500 psi for two divers?

[doctormike]

You have one diver who is now in an emergency situation (OOA) according to all I have learned in six months of diving and reading profusely here and about 20 books, and probably 10-20 blogs... that one single fact becomes the limiting criteria in the scenario. How much air diver B has in their tank is now IMMATERIAL, and given the depth, you surface immediately on shared air and do not worry about a safety stop... even if the dive profile included 12 minutes at 100ft, you might go to 20 feet and ride it out until your tanks on fumes, but it seems that surfacing and being done for the day is the better part of valor, and safer choice overall.

Speaking as a guy who took a chamber ride after a recreational dive within NDLs, I disagree with this statement. If you can make a safety stop, you should. That means, if you and your buddy are sharing gas from a single tank, an there is enough gas for you both to spend 3 minutes at 15 feet, you should do it.

Obviously, a safety stop is by definition not "required", but we shouldn't go overboard in minimizing it's importance - especially if there has been significant nitrogen loading during the dive. Everyone bubbles after an ascent, but it's not clear why some people develop DCS after limited profiles and others remain without symptoms despite more aggressive dives, even after missed deco. Remember too that in a situation like the OP described, someone is likely to be panicked and surfacing faster than the recommended rate as well, which also contributes to DCS; a safety stop has the added benefit of limiting the ascent time.

Obviously, having something to breathe is more important than anything else. But even in an air sharing situation you can calm down, assess your options and make a smart decision.

 

[decompression]

Getting to the next source of air (surface, stage, hang bottle) should be the prime goal of any dive. Simply stated, you want to finish the dive safely. Every diver needs an ascent strategy which could be any one of several. I prefer to teach my OW students something that is not as arbitrary as "500 psi".

It's ludicrous for a new diver not to be reassured that they will make it safely to the end of the dive. Rock bottom is simple to figure, is reliable, flexible and easy to apply. The situation of an OOA conflicting with my survival or a moral quandary is one I would rather avoid completely.

For the vast majority of divers that aren't familiar with rock bottom, there is a wealth of info availible.


Sent from my iPad using Tapatalk

 

[eelnoraa]

So, are you saying that when you use the term "rock bottom," you don't actually mean the specific concept called rock bottom but rather any of the methods people use to make sure they have enough gas for their ascent?

Actually, the other way around. I learned and used the concept long before I know it is called "rock bottom". In my training, we just called it minimum reserve requirement.

What i am saying is whatever it is called, it is not important. The concept meaning and how to use it is all that matters.

---------- Post added August 21st, 2014 at 10:37 PM ----------

You have one diver who is now in an emergency situation (OOA) according to all I have learned in six months of diving and reading profusely here and about 20 books, and probably 10-20 blogs... that one single fact becomes the limiting criteria in the scenario. How much air diver B has in their tank is now IMMATERIAL, and given the depth, you surface immediately on shared air and do not worry about a safety stop... even if the dive profile included 12 minutes at 100ft, you might go to 20 feet and ride it out until your tanks on fumes, but it seems that surfacing and being done for the day is the better part of valor, and safer choice overall.

If you don't have enough gas, of course skip the safety stop and get to surface. If you do, why would you want to skip it? Knowing that, why not plan to have enough gas?

---------- Post added August 21st, 2014 at 10:48 PM ----------

For a new diver, I think teaching an absolute is the best way to go about it. There's nothing pathetic for a new diver to be taught "BE ON THE SURFACE AT 500PSI" (actually, I'd just say, BE ON THE SURFACE BEFORE YOU ARE IN THE RED)... it's a clearly defined line, and unless they are under the direct supervision of a more experienced diver who is going to be responsible for their safety, they should stick to it like the gospel.

Be on surface at 500psi, if you can archive that, you are doing the planning already, because you need to know at what psi you need to start your ascent at certain depth. Now why be on surface at 500psi doesn't always work? Because that 500psi is what you have extra if you need to share air in your ascent. Will 500psi enough to get a diver to surface? it depends on the depth and SAC of the diver. At 100ft, it probably not enough espeically the OOA diver will most likely be in stressed. At 60ft, it maybe OK. I don't think be on surface at 500psi is patheic, but there is better plan that that.

 

[TracyN]

to be honest i dont know why my question caused so much irritation ! it was just an hypothetical case because im curious and i will try to avoid.
i really appreciate all answers, from all of you but seems like all the ones who answered are instructors or have more than 100 dives ... no offence but i wonder how some of you were with just 4 dives.

i dont care if im supposed to be able to plan a dive on my own after the OW. I think it would be an irresponsibility from my side to assume that i have to sit down with the dive tables , plan the whole dive and just jump in. I thought one of the rules of diving was not to go out your comfort zone? well , if with 4 dives i have to plan my next one i would be right out my comfort zone and NO, im certainly not prepare for it at the moment. So yes, im going to study this and keep relying on others with more experience, for now =)

This is a very dangerous mindset to have. Personally I would not even get into the water with someone who has no idea how to safely plan a dive or how to participate in dive planning. This is one reason I am apprehensive about having to instabuddy with strangers on a dive boat. Furthermore it's just flat out dangerous to put blind faith into someone else keeping you safe. Just because they have DM or instructor behind their name does not make them superman. Also they are human too, what if an emergency happens to them? Would you be able to help them? Would you be able to get yourself back to the surface or to the dive boat if they became incapacitated? These are serious questions to ponder and none to be taken lightly.

 

[Storker]

Tatiana:

Out of sheer curiosity (based on my perception of differences between diving practices in Northern Europe and in warm climate resorts), I checked your location and I was quite surprised to see that you're located in the UK. You consistently use imperial measurements, and the diving practice you obviously employ is definitely something I don't associate with UK or Nordic divers. Did you take your OW class while on vacation, e.g. in the Caribbean?

I'm also curious to know if you have ever dived in your home country. If you ever consider doing that, I would strongly recommend you to work on your knowledge and ability to plan and conduct a dive without depending on a DM for your safety. Because you probably won't find a DM to hold your hand during the dive. If you work to develop your competence, you will probably also discover that some resort operators market and use diving practices which are definitely unsafe (e.g. taking divers on single tanks to depths well beyond rec depths, or taking untrained OW divers on cave penetrations, even without proper gear and redundancy. I'd like to recommend Jim Lapenta's excellent essay on who is responsible for what, which is a sticky in this subforum.

Remember that SCUBA diving is perfectly able to kill you, in some of the less nice ways you can imagine, so to rely on some random stranger for your safety is not particularly recommendable. Even if that random stranger has a DM cert. On the other hand, with proper procedures and preparations, SCUBA diving is probably less dangerous than your daily commute.

Good luck with your future diving!


EDIT: And I'm quite convinced that people aren't replying harshly out of irritation. I sincerely believe it's out of genuine concern for a fellow diver.

 

[TatianaSilva]

i did it in the caribbean and diving in northern europe is not what im looking for right now. i spoke with some english divers and i prefer to wait until i have more dives on my back .
I am not saying that i will not care about anything and just go with the DM, its only that takes ME time to PLAN 100% a dive when in the OW we just talked about it but didnt actually plan it on my own . Im sure i know when and how to ascend guys but i like to do specific questions.

my question was if ,in average, is enough to ascend from 18 m with 500psi for two divers , with or without safety stop. Just in case at some point this happens, it doesnt exactly mean that i would be silly enough to still be diving with 500psi for myself.

 

[rivers]

Tatiana, I have sent you a PM offering to dive with you locally. The water in the shallows (above 12m) is still warm (about 20*c). I can also probably source some single cylinder kit for you.

 

[Storker]

diving in northern europe is not what im looking for right now. i spoke with some english divers and i prefer to wait until i have more dives on my back

With a decent mentor and proper practices, there's no problem to dive in your home waters at your experience level. We do that immediately after certifying OW. And the green waters we have up here have their own particular charm, well worth experiencing:

 

[fire_diver]

i did it in the caribbean and diving in northern europe is not what im looking for right now. i spoke with some english divers and i prefer to wait until i have more dives on my back .
I am not saying that i will not care about anything and just go with the DM, its only that takes ME time to PLAN 100% a dive when in the OW we just talked about it but didnt actually plan it on my own . Im sure i know when and how to ascend guys but i like to do specific questions.

Great! We want you to ask questions! A new diver looking for answers is 1000 times better than one who just keeps guessing and hoping everything is fine. As you probably figured out from this thread, some times the question asked can draw a large amount of discussion about things you didn't specifically ask. Some times those questions can reveal deeper source problems you also need help with.

As for dive planning, I bet you did the real work of "planning" in those discussions and just didn't realize it. Dive planning isn't difficult and can be done mentally in a few seconds. Just be sure to TALK with your dive buddy and make sure you both are on the same page before you splash.

1- do you know the dive area? Either you have dived it before, or the DM will describe it in the pre-dive brief. ( Example, diving a patch reef with sandy bottom with max depths of 66 ft )

2- How much air do you have? Check your gear and see what your starting point is

3- What is the max depth you will dive to? You don't have to dive to the sand on any dive.

4- How long will we dive? Do you have a set amount of time to make the dive (some dive boats sets a limit), will you be diving the NDL, or will you dive until you reach your mandatory "end the dive pressure"?

- A good gas-rule to follow for non-current dives is 1/3's. Dive out until you use 1/3 of your starting gas then begin working back to the starting point, end when used 2/3, ascend and you should have a good reserve for both.

Once you make those choices, you have most of your plan. If you were going to plan the dive you could say "OK, we have a reef extending east and west of us with a max depth of 66ft. We have an NDL of 45 minutes. We both have 3000psi in our tanks. We will start at the sand and dive to the west until one of us reaches 2000 psi or our dive time reaches 20 minutes. Then we will turn around and head back to the anchor line, we should reach that with at least 1000psi left or with about 40 minutes of our dive time used. Then we will ascend up the line and hold at 15 feet for 3 minutes before surfacing. If one of us has a gas emergency we will share air and ascend normally watching our remaining air. If possible we will still do our safety stop on the way up, then we will surface swim back to the boat."

That's it, that's a basic dive plan that uses tables (since you don't a computer yet) and considers your gas usage and ascent plan. Once you and your buddy learn your actual gas usage rate (SAC), you can begin making more detailed dive plans for air usage if you are looking to maximize dive time.

 

[flots am]

my question was if ,in average, is enough to ascend from 18 m with 500psi for two divers , with or without safety stop. Just in case at some point this happens, it doesnt exactly mean that i would be silly enough to still be diving with 500psi for myself.

I had attached a spreadsheet to calculate this for you, but decided that you really need to know how to figure this out for yourself.

However just to make things clear, the answer is "No."

Getting a slightly stressed diver (you) and a pretty stressed diver up from 18m will require about 15 CuFt of air. This is based on a few guesses at stress level and SAC rates and time, but shouldn't be too far off.

At 500PSI, you have about 9 CuFt of air. Getting your buddy to the surface will require about 6 CuFt more than you have.

This means that you will soon both be out of air and still underwater.

If you learn nothing else in SCUBA, you need to know how to make sure that you have enough air remaining to get you and your buddy to the surface.

However being a no-decompression dive, it is possible to simply surface at any point, however it's also easy to do this wrong when panicked, and there are no guarantees of safety.

It's much better to just make sure you always have enough air.

flots