Bent on the VR3?

[Mark Chase]

To keep Zac happy here is what JJ had to say about He in deco gas:



9.7 Unconventional Decompressions

Many divers are led to believe that from a decompression standpoint, helium diving is dangerous and difficult. Overcoming these misconceptions frees divers to look at the application of helium in a variety of areas. Jarrod Jablonski and George Irvine were two of the earliest pioneers in the common use of helium mixtures in unconventional situations, e.g. shallower than 100 feet (30m). Lengthy decompression obligations from bottom times in excess of six hours at 300 feet led to an examination of nitrogen complications. An analysis of these diving profiles revealed that, particularly on long immersions, the true difficulty in decompression efficiency was the removal of nitrogen from slow compartments. During these dives, nitrogen is particularly troublesome because decompression time spent from 150 feet (45m) to the surface becomes so extensive that divers accumulate substantial nitrogen loads. During these long immersions, Jarrod Jablonski began successfully diving with helium enriched decompression gasses all the way to 30 feet (lOm).

As a result of their analysis of the data, GUE and WKPP divers started to radically reduce decompression time, particularly near 100ft (30m), convinced that the intermediate decompressions caused a significant accumulation of gas that would then have to be eliminated. Given their experience, these explorers are convinced that popular dissolved gas models (such as Haldane and Buhlmann) are inaccurate and produce inefficient decompressions. These models treat helium in a highly conservative manner, further highlighting the problems with dissolved gas models.

When doing very long deep dives with elevated helium mixtures, even dissolved gas decompression models demonstrate reduced decompression obligation. This is because the elevated off-gassing rate of helium is particularly favourable for such long dives. However, shorter dives, i.e. in the 20-30 minute range, are more problematic. For example, calculated decompression for 30 minutes at 300ft (90m) with no helium results in about 10 minutes less decompression than with helium in both Nitrox mixes, and about five minutes less than with helium in the 120 foot decompression bottle. It is likely that this additional time is not an accurate reflection of reality, and that new bubble models, such as the Varying Permeability Model (VPM), demonstrate more realistic parameters.

It may be that helium is treated too conservatively, and that it is either able to be eliminated more rapidly and/or is tolerated at higher pressure. Over the years, leading divers and researchers have become progressively more convinced that helium is a much better gas than previously thought. New diving efforts are highlighting a notable change in the common gasses breathed, as well as the shape of decompression profiles.


Below is the RULE OF THIRDS in the training manual writen by JJ

11.3 The "One Third" Air Rule
Environments that allow divers to make an immediate ascent to the surface do not usually require that a large emergency gas reserve be maintained. Commonly, divers strive to return to their dive boat with 500psi/ 35bar remaining in their tanks. However, as the complexity of a dive increases, so must one's attention to gas management? When a diver's ability to make a free ascent is limited or prohibited, a greater reserve of gas must be maintained. Any number of factors may limit a free ascent to the surface. Overhead obstructions, such as being in a wreck, below ice, or in a cave, are obvious barriers to an immediate ascent and thus require reserve supplies. Less obvious examples include deeper open water dives and/or decompression dives.

To maintain sufficient gas reserves, cave divers established the rule of thirds. This Third's Rule enables divers to easily manage their gas, while leaving ample reserves for exiting and for emergencies. In overhead diving such as cave, wreck, or ice, the initial one third is used for penetration, while the remaining two thirds are reserved for return and emergencies. While diving the Thirds Air Rule, it is essential that divers carefully monitor their gas and always maintain a sufficient volume to allow them to exit safely from the farthest point in the dive. This reserve volume also takes into account the unlikely event that a team member could experience a catastrophic gas loss at the farthest point. Ocean dives that require additional gas reserves demand that individuals begin their ascent with at least one third of their starting volume still remaining.


Hopfulley this clears up my errrrr mistakes

ATB

Mark Chase