Question 1

What is rock bottom in scuba diving?

Accepted Answer

Rock bottom is the minimum tank pressure at which you must begin your ascent so that you and your buddy can reach the surface with a planned reserve, even if one of you loses all gas at depth. It accounts for problem-solving time at depth, the ascent, and the safety stop, and is a core rule of technical dive planning.

Question 2

What is minimum gas?

Accepted Answer

Minimum gas is the volume of gas required to get two divers from the deepest point of the dive back to the surface, including a safety stop. It is calculated from your SAC rate, depth, and ascent rate. Rock bottom is simply that minimum gas volume expressed as a tank pressure plus your surface reserve.

Question 3

How is rock bottom calculated?

Accepted Answer

Rock bottom is the sum of three components: problem-solving gas at depth, ascent gas, and safety-stop gas. Problem gas is the time you spend resolving an issue at the deepest point; ascent gas is consumed over the ascent at an average pressure; safety-stop gas covers a 3-minute stop at 5 m. The total is divided by your tank capacity and your reserve pressure is added on top.

Question 4

Why assume two divers for minimum gas?

Accepted Answer

The worst-case scenario is a complete gas loss for one diver at maximum depth, forcing both divers to share a single tank. Planning for two divers on one tank ensures you can safely exit even in that emergency. If you dive solo or with a redundant gas source, you can set the diver count to 1.

Question 5

Does Nitrox change my rock bottom?

Accepted Answer

Rock bottom is driven by gas volume, not gas mix, so your minimum gas is essentially the same for air and Nitrox. The gas you choose affects other limits such as MOD and oxygen exposure, which you should plan separately. A richer Nitrox mix may, however, change your maximum depth and therefore indirectly your rock bottom.

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