Planned deco on a recreational dive?

[Bob DBF]

The recommended limits of OW make it pretty hard to exceed your NDL.

May be the focus of attention should be on the actual limit of ow training being NDL, not an arbitrary depth limit.

Why is there a limit at 40m?

Because the agencies revised it down from 190' at some point in time?


Bob

 

[boulderjohn]

Why is there a limit at 40m?

According to the Encyclopedia of Recreational diving, it was a combination of factors, including both the fact that you get almost no NDL time below that and, even more importantly according to that info, the concern of narcosis.

 

[Storker]

According to the Encyclopedia of Recreational diving, it was a combination of factors, including both the fact that you get almost no NDL time below that and, even more importantly according to that info, the concern of narcosis.

Exactly the same reasons that I - a rec diver who hates being narked - see no reason - for me - to go even as deep as 40m.

 

[stevensamler]

According to the Encyclopedia of Recreational diving, it was a combination of factors, including both the fact that you get almost no NDL time below that and, even more importantly according to that info, the concern of narcosis.

GUE T1 dive profile , trimix , deco gas , conservative but aggressive.

 

[archer1960]

Maybe not a concern if your lifetime dives is less than the numbers quoted.

More of a concern if you do that volume of dives every 60 days.

Just saying....

Yeah, but the actual number is probably more like one case per several thousand recreational dives, or less.

 

[DevonDiver]

Yeah, but the actual number is probably more like one case per several thousand recreational dives, or less.

DAN report 2016 estimated 3 million dives conducted in the USA per annum.

Statistically, that'd result in a lot of bent divers per annum.

On a per person, bends per dives, perspective, statistics don't really enlighten. That's because people have varying susceptibility to DCS.

Also, people conduct varying extremes of dives, with varying degrees of qualification and experience. In short, some people dive conservatively, while others dive aggressively... relative to their experience, equipment and training.

That IS relevant to this thread.

Pushing 'deeper into the grey' or doing dives with mandatory stops has an obvious impact on DCS risk...and that should correlate to a much higher prevalence of DCS incidents.

I've not yet seen any statistics that breakdown DCS incidents based on dive qualification and experience versus relative 'aggressiveness' of diving (depth, time and relative saturation as indicated by proximity to a given no-stop limit).

I wonder if/how studies like DAN's determine a recreational or technical dive. Would a dive be considered 'technical' in their statistics if it merely exceeded no-stop limits?

Depending on definitions, you might find that there were much higher statistical risks in 'recreational' decompression diving, that aren't apparent because they get bundled into 'technical diving' figures.

As example, statistics might indicate X fatalities on "cave dives", but don't differentiate between qualified cave divers and untrained divers who enter caves and perish.

Either way, risk statistics applicable to no-stop recreational diving shouldn't be used to vindicate exceeding no-stop limits.

No-stop limits exist to insulate divers against the risk of DCS and the severity of DCS when it does present itself.

Exceeding those limits should mean you lose that 'insulation' and have ventured beyond statistical safety boundaries associated with 'recreational' diving (as its commonly, or agency, defined).

 

[boulderjohn]

GUE T1 dive profile , trimix , deco gas , conservative but aggressive.

I have no idea what you are saying here. What does this have to do with the rationale behind assigning 130 feet as the maximum depth for recreational diving?

 

[Subcooled]

It is a fact that breathing air at -45m affects ones brain. I speak from experience - having done both wet dives in 3ft visibility to -45m and dry dives in a chamber to 6ATA. The brain just isn't what it used to be. Short term memory fails and all reasoning with that. Things become literal and fingers stiffer. Environmental awareness suffers. One becomes slow and dumb. Dives to these depths can of course be done, but planning is paramount as memory works but reasoning not. Plan for failures. It would be much healthier to use some helium. Sometimes that is not economically possible and then a risk vs. cost analysis has to be done.

Decompression happens on all dives. Once you have done 500 dives (or 100) and you are in control of your buoyancy, then you can make mandatory decompression dives. If you loose control of your buoyancy on a mandatory decompression dive though, then you pay for it and your pay dearly. Using pure oxygen at the end of the dive (in the shallows) shortens the mandatory stops or reduces the risk of DCS, but brings with it some new risks. Using oxygen and doing the gas switches requires proper training. Decompression dives on one gas only are simpler - but you need to maintain depth and plan the ascent. And you cannot hurry. You need a lot of time.

 

[Rusty Roo]

Just did a few cheeky deco dives in the maldives and still here. My computer also gave me a 30 hour no fly time but flew after 24 hours and didn't die. REAL WORLD TESTING.

 

[Storker]

REAL WORLD TESTING.

Anecdote ≠ data.
Even the plural of anecdote ≠ data, and your "study" has n=1.