Total of 12 dives and already a few lessons and one almost "near miss"

[yle]

The entire CNS toxicity process is poorly understood last I knew. It is a combination of time and dosage, and likely a set of unknown factors. The original studies showed that some people could operate fine for hours at 2.1, and then the next run they would tox at 1.5 after 20 minutes.

But it's not a rapid process unless you do something insane like breath 100% oxygen at 100 feet. You can drop below the safe depth and it's fine if you don't stay there. It usually takes a while to mess you up. But you should still avoid doing this, as the penalty for being wrong is typically death.

Yup. Exactly. And as you describe above, that "takes a while to mess you up" could be a couple minutes or a couple hours. Which is why anyone giving specific advice on this topic that is based on their personal experience (I have witnessed instructors doing this with their students: "this is what I do, and it works for me so it should work for you also") is irresponsible.

 

[Storker]

Divers are generally more concerned about CNS oxygen toxicity, which is primarily caused by breathing oxygen at a partial pressure of greater than 1.6 atm (of course this can only happen if you're breathing gas at an elevated pressure, i.e. as we do underwater... can't happen in a typical hospital environment.)

Um... Chamber?

What's interesting, though, is that AFAIU there seems to be a higher risk of CNS tox at moderate pPO2s underwater than topside in a chamber. And of course you don't run quite the same risk of drowning if you tox in a chamber...

 

[Basking Ridge Diver]

Which is why anyone giving specific advice on this topic that is based on their personal experience (I have witnessed instructors doing this with their students: "this is what I do, and it works for me so it should work for you also") is irresponsible.

As a newbie you need some type of boundaries - where else are you going to get that information from? Sure you can read books but then someone needs to give you specific advise on books too...
Maybe it is semantics but I am not sure this is irresponsible in my opinion. What is irresponsible is to take any information from an instructor, the internet as gospel and not do Due Diligence and so it falls back on the diver. It always had and it always should - you need to be responsible for you...

 

[yle]

Um... Chamber?

What's interesting, though, is that AFAIU there seems to be a higher risk of CNS tox at moderate pPO2s underwater than topside in a chamber. And of course you don't run quite the same risk of drowning if you tox in a chamber...

I thought about chambers. But that's why I explicitly wrote typical hospital environment. The vast majority of nurses administering O2 to patients in hospitals are not in recompression chambers. My post was written to Sapphire, after she mentioned "in my field..." and described their concerns about oxygen toxicity. I believe her "field" is nursing... so my post addressed the typical hospital environment that she was likely referring to.

I am willing to bet Sapphire attends to patients that are not in recompression chambers... but we'd need her confirmation to be sure.

 

[yle]

As a newbie you need some type of boundaries - where else are you going to get that information from? Sure you can read books but then someone needs to give you specific advise on books too...
Maybe it is semantics but I am not sure this is irresponsible in my opinion. What is irresponsible is to take any information from an instructor, the internet as gospel and not do Due Diligence and so it falls back on the diver. It always had and it always should - you need to be responsible for you...

Yeah... I probably should have provided more context for my comment; I was thinking specifically about advice concerning the use of nitrox. Many years ago, before I was an instructor, I overheard a very experienced instructor telling students (we were all on a boat) that they should ignore the 1.4 ppO2 limit recommended by most basic nitrox courses, and that using 1.6 instead would "allow them to go deeper." He told the students it always worked for him, so there was no problem with them doing it also. He even told the students that he had spent plenty of time at ppO2's higher than 1.6 and had never suffered ill effects.

That incident stuck with me over the years, and after I became an instructor and came to better appreciate how important it was for me to share information that would allow my students to progress with their diving in a safe and enriching way... I understood just how irresponsible this guy was. He was boasting, and his motivation was to impress on the students just how awesome he was and how they should aspire to be just like him. But what he didn't tell them was why the 1.4 limit is recommended: not because exceeding it will necessarily be a problem, but because the factors that affect oxygen toxicity are complex and the consequences dire... so a conservative limit is a good idea, especially for newer divers.

It was this incident I was thinking about when I wrote about some instructors being "irresponsible": those that focus on keeping their scuba universe revolving around them instead of what is best for their students.

 

[yle]

What is irresponsible is to take any information from an instructor, the internet as gospel and not do Due Diligence and so it falls back on the diver.

Good point... all students should know that if anything from course materials seems to conflict with something the instructor says (or even something from the internet), further research should be done until the issue is resolved.

 

[SapphireMind]

I thought about chambers. But that's why I explicitly wrote typical hospital environment. The vast majority of nurses administering O2 to patients in hospitals are not in recompression chambers. My post was written to Sapphire, after she mentioned "in my field..." and described their concerns about oxygen toxicity. I believe her "field" is nursing... so my post addressed the typical hospital environment that she was likely referring to.

I am willing to bet Sapphire attends to patients that are not in recompression chambers... but we'd need her confirmation to be sure.

Definitely not. Just regular old ventilators I am an NP (for those not in the US, it's a mixture of responsibilities between nurse and doctor) and care for neonates primarily.

 

[Bob DBF]

I thought about chambers. But that's why I explicitly wrote typical hospital environment. The vast majority of nurses administering O2 to patients in hospitals are not in recompression chambers.

The vast majority of hyperbaric chambers in hospitals are not recompression chambers capable of treating divers. They are capable or 1.5 to perhaps 3 ATM, used for treating a number of maladys like CO poisoning and wound treatment. I would guess most are small, made for one person lying down.

 

[wnissen]

At this point he's gassed(3 surface swims, plus diving, rolling etc) He realises his breathing is shot, probably affecting his bouyancy, so the dive is shot. Inflates his BCD, removes his reg and tells the DM he's done...DM reaches behind him and pulls the dump valve!!. Mate gets a gutfull of water, pushes off the DM, reinflates and we return to the boat...(is it EVER ok to touch somebodies BCD, except in an emergency?)

This part hasn't gotten enough attention. I accidentally deflated my own BC when my reg was out and that experience was startling enough. If someone else did it to me without asking I would be apoplectic. Even with a reg in I wouldn't want someone else changing my buoyancy. Under the water is a different story, you might not be able to explain what you're doing. One time my buddy began ascending rapidly and I had to grab their BC in a hurry, but there's no excuse on the surface, IMO. Curious if anyone trained as a DM has an opposite perspective.

 

[Altamira]

Rather than clipping your fins on and climbing a ladder, I suggest you agree some words with the boat crew before you hand over your fins. On our club boat you don't let go until you hear the words "I have" from the crew. That will cut down the chance of losing kit.

As for weight checks these are important and you need to record the weight used your equipment and wet/dry suit used in your log book that will help you identify any issues. Note also the salinity of water can change especially between fresh and salt water but also at river exits and in places like the Red Sea.

One trick I've found over years to help the get under water is to think down in your head, make sure you have exhaled from your lungs and stop finning

I'm on the opposite side of the "fin clipping" technique than @CraigfromUK. Instead of handing up my fins even with a positive handoff, I clip my fins to my bp/w D rings before climbing the ladder. I do this for two reasons. First, several years ago, a boat crew member said "I got it" as I was passing up my fins, but he did not really have a good grip on it, and my very negatively buoyant Apollo Bin fin headed for the bottom. Luckily it was only in 40 fsw, so it was easy to retrieve, but could have ruined my day had it not been recoverable. Second, although I have never fallen off a ladder, I want my fins with me in the event I wind up back in the water.