What Scuba Tank Gas Mixture Do Divers Use?
The air which we breathe is composed of several gases. It is a mixture of mainly nitrogen and oxygen with trace amounts of carbon dioxide, argon, and other gases. Scuba tanks contain mixtures of different gases and this is what allows divers reach further depths below the ocean surface. However, the most common air mix is atmospheric air and it allows for dives of 40 meters and below. Although some divers have gone beyond 40 meters on atmospheric air, 40 meters is the acceptable depth recommended by most training agencies. For deeper or longer dives, special gas mixes such as nitrox, hydrox, and Trimix & heliox are safer alternatives to simple compressed air. These blends give a diver more freedom and require special certifications to be used.
Below is a description of the three gas mixes which are available for scuba diving:
Standard atmospheric air is over three-quarters nitrogen, less than one-quarter oxygen and with trace amounts of other gases. Nitrox contains elevated percentages of oxygen, between 32% and 40% of the entire gas volume. This mixture allows divers longer dive times and at shallower depths with a significantly lower chance of suffering from the bends. However, there are certain risks associated with the use of Nitrox- going beyond the limit of a dive with nitrox results in the inhalation of oxygen at an unsafe partial pressure which leads to oxygen toxicity eventually.
Therefore, diving with Enriched Air Nitrox (EANx) requires special safety training, a gas analyser and a scuba tank fill location with compressor capable of producing and determining the desired gas mixture.
- TRIMIX & HELIOX
With trimix, oxygen and nitrogen are partially replaced with helium. This gives divers the opportunity to go deeper than nitrox permits and with less risk of oxygen toxicity. Heliox is a diving gas mix with about the same amount of oxygen as regular air but with nitrogen completely replaced. Removing the nitrogen from the mix increases the depth and time limits. Since it has a lower percentage of oxygen than nitrox, there is little risk of oxygen toxicity. The use of heliox does require a secondary tank of air or nitrox for use in the shallower sections of the dive. The major disadvantage of heliox use is the loss of body heat because heliox is a poor temperature conductor. This causes the body to lose more of its natural heat faster, leaving a diver prone to hypothermia. Another disadvantage is that helium is rare and expensive to purchase.
Hydrogen is cheaper and more abundant than helium. This makes hydrox a more affordable alternative to heliox. Hydrogen barely has any toxicity issues and can be used at all depths. The main problem with hydrogen is that it is quite risky due to extreme flammability. Hydrox is quite new and is used mostly in extreme commercial diving, farther than where trimix or heliox reaches.