What is a key characteristic of a dive using EAN40?

A dive utilizing EAN40 is characterized by its oxygen content, which consists of 40% oxygen and 60% nitrogen. This specific blend is often employed to reduce the overall nitrogen exposure during dives and to enhance the diver's experience with reduced nitrogen narcosis and longer bottom times compared to air.

The presence of 40% oxygen is significant because it dictates the maximum operating depth for safe usage of this gas blend. Divers can optimize their dive profiles to take advantage of the increased oxygen, which can enhance their physiology and potentially minimize the risk of decompression sickness when managed properly within prescribed depth limits.

While it is true that EAN40 is not suitable for very deep dives—due to increased partial pressure of oxygen and the toxic effects that can arise—this does not change the fundamental characteristic of the gas mix itself. The nitrogen content is also lower compared to regular air, but the direct key characteristic here remains the mixture's oxygen percentage, thereby affirming the correct option regarding EAN40.