Current opinions on Padi Tec-rec?
- Thread starter Jake
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) I did on air last summer makes me dead or a criminal?
markmud
Self Reliant Diver--On All Dives.
I used to live up Phoenix Lake Road. Lived there for about 12 years.
I always upgrade to economy plus and get preferential boarding. I like flying better that way. I seem to feel better when I am not flying with the cattle class back aft. Nice people, but when we are all crammed-in like sardines, everything seems tedious.
Manhattan "up" for both of us,
markm
I actually live off of Wards Ferry rd, P.O. Box is Jamestown.
Flights to Truk already run over 2k and tend to be packed to the gills so much so that they choose to leave my and my dive parteners gear in Guam for a few days. I’m flying to Bangkok at the end of the month doing the PE for that one, about 1/2 the cost of a sardine seat on United.
My read of the link you posted is that it says TMX45 can be done as an add-on. To me, that sounds like you can do Tec45 and TMX45 over consecutive days. It does not necessarily mean that the deep dives for Tec45 can be replaced by the deep dives for TMX45. In other words, my read is that you'd still have to do deep dives on air.
In contrast, TDI AN/DP, when combined with Helitrox, is still the same number of dives (as AN/DP) alone and the deep dives for AN/DP would be replaced by the deep dives for Helitrox.
Consideration of gas density in diving planning, p. 72.
You're being facetious, surely
If you run a course to 100m equipping your students with a Spare Air and don't teach your students about gas (volume) management, ensuring they have ample gas for the dive, then yes, you should be culpable if they have an injury.
If you run a course to 40m on air and don't teach your students about gas density management and ensuring they have a proper gas for the dive, then yes, you should be culpable if they have an injury.
Let me be perfectly clear.
There is no controversy in stating that the maximal gas density one could sensibly plan for on a dive, particularly a course dive, is 6g/L, equating to well under 40m on air (about 35m if memory serves).
If planning insensible dives (for instance to 40m on air) with one's students and they get injured, yes, one may well be legally culpable. As one should be.
Trimix shouldn't be optional on deep (course) dives, but obligatory.
I was not being facetious. Prior to looking at the page you referred to, my thoughts were that 6g/l was a limit that really applied to diving on a rebreather. I was not aware of data that showed similar results for gas densities on open circuit. Having now read that and seeing in there where it explicitly states that open circuit trials were done and the observed results were virtually identical, I will have to give this some more thought. My initial reaction is to change my thinking and agree with you in part. I'm inclined to agree that open circuit courses should at least be required to teach this information regarding gas density. I'm less inclined to agree that, having taught the information, if a course includes diving with higher gas densities it should make the instructor legally culpable or however you put it.
I do believe that with suitable training, there are dives that can be done safely on open circuit with higher gas densities. I.e. dives with benign conditions and reasonable expectations of low to no real work. As such, I don't think any agency should be limited by any kind of law or legal ramifications from offering that training.
Regardless, you seem to be avoiding giving a direct answer to my question. So, let me try it again.
If you want to ban something because it is unsafe, you should have some statistics to back that up. The statistics in that paper are based on work-loaded dives. What are the statistics for dive failures at, say, 7 g/l, when diving open circuit with little to no work involved?
What are the statistics for diving deeper than 100m?
Which one do the statistics tell us is actually safer? I'm not being facetious or sarcastic. I would genuinely like to know. I have read some statistics in the past regarding deep diving that left me with the impression that deeper than 200' is statistically more dangerous than diving to 130' or less. And, deeper than 250' was even more dangerous. And, deeper than 300' was quite a bit more dangerous. As with gas density of 6g/l, depth seemed to have an inflection point where deeper became significantly more dangerous.
If the statistics show that diving deeper than 60m(200') is more dangerous than diving to 55m(180') on air, then would you be suggesting to make instructors legally culpable for taking students on training dives to deeper than 60m?
Personally, I have never gone deeper than 200'(ish) yet. But, I have been to anywhere from 160 - 180(ish) on air maybe half a dozen times. I felt really narced once, but I never felt short of breath (a possible symptom of CO2 retention - a risk associated with higher gas densities). Comparing that to diving with a hypoxic mix (as you would if going deeper than around 200'), my gut feeling is that diving to 180 on air is, in general, safer than diving deeper than 200'.
Air hits 6g/l around, very roughly, 130'. At 150', having 20% helium in the mix keeps the density below 6. Realistically, you can replace all the nitrogen with helium. I.e. you can have a breathing gas that is only O2 and He. The deeper you go, the less O2 you would have in it (so that you keep your ppO2 at 1.4 or less at the deepest part of your dive). So, for example, if you were going REALLY deep, you might have 5% O2 and 95% He. E.g. if you were diving to 270m (890 feet), 5% O2 would give you a ppO2 of 1.4 at the bottom. At that depth, with that mix, you would have a gas density of approximately 6.8g/l (if I've done me maths properly).
Bottom line: For any "reasonable" depth, you CAN use enough helium to keep the gas density at a safe maximum.
Dan_P
Contributor
Fair game
Couldn’t agree more!
Okay.
I’ve given this a lot of consideration for a long time, also because it has obvious implications to my professional life - when I refuse to run courses to 40m on air, there are training continuums that I can’t offer - including the one most widely recognized.
To be clear, the “easiest” option for me personally, would be to just do it and take the money. I’ll expand on my logic for making a different choice, below.
Dives with benign conditions and no work can be pulled off with high density or Work Of Breathing (WOB), absolutely.
But if stress occurs and spurs on higher respiration rate, CO2 levels WILL rise if I’m in a high-gas-density environment.
I cannot guarantee that no outside stressors (real or perceived) enter the equation and tips me or a student into a viscious cycle of hypercapnia.
I’d like to answer.
But first, how can you guarantee that no work will be involved?
A plan for an easy dive is good, but it’s problematic if the gas choice means that if anything starts to go sideways, you panic and drown or pass out and drown.
You’re right that the QinetiQ trials involve different levels of work, but that’s not the issue.
That’s done to give strong measurables in a trial.
The real issue is that the body loses the ability to off-gas CO2 effectively past a certain gas density level, REGARDLESS of the workload.
The body of knowledge available on this is strong enough to get the Royal Navy’s standard max. operating depth for rebreathers with nitrox backed down to 30m.
https://www.diversalertnetwork.org/files/Tech_Proceedings_Feb2010.pdf
It’s not like mainstream scuba knows better and thus maintains a deeper limit.
If anything, they’re maintained either out of ignorance, arrogance or because a lot of mainstream organizations can’t get insurance by any broker on the planet and thus have to cover legal expenses out of their own pocket, and therefore won’t risk legal liability from previous injuries/fatalities by bringing back down their limits from e.g. 40m to 30m.
I am uncertain if you mean general statistics or gas density numbers from QineticQ tests, but;
There are more different risks to manage with increasing depth.
The core content I’m addressing here, is HOW risks are managed.
For instance, diving to 100m has more risks involved than diving to 40m, but diving to 100m with a gas density of, say, 5g/L is reasonable where diving to 40m with 6,5g/L is not because we KNOW that gas density level is beyond reasonable limits. That is, the comparatively fewer risks on that 40m dive are managed more poorly.
In my logic, the difference lies not with the number of risks but how they’re addressed.
On another note entirely, I’m generally more concerned with the consequence of a failure than the probability of it.
It may not be.
We’re generally pressed for statistics with clean numbers and a big data sample, let alone evidence, to point to, so let’s focus on our gut feelings;
Mine is that a 60m dive O/C on air is SIGNIFICANTLY more dangerous than a 75m O/C dive on a suitable trimix, because I’m introducing myself to a scenario where increased WOB or respiration rate might well kill me on its own due to my choice of a high-density gas.
On a rebreather, one opts for an O/C fallback (bailout) specifically to avoid that eggs-to-basket ratio.
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