Helitrox and deep air diving courses

air helitrox
deep air diving

After the Entry levels technical diving courses such as Advanced Nitrox and Decompression Procedures you can dive deeper on air with the helitrox deep air diving courses like the Extended Range course or add Helium to your Deco Procedures course and become a Helitrox diver. Most agencies are changing their ways and are now including Helium to the technical diving levels of 40, 45 meters depth. Yes helium can be expensive in places but the agencies see that the use of Helium is a safer way to dive than on air to cut the effects of inert gas narcosis. The Extended Range course from TDI or the SSI Extended Range still lets you dive to 55mtr on air, as they realise Helium is either unavailable or way too expensive.

What is Decompression diving?

The decompression of a diver is the reduction in ambient pressure experienced during ascent from depth. It is also the process of elimination of dissolved inert gasses from the diver’s body, which occurs during the ascent, during pauses in the ascent known as decompression stops, and after surfacing until the gas concentrations reach equilibrium. Divers breathing gas at ambient pressure need to ascend at a rate determined by their exposure to pressure and the breathing gas in use. A diver who only breathes gas at atmospheric pressure when free-diving or snorkelling will not usually need to decompress, Divers using an atmospheric diving suit do not need to decompress as they are never exposed to high ambient pressure.

Inert gas

When a diver descends in the water the ambient pressure, rises. Because breathing gasses supplied at ambient pressure, some of this gas dissolves into the diver’s blood and is transferred by the blood to other tissues. Inert gas such as nitrogen or helium continues to be taken up until the gas dissolved in the diver is in a state of equilibrium with the breathing gas in the diver’s lungs, at which point the diver is saturated for that depth and breathing mixture, or the depth, and therefore the pressure, is changed. During ascent, the ambient pressure is reduced, and at some stage the inert gases dissolved in any given tissue will be at a higher concentration than the equilibrium state and start to diffuse out again. If the pressure reduction is enough, excess gas may form bubbles, which may lead to decompression sickness, a possibly debilitating or life-threatening condition. It is essential that divers manage their decompression to avoid excessive bubble formation and decompression sickness.

Bubble formations

helitrox course
Steve line drill, no mask swim

The mechanisms of bubble formation and the damage bubbles cause has been the subject of medical research for a much time and several hypotheses have been advanced and tested. Tables and algorithms for predicting the outcome of decompression schedules for specified hyperbaric exposures have been proposed, tested and used, and in many cases, superseded. Although constantly refined and generally considered acceptably reliable, the real outcome for any person diver remains slightly unpredictable. Although decompression retains some risk, this is now generally considered acceptable for dives within the well-tested range of normal recreational and professional diving. Nevertheless, all now popular decompression procedures recommend a ‘safety stop’ additional to any stops required by the algorithm, usually of about three to five minutes at 3 to 6 metres (10 to 20 ft), even on an otherwise continuous no-stop ascent.

Decompression may be continuous or staged.

A staged decompression is interrupted by decompression stops at calculated depth intervals, but the entire ascent is actually part of the decompression and the ascent rate is critical to harmless elimination of inert gas. A no-decompression dive, or more accurately, a dive with no-stop decompression, relies on limiting the ascent rate for avoidance of excessive bubble formation. The elapsed time at surface pressure immediately after a dive is also an important part of decompression and can be thought of as the last decompression stop of a dive. It can take up to 24 hours for the body to return to its normal atmospheric levels of inert gas saturation after a dive. When time is spent on the surface between dives this is known as the “surface interval” and is considered when calculating decompression requirements for the next dive.


deep air diving skill practice
Instructor candidates Larry and Steve

The National Association of Underwater Instructors (NAUI) uses the term “helitrox” for hyperoxic 26/17 Trimix, i.e. 26% oxygen, 17% helium, 57% nitrogen. Helitrox requires decompression stops similar to Nitrox-I (EAN32) and has a largest operating depth of 44 metres (144 ft), where it has an equal narcotic depth of 35 metres (115 ft). This allows diving throughout the usual recreational range, while decreasing decompression obligation and narcotic effects compared to air.[24]

GUE and UTD also promote hyperoxic trimix, but prefer the term “TriOx”.

Other divers question whether this terminology is useful, and feel that the term Trimix is enough, modified as right with the terms hypoxic, normoxic and hyperoxic, and the usual forms for indicating constituent gas fraction.

The TDI Helitrox Diver Course examines the theory, methods, and procedures for planning staged decompression dives utilizing helium in the breathing mixture to cut the effects of inert gas narcosis.

The TDI Helitrox Diver Course trains divers how to plan and conduct staged decompression dives to a maximum depth of 45 metres/150 feet. The most common equipment requirements, gear set-up, and decompression techniques are also presented during this course. Students are permitted to use enriched air nitrox and helium mixes with no greater than 20% helium content, and up to 100% oxygen for decompression diving.

This program is designed as a stand-alone course, or it may be taught in conjunction with TDI Advanced Nitrox at the discretion of the instructor.