Diving nitrox through twin Al 80's?

[muddiver]

Yes, there is a special certification for diving double cylinders filled with Nitrox if you have only dove a single cylinder filled with Nitrox. It's a very rare PADI Specialty only available through PADI DIR instructors. I am qualified to ensure you meet the required qualifications, and you can even do it on line! Send me $300.99 and I will forward the link to the PADI DIR training site. When you finish the 15 minute course I will send you your Nitrox Doubles certification card for free!

 

[ninjadoc47]

I was told by a local PADI instructor that I had to get a certain certification in order to dive twins filled with the same mix of nitrox. Why? If it's the same blend, and I'm breathing from both tanks at the same time just for extended bottom time, as long as I don't break the PPO limits of my mix, what could happen? He said it could kill me (somehow )????

The reason I ask, is I want to dive Venice Beach Fl for some shark teeth, and I want to rig the tanks with 36 or 40% nitrox so I can stay down longer collecting dem toofs.

hey bud, please allow me to answer this simply as 1) not to agitate or confuse you 2) avoid a unneeded drawn out debate. your instructor is correct in not wanting you to dive but for the wrong reasons, doing doubles means you have been trained to handle a higher echelon of diving. bud is getting a few teeth worth your life?, I am only commenting as a dive medical professional( I run chambers for the military), don't be a story in scuba diving mag and be that guy a lot of folks here will be shaking their heads. If you want to do it , get the cert and not that stuff the other guy who's a Dm is trying to spout, doubles mean technical diving , techheads are NOT looking for shark teeth they are looking for large scale history(caves, wrecks, etc) dive smart for your family, yourself and for the community of diving , cheers mate. Manny

 

[TSandM]

Doubles do NOT mean technical diving. I know a LOT of people who dive doubles who do no, or few technical dives. Doubles are useful for redundancy for deeper recreational diving. They are also delightful for extending dive time in the shallows, where neither decompression nor thermal tolerance will end the dive.

 

[Dr. Lecter]

doing doubles means you have been trained to handle a higher echelon of diving . . . I am . . . a dive medical professional( I run chambers for the military), . . .doubles mean technical diving . . .

Simply stunning. I mean, I heard standards had slipped, but…wow.

 

[jwelburn]

nijadoc47, doubles don't mean anything but more gas. They are a tool, nothing more or less. Nobody ever told me that I shouldn't own a socket wrench, because I'm not an airplane mechanic and airplane mechanics use socket wrenches.

I agree with the posters that say you should learn the failure modes and how to deal with them, however for a dive within recreational limits it's not absolutely necessary IMO. (but still, it's not that complicated, so learn it...) If you have a failure, begin a proper direct ascent to the surface just like you would if your single tank had a failure. If you are staying withing recreational limits, you'll be just fine. Folks have been diving single outlet manifolded doubles for a long, long time for many, many non-technical dives, without any problems (not counting the standard piss-poor decisions/planning or heart attacks).

There is a pretty solid group of technical divers here on Oahu. You know what their doubles are filled with most of the time? 32% nitrox, or *gasp* just plain air. There are lots of places for long range but relatively shallow shore dives in the neighborhood of several hours in length. So even though we are "technical" divers, these dives are not outside of standard recreational limits. My Suunto Zoop doesn't even get close to nervous on these dives. The mere presence of doubles on the dive did not make it magically "technical", it just made it longer.

To the OP, I love diving doubles. They are wonderful for these longer duration dives. That said, I highly recommend reading the gas planning article by NWGratefulDiver, and paying particular attention to minimum gas calculations. It is hard to keep the temptation at bay to push the envelope with that much gas, so having the hard-stop limits there helps keep you from getting over your head while still allowing you all the flexibility you want to just "follow the teeth" until you hit it.

*Also, the fact that the instructor said "same mix of nitrox" seems ridiculous. I don't recall any agency or group that recommends putting air in one side and nitrox in the other or anything like it.

---------- Post added August 5th, 2014 at 07:35 PM ----------

Haha, had to take a break writing to deal with kids and TSandM and Dr. Lecter beat me to the punch!

 

[Scubadude_LA]

Plenty of good comments above.
Doubles can be a double edged sword if you rely on them but don't understand them.
Pretty simple in the big picture though.
80's are one thing, jump to steel and you need to rethink buoyancy and the respective redundancy on that.
Then there is the gas management of extended time and either lost deco or lost backgas (which is where your instructors concerns may have come from depending on where you are, I didn't read the thread too closely, so sorry if I missed anything).
Nuff said...


Edit: Sorry, I read again and saw 36-40%. So you can't get too crazy with that high O2 without other issues that you already know about from Nitrox use.
DIVE PLAN
Surface interval = 5 day 0 hr 0 min.
Elevation = 0ft
Conservatism = + 2

Dec to 70ft (1) Nitrox 38 50ft/min descent.
Level 70ft 68:36 (70) Nitrox 38 1.18 ppO2, 48ft ead
Asc to 20ft (71) Nitrox 38 -30ft/min ascent.
Surface (72) Nitrox 38 -30ft/min ascent.

OTU's this dive: 92
CNS Total: 32.5%

155.1 cu ft Nitrox 38
155.1 cu ft TOTAL

That plan is an expended set of AL80s at 3000 at .7 RMV
There are infinite combinations of Mix/depth/Time/BlahBlah. You need to understand what you are doing.
If you have to ask, Stop, some mentoring/training might be in order. Sorry to sound harsh, but I have not seen a way to delete a post on this site, so it's here for life, just cleaning up after myself.
No super deal breaker, just be warned. Heck there is no law that I know of that requires certification, But it is generally a good thing.
But I agree that the Nitrox/Doubles thing is sort of bogus. Nitrox passing NDL or past CESA depth or overhead is another story.

 

[Boosted98gsx]

Thank you all for your comments. They are pretty much right up my way of thinking. I am a "plan your dive and dive your plan" diver, so I would obviously be researching my limits and decomp stops.

I don't think I was very clear in my intended depth to use this kind of setup. Venice beach "boneyard" is at ~30ft depth. Virtually no risk of decomp issues as long as basic limits are heeded. That's why I want to run doubles on 36%.

I am an engineer (mechanical) by profession, so double edged swords and understanding both sides of an equation are parts of my mindset.

Muddiver, check is on the way, please be sure to hold your breath while waiting for it to show up....

 

[Dhboner]

ninjadoc47....I know you mean well but diving doubles does not necessarily equate to technical diving and need not be any more risky than single tank diving. For a lot of divers, doubles provide redundancy on short, recreational dives. Provided you can execute a shutdown, doubles can ramp up your safety factor on even shallow water, fun dives.

 

[kelemvor]

Simply stunning. I mean, I heard standards had slipped, but…wow.

I'm pretty sure I have heard that putting your DC into deco means you're tech.

 

[rhwestfall]

Highly technical....