Buddies kept grabbing/pulling me to ascend faster than computer said was safe

[TSandM]

The value of a board like this is that you will get a wide variety of opinions on any topic. Some will be of more value than others, but all of them are food for thought, and may cause the original poster or other readers to consider possibilities which would not have occurred to them without the input of the community here. When ANY story of a dive incident is told, there are two sides, and most of the time, we don't get to hear the other one. But sometimes one can imagine it -- and sometimes those imaginings are undoubtedly completely wrong.

Here, you have a very, very strange behavior on the part of the OP's buddies. I've been diving for ten years, in a lot of different places and around a wide variety of divers, and I have never seen anyone dragging a diver to the surface. I've seen people swim away from their buddies, and people ascend at vastly different rates. I've seen people hold divers DOWN when ascent rates are uncontrolled (I have done that myself). Because the described behavior is so unusual and egregious, I don't blame many posters for assuming there HAD to be a good reason why it occurred. But we don't know why it was done, because we haven't heard from the people who did it. And we do know, from stories told here, that there are some strange divers in the water.

It's likely most everything that can be said about this incident has been said. It is rude to lay hands on another diver, and it causes them significant difficulties managing their own buoyancy. It is difficult for a new diver to know what to do, when they think they are doing what they should, and someone with more experience is telling them otherwise. Running out of gas underwater is very dangerous and the precipitant of many fatalities, and if the draggers in this case thought that was the problem, they should have explained that in the post-dive discussion. Otherwise, slow ascents in the shallows are generally desirable, and no one should argue with someone's desire to follow their computer's ascent rate, assuming there are no safety considerations (bad ocean conditions or boat traffic) to mandate getting out of the shallows.

I hope the OP has not been put off with the criticism, but has simply taken the various posts as information, to look at the situation from a variety of perspectives, and learn from it.

 

[oldschoolto]

I was on a dive where the depth was 90ft and this was only my second time going deep. I was certified PADI in April 2014 and AOW August 2014. I have a Galileo Luna dive computer. For those who don't have one, it has a bar on the right side that lets you know if you are ascending too fast. You are not supposed to go much further than halfway on the bar. I would also like to preface this story with the fact that I used 2474 psi during the dive and started with about 3100-3200 so when I surfaced I had between 626-726 psi so I would have had time to take a slower ascent. In addition, my computer said the dive lasted for 17 minutes.

I was partnered with someone who had been diving for 30 years. When we went down we were separated from the group and descended and were just roaming the bottom when another diver joined us. The dive master had said that we would be headed North along the reef. We were headed south, so I used my buddies slate to say "They were headed North should we go that way" but I couldn't get a response from him and he was just looking around and started swimming again south. I figured we were separated from the group anyway, so we could just dive and head up when we were low on air. A few minutes later, he comes to me with his slate which read something about going North. I was trying to point that we should go north and which direction it was but he kept pointing south and I couldn't get him to turn around. So when I got to 1100 psi I told him we needed to head up.

We started to ascend and at first I was having trouble going up because I had emptied all my air (found out I shouldn't do that later in the day) and was only ascending as fast as my computer told me too. He kept motioning for me to go faster but i listened to my computer. Because he kept motioning I started going up faster until my computer started beeping at me. So I slowed down within my computers range. He then grabbed my hand and started pulling me up. It really freaked my out because my computer beeped and said "ascent too fast". I pulled my hand out of his grasp. He then started gesturing for me to go faster and I kept pointing at my computer. He grabbed my hand 2-3 times more and I kept pulling my arm out of his grasp. By this time I am really freaking out because the other guy is starting to get close and keeps motioning for me to go faster. Finally they back off and I try to do a safety stop. Within about a minute they are motioning for me to come up. I then sense someone behind me and could feel him grabbing my gear because I felt a pull. After that it's hazy because I was so freaked out, but I remember that they did back off. But when they kept grabbing on to me I just went up because I was really panicking. My ears were killing me because I had not had a chance to clear them.

After we got back on the boat my original buddy said something about he thought I was narcing out. They both said I was ascending way too slow and that I didn't need a safety stop because we had only been down there about 15 minutes. The diver who had joined us, who I will mention is learning to tech dive, came up to me later and said that when a group of "advanced" divers agree about something that you should listen i.e. I was ascending too slow and I should have listened to them and come up faster. And that computers sometimes fail and he never uses his. I will add that when the dive shop owner looked at my computer he said that by looking at it I ascended too fast.

I am wanting to get people's opinion on what I should have done. What would you have done in that situation. Is it ever ok for someone to grab you if you are conscious? And at only 30-40 feet? If the computer says I am ascending too fast and I have enough air to make it to the surface is there any reason I should speed up. Am I wrong for being utterly enraged? When I came up I tried to explain to the dive master but was so upset I didn't know how much air I had when I was ascending and just shut up because I was on the verge of bawling. I let it go and just buddied up with someone else for the rest of the trip. It wasn't until I spoke with the owner and he looked at my computer that I knew (after surfacing) I had had enough air to slowly ascend.

I have one other question. I was skeptical about my buddies abilities b/c before we got in the water he didn't even know how we were supposed to descend and I had to tell him what the dive master had said, he didn't know which way was north (with a compass), and kept staying in front of me and never looking back. I had to chase him to tell him I was low on air. Does the length of time a person has been diving have any bearing on their abilities and safety skills? Can someone be diving a long time and just cheated death? I ask b/c I have a tendency to be highly critical and don't know if I'm just being nit picky.

Alicia.....

I personally want to apologize to you if my posts in anyway hurt you... That was not my intent... Most of all I want you to know that poor training is all to often the cause of poor diving ....

I was very serious in saying you need to find a mentor to dive with and take your time... It's not a race to get ratings , I started diving 40+ yrs ago and I'm just fine going to 20 -40 feet playing around on a reef... No reason to go deep till you get all your basic learning squared away..

And have fun... Good luck...

Jim...

 

[Frosty]

Alicia--I genuinely feel its worth having a serious frank and open discussion with the DM concerned on land.
Ask him for an explaination as to what happened.
You may very well be correct and the buddy concerned might be a doofus.
But its possible he was doing his best to look after you.
Theres nothing lost by finding out
and it will lay any concerns to bed once and for all so you can go forwards with your diving

 

[EFX]

As mentioned in previous posts some slower tissue compartments may still on-gas after ascending from depth. Here is the mathematical example you requested.

P = Po + (Pi - Po)(1 - 2^(-t/HT))

P = final tissue compartment pressure
Po = initial tissue compartment pressure
Pi = Inspired air pressure
t = time at depth (or surface)
HT = tissue compartment half-time

From the Buhlmann ZH-L16 chart in Erik C. Baker's "Understanding M Values" the half-times from compartments 2 and 10 are:

2 = 8.0 minutes
10 = 146 minutes

Using the constant depth version of the Schreiner equation (shown above) we can calculate the P values for the following dive profile: descend to 99 ft for 15 minutes, then ascend to 33 ft for 15 minutes. I will work out the solution using minutes for t and atmospheres absolute for pressure. For this example I will neglect loadings on descent and ascent and assume an instantaneous depth change. To keep things simple I will ignore the water vapor pressure and make the inspired pressure equal to ambient pressure. P(n) = pressure for tissue compartment n.

At 99 ft Po = 1 atm (we were at the surface), Pi = the pressure at 99 ft. Solving for P:

P(2) = 1 + (4 - 1)(1 - 2^(-15/8)) = 1 + 5(1 - 0.27) = 1 + 3.65 = 4.65 atm
P(10) = 1 + (4 - 1)(1 - 2^(-15/146)) = 1 + 5(1 - 0.93) = 1 + 0.35 = 1.35 atm

Ascend to 33 ft for 15 minutes. Po becomes P from the previous segment of the dive. Pi = the pressure at 33 ft. Solving for P:

P(2) = 4.65 + (2 - 4.65)(1 - 2^(-15/8)) = 4.65 - 2.65(1 - 0.27) = 4.65 - 1.93 = 2.72 atm
P(10) = 1.35 + (2 - 1.35)(1 - 2^(-15/146)) = 1.35 + 0.65(1 - 0.93) = 1.35 + 0.11 = 1.46 atm

After ascending to 33 ft from 99 ft compartment 2 off-gassed from 4.65 to 2.72 atm. However, compartment 10, a much slower tissue compartment is still on-gassing from 1.35 to 1.46 atm.

I just realized that the above calculations are wrong. The values used for Pi above are for an N2 of 100%. The Pi's above should be the (ambient pressure x 0.79) for air. Running the numbers through a program I created gives:

At 99 ft: P(2) = 2.54, P(10) = 1.15
At 33 ft: P(2) = 1.80, P(10) = 1.17

Sorry, my bad.

 

[chrisch]

You don't need calculations to understand the overall point. Decompression theory uses a mathematical model based on tissue groups. These don't really exist - they are just used to build the model. If the total underwater duration (including the safety stop) is shorter than the slowest tissue then that tissue group is still on-gassing even on the safety stop. Ergo even on a normal ascent (at whatever speed) some on-gassing is taking place. The statement that there is on-gassing during the ascent is - at a pedantic level - true of every dive you make. Only saturation divers escape this fact.

The model works dynamically to create a "controlling group". This is the tissue group that has sufficient saturation to require some off-gassing before surfacing. For a ten minute bottom time the ten minute group will be saturated. An instantaneous return to the surface will cause this group to off-gas at the highest possible rate. This is the most important consideration and the ascent profile should allow this tissue group enough time to off-gas to a "safe" (whatever that is) level.

As you ascend the pressure decreases and although on-gassing is taking place the potential saturation pressure is diminished. In order for a super slow ascent to generate a decompression penalty a slow tissue group must be loaded up enough to cause that penalty.

We can quickly see what these times might be by looking at a published decompression table. Thus avoiding the need to do complex calculations. The PADI RDP shows 25 minutes no stop for 90 feet. The OP had 15 minutes more no stop time. At an ascent rate of 10 feet per minute - pretty slow - the bottom time at 80 feet is 10 plus 10. The RDP shows 30 min no stop for that depth. The "spare" no stop has increased now to 20 minutes.

Slow ascent on-gassing is an issue for deep decompression diving. For recreational level diving the ascent rate is probably optimal at around 30'/min with a slow last 10 feet. I see no reason to drag anyone to the surface if they are ascending at just 20'/min to be totally honest.

 

[boulderjohn]

The model works dynamically to create a "controlling group". This is the tissue group that has sufficient saturation to require some off-gassing before surfacing. For a ten minute bottom time the ten minute group will be saturated. An instantaneous return to the surface will cause this group to off-gas at the highest possible rate. This is the most important consideration and the ascent profile should allow this tissue group enough time to off-gas to a "safe" (whatever that is) level.

It's not like filling a cup. After 10 minutes, the 10 minute compartment is 50% saturated at that depth. It takes 60 minutes to fully saturate the 10 minute compartment.

We can quickly see what these times might be by looking at a published decompression table. Thus avoiding the need to do complex calculations. The PADI RDP shows 25 minutes no stop for 90 feet. The OP had 15 minutes more no stop time. At an ascent rate of 10 feet per minute - pretty slow - the bottom time at 80 feet is 10 plus 10. The RDP shows 30 min no stop for that depth. The "spare" no stop has increased now to 20 minutes.

My reading skills must be unusually poor today. I have no idea what you mean here. I hope I am just not understanding what you are trying to say , because as I understand your argument, that is simply not how the tables work.

 

[Basking Ridge Diver]

The value of a board like this is that you will get a wide variety of opinions on any topic. Some will be of more value than others, but all of them are food for thought, and may cause the original poster or other readers to consider possibilities which would not have occurred to them without the input of the community here.

The danger is when you only listen to one point of view. When I first started here - I remember seeing posts about how dangerous some posters could be. I really had no idea what that meant - but the more I read the more I am beginning to understand. If you don't question someone on their post and you take it as gospel - you can be in serious trouble. Because I have seen some outlandish postings - and I dont believe there was malicious intent - I really believe some posters dive thinking their way is the only way based on faulty logic, faulty training or misunderstanding of concepts.

This board makes me laugh, makes me think and more importantly makes me seek to understand so I can learn from others. That to me is the benefit of this board - but you must verify any information that you pull down from the web or this board and apply it as you see fit...

 

[chrisch]

...., because as I understand your argument, that is simply not how the tables work.

It's not an argument. I am trying to find a simple way to show that as one ascends the on-gassing process diminishes. I guess this really needs a spurious debate with too much maths for people to stop beating the dead horse. As I said before if people want to have a maths discussion on tek to tek fine. IMHO the constant reassertion that the OP is at fault and that somehow or another a slow ascent from a shallow recreational dive is a scary and wrong thing to do is not helping. I appear to have provoked yet another response about decompression algorithms and mathematical theses of modelling real world data. For that I apologise. Slowly Ascend From Every dive is good advice. I doubt the OP is still here to read it.

 

[redacted]

It's not an argument. I am trying to find a simple way to show that as one ascends the on-gassing process diminishes. I guess this really needs a spurious debate with too much maths for people to stop beating the dead horse. As I said before if people want to have a maths discussion on tek to tek fine. IMHO the constant reassertion that the OP is at fault and that somehow or another a slow ascent from a shallow recreational dive is a scary and wrong thing to do is not helping. I appear to have provoked yet another response about decompression algorithms and mathematical theses of modelling real world data. For that I apologise. Slowly Ascend From Every dive is good advice. I doubt the OP is still here to read it.

Sure, only in more extreme cases can an ascent be too slow and result in a decompression obligation after the ascent begins, but it is quite possible if the diver is pushing NDLs. But there are other parameters to consider including your buddy, the impact on subsequent dives, and the fact that you may actually be sharing the ocean (and the mooring line) with other divers who would also like to get back on the boat where they can commence an SI in preparation for the next dive.

I don't believe anyone was trying to "drag" the op to the surface. Had that been the case, the op would not have been able to pull her had away each time. I suspect the buddy was simply trying to encourage her to start the ascent initially when the dive was called and then move along with the ascent to get out of the way of other divers. I doubt if the buddy realized the initial problem the op had with operating her BCD and the very conservative ascent rates mandated by the op's computer.

Of course, if I am wrong about the mooring line, I'm sure the OP will let us know.

 

[kr2y5]

Question to the OP: has anyone, at any point during the ascent, made any effort whatsoever to explain the REASON why you should ascend faster? Whether written on a slate, shown with a gesture, pointing to SPG, or in any other way? Sounds like perhaps that was not the case? And if so, then regardless of whether ascending faster was the right thing to do, the particular strategy chosen to make that happen was ineffective...