We have for our clients a Nitrox membrane, there are only two on the island of El Hierro, free nitrox course, we have only eight bottles Nitrox, and the possibility of taking courses to use the Nitrox mix to 32% and 36 % in the waters of El Hierro.

For newcomers.

The air in its natural state contains 21% of oxigeno and 79% of nitrogeno. Nitrogeno is the greatest enemy of the diver. When we are out of the water and at sea level, we are at 1 atm. Although not noticing, or see, we have a power over us that crushes us, this is called atmospheric pressuresn rica and measured in atmosphere (atm).
Every ten meters of salt water upon us, we will add another atmosphere of pressure on our bodies, ie -10 m under the water will be at 2 atm.

Nitrogen is an inert gas for us, ie never use as it comes with the freed oxygen. This process of sea level does not affect us, but under water is another matter. With increasing pressure on us (ie lowering) our pass capillaries into the blood nitrogen and thus reaches the tissues where it accumulates. This occurs until it becomes saturated, some more than others, and others more quickly. For example, the blood absorbs much nitrogen but then released very quickly, whereas the brain, fat and joints absorption is slower but also their release. Our body releases nitrogen losing pressure (ie climbing).
Here is the key, if we have accumulated a lot of nitrogen during the dive will be liberated with safety to avoid the famous Decompression Sickness. This is going up too fast or doing safety stops, the dissolved nitrogen absorbed in the blood, pressure to lose the familiar form microbubbles that we can plug arteries or prevent the proper functioning of any tissue or organ. That is like a can of Coke, if we wave the bubbles explode when opened, here more or less the same.
Hence the importance of Nitrox (Enriched Air aptly named) that it does is increase the proportion of oxygen in the air in the bottle of 21%, which is natural, and upload to 32% or 36% for curve to increase security at a particular depth and make diving safer, which was very useful on the island of El Hierro.