Can someone analyze this incident please?

[vladimir]

Well, the Suunto may be conservative, but that's only in terms of NDLs. It won't ask you for deep stops.

My Suunto D9 gives the option of a "Deep Stop algorithm."

 

[Hatul]

Yes the newer Suuntos do have deep stops. But in any case it sounds like there was a lack of communication with the buddy. If you were running low on air she should have skipped the deep stop, but that requires that you communicated to her the low on air situation and she responded properly. Deep stops are optional so she should have come up with you.

Adam

 

[RedCash02]

I am moving towards the anchor line at 1000 psi as started the dive at 3000 psi. In my understanding, rule of thirds means when you reach 1000 psi you end the dive and go up! It does not mean that at reaching 1000 psi its now time to do deep stop at the same depth with the same air.

What you explain is no where near the real rule of thirds; people have already explained it properly in previous posts. Many people, including myself, do not use the rule of thirds on recreational dives with direct access to the surface. That being said, you should have never waited until just 1000psi to start "moving towards the anchor line" at 100ft. The margin for error is just too small.

Imagine if your buddy had a total failure of her regulator and came panicking to you. It's not uncommon for a person in that state to grab the reg right out of your mouth rather than your octo. You didn't notice her coming and you're choking on some water you inhaled. You first have to stabilize the situation and begin an immediate ascent sharing air. Both of you would have elevated heart rates and probably be sucking air like Hoovers. You're now doing a free ascent in what unfortunately has become a ripping current with your buddy attached to you. Your unknown buddy, or you, may not be good at buoyancy control without an ascent line or any point of reference. You're drifting a long way, so you probably need to think about shooting a bag soon. Is 1000 psi enough for all of this? Maybe, but is that extra couple of minutes of bottom time really worth it?

 

[DandyDon]

I turned and headed back towards the rope while I had 1/3rd gas in my tank. This means I am moving towards the anchor line at 1000 psi as started the dive at 3000 psi.

I was trying to help but it may not be possible. Others have tried to explain this as well...

See Rule of thirds (diving) - Wikipedia, the free encyclopedia

You were surely never trained to head back with 1/3....??

 

[Centrals]

I waited for her at 15 ft and she met up with me after my own safety stop was over and while I was only hanging there waiting for her. I could have exited the water but since I was only 15 ft I thought Id hang some more. At 15 ft, It takes a long time to exhaust a tank and even if it is exhausted you can break the surface with ease. It was not a near death experience by any means but I wantd to know what do other people do? Do you guys jut follow your computers and surface abandoning your buddies or do you stick with your buddy abandoning your computers?

I will do the same as you and surface with her together.
Never leave anyone alone even at 5m.
I hopes you two talked over it afterwards.

 

[Deefstes]

I'd like to make some general comments based on three themes that seem to be pretty dominant in this thread:

1. People seem to be very hung up on safety stops - to the point where the stops are not even safe anymore. The original post doesn't describe the scenario well enough so that one could really be sure what the best course of action would have been (ie. repetitive dives? Did the buddy know of the OP's gas situation? etc.) Based on the info that was shared though (assuming no repetitive dives and that the buddy knew of the OP's gas situation) I would have thought it made no sense for the buddy to stick so religiously to the "safety" stops advocated by her computer.

2. Deep Stops: To the best of my knowledge there is absolutely no data available to suggest that adding deep stops to a recreational dive adds any level of additional safety. I'm not talking about deco diving because there it's a totally different thing. Bearing that in mind, I don't think it makes any sense to do deep stops while one member of the buddy party is running low on gas.

3. Computers: How on earth did we survive when we were diving without computers? This thread seems to have a lot of "my computer said this", "her computer said that", "you should have listened to this or that computer" etc. I really think we should rely more on training and common sense than on computers. If this was just a recreational dive within NDL limits, I would be willing to skip any of those stops advocated by any of those computers if it meant that I could stay with my buddy and finish the dive with sufficient gas reserves. Those issues are way more important to me than what the computer says.

 

[Dive-aholic]

This is where the rule of thirds came into this thread, perhaps because he accidentally said Deco-stop when he meant Safety-stop...

True, but in the post I quoted the OP states he was using the rule of thirds.

There was no explanation for the term which may be new to him? Which agencies teach rule of thirds for recreational diving?

No agencies, but there are instructors that do.

Now we did clarify that he was not Deco diving as erroneously stated early here, so I think we can get off his back at any time now.

Just because he wasn't doing a decompression dive doesn't mean you shouldn't use proper gas management in your dive planning. Actually, it sounds like they didn't even have a plan other than descend, turn when they felt like it, and ascend. That is why there was an issue. If they had discussed the dive before getting in the water, this issue would not have occurred.

I turned and headed back towards the rope while I had 1/3rd gas in my tank. This means I am moving towards the anchor line at 1000 psi as started the dive at 3000 psi. In my understanding, rule of thirds means when you reach 1000 psi you end the dive and go up! It does not mean that at reaching 1000 psi its now time to do deep stop at the same depth with the same air. But I realize that my buddy is doing a deep stop pretty much at the same depth at which we were diving. This causes hesitancy on my part to ascend. I waited for sometime, not knowing how long her stop would take. Hell I didnt even know it was a stop. I had no idea why she was not coming up. I do not recall how long I waited but that wait was causing me to go below 1000 psi on my tank. I chose to let her do her thing (whatever it was) and started to ascend. But I am confused if this is an ethical thing to do because it is my training to stick close to the buddy at all time. So I rise until my computer tells me to do my stops. This obviously is happening at depth different from her stop depth so this would be calld buddy separation. Once I finished my safety stop at approx 15 feet, I had the option of surfacing with 500 psi gas in my tank or staying on the rope as courtesy to my buddy who is inching up the rope. I chose to hang on the rope just so that the other person doesnt feel ditched. While doing this I am pushing below 500 psi but I dont care because I have fulfilled all my safety stop obligations and surface is only 15 feet away. After a very long wait I am joined at 15 feet by my buddy and we surface fairly close to each other. I am below 500 psi when I get out.

Your understanding of the rule of thirds is incorrect. It's already been explained. But even if you don't use the rule of thirds for gas management, you need to use something to plan your gas usage. Turning to head back to the anchor with 1000 psi in your cylinder at a 100' depth is not appropriate.

Here's an example. Let's say your respiratory minute volume (RMV) is .8. That means you breathe .8 cubic feet per minute at the surface. This means you will breathe 3.2 cf/min at 100'. An AL80 holds 77.4 cf when it is filled to 3000 psi. At 1000 psi, you have 25.8 cf of gas in your cylinder. You will be breathing about 125 psi per minute. That gives you 8 minutes at 100' to deal with any issues if your RMV remains the same.

Now let's add another incident. Your buddy's 2nd stage free flows and she runs out of air. (I had a student diving a HP 120 with 2000 psi in it with a 2nd stage free flow at 70'. He was down to 500 psi by the time he shut down the valve. He shut the valve in less than a minute.) So during that minute you are now down to 875 psi and air sharing with your buddy. (If the 2 of you are fast enough to get the valve shut down and begin sharing air within a minute.) If her RMV is the same you now only have 3.5 minutes at 100'. At this point you can't even swim to the anchor. You have to make a direct ascent. At 60 fpm (which is ascending faster than I would recommend) you will get to 15 feet in 1.5 minutes. With an average depth of 60 feet during the ascent, that means the both of you will breathe 4.5 cf of gas. That's another 175 psi, bringing you down to 700 psi. 3 minutes at 15' uses another 275 psi, bringing you down to 425 psi. So, you're safe, right?

Wrong. Likely what will happen is both of your RMVs will go up because of the incident. You will now be breathing at a rate of 1.2 cf/min (that's being generous, by the way). So during that minute, you breathe 4.0 cf, dropping your pressure to 845 psi. Your ascent to 15' uses 260 psi, dropping your pressure to 585 psi. 3 minutes at 15' uses 405 psi, leaving you with 180 psi to make your final ascent to the surface.

Again, looks okay, but, like I said, I'm being generous with the 1.2 cf/min RMV. It's likely to be higher. It's likely to take more than a minute to shut down the valve and begin sharing air. And also, your SPG is not calibrated in any way. I have hooked up 5 different gauges to the same cylinder and seen 5 different pressures ranging from 100 to 500 psi difference. So you can't be sure that you really had 1000 psi in your cylinder. It could have been 800 psi, or even less.

Basically, what I'm trying to say is plan your dives. Use appropriate gas management. Read the article by Bob Bailey/NWGratefulDiver that TSandM linked. If you keep diving the way you did on that dive, you will become a statistic.

 

[TSandM]

Although I was not taught to use the rule of thirds in this way, it can be used for the kind of dive you did. If you had said, "I will use one third of the gas I have going out, one third coming back, and reserve the final third for emergencies," it would have worked out okay. You would have turned back at 2000 psi, and had 1000 psi more gas for the ascent. You would have been okay.

As I said in my initial response, this dive is an example of bad gas planning and poor pre-dive communication. Fussing about what either of you should have done at the end of the dive is silly. The answer lies in communication before you got in the water. (Although some communication on that upline might have helped . . . )

 

[fish149]

I've got the Mares puck computer and if I dive deep enough it will call for deep stops even though I'm within no-decompression limits. This might be what was going on with her.

 

[MRadke]

My buddy and I both dive suunto. I got stuck with a longer stop when I violated my NDL time while his computer showed no violation. My average depth was slightly deeper than his, which caused the issue. I still surfaced with 500 psi on an AL80, so life was good and a lesson was learned. My buddy stuck it out with me on the safety stop.