I don't believe it's really a question of how long: it only takes a few moments of breathing the wrong gas for it to be fatal. It's by far the easiest mistake to make, yet the most preventable (i.e. by having a robust gas switch protocol that involves a buddy verifying your mix before the reg goes in your mouth).
This class might have been wreck only but it's also taught in combo with AN/Deco - in that you are only taught to carry one deco gas and yes it is checked for proper depth with your buddy. What you aren't seeing is John is a big fan of gas switches on the fly - he really likes to see efficient deco being done - not sure how to describe it. After dives in classroom, we looked at gas switches, where they happened, how it effected your run time etc...
In Tri mix, with multiple deco bottles, you prepared for your gas switch before you left the bottom - again, it goes back to the efficiency he's trying to teach.
He teaches a method, whether you utilize every letter to that method is up to you. There is a lot of stress in the classroom about correct gas switches and the bad results that can occur.
Cool. So you're on the it's ok to kneel to perform basic early technical skills bandwagon? Specifically because they didn't come to him to learn to shoot an smb or drop a stage but to penetrate a wreck? That's scary. There should be a certain level of skill required by any class at that level. Kneeling to perform a task shows a lack of skill. I am on the bandwagon that kneeling for skills should be strictly forbidden from OW classes up. Apparently agencies feel the same way too since they're moving that way.
I personally think that's BS. There's a time and place for everything.
I will concede that a couple of breathes or limited time on the wrong bottle probably won't kill you. I think the issue with John's technique is what is safer? You plan on doing a buddy check on the gas anyway immediately after switching, right? Is it safer to do the buddy check before you put the bad gas in your mouth or after you put the bad gas in your mouth? If you don't plan on doing buddy checks that is one thing, if you actually do plan on doing buddy checks then John's technique is an increased risk (even if minor) for ABSOLUTELY no reason. Staying on your back gas a minute longer 100% won't kill you. Breathing the wrong gas for a minute might not kill you, but it is not 100% won't kill you.
Yes his method of gas switching is riskier - it's a choice that is talked about in class. It's a method you can choose to do or not do.
It seems like everyone who's taken a class with him says he's fabulous
and everyone else, based on your video and others
questions what was so amazing about the instruction if your buoyancy, trim, kicks, SMB, linework and other basic skills seem to be below what we expect from intro to tech students.
I know in the classes I took with him, we never once talked about style points - well we talked and laughed about them. He teaches buoyancy, fining etc in ITT - wreck diving class is more of a wrestling type class.
John focuses a lot on CO2, much more so in the deeper classes but it's high on his list of priorities. I call it lazy diving, call it whatever you want. There is an underlying method that he wants you doing the absolute minimum effort underwater - why be neutral fining into the current if you can kneel - why fin your way thru a passageway when you can pull yourself along? CO2 CO2 CO2 bad bad bad - he says something related to CO2 about every five minutes - maybe that's a partial reason he teaches the way he does.
I noticed two issues, the first, which as mentioned in the narration, was that the initial ascent rate was fast. It looked to be around 60 feet per minute for a full minute - going from 130 to around 60 feet. I often do the first 30 feet of an ascent that fast, but generally not for 60 feet. Was the computer complaining about that?
The other question, I had was about the technique of BC inflation and putting air in the smb at depth. I don't think I would have any questions about that, IF the smb was released at depth. However, presumably the diver is neutral or close to it on the wreck, he dumps most or all of his air into the smb, As indicated in the narrative, this preserves the perfectly neutral condition. However, this seems to be a potential big problem.
What happens on ascent? The smb is expanded and pulling the diver up and he has little or no opportunity to vent the smb. I can see how, depending on the amount of air added to the smb at depth, that this could cause an ascent to get out of hand quickly. If the diver were using a BC and dry suit, he might have to be dumping air from three different sources to control things. I didn't notice you venting the smb on ascent. I really don't see any benefit in this.
I would think, it would be preferable to either add a little air at depth and let it go, or ascend to a reasonable stop depth and inflate the smb and let it go, but carrying a partially full smb that is expanding during a good portion of the ascent seems to add task loading and potential negative consequences for zero benefit that I can identify. Is this issue partially why the ascent was kinda fast from 130 to 60 or so? Is there a benefit to partially filling and then carrying the smb?
And I should mention, the OP should be recognized for exercising considerable patience while receiving a lot of less than positive feedback on this thread.
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A Moderator is taking the liberty of singling out this excellent observation with boldface.
@Zack-Bloom is to be congratulated for keeping this thread on a very even keel, despite some not-so-veiled criticism.
The SMB elevator - complicated stuff with many things that can go wrong but when you get it figured out, it's an art. Again, it's big picture teaching I think. Transfer wing air to SMB while you're neutral and start heading up - it doesn't take long before the SMB and air in your BC are pulling you up - you watch your computer to monitor speed - vent your BC to adjust and release the SMB when you hit the depth you want - oh yeah - do your first gas switch while all this is going on..... Complicated
It's what he teaches - do it or don't do it - your choice. It comes back to his broad thoughts of reduced physical effort and efficiency in your deco. There's a lot of talk in class about ascent rates, how they effect your deco obligation, the ATM delta and how at greater depths you should really be ascending faster...... It's a skill that is taught for a reason - it's a complex skill - it's a skill that I don't really know if it applies to 150' dives as much as it applies to 300' dives. I don't square profile dive much, I practice it when I can because I think it's fun, I like the complexities - I don't really dive to depths that a slow ascent kills my deco obligation.
John certainly isn't for everyone. John is in no way set in his ways, some old school diver - I think he's quite the opposite. He has a wealth of real world experience - he does things because they work for him, not because everyone else does. If you want to do something different, just ask him, explain your reasons, he'll talk it through with you and you might just be suprised that he understands and agrees with you. Pretty funny story when after six or so dives with him, he asked me why I had a seven foot hose...........I don't think the man is trying to impress anyone, flaunt anything - I think he cares about you living to dive another day and tries to teach you the skills and reasoning behind them.
Hopefully will be back there diving with him the end of October for some more fun if there's room on the boat.
