Technical or Nitrox Diving at Cocos Island

On a recent visit to Sea Hunter at Cocos Island I discussed with owner Avi Klapfer the reasons for his enthusiasm about technical diving using enriched air with a higher percentage of oxygen (known as Nitrox).

Avi said what many Cocos aficionados already know: to get the best schooling hammerhead encounters divers often go to depths of 60-110 feet and stay as long as they can.

If a diver remains at those depths on regular compressed air for very long, he or she approaches the limits of no-decompression diving. What Avi wanted to achieve was a better margin for his guests, a way to enjoy the sharks and not approach the no-decompression limits.

The usual air in a scuba tank has 21% oxygen, with the rest of the mix principally nitrogen. The oxygen is the fuel for our bodies; absorbing the nitrogen, however, has no benefits and can actually cause various problems.

If we enrich the air in our tanks and breath (through our own regulators) a mixture of perhaps 32% oxygen and 68% nitrogen we both increase our fuel and reduce our potential problems by having less nitrogen absorbed.

In an over simplified way, that is the essence of enhanced-air diving. At its simplest level you put your own regulator on a standard scuba tank filled with enriched air, and you use a decompression computer which has been set to the higher percentage of oxygen in that tank. That’s all there is to it.

Yes, it is possible to be even more advanced, to use semi-closed or closed circuit rebreathers. For normal sport diving however, merely having enhanced levels of oxygen in your tank confers wonderful benefits with very few drawbacks.

Because of the singular nature of the marine life and undersea landscape at Cocos Island (discussed below) Sea Hunter and Undersea Hunter have become the industry leaders offering instruction and enriched-air tanks for visiting divers to this very special place.


You are at Cocos Island, some 300 miles (500 km) off the Pacific coast of Costa Rica. You are now ready to dive in one of the best diving locations on the surface of the planet. You strap on your air diving computer and you plan to make the best dive that your tank of compressed air can offer you. You reach the bottom found at Cocos perhaps at 100 feet or more, and after a short period of time, you have to ascend to shallower waters if you are to avoid any decompression. Looking down as you ascend, you see that some divers who started the dive with you are remaining on the bottom. They are wearing scuba tanks with a special green and yellow identification: NITROX.

Why use Nitrox? Well, to start off, if our original diver would have had his scuba tank filled with Nitrox, he would have been able to extend his bottom time quite substantially without ever reaching the “no-decompression” limits. Depending on the gas mix of Nitrox, which is merely enriched air with a higher percentage of oxygen we can enjoy as much as 20-30% more bottom time. That advantage is well worth the short time it takes for training and the extra cost for each Nitrox fill.

Why does enriched air confer these benefits? By reducing the amount of nitrogen in our breathing gas, there is much less to dissolve in our blood for the same time at a given depth. This translates to more bottom time. For example, Nitrox divers using 36% oxygen enriched air could dive to a depth of 113 feet but only be at the equivalent air depth of 85 feet. There are other advantages to Nitrox; you will find that you have shorter “surface interval time’ due to less off-gassing required. Furthermore, at the end of a busy diving day, you’ll feel less tired due to the reduced amount of time required to off-gas as well as a richer oxygen content to metabolize.

All in all, enriched air diving is perfectly suited for your dives at Cocos Island, where you will find many of the best encounters with schooling hammerheads occur at depths of 60-110 feet.

Most important, to receive all of these wonderful benefits you do not have to change your diving technique at all. If you would like a brief course in enriched air diving (offered during your cruise) you can then be a Nitrox diver!

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Modified 05-21-97