Learn to manage gas on your dives with the rule of thirds, the rock bottom concept and how dive computers calculate nitrogen saturation in real time.
Gas management is one of the most critical skills any diver must master, yet it is one of the most underestimated once the basic certification has been obtained. Knowing how much gas you have, how much you need to return to the surface safely, and when it is time to turn around are decisions that can make the difference between a successful dive and a real emergency.
The concept of rock bottom is the minimum pressure at which you must reach the surface with enough gas to handle an emergency. There is no universal number: it depends on depth, the diver's consumption rate, equipment configuration, and the number of people in the group. Many instructors recommend not going below 50 bar without having begun the ascent.
The rule of thirds divides available gas into three equal parts: one third for the way in, one third for the way out, and one third as an emergency reserve. It is especially useful in cavern dives or any environment where it is not possible to ascend directly to the surface.
Henry's law explains that gases dissolve in liquids in proportion to pressure. At greater depth, more nitrogen is dissolved in the tissues. If ascent is too rapid, the tissues do not have time to release that gas and bubbles form, which can cause decompression sickness.
The recommended ascent rate is 9 meters per minute or less. The safety stop at 5 meters for 3 minutes significantly reduces the risk of decompression and should become an automatic habit.
Dive computers calculate in real time the saturation of each tissue compartment, adapting limits to what the diver has actually done. Unlike traditional tables, they track the actual profile and provide more precise margins.
Repetitive dives add complexity: the residual nitrogen that remains after a first dive does not disappear immediately. The limits on the second and third dive will be shorter.
The use of nitrox reduces the nitrogen load by having a higher oxygen percentage. Nitrox 32 or 36 extends bottom times, but has its own limit: excess oxygen is toxic, so there is a maximum operating depth that must be respected.