Which do you think is less dangerous at 160ft? Open-circuit air or CCR trimix?

[rongoodman]

Let me just briefly quote some famous and highly respected divers on deep air dives.
1947 Frederi Dumas 308 ft
1961 Hal Watts 350 ft
1965 Tom Mount 360 ft
1971 Sheck Exley 466 ft
1993 Bret Gillian 475 ft

Perhaps there's a reason that the last of these dives was carried out over 30 years ago.

 

[PfcAJ]

Yes, yes, I have heard all this, many times before. I can also quote may divers who have lost their lives on rebreathers. The ratio of rebreather deaths to open circuit scuba deaths has been quoted as about 5 to10 rebreather deaths to every single open circuit scuba death.

Certainly, I have dived with some individuals who have experienced narcosis at 100 feet. In fact, I rescued a buddy diver who was narked out (asleep on the bottom with his eyes open) at the end of a 25 mins deco dive at 140 feet on air.

Consequently, for some people narcosis is a serious problem. However, some individuals can function despite narcosis at considerable depth.

Whether you use a rebreather or open circuit scuba, it is a question of analysis of dive site conditions, individual susceptibility/capability with narcosis, individual perception of risk, good risk assessment to identify and mitigate problems and proper dive planning.

Also, trimix is not easily available all over the world. In some cool remote locations, all you can find is air. Therefore, if you have a rebreather you may have to use air as a diluent.

In conclusion, whether you use a rebreather on trimix or open circuit on air to 160 feet, both approaches present risks. It is your individual choice based on sound risk assessment. To quote Sheck Exley "what works, works".

Let me just briefly quote some famous and highly respected divers on deep air dives.
1947 Frederi Dumas 308 ft
1961 Hal Watts 350 ft
1965 Tom Mount 360 ft
1971 Sheck Exley 466 ft
1993 Bret Gillian 475 ft

Sheck died breaking his own rules.

Great example.

 

[CG43]

Perhaps there's a reason that the last of these dives was carried out over 30 years ago.

The list goes on :

1999 Scarlett Watts women world record deep air 129 m (425 feet) .
1999 Mark Andrews men's world record deep air 158 m (519 feet)

But what impressed me the most is that Hal Watts dived with 55 divers to depths between 100 m (300') and 127 m (415') without one accident .
Hal Watts

 

[Nick_Radov]

For any dive up to 200 feet on air I am comfortable with open circuit. For me narcosis is just a single risk and it is workable.

Rebreathers on trimix remove the risk of narcosis but introduce a whole swag of other risks. Hyperoxia, hypoxia, hypercapnia, flooding, sodalime inhalation, etc.

Hypercapnia is just as much a risk on open circuit deep air due to the relatively high WOB and gas exchange issues.

In Cousteau’s day, the above simply weren't available to the pioneers. It is available and trained these days. A bit of narcosis is OK, but being off your face with narcosis at 50m/165ft isn't fun and you're absolutely relying on your experience to get through the dive. Personal memories of having an in-depth conversation with lobsters and blennies... I choose trimix and a rebreather so I can enjoy the dive and rummage around in the sunken museum, whilst doing a long dive and reliable deco so I can do the same for the rest of the week.

Even Jacques-Yves Cousteau himself had switched from air to trimix starting in 1976 for the really deep dives.

1975-6 Cousteau

THE TEAM Expedition Leader (France): Jacques-Yves Cousteau Divers: Albert Falco (Chief Diver/cameraman), Raymond Coll (cameraman), Bernard Delmotte, Patrick Delmotte, Marc Zonza, Ivan...

hmhsbritannic.weebly.com

 

[Nick_Radov]

Let me just briefly quote some famous and highly respected divers on deep air dives.
1947 Frederi Dumas 308 ft
1961 Hal Watts 350 ft
1965 Tom Mount 360 ft
1971 Sheck Exley 466 ft
1993 Bret Gillian 475 ft

When was Bret Gilliam considered to be "highly respected"? My understanding is that he was always considered to be more of a clown and an embarrassment to the sport. But I'm a relative newcomer, so perhaps I'm missing some context.

The Call of the Wah-Wah

The lingering legacy of DEEP AIR in the era of MIX—from the aquaCORPS archives

indepthmag.com