Wireless,

MikeS's statements are common knowlege to all divers. He's an expert & can correct me if I misspeak.

Regarding weights:
MikeS's point was that weights are a critical safety device, dropped in an emergency to acheive positive boyancy & ascend. If dropping your weights means you stop breathing, you have a problem.

Regarding pressure/air:

At 10 meters (33 feet) atmospheric pressure is doubled from the surface (1 atmosphere at sea level, 2 atmospheres pressure at 10m).

SCUBA gear stores compressed air and de-compresses it to "atmospheric" pressure when you inhale through the regulator. At 10m, "atmospheric" pressure is doubled, and it takes twice as much air to fill your lungs to full capacity. You consume compressed air from the tank twice as fast as you would floating at the surface. Every 10m you descend you consume more air with each breath. At 40m, the approximate limit for safe recreational diving, you are consuming 4 times as much air with each breath as you would at the surface!

As I said in my previous post, the problems are numerous & complex, but the idea is still exciting.

Peski