Determining Turnaround Using Tables
The basic steps involved in using a table-based approach to determining gas turnaround are the same as they are for divers using identical cylinders: identify the controlling diver; determine penetration gas volume; and, calculate turnaround for individual team members. The difference is, we now base our calculations on actual volume instead of pressure.
Example: Diver A’s steel 95 is filled to 2,400 psi, which the table indicates is 86 cubic feet. Diver B’s aluminum 80 is filled to 3,100 psi, which the table tells us is 81 cubic feet. This makes Diver B the controlling diver.
Example: Diver B’s penetration gas is represented by a pressure of 1,000 psi or — according to the table — 26 cubic feet. Diver A’s penetration gas volume must be represented by a number that is equal to or slightly less than this; according to the table, this is 25 cubic feet, or 700 psi — 300 psi less than it is for Diver B.
Example: Continuing the previous example, Diver A’s turnaround is 1,700 psi; Diver B’s is 2,100.
Some cave divers who use dissimilar cylinders avoid doing precise gas-turnaround calculations because they are intimidated by the complex mathematics they believe are required. As you can see, however, consulting a simple table can greatly simplify the necessary math and help reduce the possibility of mathematical error.