Blue Hole death - a defence, sort of!.

[Mark Chase]

I have always been willing to risk a PP02 of 2.0 in an emergency and I have gas switched on to 2.0 a couple of times without ill effect but I always knew the risks.

In planning a dive for 2007 to 145m using Heleox (Helium and Oxygen no Nitrogen at all) I have done some digging and I have been horrified to learn that a working pp02 of 1.4 -1.5 is recommended with a switch to 100% 02 at 12m on to a PP02 of 2.2.

Apparently Comex are doing this sort of thing for working dives?? The CNS runs into 10s of 1000s. I have been discussing this with well respected sources who are actually doing dives like this and frankly it blows my perception of what is safe and what is not right out the window.

That said the guidelines of max 1.4 pp02 for the working phase of the dive 1.6for deco and a max CNS of 100% can work with a massive amount of diving so why risk the silly high numbers. However, it is worth knowing and understanding that it can be done so on those occasions your pushing it a bit you can more accurately asses your risk exposure.


One thing for sure 02 tox is not an on / off switch at X level. Some people tox at levels under the recommended max and a tox is more often than not fatal so unless there is a damed good reason to risk it, why bother?



ATB

Mark Chase

[Finless]

I have always been willing to risk a PP02 of 2.0 in an emergency and I have gas switched on to 2.0 a couple of times without ill effect but I always knew the risks.

In planning a dive for 2007 to 145m using Heleox (Helium and Oxygen no Nitrogen at all) I have done some digging and I have been horrified to learn that a working pp02 of 1.4 -1.5 is recommended with a switch to 100% 02 at 12m on to a PP02 of 2.2.

Apparently Comex are doing this sort of thing for working dives?? The CNS runs into 10s of 1000s. I have been discussing this with well respected sources who are actually doing dives like this and frankly it blows my perception of what is safe and what is not right out the window.

That said the guidelines of max 1.4 pp02 for the working phase of the dive 1.6for deco and a max CNS of 100% can work with a massive amount of diving so why risk the silly high numbers. However, it is worth knowing and understanding that it can be done so on those occasions your pushing it a bit you can more accurately asses your risk exposure.

One thing for sure 02 tox is not an on / off switch at X level. Some people tox at levels under the recommended max and a tox is more often than not fatal so unless there is a damed good reason to risk it, why bother?

ATB

Mark Chase

Mark,

That is scary BUT a PPO2 for a 145 mtr dive with some bottom time is not the same as a bounce dive where ascent rates will be much higher than ......... actually I'm talking b*ll*cks again ............. or, at least, I'm assuming.

Most of my diving maxs out at 40 mtrs so I have no real practical knowledge of deeper (certainly to your max depths) - I wonder if the onset of hyperoxia increases in a non linear fashion with depth?

I have always understoof it that commercial divers worked to a PPO2 of 1.8 and, perhaps, higher if surface monitored?

Bryan

[Mark Chase]

Mark,

That is scary BUT a PPO2 for a 145 mtr dive with some bottom time is not the same as a bounce dive where ascent rates will be much higher than ......... actually I'm talking b*ll*cks again ............. or, at least, I'm assuming.

Most of my diving maxs out at 40 mtrs so I have no real practical knowledge of deeper (certainly to your max depths) - I wonder if the onset of hyperoxia increases in a non linear fashion with depth?

I have always understood it that commercial divers worked to a PPO2 of 1.8 and, perhaps, higher if surface monitored?

Bryan

The commercial divers are indead connected to the surface and using comms and hard hats etc. but lets face it it wouldn't do them any good to be toxing all the time even if it were OK to do so in that rig.

Accepted practice for divers is to lower the PP02 on very deep dives to 1.2 or evel 1.0 to keep CNS down and reduce the possibility of a workload related hit. But surely the comm's divers are working a damed site harder than we are.

Its all a bit odd.

ATB

Mark Chase

[Finless]

The commercial divers are indead connected to the surface and using comms and hard hats etc. but lets face it it wouldn't do them any good to be toxing all the time even if it were OK to do so in that rig.

Accepted practice for divers is to lower the PP02 on very deep dives to 1.2 or evel 1.0 to keep CNS down and reduce the possibility of a workload related hit. But surely the comm's divers are working a damed site harder than we are.

Its all a bit odd.

ATB

Mark Chase

Mark,

In all probability, what is odd are the assumptions or half remembered facts that I have been working on and spouting off about. As mentioned, I rarely get below 40 mtrs so I can only talk about my personal experience. With you going much deeper than me (you really should learn to control your descent rate! ) I'm sure your extra training etc puts you in a much more informed position.

I have done a few dives at PPO2 1.6 with no ill effect. However, you are right and I need to re asses my thinking on this.

Rgds
Bryan