Diving is a
sport of pressure
Diving is a sport of pressure.
As depth increases, the surrounding pressure rises, changing the volume, density, and solubility of gases and directly affecting your body and gear. This guide helps beginners understand why those safety rules exist, in the order pressure → gas laws → equalization → nitrogen narcosis.
One atmosphere every 10m
Because of the weight of water, pressure increases by about one atmosphere for every 10m of depth. Adding the surface atmospheric pressure gives the absolute pressure (ata). The greatest pressure change happens near the surface (a doubling from 0→10m) — so careless ascents and descents in shallow water can actually be more dangerous.
Three laws explain nearly everything
Almost everything in diving physiology can be explained by three laws.
Volume ∝ 1/absolute pressure — air spaces (lungs, mask, ears, BCD) compress on descent and expand on ascent.
Partial pressure = fraction × absolute pressure — the starting point for nitrogen narcosis and oxygen toxicity.
Dissolved gas ∝ partial pressure — decompress too fast and nitrogen forms bubbles (the origin of decompression sickness).
- Never hold your breath — especially on ascent. As the air in your lungs expands, holding your breath can lead to pulmonary barotrauma and arterial gas embolism (AGE). Always breathe slowly and normally.
The most common injury is middle-ear barotrauma
Matching the pressure in your air spaces to the surroundings is equalization; failing to do so causes barotrauma. Techniques include the Valsalva (pinch your nose and gently blow) and the Toynbee (pinch your nose and swallow). Equalize early and often before descending, never blow too hard, and if it does not work, abort the dive (ascend).
- A blocked nose or sinuses from a cold or rhinitis increases the risk — if you feel unwell, postpone the dive.
Drunk on depth, but reversible
As you go deeper, the partial pressure of nitrogen rises and acts like an anesthetic, dulling judgment and focus (‘drunk on depth’). It can typically appear from around 30m, but varies greatly between individuals and days. Ascending brings a fast and complete recovery (no lasting effects). The response is simple — ascend to a shallower depth.
- The onset depth of nitrogen narcosis (~30m) varies greatly by individual and by day — many divers do not notice it at all.
- Figures are based on training-agency and peer-reviewed materials.