Question Did technical divers dive according to ppo of 2.0 in the past?

[Yosilogen]

And if so, were there any accidents or problems that worsened the conditions for limit in ppo for technical diving?

 

[Capt Jim Wyatt]

I recall doing deco on pure O2 at 40 feet back in the late 1970s. It is a terrible idea and a dangerous practice on open circuit or on CCR.

As a U.S. Navy diver we routinely did 2.0 PPO2 deco while in a surface supplied rig. MK5, MK12 and others. Inside a hat if you tox you may get some head injuries but you won't die.

On OC or CCR if you tox - you die.

It is simply an interesting historical fact and anyone trying it today would be a fool.

 

[Capt Jim Wyatt]

were there any accidents or problems that worsened the conditions for limit in ppo for technical diving

We have had people tox and die at PPO2 of 1.4
Some people have a lower convulsion threshold than others. I never dive at 1.4. I stay at 1.2 for the working part of my dive. Deco at 1.6 seems to be OK.

There are MANY MANY articles, abstracts and discussions about this topic here on SB and elsewhere.

 

[Angelo Farina]

When I started diving, in 1975, the large part of the 6.months-long course was done on the ARO, a pure-oxygen closed-circuit rebreather, with pendular configuration (single hose, so no "loop").
My OW certification includes using this CC rebreather down to a max depth of 10m, which means a ppO2 of 2.0 bar max (depending on how well the system was flushed from air and filled with pure oxygen).
But this was purely RECREATIONAL diving.
In 1975, technical diving was not existing yet. The separation was between recreational diving (which did assume max depth of 50m in air, and with deco stops) and commercial diving (same limits, but "for work"), then there was "high depth" diving, which was up to 100m with gas mixtures (at the time usually normoxic).
Also for those doing "high depth" diving the ppO2 < 2.0 bar was assumed.
After a number of deadly accidents, the max value of ppO2 was progressively reduced. It was 1.6 bar for most of my diving career, and I found it was further reduced to 1.4 bar when I bough my first diving computer in 2019.

 

[Angelo Farina]

I recall doing deco on pure O2 at 40 feet back in the late 1970s. It is a terrible idea and a dangerous practice on open circuit or on CCR.

As a U.S. Navy diver we routinely did 2.0 PPO2 deco while in a surface supplied rig. MK5, MK12 and others. Inside a hat if you tox you may get some head injuries but you won't die.

On OC or CCR if you tox - you die.

It is simply an interesting historical fact and anyone trying it today would be a fool.

With the ARO, the usage of a Full Face mask was mandatory.
Still not very safe, but better than a mouthpiece...

 

[Capt Jim Wyatt]

In 1975, technical diving was not existing yet,

Not in "name" but we were doing cave dives with O2 decompression and carrying stage bottles as early as 1972. That is one definition of technical diving.

 

[Angelo Farina]

Not in "name" but we were doing cave dives with O2 decompression and carrying stage bottles as early as 1972. That is one definition of technical diving.

All this was purely recreational, at the time, and remained recreational for decades here in Europe.
The separation between rec and tech was originated by commercial (for profit) training agencies, which did not want to face the risk associated with some challenging activities, which instead were routinely taught and practiced in club-based no-profit organisations (CMAS, BSAC etc.).
So they did define a strict limit for rec activity: no deco, no overhead, single tank, single regulator, etc...

 

[Capt Jim Wyatt]

All this was purely recreational, at the time

It still is recreational.