sudden uncontrolled ascent!

[Brewski]

As Vkalia mentioned, you may be carrying more weight than you need. your PPB instructor should work with you to correct this. A good test is to enter the water with the tank you finished diving with previously, containing 500 to 800 PSI roughly, then adjust the amount of weight used to achieve neutral bouancy with no air in your BCD.
Also as mentioned before pushing the dump button with the inflator hose held low will not exaust the air from your BCD because the hose is not the highest point in the system.
Did you know you can pull the inflator down to open the exhaust valve on your shoulder?
Practice this, also practice using the pull dump on your right shoulder and the one on your left hip. The key is to comfortably be able to operate your BCD without having to think about it.

 

[vkalia]

I didn't say narcosis caused a loss of buoyancy. I said I thought the OP's judgment about how much air was needed in the BC might be off, or their motor skills to limit the time pushing the button might be off.

That's what I meant as well, which is why I wrote "narcosis causing impairment which caused the runaway ascent." Perhaps I should have been more clear, mea culpa.

One of my first narcosis episodes involved hallucinating at 100 fsw. I became convinced I was beginning an uncontrolled ascent, and dumped all the air out of my wing and drysuit (and of course, went splat! into the bottom). Had I been on a wall or somewhere with poor visual cues, I might well have thought I was sinking, and might have blown a similar amount of gas into the wing and ended up like the OP.

With all due respect, extrapolating from 1 data point is not very useful. Hallucinating at 100fsw is not only not common, it is *extremely* uncommon. For that 1 instance, I can probably name 1000+ divers I have personally dived with at depths of 100fsw who have NOT had any adverse effect. Heck, when doing the cognitive function test at 30m, <10% of my students (sample size of several hundred) actually show -any- significant difference in ability (let alone significant enough to impair their ability to add air to a BCD).

Having misspent part of my early days doing deep air before wisening up (and nearly dying atleast twice due to accidents and massive amounts of blown deco both indirectly contributed to by narcosis), I am the last person to under-estimate the risks of narcosis - quite the opposite, in fact.

However, I submit that proposing narcosis as a potential cause of this problem on a 90ft/27m dive in warm water is a bit misleading.

For one, what is more likely - a beginner diver simply makes a mistake and messes up her buoyancy, or that s/he is so impaired at 90ft/27m that they simply dont know how much air to add?

By putting this rather low-probability cause on the same pedestal as far more likely causes, you are just muddying things for the OP and for others who might be reading. Now, instead of having people who realize that hey, sometimes compost happens and we learn from it, you potentially have someone who is worried about her brain going zombie... and at 27m, nonetheless.

And you are grossly overstating the narcosis risks of a warm-water dive to <100m. I know it is fashionable on SB to make a big deal out of every little risk pertaining to diving, and maybe it may not be a bad idea for people to be more careful rather than less, but at some point - especially on the "Advanced Scuba Skills" board, it may be more useful to NOT dumb things down so much.

Cheers,
Vandit

 

[D_B]

I though TSandM's posts were pretty clear on the conditions , and a reasonable possibility, given the lack of more info from the OP's other dives and comfort/skill level


All good points on weighting and learning to use the other dumps and getting familiar with them
.. If I'm head up, I never use the pull dump on the inflator hose, I just use the other shoulder dump, or raise the hose and use it normally
... weight ... I had two extra pounds over my normal 13lbs due to putting it in to compensate for a vest, and forgetting to take them out again when I did not use the vest on subsequent dive ... all through the dive I kept thinking my buoyancy control is all gone, seemed all touchy, was really disappointed in myself .. then pleased to discover those two extra pounds ... learned that two pounds is enough to be readily noticed, and that I should inspect my gear configuration for every dive

 

[iztok]

Moderator, can you move this perhaps to "New Divers and Those Considering Diving" thread? It is better fitted there.

 

[AfterDark]

vkalia: For that 1 instance, I can probably name 1000+ divers I have personally dived with at depths of 100fsw who have NOT had any adverse effect. Heck, when doing the cognitive function test at 30m, <10% of my students (sample size of several hundred) actually show -any- significant difference in ability (let alone significant enough to impair their ability to add air to a BCD).

The point being made here about narcosis is that often times one can be narc'd and do a dive with no adverse affects. Nobody but me knew I was narc'd until I mentioned it on the boat after the dive. I my case it was a inability to concentrate enough to do simple 3rd grade math. I wouldn't have known I was narc'd if I hadn't tried to recaculate my decom time. I would think a diver that was over weighted in a uncontrolled ascent would have the advantage of not having to dump a lot of air to slow down. A diver that is weighted correctly gets the "feeling" of sinking then adds too much air to the bc would pickup speed fast once leaving the bottom. Slowing that ascent would require a lot of air to be dumped. Food for thought. We weren't there, we're just guessing.

 

[D_B]

a diver that is overweighted will have a larger amount of air in wing, causing the need to dump more air , and sooner, than if they were correctly weighted and starting off with less air ... more air is "touchier" , the slightest depth change causes a bigger volume change .. as I learned when I was only 2lbs heavier than normal

 

[fnfalman]

For the OP,

A lot of excellent advices had already been given to you about how to prevent runaway ascend. I'd like to give my own two cents about how to undo your runaway ascend.

First of all, sometimes when you're horizontal in the water (perfectly trimmed like you're suppose to be), you don't raise the corrugated hose high enough above your head so that the air can vent out. Next time, tilt your left shoulder up (as though you're trying to swim sideway) and really raise your arm. That action "should" untrap the air in the BC. If that action doesn't work, just go vertical and raise the corrugated hose way above your head and dump like crazy so that you can halt your uncontrolled ascension.

Or point your head down and kick hard as though you're trying to swim down and then grab for the pull dump valve near your butt (if your BC has one there). I've never had any problem with trapped air when I point my butt up and hit the bottom dump valve.

Also, don't forget to flare your body out (starfish style). Spread your legs and arms out in order to increase drag. You will find it surprisingly efficient to slow your ascension this way while you figure out what to do in order to get the air out of your BC.

 

[Web Monkey]

you should have been able to control your asent buy swimming down, slowly. to slow your asent.

Many BCs have more than 50Lbs of lift and some have even more. There isn't a human alive that can successfully fin against that much lift.

The OP needs to learn how to use the BC's dump valves. There isn't an inflator in the world that can keep up with an open dump (they're designed that way).

And as long as we're talking about runaway ascents, it's also nice to know how to disconnect the inflator's air hose in case it sticks open or leaks air into the BC.

Terry

 

[vkalia]

The point being made here about narcosis is that often times one can be narc'd and do a dive with no adverse affects.

No, that is not the point here. The point made was quite the opposite - that someone did a dive to 90'/27m and was narc'ed enough to HAVE an adverse effect (unable to realize how much air she put into a BCD).

My point is that the odds of that severe narcosis happening at 27m are *extremely* low and it probably muddies up the waters for the OP when it comes to figuring out what went wrong. Sometimes, the simplest answer is indeed the correct one.

I would think a diver that was over weighted in a uncontrolled ascent would have the advantage of not having to dump a lot of air to slow down.

Actually, that is a common misconception and here is why. Overweighted divers have MORE air in their BCD when they start to go up. As the runaway ascent starts, this air expands - the percentage of expansion is the same, but when there is more air in the BCD to begin with, the actual expansion amount is higher. So the diver needs to dump more air.

A simplified example:

With the proper amount of weighting, let's say you need to add 1l of air to your BCD at 10m to be neutral. Now, if you go up by 1m, pressure decreases by 0,1 bar or 5%, and so the volume of air in the the BCD increases by approx 5%*. So your 1l of air becomes 1.05l (1,052 to be precise) and so you are now approx 50g positively buoyant.

Let's say you are heinously overweighted and need 10l of air in your BCD to become neutral. Now, you go up by 1m. The air volume change is still 5%, but 5% increase over 10l becomes 10.5l - so now you are 500g positively buoyant.

Therefore you need to release more air. Makes sense?

Many instructors make the same mistake - someone loses their buoyancy and goes up, they ADD more weight to the belt, when they should be considering reducing it.

Edit - Another point, completely un-related to this: not all BCDs have pull-dumps built into the corrugated hose. So just grabbing the inflator hose and pulling may not have the expected results.

Vandit

*For those who love accuracy in math - yes, I am aware that the increase in volume is not EXACTLY 5% if you apply the Boyle's Law variant of PV = nRT, but this is not a physics lecture. 5% is close enough.

 

[Johan Broere]

Wow, you got lucky and some day when "20 dives under my belt" means that you still have a lot to learn, I hope you will be able to understand how lucky you were. Please practice. Shallow. We can all learn from someone else mistakes too, So I keep reading . . . . . .
I don't understand the lol's in some of the responses. My kids use lol a lot. They are teenagers.
Just last weekend a diver wanted to save 30 dollar. "No we don't need no divemaster". Still in a coma.
Yes, I implied that teenagers sometimes are stupid !