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

[kensuf]

I wouldn't do it now for a couple of reasons. First, while I wasn't paying attention, I have turned into a old man. Second. tri mix is still relatively cheap. When you are willing to plop down 15k for a rebreather, 7k for a scooter, more for dry suit, heaters, misc other junk, complaining about the occasional $200 tri mix fill sounds dumb.

I just had this same conversation over wings last night...

 

[broncobowsher]

$200 x 50 dives =$10,000
50 dives is not that many.

 

[old frogman]

Depends on the specific scenario. FWIW, my comments early on in this thread were based on this likelihood/consequence view.

Also, don't conflate the number of risks with "overall risk". An airplane has a higher number of risks compared to driving cross country, but flying is much safer overall.

Yes, specific scenario appears to be an important consideration. It should provide the information/evidence on which to develop a potential incident list which may then be assessed for risk. I would imagine that the individual diver or diving team capability and perception of risk may have some influence on accepting the risk.

 

[ofg-1]

$200 x 50 dives =$10,000
50 dives is not that many.

Yes, 50 is more than 40, but less than 60. Whats your point?

 

[broncobowsher]

Point is a moderate number of dives with $200 fills will add up faster than you think it will, to the point a rebreather is actually an affordable option. To say a $200 single dive is the affordable option over buying $15k of rebreather is a false comparison.

 

[old frogman]

Back in the stone age, 1970's, I worked at a commercial diving school. The school was run by ex Navy divers, so a lot of the things we did were right out of Navy training.

One of the exercises, we ran every student to 190' on air, I must have put 80 or so through this. We gave them simple puzzles and math problems to solve asked them to sign their name.

About 20% had no issue with the puzzles or problems. About 20% drooled, laughed or peed themselves rolling around on the floor of the chamber. All of the rest had varying levels of difficulties solving a problem or puzzle. Some could not spell their name. And this was a 10 minute bottom time.

I did Dipolder II once on air, the only thing I vividly remember is my sealed beam light imploding and having to come out on a 3 D cell U S Divers light. The rest is fuzzy except freezing my ass off at deco. We did a lot of of air dives. Most people did not carry O2, we did a metric ass load of air decompression. 160 feet on air was just another Tuesday night after work dive.

I wouldn't do it now for a couple of reasons. First, while I wasn't paying attention, I have turned into a old man. Second. tri mix is still relatively cheap. When you are willing to plop down 15k for a rebreather, 7k for a scooter, more for dry suit, heaters, misc other junk, complaining about the occasional $200 tri mix fill sounds dumb.

This is very interesting. Out of a sample of 80 divers pressurised to 190 Ft on air, about 20% had no problems with puzzles or problems. While it may be argued that the sample may not be big enough, it does provide some evidence that some divers can operate deep on air. I wonder if any research has been done to explore this phenomenon.

Similar phenomena exist with decompression shedule, oxygen tolerance, hypothermia

Point is a moderate number of dives with $200 fills will add up faster than you think it will, to the point a rebreather is actually an affordable option. To say a $200 single dive is the affordable option over buying $15k of rebreather is a false comparison.

$15K plus the cost of a basic course (about 5 days) buys you no deco dives to 40 metres. No advantage over OC air.

If you want to buy deep dives on tri mix requiring deco, it's going to take more courses and a few years to achieve. It will probably cost about $50K+.

Don't forget annual servicing costs and periodic refurbishment costs. Also, if you want to be safe, you need to dive the rebreather regularly. It is a complex beast with lots of potential failure points.

If you have the money, and believe you have the right attitude for rebreather diving. Go for it.

 

[nadwidny]

This is very interesting. Out of a sample of 80 divers pressurised to 190 Ft on air, about 20% had no problems with puzzles or problems. While it may be argued that the sample may not be big enough, it does provide some evidence that some divers can operate deep on air.

It provides evidence that 80% of divers have problems. That's a pretty effing large percentage that are going to be messed up on air at that depth. Thanks for adding to the proof that deep air is stupid.

 

[lostsheep]

$15K plus the cost of a basic course (about 5 days) buys you no deco dives to 40 metres. No advantage over OC air.

Ok boomer.

All in on my CCR with training was ~$8.5K and at least 2 of the dives during training were to 45m.

NO advantage? Avoiding narcosis is as clear of an advantage as you can get when in an inherently dangerous environment. Gas density / co2 retention concerns is another clear advantage.

I don’t give a **** if you want to dive deep air, but stop justifying it with demonstrably false statements.

 

[old frogman]

Ok boomer.

All in on my CCR with training was ~$8.5K and at least 2 of the dives during training were to 45m.

NO advantage? Avoiding narcosis is as clear of an advantage as you can get when in an inherently dangerous environment. Gas density / co2 retention concerns is another clear advantage.

I don’t give a **** if you want to dive deep air, but stop justifying it with demonstrably false statements.

It provides evidence that 80% of divers have problems. That's a pretty effing large percentage that are going to be messed up on air at that depth. Thanks for adding to the proof that deep air is stupid.

To lost sheep,
Your two dives to 45m. Where they on air diluent or trimix diluent? Either way you can do 45m on air OC. Ref. TDI Decompression Procedures Course - entry level course for technical diving.

To nadwindy,
I agree. If you fall in the 80% group you are definitely taking a risk on deep air. You definitely should be following current established rules.

 

[ginti]

If you want to buy deep dives on tri mix requiring deco, it's going to take more courses and a few years to achieve. It will probably cost about $50K+.

You do mod1, some practice dive (20? 50? If you really want to stretch, 100h, which is doable in one/two years but will definitely cost less than 5k for most people including extra expenses like driving etc. At least here in Europe), then Mod2. If you have previous tech experience maybe you can even go faster.

INCLUDING FUN DIVES we are definitely below 20k for most divers.

Btw, this wasn't the point of @ofg-1 at all - his point was, if for once you have to go for trimix, just go, it won't change much overall.