“Tank factors? Aren’t those things people should consider when purchasing a tank? Things such as size, color and buoyancy characteristics?” This was asked by an employee at a local dive store when he overheard me talking about dive planning. It didn’t really surprise me at the time as not many people have heard the term tank factor. The truth is, tank factors are a critical part of planning our dives and divers should have an understanding of what they are in order to plan their dives properly.

Tank Factors Simplified

To determine a tank factor you need to know two things; 1) the tank’s rated pressure and 2) the tank’s rate volume in cubic feet. For example, a standard aluminum 80 tank is rated to 77.6 cubic feet at 3000 psi. We can think of tank factors as a ratio. A ratio that says every one (1) PSI is equal to X cubic feet of gas. We can use simple math to find this. We divide the tank’s rated volume divided by it’s rated pressure. Using a standard aluminum 80 tank, the tank factor would be 77.6 / 3000 = 0.025. This says that one psi is equivalent to .025 cubic feet. Different sized tanks will have different tank factors. If you are diving doubles, then you multiply the tank factor by two (since you have two tanks).

Applying Tank Factors

So by now, you know what a tank factor is and how to calculate it. You may be asking, “What do I do with it?” If I consumed 100 psi of gas per minute (on the surface), that is equivalent to 2.5 cubic feet of gas. It would take me 30 minutes to empty the tank with that consumption rate. This consumption rate is high, but I wanted to use numbers that make the math easy to understand. Of course, this calculation hasn’t been adjusted for depth.

Summary

The tank factor is a critical component to determining gas reserves and consumption. We’ll save those calculations for a future post. Every diver should know that when someone mentions tank factors, they are talking about the ratio between the tank’s pressure rating and it’s volume.

Dive Safe,
Duane
Precision Diving