Equivalent narcotic depth

Equivalent Narcotic Depth (END) is a concept used in technical diving to assess the narcotic effect of breathing gases used in deep diving. The END is the depth in sea water at which a particular nitrogen-oxygen mixture would have the same narcotic effect as the actual gas mixture at the actual depth.

Concept

The concept of Equivalent Narcotic Depth is based on the observation that the narcotic effect of a gas is proportional to its partial pressure. This is known as the Dalton's Law of Partial Pressures. Therefore, the narcotic effect of a gas mixture at a given depth can be compared to the narcotic effect of a nitrogen-oxygen mixture at a different depth.

Calculation

The Equivalent Narcotic Depth is calculated by dividing the partial pressure of nitrogen in the breathing gas by the fraction of nitrogen in air (0.79), and then subtracting 1 to convert from absolute to gauge pressure. The result is then multiplied by 10 to convert from atmospheres to meters of sea water.

Applications

The Equivalent Narcotic Depth is used in the planning of technical dives to determine the appropriate breathing gas for a given depth. It is also used in the analysis of diving accidents to determine the likely level of narcosis at the time of the accident.

See also

• Decompression
• Diving Cylinder
• Diving Regulator
• Scuba Diving