I'm fairly new to this, but so far my little experience has been that I never need to touch the inflator when ascending. In fact, I think I could disconnect it with confidence and orally inflate at the surface if need be. So far, what I do is let out some gas, then use my lungs and/or swim up to the next stop, then use my lungs to hold the stop, then let out some more gas and/or swim to the next stop and so on.
Am I doing it wrong (tm)?
The concept of using lung volume to control buoyancy was never discussed in my OW class. Some OW classes are so insistent about never stop breathing/never hold your breath that they have students virtually hyperventilating.
More focus on the mechanics of breathing would be a benefit. Often new divers are hyperventilating , putting so much air in their lungs that it effects not just SAC but also buoyancy!
Students need to breathe NORMALLY with a relaxed airway! We need to educate divers about the fact that we naturally have a pause.... exhale...inhale... slight pause exhale with a relaxed airway. There is a difference between that pause with a relaxed airway and HOLDING YOUR BREATH or SKIP BREATHING!
Breathing is a voluntary and involuntary action so when we think about our breathing ... we change our breathing. If you want to learn about this... watch someone breathing when they don't realize you are watching them.... then tell them you want to watch their breathing and how they do it and tell them not to change their breathing at all... try this with different people. This "experiment" will help to recognize normal breathing... then compare it to how you breath under water.
Any time someone talks about using lungs to control bouyancy for safety sake it must be stressed that it means you may take slightly deeper or shallower breaths but you must keep your airway "relaxed" and not HOLD your breath! You must not over inflate your lungs or deny the air your body needs.
A properly weighted diver should not need a lot of air in their BDC... of course that is also greatly effect by the exposure suit. I use virtually only my lungs for bouyancy in my summer gear... more use of BCD in my 3mil and more again in my 5mil
I would be interested to hear form other divers who use 7mil or drysuits when or if they use their lungs for the fine tuning of their buoyancy. TSandM please correct me if I have not explained this well. I just think education is important when it comes to this topic/technique.
John Lippmann and Dr Simon Mitchell (Deeper into Diving) and Mark Powell (Deco for Divers) both write that increased activity increases nitrogen on/off-gassing. Both books recomend light activity during the decompression phase of the dive as being beneficial but heavy excercise during the dive increases DCS risk.
Dr Michell has an astounding background as a Hyperbaric Specialist having been in charge of the Hyperbaric Unit in Brisbane and Sydney Hospitals as well as the NZ Navy. He is also a brilliant speaker if you every have a chance to attend a presentation by him.. Jump at the chance!. We had some very interesting discussions with him about the role of cold, gender, age and body fat content in DCS.
It sounds like the divers were either not very experienced or proficient. They may or may not have had watches and may or may not have had more of a plan than go up before the air runs out.
One got lucky and one didn't. The distribution of when DCS occurs at a particular time/depth is quite wide for a particular individual on a particular day.
There is nothing about how this dive went down that would suggest proficient divers... from diving at these depths with a plan to go up when air gets low to not being able to control BC's and ascents.
It's tragic and a wake up call of what can happen. Just because you might be able to get away with poor diving techniques doesn't mean that you're guaranteed to be able to do this.
Sure, technical divers can dive without computers. Anyone can dive with only time and depth if they are proficient but there's nothing in this thread to indicate that they are proficient divers.
The real lesson or maybe surprise or at least reminder is that just because DCS doesn't occur all that often and when it does it's usually less severe than this case doesn't mean that any one diver can count on it not being severe.
People walk away from car crashes with only minor injuries more times than not but when circumstances are only a bit different the results can be completely different. Many teenagers get away from street racing and some die from it...other's live to grow up and suffer no repercussions and yet it is a bad idea in either case.
I think that's more or less the situation here...blown deco and a rapid ascent.
I hope sk will be able to give us the information about the dive plan. I am hesitant to conclude there was NO plan or proficiency of the divers based on what we know. Has the BCD/ inflater checked to see if there are any issues with them?
Proficient divers sometimes get Narked, distracted which is why I like the alarms on my computer.
I agree with you the differences in physiology and even health at the time of the dive can also effect who gets a hit when and how bad. How well rested, hydrated, nourished, or incubating a virus impact our DCI risks to some degree as well!
Just my .02
