Depth changes everything about the diving experience. Pressure increases by one atmosphere for every 10 metres of seawater. At 30 metres, a diver experiences 4 atmospheres of absolute pressure — four times the pressure at the surface. These physical realities affect your gas supply, your body, and your equipment in ways every diver must understand.
Depth and Gas Consumption
Because your regulator delivers air at ambient pressure, the deeper you dive, the more air molecules are in each breath. A diver who consumes 15 litres per minute at the surface will consume approximately 60 litres per minute at 30 metres. This reduces your bottom time dramatically and requires careful gas management planning.
Depth, Narcosis, and Physiological Effects
| Depth | Nitrogen Narcosis Risk | Physiological Notes | Min. Recommended Certification |
|---|---|---|---|
| 0–18 m | None | Standard recreational range; no narcosis | Open Water |
| 18–30 m | Low (some sensitivity) | Mild narcosis possible in susceptible individuals | Open Water (to 18 m) / Advanced Open Water (to 30 m) |
| 30–40 m | Moderate to High | Noticeable impairment for most divers; reduced judgment | Advanced Open Water + Deep Diver specialty |
| 40+ m | Severe | Significant cognitive impairment; decompression obligation likely | Technical diving certification required |
Light Absorption at Depth
Water absorbs light wavelengths selectively as depth increases. Red is absorbed first (within 5 metres), followed by orange and yellow. Below 20 metres, the underwater world appears almost entirely blue and green without an artificial light source. This is why underwater photography requires strobes or video lights to restore accurate colour.
Managing Narcosis
Narcosis cannot be reliably predicted — individuals respond differently, and your susceptibility varies day to day depending on fatigue, anxiety, and previous gas exposure. If you feel unusual at depth, the correct response is to ascend 5–10 metres. Symptoms resolve rapidly as pressure decreases.