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

[CG43]

If you join a project in shallow waters, you'll see how even at very shallow depth our mental abilities massively decrease. I did quite some projects in shallow caves (depth less than 10m) and, really, our problem solving abilities are extremely low compared to ambient pressure. Problem is that rec diving doesn't involve problem solving, so we don't realise it. Until we have an accident and we need to solve the unexpected problem.

This is very interesting !
Since cave is a strong influencing variable in addition to deep, I would initially think to avoid mixing better.
It will certainly interest many here if you can write something about the structure and results of your study.

 

[ginti]

This is very interesting !
Since cave is a strong influencing variable in addition to deep, I would initially think to avoid mixing better.
It will certainly interest many here if you can write something about the structure and results of your study.

They were not *my studies* - just geological projects led by other divers or scientists. So I have no results to share about cognitive performance, sorry for that

 

[justinthedeeps]

People who plan dives to 50m and then go to 60m are careless and have no discipline. I’ve never done it and actually never could as I always plan to the deepest part of a wreck. In the case of the Aikoku Maru I’d plan the dive to 64m. I think that poor discipline might be a result of blindly following a computer. I’ve left some nice stuff on the bottom as I ran out of time to get it on a bag.

Tour/guide/company/instructor/agency polices are rightly strict about things like this, and of course you are right. But SCUBA like all 'outdoor adventure' pursuits has been an exploratory activity for a very long time. Cruising around at 55 metres on air was once (even recently) also a standard. You just prefer a different standard now.

While most of us agree that it is suboptimal and a serious safety risk now that additional options are available, it may still well be some other person's plan. Totally valid to discuss what we reckon is objectively safer given today's options and training opportunities.

People widely used to climb 8000+ metre peaks without supplemental oxygen, and apparently some still do, whether or not (Training Agency That Makes Sensible Rules for its Customers and Members) recommends it

Now how about, is it a safety risk to choose a CCR for a 15-metre (50ft) dive? With all those additional possible failure/risk scenarios? The answer may well be yes, but person-to-person variation in protocol and decision making may still make more difference than the CC/OC comparison.

 

[Wibble]

Now how about, is it a safety risk to choose a CCR for a 15-metre (50ft) dive? With all those additional possible failure/risk scenarios? The answer may well be yes, but person-to-person variation in protocol and decision making may still make more difference than the CC/OC comparison.

I'd choose the rebreather over OC for a 15m/50ft dive most of the time. Obviously if doing a cattle boat for a long 45min dive, then may as well blow bubbles. But if diving it by myself for a couple or three hours looking at pretty fish, the rebreather wins hands down.

Same with overheads. The rebreather's much more safe than OC as there's so many options should something fail. The only things that would drive me to use OC over CCR would be tight restrictions or a punitive carry to dive base.

Obviously rebreather divers have the option for either; OC divers have no other choice than OC.

 

[old frogman]

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.

 

[rjack321]

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.

In a cave or overhead? Cause this is how the Rouse's died

 

[lermontov]

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.

single risk? -its risk you cant escape from unless you ascend, like all things its ok until it starts going pear shaped - having to make critical decisions while you're narced is a bad situation but the decision making needs to be done now not when your 30m higher up the water column and at 7 atmospheres your going to be sucking though gas pretty quickly

Being under pressure and narced will turn your powers of reason to mush. Even in a relatively straight forward dive just being able to work out which way to go to find the ascent line can be challenging.

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

all those things are covered with redundancy thats why you train for it and even if you have to abandon the ccr you are back to OC -which is brings you back to the original comparison anyway

ccr gives you something OC cant - time

 

[rddvet]

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.

Edit: Nevermind. Its worth the headache to reapond to this how i wanted to

 

[old frogman]

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

 

[Wibble]

Years ago we used to drive cars without seatbelts; motorcycles without helmets; didn't use high-visibility jackets on building sites; smoked a lot...

Nowadays we have better knowledge about diving and understand that narcosis, gas density and oxygen limits are a real safety issue and we've adapted to using those. Similarly computers for real-time decompression strategies and planning.

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.

Think of early flight using wooden biplanes and unreliable engines. Sure, there are still people who fly vintage wooden biplanes nowadays, but this is rare as people prefer reliability and safety to get to their destination and enjoy the flight.