Nitrox best mix question

[black1]

Thank you all very much for your advice and concern, the agency im using is P.A.D.I. and although i feel i have expierience it did alarm me and make me question as soon as i heard the mix for that dive and i questioned the judgement. I will be speaking to her soon and will ask plenty of questions and voice my concern. I would like to dive to the recreational limit of 130ft but only using a PPO2 of 1.4 for safety reasons, the area off of Pompano/Ft Lauderdale as anyone familiar knows can have and usually does have a strong current around the wreck sites and pushing the PPO2 to 1.6 is not being safe in my opinion and that is the only opinion i go by. If we talk and she says it will only be to the recreational limit at 130ft the i will give it more thought and will use either a 26 or 28 and no more higher mix, i use HP Steel 120's but safety is my main concern and what i abide by when diving, again thanks all. For those who have dove it what are your thoughts on it, thanks.

 

[JDMerk]

Why not just dive it on air? Hell its cheaper and you know your not going to tox at those depths. As somebody already stated I also believe EAN26 would be the wisest choice with a MOD of 144 (if you insist on diving EAN) but on that mix your EAD is 131.8...compared to the air tables your gaining roughly 2min MDT...whats the point. Your pushing the limits of Nitrox, going with some off the wall mix for 2 min?

 

[AzAtty]

Not wishing to sound too harsh, but if you have to ask this question you don't have the training necessary to plan the dive.

I assume you're taking the PADI AOW course and the dive in question is your "deep adventure dive." It also appears that your instructor plans to exceed 100 feet on the dive. If so, your instructor will violate PADI standards. The depth limit on any dive conducted as part of the AOW course is 100 feet. The program guide mentions that depth limit twice in boldface type, so it's kind of hard for an instructor to miss it.

 

[Walter]

It also appears that your instructor plans to exceed 100 feet on the dive. If so, your instructor will violate PADI standards.

Excellent point. It's been too long since I've dived the Harvey to remember for sure, but I'm not sure you can reach it without exceeding 100 ft. If that is the case, you need another site for the dive. The Captain Dan is an excellent wreck sitting in 110 feet of water. You can have a very nice dive on it without exceeding 100 ft.

 

[eponym]

I would like to dive to the recreational limit of 130ft [snip]

When SSI revised their recreational depth limit a couple of years ago to 100 feet, the quip was that instructors were saying "limit" but students were hearing "goal."

Black1, I'm not saying that applies to you, I don't know. I do like that you appear to understand planning your gas needs (quantity, mix, reserve). I assume your performance under narcosis has already been vetted at 100 feet. Increasing severity at 130 feet is a concern. Don't assume that EAN26 (or any EAN mix, for that matter) will give you any advantage over air in regard to narcosis.

Let us know what you do and how it goes!

-Bryan

 

[Reg Braithwaite]

...I would like to dive to the recreational limit of 130ft but only using a PPO2 of 1.4 for safety reasons

Unless you have a lot more experience than the 0..24 dives in your profile and judging by the fact that you are only taking AOW now, I would say you and I have a lot in common. Namely, we don't know jack about diving.

Now let's be honest with each other, shall we? Diving to 130', on a wreck, with potential for current, is not a safe diving activity in and of itself. This is something we train for, prepare for, work towards. You and I take things like AOW so that we can then go on 60' and 70' and 80' under very benign conditions and get used to depth and air consumption and gas planning and deploying SMBs. We dive to 40' and 50' and 60' in current so we can get used to handling current and doing drifting ascents and learning what signaling devices we need to maintain contact with our boat.

We might even take something like IANTD's Deep Diver course to prepare ourselves for the further rigors of diving below 100'. We dive with mentors and take instruction and yes, ask questions on SB. Then ,after a lot of this kind of thing, we do a dive to 130' on a wreck. Yay!

But if you do that without any preparation, you will probably survive. But did you survive because you were ready and prepared and executed a safe dive? Or you just didn't run into any bad luck? If you were "lucky," then there is no pride of accomplishment, it was just a stunt. But if you prepare for it and are truly ready when you get on it, the pride won't come from the dive, the pride will come from the preparation.

I speak to you as someone who is walking this exact path. Last year I dived a multilevel wreck to 134 feet in cold, dark water with a very experienced buddy. We had agreed on all sorts of protocols for aborting the dive or stopping shallower, and I was only at 134 feet for a minute or so before we started ascending, we spent most of our time around 110'. But still, looking back, I was not ready and I would not counsel anybody to do the dive I did no matter who was alongside them.

Instead, I have set a goal of going back a year after my first dive on that wreck and doing it again. I may not be ready, in which case I won't do it. But since setting that goal, I have taken more instruction, I have practiced drills, and I have gotten in with a crowd of experienced buddies who are helping me with my progression. And there will be even more training and practice between now and my return to that area in August. And if I am ready, I will do the dive again. And this time, I won't be proud of the dive, I'll be proud of what I did in one year to get back there and do the dive properly.

I strongly encourage you to treat this dive as a goal, but not in the sense of "I want to do the dive," but rather in the sense of "I want to use this dive as a demonstration of my training and readiness." Focus on the readiness, not the dive.

JM2C, as stated above I am new to this diving thing myself.

 

[rstofer]

I would go with Walter's advice and keep that ppO2 down to 1.4 ATA. As I see it, this EANx 26 mix would have an MOD of 145 feet.

If you actually hit 145', the EAD is 134' and your NDL from the PADI Air RDP is 8 minutes.

If you ascend at 30 fpm, it should take just short of 5 minutes (out of the 8). This dive, for a non-deco recreational diver, is just silly. All that risk for 3 minutes on the bottom.

Richard

 

[Blackwood]

We might even take something like IANTD's Deep Diver course to prepare ourselves for the further rigors of diving below 100'.

I took that course. It lasted over a year, and we only got deeper than 100' on four occasions.

 

[Blackwood]

your NDL from the PADI Air RDP is 8 minutes.

If you ascend at 30 fpm, it should take just short of 5 minutes (out of the 8).

Based on a conversation I had last week, per PADI table methodology the ascent doesn't count towards bottom time. BT = Surface through the bottom until you begin your direct ascent. So if you descend at about 60FPM, you'll have roughly 6 per the RDP.

 

[rstofer]

Based on a conversation I had last week, per PADI table methodology the ascent doesn't count towards bottom time. BT = Surface through the bottom until you begin your direct ascent. So if you descend at about 60FPM, you'll have roughly 6 per the RDP.

You are correct, I was in error. PADI does not include the ascent time but they do include the descent.

Richard