runaway ascents, what to do?

[TSandM]

A dive pro, dealing with trainee divers, shouldn't be in a position where they couldn't anticipate and prevent this problem before it became uncontrollable.

A laudable ambition. In reality, given that one HAS to take one's eyes off the student occasionally in order to navigate, things can get dicey. I have been astonished at how fast serious buoyancy issues occur with students.

 

[aquaregia]

Buddy line? Tie it to their dumps and fly them like a kite!

I use touch contact a lot, even if visibility doesn't require it. We hold hands and if I need my hand I use it to place my buddy's hand on my shoulder; I go back for it once I'm done with what I'm doing. For a less homoerotic dive experience, we also sometimes just push our arms against each others'.

When assisting with classes, I usually watch students pretty closely after the start of the ascent. We almost always have gradual ascents, which makes this a bit easier. Once I see that they're having trouble venting, usually because they're trying to dump from the inflator while swimming down, I just grab their butt-dump and let a little out. I've had pantomime work with newer divers, but for trainees I just grab it myself. There's enough going on already.

 

[Jim Malone]

Thanks for the replies.
It was usefull to see so much valid points.
The whole buddyline is something we inherited from the CMAS era in Europe.
Visibility is sometimes a big issue.
We are used to "muck diving here"
The visibility was so bad the last dive i couldn't even read my instruments during the first 6 meters!
We used a buddyline because this was a drift dive with a max visibilty of 1 meter at 8 meters ( we don't do these dives with students)
I was glad i had the buddyline on because almost every dive would end in a lost buddy.
I wil reposition myself again when diving with first timers to above and on their left.
My former instructor told me not to deflate the BCD of new divers because it would ruin their learning curve, even in a possible blow-up.
The reason i intervened too late was because at the moment of the mishap i was trying to bridge the 4 meter between my instructor and his student and us.
Visisbility was so bad i could only see their fins, but my student was lagging behind.
Trying to catch up i was maybe a meter from my student but this was enough for him to float upwards.
I was wearing a drysuit myself so i could only dump my BCD, trying to keep him down.

 

[aquaregia]

Why do you prefer a buddyline to touch contact?

 

[BrianKon]

Are your buddy's using back-inflate?

New divers and back-inflate just don't mix. The inherent air traps that exist in back wing designs are beyond new divers to manage. There is a protocol for venting air, most new divers regularly fail to put themselves in the proper position to vent air in a Jacket-style BDC let alone a back-inflate, but hey just gotta have it (peer pressure). I have had two incidences recently, one at 90 feet and one at 35 feet. There were no runaway ascents, but there could have been.

As a previous poster mentioned, a trained DM will keep a keen eye on those new divers. As a new DM, make sure you can identify an air trap in a back inflate design and respond accordingly. Get the diver in an upright postion try to vent, you may have to squeeze the BCD to release trapped air. Get familiar with most all back-inflate systems, some are more prone to trap air than others.

I remember my first incident as a new DM, when i could not identify an air trap, luckily for me I was with another very experienced DM and he came over to assist.

My most recent diver had 10 dives and was AOW, just got new gear and dove with it a couple times, before the 2 tank boat dive I guided. I am unclear whether he had it for his AOW, but i would suspect not, due to buoyancy issues, I should have asked if he did the Peak Performance Buoyancy - but I am pretty sure he didn't.

No never mind, one advantage to also being an instructor is to be able to give advise that a DM could become liable for. I took the extra time on the remaining dive, and the subsequent dive to offer additional training and skills practice that allowed him to experiment with different scenarios, during the surface interval and after the second dive continued with some additional tips and things to look out for. I have no doubt his next dive will be an excellent experience.

hope this helps

 

[snowblind80]

Speaking as someone who has recently completed the PADI open water course, I think the main thing new divers would benefit from would be practising using the rear dump valve in their BCD. I had a few moments where I began an unintentional descent. I managed to get control of it using the valve on the inflator, but I had to change my body position first so I has more vertical. This delayed my adjustments to my bouyancy and would also have decreased the drag slowing the ascent. I've found that sticking my ass up in the air and tugging on the rear dump valve works much faster. We were told about the other dump valves in the BCD as part of the course, but were never told to try them out.

I've also reduced how much weight I take since my first dives, which helps my bouyancy a lot.

 

[rongoodman]

The nice thing about using the rear dump valve is that when you're in the right position to make it work, horizontal, you're also able to use your fins to kick yourself down at the same time.

 

[herbdb]

This problem was predictable. A diver with little experience, none in cold water, is a recipe for runaway ascents and descents until they learn to anticipate the changes. I have been there myself when I began diving in our local quarry. My previous experience was all warm water with a short 3/2 suit, probably very similar to your buddy.

A thourough briefing on this problem, including how to recognize it and the importance of anticipation is a good start. Follow up with a dive or two in shallow water with multiple depth changes to practice staying ahead of the problem. I am not a dive professional, but having been there myself, I make it a point to share my experiences when I dive with someone in similar circumstance.

Popping to the top is not only potentially dangerous, it is embarrassing.

 

[Ayisha]

Step #1 - Help your divers get their weighting sorted out. Over-weighting is one of the primary issues leading to ascent control. Any excess weight translates directly to more air in the BCD. More air in the BCD leads to a proportionally greater expansion of air during the ascent - especially in those final 10m. 2lbs of excess lead equates roughly to a lite of air in the BCD. Every extra lb of surplus lead makes buoyancy control proportionally more difficult. Tackle the root of the problem (weighting) and you might not have such difficulty having to deal with the symptoms (uncontrolled ascents).

For a diver to drag both themselves and you to the surface would require a huge amount of surplus buoyancy. That is only likely to happen in 2 circumstances; either they have an LPI stick or they are overweighted massively...leading to a huge volume of air in their BCDs at depth, which then expands enormously as they ascend. A properly weighted diver should have a virtually empty BCD at depth... with only enough air to compensate for exposure suit compression. That amount of air should never be enough to drag one or more divers to the surface!

That should be made a sticky. Considering how prevalant being overweighted is, even grossly overweighted, the concepts of correct weighting and neutral buoyancy seem to be very misunderstood.