Ascent Rates-Split from Catalina Diver died today

[watboy]

I don't want to add to the thread hijack so maybe this should be posted separately but is there any data as opposed to theory that shows smokers are higher risk? I ask because I've come across a lot of DMs/Instructors/Guides that smoke. Admittedly this is often in poorer countries where smoking is more prevalent but it is certainly not exclusive to poorer countries. There's a lot of down time when diving - smoking is great at killing time (yeah, leave the obvious retort at the door ). Anyhow, main point being - is there any actual data showing smokers to be at higher risk of DCI?

J

Extending the tangent, why not include overweight divers, or those who are heavy drinkers. Or even older divers.

 

[drbill]

In the specific case of the deceased Catalina diver, the incident occurred during their descent. Therefore there would be little nitrogen in her body requiring off gassing. The concern would be over expansion. The instructor told me the deceased was exhaling on the ascent.

When I experienced equipment failure at 75 ft, I ascended at a rate of 1 ft per min with little air in my lungs. I couldn't "hold" my breath for 2+ minutes! However, my normal guideline is the 30 ft per minute one, and almost all my ascents involve much slower gradual ascents thanks to the sloping topography off Catalina Island.

 

[DCBC]

I've started another thread in the advanced section; so as to include decompression and allow more extensive discussion (outside of the basic discussion area).

 

[Kingpatzer]

Since now we know slower is better . . .

Some current research is suggesting that slower is not always better. There appears to be a measurable advantage even within recreational limits to having a faster (not fast!) ascent from lower depths combined with deep stops, and a slow (30'/m) ascent from a moderate depth.

There is some controversy over these findings, and for every paper I find talking about advantages I find one complaining about the study methodology. But the fact remains that the biology and physiology of what's going on just isn't as well understood as we would all wish.

All of that said . . . 30' is the most common agency recommendation, and while it may not be the optimal answer, it is the best pragmatic response at this time. Faster than that without significant expertise and insight into why you are doing so and you may be pushing the limits of safe diving.

 

[Bubbletrubble]

Some current research is suggesting that slower is not always better. There appears to be a measurable advantage even within recreational limits to having a faster (not fast!) ascent from lower depths combined with deep stops, and a slow (30'/m) ascent from a moderate depth.

Here is a PDF link to the Marroni et al. paper reporting the effect of deep stops combined with various ascent rates in recreational dives with a max depth of 82 fsw. As Kingpatzer pointed out, the study demonstrated that:

1. Slow ascents (3m/min) produced higher Doppler bubble scores than faster ascents (18m/min) and
2. Including a 15m deep stop for 5 min in addition to a 6m shallow stop for 5 min gave the lowest bubble scores.

It should be noted, however, that there is no conclusive evidence (as yet) to support a strong correlation between the presence of Doppler detected bubbles and DCS risk. A relatively small sample size (8 dive profiles done by 22 volunteer divers, with 2 subjects being excluded after the 4th dive due to pregnancy) was used, and only a few dive profiles were tested. But don't take my word for it. Read the paper if you have a few minutes to spare.

In the future, we may see a shift in recommended ascent rates from "slower is better" to variable rates dependent on depth (slightly faster at greater depths and slower or very slow for shallow depths). Hope you find this paper interesting...

 

[Jasonmh]

...

When I experienced equipment failure at 75 ft, I ascended at a rate of 1 ft per min with little air in my lungs....

I am assuming this is a typo, or I didn't understand what you were trying to say. I don't think you mean that you ascended at a rate of 1ft/min, taking 75 minutes to ascend.

 

[Jax]

Funny how that worked all those years for so many people but today it's akin to witchcraft. I don't get it? Does anyone know what that rate of ascent would be? Dare anyone risk their life trying it?:shocked2:

Scuba Diving Bubble Mechanics

I have no knowledge of the accuracy of this document, but it does pass the common sense test.

What think you?

 

[Thalassamania]

Mr. Holt's objections to following your bubbles are:

1. First, I want to apply the laws of Physics that are taught in the Basic Scuba Diver course. When a diver exhales bubbles into the water, the bubbles begin to expand as they rise. As they expand they increase their buoyancy and therefore travel to the surface with increasing speed which causes them to expand faster and travel even faster towards the surface.
2. Second, it is extremely difficult to follow bubbles, especially when there are more than a few divers, there is poor visibility, or when there is substantial current.
3. Third, it is extremely difficult to slow your ascent rate after you have passed the bubble you were watching. By the time your realize that your gaining on your bubble, its to late - You are going to fast!
4. Forth, 60 feet per minute is too fast to begin with! Many hyperbaric specialists throughout the world are now recommending an ascent rate of 30 feet per minute. NAUI has adopted this ascent rate of all diving activities, save one. The Emergency Swimming Ascent, for which 60 feet per minute cannot be exceeded

1. You need to keep shifting to the smallest bubbles. Try it out, see what size bubble stays with you as you ascent 5 ft on your depth guage then 5 seconds on your watch. It's really not that hard
2. It is not extremely difficult to learn to do, but it does cut into your SA during the ascent, when awareness of what it going on around you is critical.
3. Techniques like the air siphon that I have covered in other threads make avoiding the positive feedback loop problem rather simple.
4. It is starting to appear that the best instantaneous ascent rate may well be approximated by the depth that you are at (e.g., 120FPM at 120FSW, 60FPM at 60FSW, 30FPM at 30FSW, 15FPM at 15FSW to the surface).

 

[Bubbletrubble]

When I experienced equipment failure at 75 ft, I ascended at a rate of 1 ft per min with little air in my lungs. I couldn't "hold" my breath for 2+ minutes!

I am assuming this is a typo, or I didn't understand what you were trying to say. I don't think you mean that you ascended at a rate of 1ft/min, taking 75 minutes to ascend.

Although Dr. Bill is believed to have god-like diving prowess, his breath-holding capability is likely in the range of mere mortal. I think he meant to write that his ascent rate for that incident was "1 ft per sec."

 

[jviehe]

Wow!! I sure generated a lot of hostility with my question. Perhaps it was the phrasing.

Of course, my instructor taught me how to ascend from a dive and made sure I know how to do it properly.

The question was when does it become dangerous to deviate from the recommended rates?

For those who were civil and thoughtful with the responses, Thanks!

For the rest Well...........

Well hopefully you got it answered. Just be sure to take the internet for what its worth. There are some great books out there on physics and physiology of diving you can read to get even more detailed answers. For practical purposes, it isnt safe ever to exceed the recommended ascent rates. Follow your training, use your guages to monitor your ascent rate. If you exceed it, monitor yourself for DCS. If you have trouble maintaining a slow ascent rate, practice, use an ascent line.