Diver vs DM Responsibilities

[Blasto]

I find it extremely hard to believe that someone diving an AL 80 could accumulate 20 minutes of deco and still have the gas to do it.

It's certainly difficult. But, in the OP, the exact wording was "ended up in deco and spent 20 minutes at safety stop”, which likely indicates less than 20 minutes of deco.

Many rec computers (Suunto) will have you do the deco, then still do a safety stop. That's still 15+ min of deco, but the computer could be already set to "punish" her for violations on the last dive, which some rec-only computers do.
Alternately, she could have accumulated 5-10 minutes of deco, then voluntarily extended the safety stop to 8 or 15 per RDP rules, even though they don't apply.

3. Provided the proper redundancy, planning and support is there, staged decompression diving is perfectly normal. In some training disciplines it is introduced very early in the dive's experience and is unremarkable in some regions.

Agreed completely, I'm familiar with some that don't have the concept of NDL at all, just deco tables; every dive treated as a deco one, however little of it there is.

The only thing that makes OP-like situations dangerous is that vacation-style rec diving has chosen a different approach, to take only the absolute minimum of equipment, barely tolerant of a single failure between two sets, and use the surface as a safety net for everything.
Air issues - ascend; buoyancy issues - drop weights thus ascend; buddy separation - ascend; forgot to plan the dive - run the SPG down to X bar/psi and ascend.

That's the issue with deco in vacation gear, not the difficulty of performing controlled decompression. Since rec gear and training relies on immediate ascent as the only response to most emergencies, deco obligations leave them without a response at all. This makes deco diving 2-3 orders of magnitude safer in a tec rig than in a rec one (multiple vs single failure away from possible death), so people racking up a genuine deco obligation in rec gear put themselves at risk comparable to an entire career of tec diving, not a single tec dive.

The only things that keep them from clogging up A&I are computer conservatism and the small capacity of common rental tanks.

 

[gcarter]

...vacation-style rec diving has chosen a different approach, to take only the absolute minimum of equipment, barely tolerant of a single failure between two sets, and use the surface as a safety net for everything.

...

Since rec gear and training relies on immediate ascent as the only response to most emergencies

The above completely ignores and dismisses the buddy system as being relevant or useful. I know you are trying to make a point, but a whole lot of divers do actually take the buddy system seriously. I have been on dives where divers had equipment issues or failures that were resolved at depth without resorting to the "surface safety net" because the buddy system actually works.

The only things that keep them from clogging up A&I are computer conservatism and the small capacity of common rental tanks.

This is just condescending and not at all helpful.

 

[Blasto]

The above completely ignores and dismisses the buddy system as being relevant or useful.

It's not just relevant and useful, but also indispensable to the way the standard rental rec set works. Since CESA is just too desperate to be the first and only response to OOA.

I have been on dives where divers had equipment issues or failures that were resolved at depth without resorting to the "surface safety net" because the buddy system actually works.

What specific failures were that?

With mobility restricted by a 40" hose and no redundancy left, any air system failure in a buddy pair (unresolved freeflow, freeze, OOA) still calls for immediate ascent per SOP, although you could complete a short deco stop on the alternate. Dealing with a BC failure with a deco obligation, even in a pair, OTOH, definitely isn't part of the rec training curriculum.

I can only think of one gear failure in rec diving that allows for continuing the dive - loss of weights, made up by the buddy's weights, but that relies on being overweighted to begin with. Perhaps losing one SMB in a pair is another, but one isn't considered mandatory in the first place.

This is just condescending and not at all helpful.

I'm not trying to criticize rec diving, not at all, it's proven its safety; only specifically the practice of going into "a little" deco in typical rec gear, thinking it's only a little risk.

 

[Edward3c]

It's not just relevant and useful, but also indispensable to the way the standard rental rec set works. Since CESA is just too desperate to be the first and only response to OOA.

What specific failures were that?
With mobility restricted by a 40" hose and no redundancy left, any air system failure in a buddy pair (unresolved freeflow, freeze, OOA) still calls for immediate ascent per SOP, although you could complete a short deco stop on the alternate. Dealing with a BC failure with a deco obligation, even in a pair, OTOH, definitely isn't part of the rec training curriculum.

I can only think of one gear failure in rec diving that allows for continuing the dive - loss of weights, made up by the buddy's weights, but that relies on being overweighted to begin with. Perhaps losing one SMB in a pair is another, but one isn't considered mandatory in the first place.

I'm not trying to criticize rec diving, not at all, it's proven its safety; only specifically the practice of going into "a little" deco in typical rec gear, thinking it's only a little risk.

I’ve never understood why people consider doing a deco or safety stop when making an assisted or rescue assent. DCI or whatever can be treated at the surface, drowning can’t.

Every dive is a decompression dive, just most don’t incur mandatory stops. The important point is ‘plan the dive the dive the plan’, and that included the gas requirements. Getting into mandatory stops without planning the gas is foolhardy.

 

[gcarter]

It's not just relevant and useful, but also indispensable to the way the standard rental rec set works. Since CESA is just too desperate to be the first and only response to OOA.

At odds with your statement that the surface was the safety net for everything, but OK.

What specific failures were that?

With mobility restricted by a 40" hose and no redundancy left, any air system failure in a buddy pair (unresolved freeflow, freeze, OOA) still calls for immediate ascent per SOP, although you could complete a short deco stop on the alternate. Dealing with a BC failure with a deco obligation, even in a pair, OTOH, definitely isn't part of the rec training curriculum.

I can only think of one gear failure in rec diving that allows for continuing the dive - loss of weights, made up by the buddy's weights, but that relies on being overweighted to begin with. Perhaps losing one SMB in a pair is another, but one isn't considered mandatory in the first place.

I would need to go back to my log to be exhaustive and I am too lazy for that on a Saturday afternoon but a couple that come to mind are a leaking BCD resolved by tightening the retaining nut on the inflator hose; freeflows on several occasions that were resolved underwater ( a freeflow caused by a freeze, BTW, is unlikely to be experienced by the vacation divers you are discussing), tanks floating free of tank straps not properly cinched, fins lost and recovered, stuck inflator disconnected. None of it required resorting to the surface to resolve, and it was all resolved without having to end the dive. None of it would have jeopardized dealing with a minor (<5 minutes) deco obligation.

I'm not trying to criticize rec diving, not at all, it's proven its safety; only specifically the practice of going into "a little" deco in typical rec gear, thinking it's only a little risk.

Sometimes it IS only a little risk. Context is important, as is judgement. Uninformed acceptance of the risk without understanding is foolhardy. Informed acceptance of the risk may be quite acceptable. It is not as black and white as you make it out to be.

 

[kmarks]

Diver starts with 77.4 cubic feet in an AL 80.

A SAC of 0.5 is considered to be excellent. At 95 feet, a diver with a 0.5 SAC will breathe about two cubic feet per minute. After 35 minutes, that diver will have consumed 70 cubic feet, leaving about 7 cubic feet left--less than 300 PSI. (Not all of that will be usable.) Ascending to a safety stop at 30 FPM will take nearly 3 minutes and will consume about 3 cubic feet. Before she gets there, the tank will be so low on air that the regulator will not be able to deliver it to her, at which point she will be OOA.

I don't consider a SAC of 0.5 to be anything close to excellent. I said earlier that I average about 0.45 in warm water (I recently checked this in my Movescount account) and I don't have thousands of dives, or even 100, and only recently started to become one of the last few back on the boat. A couple of women I've been on the boat with could easily be in the low 0.3 range.

 

[Steve_C]

I would need more information before I assign blame. Back around dive 100 or so I was booked for a double dip on the Spiegel. Day before I flooded my Aeris (my fault, bad battery change) on a shallow reef dive, ran to store and bought something I could afford on the spur of the moment. Was a cheap Suunto. I read the manual that night. Next day we go out to Spiegel. Were two divers and the guide and the captain. There was a ripping current on top but zero current on the deck and great viz. First dive was basically to see how we did. Second dive guide takes us on a swim through. We are diving air. I look and see that I am running low on NDL and indicate such to DM. We are going through some rooms. I do not know what is outside the open sides. Follow guide until we exit. There is no way I am doing a free assent into a raging current. I take off for the buoy line. I run out of NDL shortly before I reach the line. Go up until I hit the ceiling and then play flag in a ripping current. at 15 ft. Lock my hands around the line and then totally relax my body so my air consumption is almost nil. DM comes by looks at my computer and air supply and lets me play flag.

Point is sometimes you have a DM with a more agressive computer who tends to dive more aggressively. We were acutlaly booked for 4 dives. had snack in the boat and went to do a drift dive. To my dismay we started at about 50 ft. Soon I was drifting at 30 ft off the bottom to stretch my NDL.

Point is, maybe the person was not good about watching NDL., maybe the DM had a more aggressive computer. Maybe the DM would ignore the diver when they indicated they were running low on NDL.

 

[mcohen1021]

Regarding blame... Blame is ultimately with the diver. It was said above by others, but I'll repeat - you were trained, you know the rules, you know the limits. If you do not remember it is on you to get a refresher.

The DM (acting as a guide, DM and operator) in my opinion should establish boat/dive rules on their trips to avoid this situation... For example, OOA or Deco situations get's you benched for the next dive or 6/24 hrs.

Recreational divers going into deco are putting everyone else on the boats enjoyment at risk and; TBH, I guess I don't understand how people go into deco to begin with since I've managed to never do it since I started diving in 1989.

 

[Steve_C]

Deco is a mathematical line in the sand. If you believe my now gone Suunto, I have been in deco maybe 15 times. If you believe my other computer (absent on the Spiegel dives above) since I dove two computers on all dives after that trip, I have never been in deco. I have seen the two computers differ by as much 15 minutes of NDL on dive 2.

The only boat rules may be to stay with the guide and let them know if you are getting low on air. Which they may or may not worry about and which may or may not have anything to do with NDL even on an AL80.

 

[uncfnp]

Recreational divers going into deco are putting everyone else on the boats enjoyment at risk and; TBH, I guess I don't understand how people go into deco to begin with since I've managed to never do it since I started diving in 1989.

I do it quite frequently...

"Riding your Computer Up" vs. "Lite Deco"