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Identical Cylinders,
Different Starting Volumes


When team members use identical cylinders, determining a gas turnaround point is relatively easy. This is due, in part, to the fact that when team members use cylinders of identical capacity, identical pressure gauge readings also represent identical volumes.

Here are the basic steps that team members using identical cylinders would follow to determine the safest possible turnaround points. Note that this procedure is the same, regardless of whether team members have identical, or different starting pressures.

  • Identify the controlling diver(s) — This is the team member (or members) with the lowest actual starting gas pressure. If all team members have the same starting pressure, they are all — in essence — the controlling divers.
  • Determine the penetration gas volume — If the controlling diver’s (or divers’) actual starting gas pressure is not a number easily divisible by three, round down to the next lowest number that is. One third of this number will represent the penetration gas volume for each team member.
  • Determine the turnaround point for each team member — Each team member should deduct the controlling diver’s penetration gas value from his or her actual starting pressure. (The controlling diver must remember to also deduct this number from his or her actual starting pressure and not the number he or she rounded down to.)

Here is an example that shows how this process works:

  • Divers A, B and C have identical cylinders. Diver A’s starting pressure is 3,400 psi; Diver B’s is 3,100; and Diver C has 2,900.
  • Diver C is the controlling diver. In so far as 2,900 is not easily divisible by three, Diver C rounds down to the next closest number that is, 2,700. The penetration gas volume is represented by one third of this number or 900 psi.
  • All team members therefore deduct 900 psi from their actual starting pressures. Thus, Diver A’s turnaround point becomes 2,500 psi; Diver B’s is 2,200; and Diver C’s is 2,000.

Dealing With Cylinders of Different Capacities »




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