Deep Diving on Nitrox question

[jhnmdahl]

I don't think anyone argues that excessive can kill you, the question is more as to what is excessive? Am I really fine at 1.6 for 45 minutes, absent secondary factors like cold water or unusual exertion, or should I stay at 80% of that time to be safe, or never exceed 1.6, or maybe pick 1.5 or 1.4 as my personal max? I certainly haven't found decisive answers to these questions, and in fact have found contrary answers to most of them.

 

[RyanT]

My tec training(IANTD) has been 1.4 at max depth and 1.6 for deco.
AFAIK, 1.6 is NEVER normal for the working portion of the dive ie. max depth.

Will you tox instantly at 1.8 or even 1.6? ...unlikely. But seriously, why push it when you don't have it? My TDI training is also 1.4 for working portion of dive and 1.6 while comfortable in deco. As wetb4igetin said, it is a normalization of deviance and just not necessary.

My suggestion that exertion is believed to have some relationship with oxygen toxicity appeared to be met with puzzlement.

Yes, its pretty well understood that exertion and thermal comfort play a role in oxygen toxicity. It's why people easily handle PO2 of 2.0 or more while sitting dry and comfortable in a chamber.

 

[Lorenzoid]

My TDI training is also 1.4 for working portion of dive and 1.6 while comfortable in deco. As wetb4igetin said, it is a normalization of deviance and just not necessary.

Yes, its pretty well understood that exertion and thermal comfort play a role in oxygen toxicity. It's why people easily handle PO2 of 2.0 or more while sitting dry and comfortable in a chamber.

I guess the guy I was talking to either did not understand what I was saying or hadn't paid attention in his DP class. I got the impression he had just recently taken the class.

 

[Diver0001]

Also, in response to my thought that a diver might conceivably be delayed and therefore spend more than a few minutes at a ppO2 of 1.6, the diver sitting across from me, who was apparently a recent beneficiary of a TDI AN/DP course, chimed in and said, "So what?" He opined that a ppO2 of 1.6 for the working portion of a dive is normal for tech divers (like him).

TDI doesn't teach that. I think he may have misunderstood something in the course. it may not kill him but what he is doing is not recommended.

R..

 

[Streydog]

OK. Dove Devils Throat today for the first time. used 32%. Dive master told us he likes to take an exit at about 114', To stay toward the top of the exit because at the bottom it was 120ft. He said there was another exit farther down that is at 130ft. My max depth was 113Ft and that was very briefly. We continuedo on to Columbia Deep and ended the dive at about 74 minutes.

 

[macado]

@NWGratefulDiver. Bob, did you ever see anyone dive sidemount with them? Are DIN valves available? I'll be traveling from now on with SM gear and a DIN-to-yolk converter for those times where I can't get a DIN valve.

I am curious if Aldora allows SM as well. of course, diving your tanks would not apply. A SM diver would have to ascend with everyone else and I am pretty sure they have DIN valves.

Aldora is a great choice for sidemount divers. I have many friends that dive with Aldora and who do sidemount. All of Aldora's HP120s/HP100s have convertible valves. Gear is removed in the water if you prefer and tanks can usually be put on in the water if you don't feel like backrolling with them. (Exception would be some spots in north where you may need to get down quickly but that would be discussed in the dive briefing)

The only issue can be sometimes those DIN plugs can get stuck due to salt / corrosion. It's really not an issue provided you let the dive shop know you're diving DIN ahead of time. I dive DIN elusively with them and they usually will remove plugs prior to boarding boat in the morning. I can maybe count one time where I couldn't remove the DIN plug due to salt or stripped plug..I keep a DIN to Yoke adapter in my bag for those reasons.

For those who don't want the Aldora centric answer....Pretty much every dive shop in Cozumel is "sidemount friendly" provided you tell them ahead of time. The difference is not every dive operators has updated their tanks to convertible valves however given enough notice they all can get DIN tanks from Meridiano (the central fill operator that most shops use).

The primary difference will be length of dives. Some operators will let you dive your tanks/profile while others *may* set a 45-60 minute arbitrary limit (cattle boat operators). Search threads for this if you want specific names. This is a huge generalization and I'm not going to pick on shops but if you're sidemounting for the sake of redundancy then that might be fine. If you're sidemounting because you want extra gas AND redundancy for a longer profile you may still be limited to shorter runtimes.

Dive operators with steel tanks like Aldora, Living Underwater, LiquidBlue are going to do longer profiles since it's the nature of all divers having larger capacity tanks which makes sidemount better suited for these operators especially if you are matched by experience level with others on the boat.

Otherwise pick an operator that lets you dive your profile on an AL80. There are several favorites but I'm pretty sure Tres Pelicanos, Blue XTsea, etc let you dive your profile and I've seen people dive sidemount with both of these operators. There are of course other operators but I just wanted to make a point here that due to the nature of the business, most operators are going to claim "sidemount friendly."

 

[WarrenZ]

I dove with Aldora October 2016 and did every dive sidemount. The first day they made me use Al80s and I had a LOT of lead on to keep them and me down. They provided me 4 tanks for the day so I wouldnt be limited and of course charged me for the gas in all 4 tanks. The tanks were DIN however they did not have left and right handed valves.

The rest of the week I was able to be given HP120s and was much happier. I kept getting the strangest looks from the DMs who wernt used to someone in sidemount being able to do a back roll fully geared up. I also was challenged to climb the ladder with the tanks on rather than pass them up which I did just to prove it could be done. The rest of the time I passed tanks up at the end of the dive.

I would use half of the tanks on the first dive and then used the rest on the next dive and we did have to ascend as a group.

As far as deep nitrox goes most of my 32% tanks tested out at 30-31.5 however I did briefly go to 1.44Po2 on one dive and the DM did a little freaking out on my behalf so 130 on 32% may be an subjective allowance.

 

[gfaith]

@macado and @WarrenZ appreciate both of your responses. My wife and I just did our SM training in Playa del Carmen and mainly want to stay on top of our diving in SM configuration (just in case I can get her back to the cenotes LOL). I also talked to CoCo View in Roatan, our next trip, and they are SM friendly too, but they have only AL tanks (DIN yes)

 

[macado]

I dove with Aldora October 2016 and did every dive sidemount. The first day they made me use Al80s and I had a LOT of lead on to keep them and me down. They provided me 4 tanks for the day so I wouldnt be limited and of course charged me for the gas in all 4 tanks. The tanks were DIN however they did not have left and right handed valves.

The rest of the week I was able to be given HP120s and was much happier. I kept getting the strangest looks from the DMs who wernt used to someone in sidemount being able to do a back roll fully geared up. I also was challenged to climb the ladder with the tanks on rather than pass them up which I did just to prove it could be done. The rest of the time I passed tanks up at the end of the dive.

I would use half of the tanks on the first dive and then used the rest on the next dive and we did have to ascend as a group.

As far as deep nitrox goes most of my 32% tanks tested out at 30-31.5 however I did briefly go to 1.44Po2 on one dive and the DM did a little freaking out on my behalf so 130 on 32% may be an subjective allowance.

Definitely agree with you on tanks not having left/right handed valves in Cozumel for sidemount. I forgot to mention that. Not sure if that is something that can be rented from Meridiano for folks that really want that..I've never bothered to ask since it never bothered me.

I find it bizarre about them giving you 4 tanks that were AL80s. Just curious if that was something you requested because of weighting concerns?

Usually the way I've seen it was the person either dives the same set of HP120s or HP100s for dive 1 and dive 2. No extra charge that way since you're using same amount of tanks. Either way.. it seems like they sorted you out for the rest of the week?

My only concern for people that are sidemounting steel tanks (especially two HP120s) is that you're usually going to be pretty overweighted. Just something that I've seen people deal with..

You might want some backup form of buoyancy. I have the same concerns when people backmount two steel tanks with little exposure protection so it's not really a sidemount specific concern.

 

[gfaith]

@macado you must be reading my mind.. My wife has a DECO SM that we put together works great in fw with double AL 80's and 2lbs of lead, but only has 20-22 total lbs of lift. Two HP80s will put her at -17 for just gas weight she will be diving in a 3mil or 5mil wetsuit.