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LOL, 90' on 100% are we still talking Apples to Apples? Out of the 1000 views on this post, you posted 3 instances of what you HEARD. The thousands of members on here dive every week, some every day. What have you personally SEEN. If we added up the cumulative dives from every member who has posted on this thread alone, we are literally talking about tens of thousands of dives. Yet, no one here has seen an O2 hit that resulted in convulsions? C'mon, it's not voodoo guys. It's rare. Certainly don't go spend an hour at 2.3ppo2, but this isn't the big scary monster people are trying to sell it to be.
Pressure is pressure. Almost all of us working in the gulf are diving wet. Most of us wear nothing but coveralls, not even a wetsuit (unless it's a mixed gas dive)
"The time limits for ppO2s [in the NOAA table] below 1.4 atm stem more from pulmonary oxygen toxicity concerns than from CNS (acute) toxicity" (Hamilton, 1989). I'm interpreting this as being more likely to have pulmonary O2 toxicity than getting a CNS hit when you go for more than 150 mins at 1.4 atm.I don't know where that chart came from. Pulmonory Oxygen Toxicity takes longer than CNS Oxygen Toxicity as far as I know.
I've seem more than one thread like this in SB. This is one where I participated.There was a thread here on SB... not too long ago, where a poster posted essentially that he was in need of getting his buddies attention, but his buddy went a little too deep, and he didn't want to exceed his MOD...
Donald (1947) reports that "The Admiralty Experimental Diving Unit was unable to demonstrate oxygen poisoning in the range of 0 to 20 fsw." This is the ppO2 range of 1.0 to 1.6 atm.Now, is diving at 1.0, 1.3, 1.4 safer than 1.6? Of course it is. But if 100 people today make a 4 hour dive at 1.6, how many of them are going to take a hit? 99% of the time, zero people in the above scenario will take a hit. For years in the commercial field, I watched this over and over and over. I've NEVER seen an oxygen hit from 1.6ppo2. That doesn't mean that it won't happen to me tomorrow. But the chances are very very slim.
I am not denying the variability. I am just saying that just because there was great variability when people were subjected to ppO2s of, say, 3.5 atm, does not necessarily mean that you will have the same variability at 1.6 atm. And even if you do have that same variability once you get past the threshold, hasn't that threshold been moved far enough ahead to make it impractical to cross it due to restrictions like the amount of gas available for the dive and nitrogen loading?The bottom line is that nobody ever toxed in less than five minutes at any ppO2, but the variability in WHEN they toxed is absolutely chilling. The variations between text subjects, and from day to day with the same test subject, are tremendous. Seeing those results has given me a great personal respect for the unquantifiable nature of toxicity risk from elevated ppO2s.
In my admittedly uneducated mind, I couldn't perceive how one could on-gas enough O2 to break the PPO2 limit in just a few seconds to a minute
When you are jetting, basically you are shooting a high pressure 3" water hose underwater to dig a big trench. Sand, sea shells, jelly fish, everything in this jet stream is blown everywhere. So, to keep this crap out of you a little, you tape up every opening in your cover-alls. I wear cheap nylon mesh gloves to protect my hands, but tape them to my sleeves. I wear steel toed rubber boots (like what cement workers wear when working in cement) then tape my coveralls to them so they don't fill with crap.
Oh, and still love the new avatar.
The PPO2 limit - like the MOD limit - is determined by depth & gas mix only, not time or gas consumption; that's pretty much the point of this thread
If I were to go on a staged deco dive using nothing but ratio deco, you better believe I'll want to put my max ppO2s as low as possible (1.2 and lower) simply because I have no way of tracking my %CNS and this is a multi level exposure dive
"I don't see how one could on-gas enough O2 in a minute or so to be dangerous . . . ."
Let's back up 30 years ago when the limit for air was 320'.
I know about 100 people who were diving 320'ish 30+ years ago on air. None of them ever took a hit, albeit a couple of them got bent.
Now, lets go to the commercial field (my field) where we spend lots of time at 1.6ppo2. Of the literally thousands of dives we've done, guess how many O2 hits i've seen? Yup, you're right, Zero!
Now, is diving at 1.0, 1.3, 1.4 safer than 1.6? Of course it is. But if 100 people today make a 4 hour dive at 1.6, how many of them are going to take a hit? 99% of the time, zero people in the above scenario will take a hit. For years in the commercial field, I watched this over and over and over. I've NEVER seen an oxygen hit from 1.6ppo2. That doesn't mean that it won't happen to me tomorrow. But the chances are very very slim.
By the way, the absurd idea that convulsions is the first symptom, is just dumb and untrue.
Thanks for the correction. I never completed the RD seminar -- only went through half of it. In the literature I've read about it I don't recall coming across a way to track %CNS. I have limited knowledge of RD. I know about it, but I don't use it. I dive with people that do use it. In the past, when we plan the dives, I've usually emailed them my tables, cut from V-Planner/Z-Planner, and ask them if they are ok with doing said profile.You know, I'll have to go back and look at the material, but I'm quite sure we used some basic calculations to compute %CNS time in both Rec Triox and my RD seminar, so I think the statement that you have no way of tracking your %CNS is untrue.
Thanks. I agree. I also agree with what Howard brings up about OW, AOW divers thinking they'll be in imminent, dire, mortal danger if they cross beyond 1.6 for a few seconds. Operating under those assumptions is not good. It is actually dangerous in the sense that people could be left out to die when there was somebody around that could have done something to prevent the death. Instructors may not be actually saying that you will die if you go beyond 1.6, but what we've been seeing here in SB is that some OW/AOW's operate under that fear.Slamfire, your post is generally excellent, and highlights the lack of solid data for making the specific decisions about acceptable ppO2s. I think the bottom line is that oxygen toxicity seizures underwater on recreational or standard technical scuba gear are almost uniformly fatal, so the guidelines have been written to attempt to reduce the risk to zero. There are at least two recorded cases of seizure and death at 1.4, but in general, prolonged exposure to that level of oxygen appears to be very safe.
Again, I agree. I also want to note that these GUE dives, more than often, involve multilevel O2 exposures. It seems that multi-level exposures brings an additional risk factor in itself. Diving 1.4 vs 1.2 is not going to give you a huge deco advantage, but I think the rationale is more about a secondary "justification" for not deviating from standard gases and training people to dive from the beginning as if they're going to do these huge high risk dives (but that's just meGUE, which prefers 1.2 for the working portion of the dive, reasons quite rationally, I think, that you are better of planning for and doing the decompression required, rather than attempting to minimize it with high ppO2s over long exposures. That's the tradeoff -- shorter bottom time or longer deco, versus increased risk of CNS (or with very long dives, pulmonary) toxicity. We have to remember that the benefit gained here really has a very small value when compared to someone's life.