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Inhaled, or exhaled, I've found that with practice it makes little difference to me.
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If I am outside of my FATR I am below 190 and a Spare Air is not going to help me. If I am above 190 I am inside my FATR and a Spare Air is just in the way.
A variety of free ascent ranges have been discussed in this long thread. Are people referring to ranges that they can make after they have taken the last breath or exhaled the last breath?
I cannot comment on what others have stated, but I will try to explain the free ascent target ranges (FATR) of myself and my students. One important aspect to this is it assumes that the Diver has a full-breath of air at the beginning of the free-ascent / CESA.
All of my basic students must attempt a free-ascent (regulator in-mouth and air available) from a depth of 50' to the surface. Advanced students do their CESA from 115' to the safety stop. I would estimate that half the basic students and one in three advanced students are successful in their attempt. The BC is empty and they are negatively buoyant at depth, so they must swim beside the instructor to maintain a maximum ascent rate of 30 fpm. The exercise is undertaken primarily to teach technique and for them to gain appreciation for depth and what it means to them in an emergency.
As a Navy diver, training consisted of doff and don of scuba at 100' and a free ascent from 100' after exhalation. I have often attempted a free-ascent in the range of 170 to 180' (from 200' or so to my decompression stop). On a full breath, I have been mostly successful, but not in all cases. If I didn't have a breath to start, there is no way I would be successful deeper than 100', probably shallower as I don't possess the fitness of my youth.
I think it arrogant to believe that you may not need another breath of air to safely perform a free-ascent from depth. One cannot be assured that you will start the process with a full breath to begin with.
Without another source of air, it is reasonable to assume that a diver will ascend too quickly in an OOA/ 1st stage malfunction situation. At the very least a secondary source of air will allow the Diver to slow his/her ascent and possibly prevent DCS or AGE. A secondary air source, just makes good sense.
It may matter more that a secondary air source exists, rather than the size of this source. The bottom line is that the secondary air source will provide you with enough air to get to the surface safely. Obviously if you are diving with an overhead, such as a cave, wreck or under the ice, a Spare Air is insufficient. If however you dive in open-water, it may provide you with enough air to insure safety. That said, so will a Pony Bottle or other secondary cylinder. You just have to decide what you want to take with you on your next diving vacation.
Great post, I wish I'd read this as part of my OW training. Amongst other things, it would have helped me to understand the 60' limit for OW divers. It appears that you are addressing a CESA as the only alternative to carrying redundant air. This makes a certain amount of sense when discussing FATR, but I wonder if your conclusion is making a few simplifying assumptions that may hold for many but not all divers.
As part of my training after AOW, I was required to practice an out-of-gas swim after exhaling to simulate the worst case OOG. I was required to swim to my instructor (who was swimming away from me slowly), signal OOG, and share air. This simulates an OOG situation where you have a buddy, you have the situational awareness to know where they are, but you are only loosely following them.
Like the FATR, I now have an idea of how far I can swim horizontally to another diver to get air. Am I correct in thinking that if stay well within this range and continue to practice out of air swims that I have a realistic secondary air source?
Of course, I am not suggesting that doing so works for all divers. It appears (from reading this thread) that some divers may not have practiced an out of air swim. Others appear to consider maintaining contact with a buddy to be an onerous burden. I am personally ok with it and typically follow the DM around when on vacation without a buddy.
On my recent trip to Conzumel we did the notorious "Barracuda" reef, a site known for being deep by NDL diving standards and for its current. Separation is a concern. I was happy to stay very close to the DM leading the dive, I viewed the cylinder on his back as my pony bottle. Many others may have preferred the freedom to swim a bit more freely.
I was happy to stay very close to the DM leading the dive, I viewed the cylinder on his back as my pony bottle.
Am I correct in thinking that if I stay well within this range and continue to practice out of air swims that I have a realistic secondary air source?
Incredibly unhelpful pseudo-philosophical pretentious quote for reflection:
"You can't reason someone out of a position they didn't reason themselves into."
...I think if most people spent as much time and effort focused on thinking/planning/gearing/practicing how to AVOID the problem in the first place as they do focusing on what to do after it's too late...they'd be far better off.
Reg, I believe it's save to say that your instruction was more comprehensive than the greatest majority of all divers taking an entry SCUBA Program. I sincerely congratulate your instructor for making the extra effort to expand the scope of his training.
Not saying SpareAir doesn't serve a purpose in some "limited operational envelope" as mentioned above, nor that you don't need to stay near your buddy, but I think if most people spent as much time and effort focused on thinking/planning/gearing/practicing how to AVOID the problem in the first place as they do focusing on what to do after it's too late...they'd be far better off.
"I'll never be in any diving situation that's beyond my control!!!"
Cocky or just inexperienced?