Triox, Trimix and Heliox question.

[Doppler]

As you have found out, most of the "new" words to describe breathing mixes are a function of marketing.

And for the record, there used to be just three helium mixes:

Trimix = A blend of helium and nitrox (the staple).

Heliox = A blend of helium and oxygen (a 20/80 for example... a truly wonderful way to visit shallow sites to see just how bloody narc'd you usually are).

Heliair = A blend of helium and air (also known as poor man's trimix... and fallen out of favor because the balance between narcosis and cns loading is... well, wrong for most applications. It is however, a common DILUENT gas for CCR divers... fill cylinder to about half of its working pressure with pure helium and then top with air resulting in something close to a 10/50... close to, mind you: never exact.)

 

[LiteHedded]

why is heliair different than trimix? is that really a thing?

---------- Post Merged at 09:54 AM ---------- Previous Post was at 09:50 AM ----------

You still have to deco from helium gases, but the total deco times really aren't that much different between helium and nitrogen based gases (maybe a few minutes here and there, depending on the algorithm).

pick the shorter one.

 

[Doppler]

why is heliair different than trimix? is that really a thing?

---------- Post Merged at 09:54 AM ---------- Previous Post was at 09:50 AM ----------


pick the shorter one.

I think because Trimix takes some basic arithmetic and sounds fancier. And yep, heliair is really a thing. At least more a thing than Helitrox... for which I am partly to blame since I worked in TDI's marketing department at the time the agency adopted the term.

 

[Akimbo]

…Heliox (no N2) is pretty much a medical gas. Even for extremely deep dives I believe they add in a little N2 to avoid the risk of HPNS.

This might help explain and expand Bombay High’s comments on exclusive use of HeO2 on saturation dives:

Slow compression not only virtually eliminates HPNS symptoms in depths above about 1,000', it manages joint cartilage compression (compression arthralgia). My brother was on a fast blow-down to about 600' in the mid-70s… within about 20 minutes. He and the other divers could barely climb into the bell on top of the transfer lock from pain often experienced by joint replacement candidates. It took them about 12 hours to recover, though minor pain persisted for days.

U.S. Navy Diving Manual — Volume 3, Page 15-24
Table 15‑6. Saturation Diving Compression Rates.

Depth Range	Compression Rate
0–60 fsw	0.5 – 30 fsw/min
60–250 fsw	0.5 – 10 fsw/min
250–750 fsw	0.5 – 3 fsw/min
750–1000 fsw	0.5 – 2 fsw/min

We used about 1'/minute on all the dives I was on and never felt anything abnormal.

Rapid compression also made his chamber ride miserably hot (heat of compression). Coolers used for dehumidification were running full bore while heating was off. That means the coolers could barely keep it close to the 90° F “shirt-sleeve comfortable” temperature for that depth.

Mixing nitrogen adds considerable complexity to the system. Diver’s breathing gas and chamber exhaust is recycled and reclaimed so Nitrogen analysis and mixing capability would have to be added to those separate systems.

Once you get deeper (~700'+), gas density becomes a respiratory work load problem even on pure HeO2, so any Nitrogen works against you.

I have never seen HeO2 as a medical gas, beyond diver hyperbaric treatments. It has been a while since I have been around open-circuit surface supplied mixed gas bounce dives (non-saturation), but I never encountered Trimix offshore or the in the Military. I heard the French used it before my time, but I can’t confirm it.

 

[Sat Diver]

My brother was on a fast blow-down to about 600' in the mid-70s… within about 20 minutes. He and the other divers could barely climb into the bell on top of the transfer lock from pain often experienced by joint replacement candidates. It took them about 12 hours to recover, though minor pain persisted for days.

Rapid compression also made his chamber ride miserably hot (heat of compression). Coolers used for dehumidification were running full bore while heating was off. That means the coolers could barely keep it close to the 90° F “shirt-sleeve comfortable” temperature for that depth.

I hope the supervisor got a boot in the ass .... what a nightmare. Its difficult to explain what the heat of compression feels like when you are bathed in Deep Mix, to those who have not experienced it. The one time I experienced it, I thought I was certainly going to die. I would much much much rather drown or freeze to death.