean, put weights on the tanks so they will sink instead of floating, and let them go. How deep do they reach before the water pressure crushes the tanks and releases the air? Also, will the answer vary depending on whether the tanks are full or empty? Does the internal pressure of the tank help to resist the external pressure of the water? Finally, can analogous values be found for propane tanks, CO2 tanks, etc? Which ones would provide the greatest buoyancy? I may not be expressing this properly. Please be patient with me. If you don't understand, ask for more details and I WILL provide them. Thanks to all who give serious replies!

• Answer:

  Scuba air tanks are designed for over 3,000 lbs per sq. inch internal pressure and are well made I would imagine that they would also withstand external pressures in multi thousands of feet also pro bally if they were full they could withstand more.. do not use a propane tank as a air tank they are not designed for pressures over 200 lbs and what are you going to use for a regulator ? Be extremely careful you are threading on dangerous waters here.. U.S. Divers is one also my gages are Oceanic Instruments. my regulater is a Mares.. Hope that helps.