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Ascent Rates-Split from Catalina Diver died today
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I have a question for you more experienced divers about this thread.
At what point does a rapid ascent become a serious safety issue? I don't remember getting anything on this in my OW training on this other than warnings that it is dangerous and to keep it slow.
Is there an approximate depth or rate associated with serious problems?
At what point does a rapid ascent become a serious safety issue? I don't remember getting anything on this in my OW training on this other than warnings that it is dangerous and to keep it slow.
Is there an approximate depth or rate associated with serious problems?
StreetDoctor
Contributor
racedude1984
Contributor
I was told do not ascend faster then your bubbles.
A rapid ascent from 4 feet without exhaling can cause an embolism. How's that? A rapid ascent from any depth that does not allow the accumulated nitrogen to safely exit the body COULD cause an issue. The recommended safe rate of ascent with most agencies is 30 feet per minute. Many computers/bottom timers have an ascent alarm that is set at this rate. For normal No Deco Recreational dives I tell my students that there is really no such thing as too slow. On OW dive #3 or 4 we will take our time coming up from the 15 foot stop and just look at the lake bed. It may take 10 minutes for this ascent. They find things, see little fish, etc.
The old adage was no faster than your smallest bubble. Kind of hard to watch for me. But with a watch and depth gauge which you should have anyway you can easily time your rate of ascent and should have been shown how. If your class did not cover this you got screwed. Rate of ascent is a serious issue from any depth. That your instructor did not covey this says volumes about the "quality" of their class
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GrumpyOldGuy
Contributor
This is the "old rule of thumb", used when everyone though 60 feet per minute was safe. It was not very good then (different sizes of bubbles from different 2nd stages).
Since now we know slower is better and use 30 feet per minute, it is obsolete. It might be useful if you have equipment failure, but not as a primary tool. Also, your last 15' should be a lot slower than 30fpm if possible as you have the maximum relative change in the shallower depths.
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ItsBruce
Contributor
The general rules are (1) no faster than 30 feet per minute, and (2) no faster than your bubbles. However, as I understand it, the critical issue is not so much how fast one ascends, but rather how quickly one can exhale to prevent lung over-expansion.
If you are particularly deep or have been underwater for a long time, you will have nitrogen bubbles in your blood stream and it is a good idea to give them a bit of time to leave your system. A slow ascent does that.
However, even when there is no nitrogen, i.e. a short dive in shallow water, you still need to let air out of your lungs as you surface. The problem, as I see it (which is what I always worry about on my ascents) is that after you exhale, you inhale and if you are inhaling as you ascent, particularly if you are breathing deeply, you increase the risk of lung over-expansion. Slowing your ascent mitigates this. However, it could not hurt to slow even more or even stop on the inhale and then continue your ascent as you exhale.
The old adage was no faster than your smallest bubble. Kind of hard to watch for me. But with a watch and depth gauge which you should have anyway you can easily time your rate of ascent and should have been shown how. If your class did not cover this you got screwed. Rate of ascent is a serious issue from any depth. That your instructor did not covey this says volumes about the "quality" of their class
I am not so sure that the 30' per minute isn't covered, IMHO. In terms of training -- any time you can give a student a mental vision as well as hearing or reading, the item is remembered. Mental vision of "as slow or slower than smallest bubble" seems to 'stick', even for non-divers. At least, that's what I hear from all the non-divers I know . . .
Blackwood
Contributor
According to the poster I responded to with this, it was not in his class. As for visual images and retention you are correct. But if none is given in the first place it is a moot point. I also take the time to make sure my students know how to do safe ascents. We practice them every pool session both vertically and horizontally. They are required to have a timing device and depth gauge. But those do them no good if they are not taught how to effectively use them.
The trouble is that too many people are put in open water who are not yet comfortable enough to even remember to look at the bubbles. They are staring at the instructor, their buddies, the surface, and trying to remember to vent the bc, kick slowly, keep sight of the line, etc. They have not been tasked enough in the pool to pay attention to that one little bubble successfully. Many of them should still be in the pool. I do one vertical descent and ascent in OW to the platform. All others are done in a horizontal position once they hit 8-10 feet on descent and to that on ascent.
There is no reason for them to be hitting the platform on their knees or at all really. I expect them to be able to stop 3-4 feet above it, get nice and neutral, and float down to it like a big snowflake. Not crash into it or even land with a thud. I expect them to ascend the same way. Slow, controlled, focused on venting and keeping their breathing steady, where their buddy is, watching their depth, and time it takes to come up. If I don't think they are ready for that we do not get out of the pool until they are.
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