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General Category => Diving Safety, First Aid & Travel Issues => Topic started by: poh6702 on 10 Nov 14, 09:54

Title: What are the causes of Out Of Air (OOA)
Post by: poh6702 on 10 Nov 14, 09:54
Branching out from the other thread about Double tank, Spare Air and Pony Bottle; people who carry these extras are to ensure that in OOA situation, at least can still get to the surface as safe as possible. As divers, we don't want to get hit by OOA, that is why we maintain our equipment, check our pressure gauge regularly, stick to our buddy when diving.

I would like to classified then in 3 categories for discussion:

1. Due to carelessness: Used almost empty tank and forget to ensure pressure above 180Bar, turn the valve in wrong direction (turn to close then open quarter turn), dive too deep (or due to strong current) and forget to check pressure. Any others?

2. Equipment failure: what are the likely cause? and what is the best way to react?

3. Disaster: what can happen? How to react?

I am a kiasi diver, hope to understand the causes and be able to avoid it as much as possible. Of cause pairing with buddy is the best solution to overcome when OOA happen.

Dive safe, dive KiaSu and dive KiaSi.
Title: Re: What are the causes of Out Of Air (OOA)
Post by: Alvin Ho on 10 Nov 14, 10:45
In now my 16th year of diving, i have had 2 near OOA situations, both my fault.

1) Shallow dive at Puri Jati in Bali. We were in water for 140min already and i was about to exit the water with about 5-10 bar left in tank when those who exited already shouted that the guide found something special. i finned over and went down to find a frogfish so i started shooting again. It was shallow depth of maybe 5-7m. After shooting a bit i found the breathing a bit hard and knew the tank was empty so i slowly surfaced.

2) During a dive photography competition in Cebu, there was a dive in pretty strong current that made photography difficult, i was shooting wide angle while others were shooting macro. I finished what i wanted to shoot so decided to help out others shooting macro. I checked my gauge and i had about 30 bar left. Thinking i had enough though it was about 15m, i went to help a friend. After helping i checked my gauge and it showed empty. I went over to my then gf to signal to her to ascend as i was still breathing normally. Halfway through our safety stop my reg again was sucking on empty so i got my gf's octo to complete the stop.

One last incident wasn't close to OOA but it wasn't that wise decision in retrospect.

I had a leaking hose/gauge/octo (can't remember) on a dive at lembeh. could hear the hissing on the surface but it didn't seem that loud or leaking that bad. But as i descended the leaking got worse. So i did a quick calculation and went to shoot the subjects at the site v quickly, spending 5min max on each subject and checking my gauge constantly. I finished my tank in about half the time i normally dive and the whole dive lasted only about 40min.


I would say most OOA situations are due to diver error. equipment failure is seldom the issue when you read dive accident reports.

Personally as a photographer i find myself diving alone quite often or find myself alone when a dive group has moved on. During such situations i find myself adjusting my dive plan to be a lot more conservative. I go shallow and i don't dive as long as i normally do. Not advocating anything but it's just the way i dive.
Title: Re: What are the causes of Out Of Air (OOA)
Post by: Chris on 10 Nov 14, 11:49
I would say most OOA situations are due to diver error. equipment failure is seldom the issue when you read dive accident reports.

I could not agree more. It is typically a combination of carelessness (as in "50 bar is for beginners, I am sooo experienced i can easily max it out to ten") in combination with something unexpected happening when you already pushed the limit. This can be anything from a bit more current than anticipated to getting distracted by something nice (especially as a photographer).
Title: Re: What are the causes of Out Of Air (OOA)
Post by: Ryoin82 on 10 Nov 14, 13:11
I think the main consideration for newbie divers will be failing to check spg regularly. Being too fascinated or trying to catch up with dm diverts their attention. There are plenty of cases where divers only Check pressure when prompted by dm, only to realize they have 20 bar left.

Could peer pressure or ego be another factor as well? U are down to 50 bar but don't want to sound out becoz u don't want to be the one to end the dive.


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Title: Re: What are the causes of Out Of Air (OOA)
Post by: poh6702 on 11 Nov 14, 09:36
I have seen burst O-ring (tank valve) while setting up gear on boat, I am curious to know whether has anyone encountered burst O-ring while diving? Logically that should not happen, because if the O-ring doesn't burst while the pressure is at the highest point, while diving, the tank pressure reduces and the water pressure is higher than on the boat, that should not happen, but in real world, has it happened before? Likewise for burst disc?

I was told (can't remember who) that regulator design is in such way that, should it fail, it only free flow, but will not have no air supply situation, is this true?
Title: Re: What are the causes of Out Of Air (OOA)
Post by: Chris on 11 Nov 14, 10:35
I was told (can't remember who) that regulator design is in such way that, should it fail, it only free flow, but will not have no air supply situation, is this true?

I believe what you are getting at is the second stage design: All but one manufacturer use "downstream" valves which if they break should be in "open position". An upstream valve does the opposite and might be jammed close instead. But as you said - the only logical time the valve breaks is when you open your tank on the dive deck. The only brand I know using upstream valves is Poseidon and I am sure there is some reason for their design... never cared as they are out of my budget anyway.
Title: Re: What are the causes of Out Of Air (OOA)
Post by: antacid on 11 Nov 14, 12:50
had a dive where one of the divers had a burst O-ring underwater. Happened on the descend so maybe around 5 minutes into the dive? Funny thing was, the diver didn't even know what happened and was wondering why everyone was crowding around her and pushing octopuses in her face. haha
Title: Re: What are the causes of Out Of Air (OOA)
Post by: aloe on 17 Nov 14, 09:06
yah, i did.. It burst onboard... replaced... then when descending, it burst again underwater. I felt and heard the bubbles.... reached behind to feel and could feel the bubbles as well. Signalled to my buddy that I'm ascending but I think she din realise. LOL! In the end, the DM came up to look for me when I was already onboard the boat. Told him i will abort dive.

It's a sign (to me) when the O ring burst twice onboard and while descending. So decided not to risk it.. =X
Title: Re: What are the causes of Out Of Air (OOA)
Post by: Solid_jim on 17 Nov 14, 22:43
divers who are dreaming lol or got nut
Title: Re: What are the causes of Out Of Air (OOA)
Post by: BareBear on 18 Nov 14, 13:41
I think it happens due to:
1. A lack of situational awareness. This is probably the most common cause (i.e. not checking the SPG, not knowing how much air you have left at all times).
2. Buddies not working well as a team / buddies with poor situational awareness. If an LP hose happens to blow underwater, the gas in the tank could drain very quickly. If a buddy is not within sight and paying attention, it could end badly.

2. Inadequate dive protocols/training.
- The SPG is inaccurate at extreme ranges, especially below 40bar. It would be better to call the dive at 40bar regardless of depth.
- The concept of minimum gas is not widely understood. This is the amount of gas that will get you and your buddy to safety doing all necessary stops along the way, should one diver have an emergency situation. "Surfacing at 50bar" is inadequate if you are diving to 30m.
- Doing bubble checks before descending is not commonly practiced among divers here. Thus if you do have equipment that is in early stages of malfunction, it goes undetected until things get more serious. This is an important drill as I have personally detected bubbling from the SPG, first stage body, hose connections, tank valves and rear dump valves that were quickly fixed because they were detected early. At minimum, you are aware you have a minor problem and you have the option to continue but be watchful if the leak is minor, or call the dive if it is more serious.
- Doing a flow check and being able to reach your valves should be mandatory whether diving in single or double tanks. In this way, if you are in doubt, you can always reach back and check your valves.

Title: Re: What are the causes of Out Of Air (OOA)
Post by: poh6702 on 18 Nov 14, 16:38
One habit I always do is immediately after setting up the gear, open the valve to check to ensure pressure is more than 180 bar, then turn off the valve to see whether the pressure gauge drop or not within few seconds, if one has a leaking system, the pressure gauge will drop very fast, if the needle can stay without dropping, at least you are sure the system is not leaking from the start. Of course if the leak will to happen after getting into water, then will need to react according to situation.
Title: Re: What are the causes of Out Of Air (OOA)
Post by: runez on 18 Nov 14, 17:12
One habit I always do is immediately after setting up the gear, open the valve to check to ensure pressure is more than 180 bar, then turn off the valve to see whether the pressure gauge drop or not within few seconds, if one has a leaking system, the pressure gauge will drop very fast, if the needle can stay without dropping, at least you are sure the system is not leaking from the start. Of course if the leak will to happen after getting into water, then will need to react according to situation.
Just remember to turn your valve on again before the dive! Or it'll become a self-inflicted OOA situation.. Haha..

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Title: Re: What are the causes of Out Of Air (OOA)
Post by: DIN on 18 Nov 14, 17:28
Just remember to turn your valve on again before the dive! Or it'll become a self-inflicted OOA situation.. Haha..

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This reminds me of a story in Maldives... an Italian lady who was overweighted, descended with her valve off. She probably couldn't swim up to the surface because of her weight. They found her body at 50m.   :(
Title: Re: What are the causes of Out Of Air (OOA)
Post by: poh6702 on 19 Nov 14, 00:01
This reminds me of a story in Maldives... an Italian lady who was overweighted, descended with her valve off. She probably couldn't swim up to the surface because of her weight. They found her body at 50m.   :(
Yeh! really anything can happen if one don't follow protocol! We also guilty our self because I believe most of us don't practice buddy check before jumping into the water. But luckily is that at least one should try to pump up the BCD and put the second stage into mouth and breath from regulator before plunging into the water, isn't it? And such problem should be detected. I did have a few times forgot to turn on the valve when getting ready to get into the water, but realized it when not able to pump the BCD
Title: Re: What are the causes of Out Of Air (OOA)
Post by: antacid on 19 Nov 14, 17:59
on the boat when you turn off your air, it's always a good habit to make sure to purge so that the SPG shows zero. So when you do your pre-dive checks, you will know if your air is turned on or not. 

people usually set up their equipment, leave it for a long time, then come back to gear up and jump in. it can get chaotic and messy if it's a small boat, and if you just glance at your SPG to check your air, you're going to be in for a big shock underwater.

1. purge regulator immediately after turning off your air.
2. when checking your air before jumping in, always breathe/purge the regulator while looking at your SPG.
Title: Re: What are the causes of Out Of Air (OOA)
Post by: Cool79 on 25 Nov 14, 02:31
Normally I will start to ascend when I hit 50 bar. U need to know how is your air consumption too, then u can gauge how much air is required for you to safely end the dive.

Normally when I am ard 20-30 m, 50 bar I will ascend. If I am at 30-40m, I will start to move up when I have half tank of air. U never know sh*t happens.
Title: Re: What are the causes of Out Of Air (OOA)
Post by: alvlim on 25 Nov 14, 15:53
Feel that its not a good practice to accent when hit 50 bar. accent should be at about 80 bar min so that even after safety stop and ended the dive, there will still be 50 bar left.
Title: Re: What are the causes of Out Of Air (OOA)
Post by: runez on 25 Nov 14, 21:37
There are loss of gas situations, and then there are out of air (gas) emergencies. The former need not develop into the latter unless multiple things go wrong at the same time.

I feel that complacency would be the cause of many OOA emergencies, like the complacent diver who:

- did not check his SPG regularly because his previous (insert number here) dives were uneventful, and because he never ran out of air before.

- went deeper than than his training and got narced without knowing it

- no longer did pre-dive checks

- no longer bothered to stay close to his buddy

- went into an overhead environment without training just because he had (insert larger number here) successful open water dives before.



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Title: Re: What are the causes of Out Of Air (OOA)
Post by: snikrs on 25 Nov 14, 22:15
With regards to surfacing with or starting to ascend with 50 bar -

I think it's more than just a good practice to plan ahead and learn "rock bottom gas management" than to simply surface at "50 bar" of gas. In most cases, 50 bar is sufficient to complete a proper ascent with a safety stop, but just simply isn't safe enough, in my opinion.

Let's say a diver has an average Surface Consumption Rate (SCR) of 20L/min, and diving a single 11L tank (80AL), as commonly found in our region. Assuming the diver is at a depth of 30m, and ascending at 9m/min, it would take him about 3 minutes to reach 5m. For the sake of conservativeness (and simplicity in calculation) the ambient pressure is assumed to be a constant 4ATM for the ascent. That journey from 30m to 5m alone will require approximately 20 bar (For the math nut: (20L/min X 4ATM X 3 minutes) / 11L ≈ 22 bar). The safety stop will require approximately another 10 bar (Assuming constant ambient pressure of 2ATM, (20L/min X 2ATM X 3 minutes) / 11L ≈ 11 bar). That's a total of 30 bar from 5m to 30m, without incidence.

In the case of a stressed diver, SCR can easily escalate to 30L/min, and what if he happens to be sharing gas with a buddy? That would mean a total of 60L/min. (≈100 bar required) And... there's still things not taken into consideration, inaccuracy of the reading on the SPG, the time taken to share gas at 30m, and any other things that might go wrong at depth, but I digress.

To put it simply, I feel that there would be less occurrences of critical OOA/G situations should divers be educated properly in planning their dive (and diving their plan), rather than just simply following the "50 bar limit". Of course, there's still the issue of complacency, like, not checking the SPG, etc. ;)
Title: Re: What are the causes of Out Of Air (OOA)
Post by: alvlim on 25 Nov 14, 22:45
With regards to surfacing with or starting to ascend with 50 bar -

I think it's more than just a good practice to plan ahead and learn "rock bottom gas management" than to simply surface at "50 bar" of gas. In most cases, 50 bar is sufficient to complete a proper ascent with a safety stop, but just simply isn't safe enough, in my opinion.

Let's say a diver has an average Surface Consumption Rate (SCR) of 20L/min, and diving a single 11L tank (80AL), as commonly found in our region. Assuming the diver is at a depth of 30m, and ascending at 9m/min, it would take him about 3 minutes to reach 5m. For the sake of conservativeness (and simplicity in calculation) the ambient pressure is assumed to be a constant 4ATM for the ascent. That journey from 30m to 5m alone will require approximately 20 bar (For the math nut: (20L/min X 4ATM X 3 minutes) / 11L ≈ 22 bar). The safety stop will require approximately another 10 bar (Assuming constant ambient pressure of 2ATM, (20L/min X 2ATM X 3 minutes) / 11L ≈ 11 bar). That's a total of 30 bar from 5m to 30m, without incidence.

In the case of a stressed diver, SCR can easily escalate to 30L/min, and what if he happens to be sharing gas with a buddy? That would mean a total of 60L/min. (≈100 bar required) And... there's still things not taken into consideration, inaccuracy of the reading on the SPG, the time taken to share gas at 30m, and any other things that might go wrong at depth, but I digress.

To put it simply, I feel that there would be less occurrences of critical OOA/G situations should divers be educated properly in planning their dive (and diving their plan), rather than just simply following the "50 bar limit". Of course, there's still the issue of complacency, like, not checking the SPG, etc. ;)

ya totally agree. but if like me not really know how to calculate gas. i would practice going up the boat with min 50 bar in tank after the dive. if have more would be better of cause.

But of cause learning to calculate the gas usage will be a very good thing to do.
Title: Re: What are the causes of Out Of Air (OOA)
Post by: runez on 26 Nov 14, 00:14
When I first learnt how to dive, I understood that some reserve would be good for emergencies etc. At that time, 50 bar (or 1/4 tank) seemed like a reasonable number and I didn't question further.

When I learned about gas planning - surface consumption rate (SCR) / respiratory minute volume (RMV), rock bottom gas (aka minimum gas) etc, I wondered to myself why the industry adopted "50 bar" as the de-facto gas reserve.

Gathering some inspiration from snickrs's dive planning, but a tad (or a lot..) more liberally, if we assume 2 divers @ RMV=30L/min each, ascending at 9m/min and performing the 3min @ 5m safety stop; the rock bottom gas is approximately:

    10m: 30 bar
    20m: 50 bar
    30m: 70 bar

There's already some buffer catered within these calculations, e.g. the divers' RMV would probably be less than 30L/min, PADI's recommended ascent rate is 18m/min and divers in an emergency may skip the safety stop.

I believe most "deep diver" courses which certify divers to 30m (e.g. AOW, Deep Diver etc) do cover a little bit on gas planning. Probably not enough, as I certainly don't remember much about gas planning from my own AOW course. But interestingly enough, if we consider the rock bottom gas estimations as above but without the safety stop, the rock bottom gas is:

    30m w/o safety stop: 40 bar

IMO, for the recreational scuba diver, 50 bar is a nice compromise between "easy to remember" and "not an excessive amount of reserve". It's also a whole lot easier for the divemaster to brief "Surface at 50 bar on every dive!". Keeping it simple does have its advantages!

Personally, I adopt a more conservative set of rock bottom gas reserves based on a different ascent strategy, but is that to say that the whole industry is wrong with the standard "50 bar reserve gas"?

Anecdotal evidence could prove 50 bar to be sufficient with this question: If 50 bar isn't enough, why aren't we seeing more cases of injured divers who ran out of gas? It does appear that the 50 bar "rule" is keeping most divers safe :)


Edit: Changes made regarding the details about AOW / Deep Diver Specialty for accuracy, thanks to blurblur for pointing it out!
Title: Re: What are the causes of Out Of Air (OOA)
Post by: poh6702 on 27 Nov 14, 17:32
I would like to put this analogy, most of us have served Army, when the CO say, he wants to inspect the bunk on Friday, OC will pass the instruction to be ready by Thursday, PC will want all to be ready by Wednesday and so for...

When the industry set 50Bar, 18m/Min, 3min safety stop, I am sure there are already safety margin built in. And if we are still putting extra margin ourself, we all end up with very short dive or everyone must carry 2 tanks.

We should follow the industrial recommendation, should not break it, then we are already in the safe zone. Whoever are more Kiasi can add more margin themselves, it is up to individual.
Title: Re: What are the causes of Out Of Air (OOA)
Post by: blurblur on 27 Nov 14, 23:19
I believe most "deep diver" courses which certify divers to 30m (e.g. AOW, Deep Diver etc) do cover a little bit on gas planning. Probably not enough, as I certainly don't remember much about gas planning from my own AOW course. But interestingly enough, if we consider the rock bottom gas estimations as above but without the safety stop, the rock bottom gas is:

    30m w/o safety stop: 40 bar

Sorry just wanna point out that the "deep dive" portion covered in the PADI AOWD course should be seen as an experience dive.

After passing your AOWD (deep dive portion is mandatory to pass AOWD), PADI recommends a 30m max depth (not 40m) and contingent maximum of 40m.

On the other hand, the PADI Deep Diver Specialty course will allow the diver to dive to a maximum 40m. Among the syllabus for the deep diver specialty is to carry a redundant air source (eg: pony bottle - not spare air).

Cheers.
Title: Re: What are the causes of Out Of Air (OOA)
Post by: runez on 28 Nov 14, 00:05
Sorry just wanna point out that the "deep dive" portion covered in the PADI AOWD course should be seen as an experience dive.

After passing your AOWD (deep dive portion is mandatory to pass AOWD), PADI recommends a 30m max depth (not 40m) and contingent maximum of 40m.

On the other hand, the PADI Deep Diver Specialty course will allow the diver to dive to a maximum 40m. Among the syllabus for the deep diver specialty is to carry a redundant air source (eg: pony bottle - not spare air).

Cheers.

Thanks for pointing it out! I've edited my original post, hopefully it's more accurate now! I didn't mention 40m though..

I did a quick search, and it seems that the standards for PADI's Deep Diver Specialty course do not require a redundant air source? (but maybe instructors can choose to include it if they want?) I'm basing my information off here (http://scubatechphilippines.com/scuba_blog/padi-deep-diver-tecrec-tec40-compared/) and here (http://www.thediveforum.com/showthread.php?8553-Padi-Deep-dive-specialty).
Title: Re: What are the causes of Out Of Air (OOA)
Post by: lovelyinn on 18 Feb 15, 01:01
Thanks for pointing it out! I've edited my original post, hopefully it's more accurate now! I didn't mention 40m though..

I did a quick search, and it seems that the standards for PADI's Deep Diver Specialty course do not require a redundant air source? (but maybe instructors can choose to include it if they want?) I'm basing my information off here (http://scubatechphilippines.com/scuba_blog/padi-deep-diver-tecrec-tec40-compared/) and here (http://www.thediveforum.com/showthread.php?8553-Padi-Deep-dive-specialty).

when I did my deep dive, we did not have any pony tank.
The only tank we had was the safety stop tank which was hanging by the boat at 5m.

normally when I am diving 30-40m, when I hit 100 bar or NDL, I would start to move to 20m range.

also most of the time, I will be diving ard 20m range. I used to like to dive deep, but not now already... unless there is a wreck, then it is a diff case.

normally I would listen to the dive brief and get to know the dive site and etc, then would discuss with my buddy for the dive plan.
Title: Re: What are the causes of Out Of Air (OOA)
Post by: moonyeap on 02 Apr 15, 17:27
Thanks for all the information in this thread !
Title: Re: What are the causes of Out Of Air (OOA)
Post by: globalcookie on 21 Sep 16, 15:59
Old but interesting thread.  I thought of reviving this thread to share my own experiences.  We learn through mistakes of others or ourselves.

I agree with Alvin Ho when he mentioned, "I would say most OOA situations are due to diver error. equipment failure is seldom the issue when you read dive accident reports. ".

There was 1 incident of equipment failure that I came across.  The hose burst during the dive, and air escape rapidly.

Coming to my personal experiences, I had 2 OOA situations in the last 2 years.  Sounds stupid but here's the experiences.

1.  Cebu Moalboal (Feb 2015)
It was my own mistake.  One word, STUPID!

In short, I was down to about 50 bars, when we came to this small cave.  There were 2 teams ahead of us, and instead of signalling to the guide that i'm down to 50 bars, I was stupid.  In short, after that cave, I was down to about 20 bars.  I should have immediately told the guide, again, stupidity.  We were going shallow, so I presumed we are going for safety stop.

At safety stop, I was OOA.  First thought, worse case scenario, shoot up.  My buddy happened to face me when I was OOA and I signalled.  Due to the initial panic, I took the spare, stuffed it into my mouth and breath!  All the precaution learnt were forgotten, I drank 2 mouths of water.  Threw that spare, took back my own (very very limited air at most) and drank another mouth of water.  Yes, I panicked, I freaked out, I was scared!  Luckily, the guide was facing me then, and quickly took his spare and purge water lodge in it, and passed to me.  I was on deco too!

That was the stupidest dive!  But that was the dive that I learn diving all over again!  This could be the scariest moments in my life.  I was almost dumbfound after that dive for the next 2 hours (but I did a last dive for that trip after that).

2.  Bali, Padangbai (Sep 2016)
This one was fully aware!  The dive was at Padangbai, Jetty.  It was shallow dive, about 14 meters at most.  The whole dive lasted (including safety stop) 84 mins.

From the first bad experience, all dives thereafter, were filled with precautionary.  I do constant gauge checks (every 5-10 minutes), dive computer checks, etc.  As I approached 50 bars, I was consciously checking gauge every other minute.  During safety stop, OOA happened again. 

Well, experience... so I was a lot more calm, took the spare regulator of my buddy and complete the safety stop.  Throughout the safety stop sharing of a single take, my eyes were glued on the gauge and my dive computer.

------------------------

In theory, OOA feeling is, we need some effort to breath (air doesn't flow out readily).  But in actual, if one haven't experience it, how does it feel like?  Try obstruct your lips/mouth with your fingers and breath.  You should feel certain resistance.

------------------------

Early this year, while doing Deep Diver course, my instructor had highlighted the importance of Deep Stop.  I wonder if many divers are aware of this (experienced divers, or those who really read/learn would know)?  So far, I have not encounter any dive where were were consciously doing deep stop.  Perhaps the guides had conducted deep stop but not told divers.  It is us, divers, who should be conscious than expect the guide to do it.

Any dives beyond 20 meters, should come with a deep stop (half way mark) for 1 minute.  This is a habit I practice since my Deep Diver course.  When I did 40m, my instructor then, told me, we will do 2 deep stop, before doing the usual safety stop.  So yes, anyone who isn't aware, do practice deep stop in your future dives.