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Grateful Diver’s
School of Diving

Bob (Grateful Diver) Bailey

NAUI Instructor 41751


Understanding Gas Management

(continued)

Turnaround pressure

For simple dives, gas management often requires no more than for you to keep a couple of simple numbers in your head. When your gauge reaches that point, you know it’s time to take a specific action. Turnaround pressure is one of those numbers.

Turnaround pressure is exactly what the name suggests … the minimum pressure at which you can safely turn the dive and begin to make your way to the surface. It is most often used for shore diving, where you will be making your way up a slope to a specific exit point … usually the same place where you entered the water.

Turnaround pressure is fairly simple on dives where you will be making your way down a slope until it is time to return, then turning around and retracing your route back to the entry point. In that case, you subtract your desired reserve from your starting pressure, divide the remaining gas pressure in half, and subtract that from your starting value.

For example, let’s say you are starting with 3,000 psi and you want a reserve of 500 psi. So your usable gas is 2,500 psi. You’ll use 1,250 to go out, and 1,250 to return.

3,000 starting pressure – 500 reserve = 2,500 usable gas

Subtracting 1,250 psi from your starting pressure yields a turnaround pressure of 1,750 psi.

In practice, however, dives with that sort of profile are rare. More commonly, you will take a certain amount of time to reach your destination, spend a certain amount of time at your destination, and then return. In this case, take note of your starting pressure and the pressure you are at when you arrive at your destination … let’s say, a wreck you want to explore. By noting how much gas you used to get there, and adding it to your desired reserve, you can arrive at a turnaround pressure.

For example, let’s say you start with 2,800 psi (short fill) and arrive at your destination with 2,100 psi. You used 700 psi to get there. Adding that to your desired reserve of 500 psi yields a turnaround pressure of 1,200 psi. So by making a simple calculation in your head, you can know that when you reach 1,200 psi in your cylinder, it’s time to start heading back upslope to end the dive.

Don’t forget that on your return you will need to add some gas to your reserves because you need to do a safety stop. By knowing your consumption rate and the depth of your safety stop you can quickly and easily calculate how much gas you need for your safety stop and factor that amount into your turnaround pressure.

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