Number one cause of diving fatalities?

[John C. Ratliff]

I have ran out of air many times, especially in the days before I had a SPG. I, however, have never done it on a really deep dive but at, say, 50-60 feet, when you begin to run low on air it becomes increasingly more difficult to draw a breath and you have to suck harder to get some air. As you ascend the air inside the tank expands. I have been in situations where I sucked every last bit of air I could get and was still able to make a normal ascent. Sometime ya just don't want to go back up

I was trying to think of a situation where this might not work--if the water was very warm at depth and very cold near the surface it might not expand enough.

Do you think J-Valves are about to make a comeback? I have a really cool one that is adjustable up to 600 psi and probably cost more than most regulators at the time.

I have a collection of various regulators, both double hose and single hose. In the 1960s, you could get either a double hose Healthways Scubair or Scuba Star, or a Healthways SCUBA double hose regulator with a restrictor orifice. This is a depth-compensated reserve system based upon making the regulator breath harder at a prescribed psig in the tank. I last year used my Scubair in twenty or so feet of water, and surfaced exactly when the harder breathing became noticable, and I had 600 psig left in the tank. The Scubair could be changed for a setting for a J-valve, in which the restriction was bypassed. The Scubair 300 was a sonic regulator, which began making bad, vibrating noises at about 400 psig. Scubapro came out with their Mark VII, which had an even more effective sonic/vibration reserve which drove the diver nuts as you could feel the vibrations in the second stage, but fell out of favor when it was reported that these vibrations not only told divers in the vicinity that you were running low on air, but also attracted sharks (doubt it, but rumor had it as so, "argumentum ad populum").

I currently use the Scubapro J-valve that can be changed from 300 psig to 600 psig with air in the tank, as long as a regulator is not hooked up and pressurized. I have J-valves on my three sets of doubles too.

In open water, even without looking at your gauge, there is no excuse for not being able to surface, even on an "empty" tank at depth, as there are still several breaths to breathe on ascent.

SeaRat

 

[dmaziuk]

I take the "argumentum" to mean that if 51% percent of the population believes something it becomes the truth.

(Veering further off-topic) See also: "democracy"

 

[tridacna]

Seawater - Wikipedia, the free encyclopedia

Although the vast majority of seawater has a salinity of between 3.1% and 3.8%, seawater is not uniformly saline throughout the world. Where mixing occurs with fresh water runoff from river mouths or near melting glaciers, seawater can be substantially less saline. The most saline open sea is the Red Sea, where high rates of evaporation, low precipitation and river inflow, and confined circulation result in unusually salty water.
​

On average, sea water weighs 64.1 pounds per cubic foot. On average, fresh water weighs 62.4 pounds per cubic foot. Thus, sea water is about 2.724% heavier than fresh water. That means that on average, a diver and all his or her gear would need to have 2.724% more weight in alt water than in fresh water. If a diver and gear weigh 250 pounds, that diver would need an additional 6.81 pounds. If a dier and gear weight 200 pounds, he or she would need 5.45 pounds.

If you are cutting it that fine--measuring the salinity of the part of the world's oceans in which you are diving and shaving the weights to get the the precise amount needed--you are way, way, way overthinking this. That's why I round to 3% and call it good.

I actually took a calibrated refractometer and SG device with me on a trip to BDA some years ago to settle this nonsense. There was less than a 0.1% difference between Bermuda and anywhere else that I dived in the Caribbean. (No difference between Bonaire or Honduras either for that matter).

 

[dmaziuk]

Which is why I said "purely subjective anecdotal experience". If it's not salinity then I must be getting more full of floaty fecal matter -- while retaining the same body weight and waist size -- with every passing year and every trip to the Caribbean.

 

[Basking Ridge Diver]

I have ran out of air many times, especially in the days before I had a SPG. I, however, have never done it on a really deep dive but at, say, 50-60 feet, when you begin to run low on air it becomes increasingly more difficult to draw a breath and you have to suck harder to get some air. As you ascend the air inside the tank expands. I have been in situations where I sucked every last bit of air I could get and was still able to make a normal ascent. Sometime ya just don't want to go back up

I was trying to think of a situation where this might not work--if the water was very warm at depth and very cold near the surface it might not expand enough.

Do you think J-Valves are about to make a comeback? I have a really cool one that is adjustable up to 600 psi and probably cost more than most regulators at the time.

I also used a J-valve when I first learned - but as I understand it a few things are at play.

First the first stage that we used was unbalanced and hence the "hard to breath" warning was all you needed to know you had a few mins to pull the J-valve to get the extra 500 psi - unless of course by accident it was pulled and you did not notice...

Second is the second stage draws gas from the tank at "ambient pressure" - the gas does not expand in the way you are thinking or describing...

If I am incorrect feel free to show where - but I believe this is how the flow of gas works from your tank to your mouth... you could say expands but that is not the way to describe it.. hope that helps anyone that is looking at the thread.

 

[John C. Ratliff]

I also used a J-valve when I first learned - but as I understand it a few things are at play.

First the first stage that we used was unbalanced and hence the "hard to breath" warning was all you needed to know you had a few mins to pull the J-valve to get the extra 500 psi - unless of course by accident it was pulled and you did not notice...

Second is the second stage draws gas from the tank at "ambient pressure" - the gas does not expand in the way you are thinking or describing...

If I am incorrect feel free to show where - but I believe this is how the flow of gas works from your tank to your mouth... you could say expands but that is not the way to describe it.. hope that helps anyone that is looking at the thread.

Basking Ridge Diver,

You have a few inaccuracies in this text. First, when you use an unbalanced first stage, the breathing either gets easier or harder as the tank pressure decreases. When using an unbalanced upstream diaphragm first stage (DA Aquamaster, early Conshelt, early Sport Diver), the breathing gets easier at low tank pressure. When using an unbalanced piston regulator first stage (Healthways Scuba Star or Scubair, Sherwood Magnum), the breathing gets slightly harder as tank pressure decreases. This is entirely different from the restricted orifice "automatic reserve" I discussed above.

Second, the second stage does not "draws gas from the tank at 'ambient pressure'" as this gas is at intermediate pressure. The second stage delivers gas at ambient pressure to the diver's mouth.

SeaRat

 

[boulderjohn]

I have ran out of air many times, especially in the days before I had a SPG. I, however, have never done it on a really deep dive but at, say, 50-60 feet, when you begin to run low on air it becomes increasingly more difficult to draw a breath and you have to suck harder to get some air. As you ascend the air inside the tank expands. I have been in situations where I sucked every last bit of air I could get and was still able to make a normal ascent. Sometime ya just don't want to go back up

As Baskingridge Diver said, the air in the tank does not expand at all upon ascent because it is in an inflexible container. What changes upon ascent is the ambient pressure. As that lessons, the regulator is once again able to provide air to you when you are at that lesser pressure.

 

[tridacna]

Which is why I said "purely subjective anecdotal experience". If it's not salinity then I must be getting more full of floaty fecal matter -- while retaining the same body weight and waist size -- with every passing year and every trip to the Caribbean.

I agree with you totally here. FOS is an apropos way to describe your argument.

 

[billt4sf]

PADI/DAN study results.

http://d35gjurzz1vdcl.cloudfront.net/ftw-files/Day1/Evidence/5.pdf

Same study in written format (not PPT presentation).
http://dspace.rubicon-foundation.or...3456789/9352/DAN_Fatalities_11.pdf?sequence=1

According to this, the big three are:

(2) Unknown - around 30 - 40%
(2) Drowning - also around 30 - 40%
(3) Cardiac - around 15%

I am assuming that "Drowning" includes OOA as well as whatever else could result in drowning.

Cardiac is much less than I had thought.

- Bill

 

[Bob DBF]

According to this, the big three are:

(2) Unknown - around 30 - 40%
(2) Drowning - also around 30 - 40%
(3) Cardiac - around 15%

I am assuming that "Drowning" includes OOA as well as whatever else could result in drowning.

Cardiac is much less than I had thought.

- Bill

Plenty of room in unknown and drowning to fit in a lot more cardiac.


Bob