The practical limits for air diving operations were established in 1915, when the US Navy USS F-4 was recovered to a depth of -92 meters. US Navy divers simply could not work at this depth, in addition to the decompression penalty they had background time limited to 10 minutes.

In 1919, an inventor named Elihu Thomson speculated that helium should be an appropriate substitute for nitrogen in breathing mixtures for diving, estimated a minimum of 50% gain at the maximum operating depth. At this time the cost of the helium mixture was high which made its use unfeasible. A few years later Texas natural gas mines were discovered that produced helium, which reduced its cost.

In December 1937, Max Nohl set a new world record deep breathing heliox, performed a -129-meter swim on Lake Michigan. Shortly thereafter, the US Navy conducts simulated dives at -154 meters. The first "helium test" of helium came with the sinking of the submarine USS "Squalus" in 1939, to a depth of -74 meters. During this rescue operation, a diver breathing air was not able to repair a connection cable used in the rescue bell. Despite the drowning of 29 crew members, the use of helium allowed the rescue of 33 men, as well as the execution of more than 100 dives without the occurrence of incidents. This demonstrated that helium was a viable alternative to deep diving operations.


Most important dates


Professor Elihu Thompson speculates that helium can be used instead of nitrogen to reduce resistance to breathing at great depth. The effects of narcosis had not yet been proven until the rescue of USS Squalus in 1939. Heliox was used with air tables resulting in a high incidence of decompression sickness so helium use was discontinued.

The US Navy begins analyzing the potential of helium utilization and in the mid-1920s on laboratory animals that were exposed in an experimental chamber for dives using heliox. Therefore, for humans the heliox 20/80 breath (20% oxygen, 80% helium) was successfully decompressed from deep dives.

Divers perform various tests on the helium mixtures, including the Max "Gene" Nohl rescue divers who could dive to -127 meters.


The US Navy used heliox in the rescue operation of the USS "Squalus".


The first saturation dives using heliox.


Hal Watts performs dual body recovery in Mystery Sink (126m). Sheck Exley and Jochen Hasenmayer used heliox in a cave-dip to a depth of -212 meters.


First mass use of Trimix and heliox: Wakulla Springs Project. Exley teaches non-professional divers regarding the use of trimix in dives performed in caves.


Billy Deans began teaching diving with the "trimix" mix to recreational divers. Tom Mount develops trimix formation, the first standards (IANTD). The use of trimix spreads rapidly throughout the American diving community.


A team combined by UK / U.S. divers, including the main wreck divers John Chatterton and Gary Gentile, successfully completed a series of dives in the RMS "Lusitania" shipwreck expedition to a depth of 100 meters with trimix.


The Guinness Book of Records recognizes John Bennett as the first diver to dive 300 meters away using Trimix.


David Shaw hits the deep record with the use of a trimix Rebreather, tragically dying while repeating the dive.



Trimix is ??a mixture of three components ("tri" and "mix"), and usually when people talk about trimix, which means it is a mixture of three gases: helium, oxygen and nitrogen. The trimix is ??used in deep dives instead of air to help dilute oxygen to oxygen (to avoid oxygen toxicity) and nitrogen (to avoid nitrogen narcosis). (avoiding oxygen toxicity) and nitrogen (avoiding nitrogen narcosis).

With a mixture of three gases, it is possible to create suitable combinations (standard or customized) for different depths or effects, adjusting the proportion of each gas. Heliox is a mixture of helium and oxygen ("heli" and "ox"). Because of its non-narcotic characteristics, helium is the preferred gas in the production of trimix blends. In deep dive, when air is breathed, the narcosis becomes progressively more evident, from the 30 meters, result of the high partial pressure of the nitrogen breathed, that affects the central nervous system. To avoid these narcosis effects, gas mixtures with inert gases with a minor narcotic potential are used which substitute part or all of the nitrogen.

Low partial oxygen pressures cause hypoxia and on the other hand high partial pressures of oxygen cause hyperoxia, a worrying factor and with very serious consequences.


The two main factors limiting deep dives are nitrogen narcosis and oxygen poisoning. When the diver is exposed to partial oxygen pressures due to several days of operation he may enter a hazy zone with unpredictable consequences (OTUs and% CNS - Oxygen Tocicity Unit and Central Nervous System see oxygen toxicity).

Nitrogen is a narcotic, with increased depth it compromises too much the diver's performance just when he most needs to have a healthy mind.

With deep diving the diver is more prone to hazards and potential accidents that does not happen at lower depths when diving with air. The diver should be lucid to control and make the best decisions without being misrepresented by the elevated PPN2 (Partial Nitrogen Pressure) in the body (narcosis - different states of narcosis or + or less being always present) due to depth. By reducing the oxygen and nitrogen content in the respiratory mixture by the addition of helium (an inert non-narcotic gas), we can adjust the mixture in order to control oxygen and nitrogen levels for the planned dip profile (e.g. diving at 100 mtrs with a narcotic equivalent equal to as if we were diving with air within 20 meters). In the process, we also reduce the density of the respiratory mixture, also decreasing respiratory effort and reducing the risk of accumulation of carbon dioxide.

Pinguim Sub thanks the Sar João Ramos- Divers (Portuguese Navy) for the transfer of part of this text of its authorship