Number one cause of diving fatalities?

[Colliam7]

As I understood the DAN study, these two were BOTH part of the identified cause of fatalities. Barotrauma associated with rapid ascent was the result of the interruption of the in the gas supply that preceded that rapid ascent.

Very good point, so Freewillow's understanding of the French data is not at all inconsistent with the DAN data.

 

[Freewillow]

I understand what you are saying. But uncontrolled ascent is NOT only due to out of air situation. The causes are varied from OOA to stuck BCD inflator, washing machine, uncontrolled buoyancy, panic, SMB faulty launch......to name a few.......

 

[boulderjohn]

I understand what you are saying. But uncontrolled ascent is NOT only due to out of air situation. The causes are varied from OOA to stuck BCD inflator, washing machine, uncontrolled buoyancy, panic, SMB faulty launch......to name a few.......

I was referring to the results of the DAN study specifically.

 

[Freewillow]

I was referring to the results of the DAN study specifically.

No problem

 

[dmaziuk]

You are the one who said:
Everybody knows salinity has nothing to do with buoyancy.
The question was "tongue in cheek."

As was the statement. "Everybody knows" is known by many names including "bandwagon fallacy" and "argumentum ad populum". It was there to further ridicule the notion that you don't need to adjust your ballast to water salinity and that dive shops want to dangerosuly overweigh their customers in order to promote accidents and lose their trade.

The difference between fresh water and salt water is 3%. For many people, 5 pounds will be about right.

Salt water is about 2.5% more dense than fresh water.

So, weigh yourself fully kitted up (dry) for fresh water, and add 2.5% of that for diving with the same gear in salt water.

Purely subjectively, water on Roatan stung my eyes noticeably worse than on Bonaire a year earlier. I ended up carrying 10 lbs of lead in a bp&w on Roatan, I was carrying 8 lbs in a rental jacket bcd on Bonaire. When I took the bp&w for a test drive in the pool, 1lb trim was all I used. It was lighter than I like after I vented the tank down to 500 psi or so, but I had no problems staying down. Same wetsuit etc. in all 3 cases, no camera in the pool.

Different water density is the one explanation I have, and the differences from fresh to Roatan in my case are more than 2.5% of total weight and more than 5 lbs absolute. So from, again, purely subjective anecdotal experience, I buy "10% extra weight to compensate for salinity" claim.

 

[boulderjohn]

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.

 

[John C. Ratliff]

As was the statement. "Everybody knows" is known by many names including "bandwagon fallacy" and "argumentum ad populum". It was there to further ridicule the notion that you don't need to adjust your ballast to water salinity and that dive shops want to dangerosuly overweigh their customers in order to promote accidents and lose their trade...

My apologies. I am not aware of either "bandwagon fallacy" or "argumentum ad populum," although I can discern the meaning of the latter Latin term. Realize that you are talking to a multitude of people here, and in my own case, you are talking to a 70 year-old. Thanks for the explanation; I am still learning.

SeaRat

 

[JamesBon92007]

I'm curious, dmaziuk, why I need to add about five pounds to my weight belt when I dive salt water rather than fresh water?

SeaRat

I immediately assumed he was joking. Nobody is that ignorant. Are they?

 

[JamesBon92007]

You run out of air by not paying attention to your SPG. People who are diving deeper than normal and going through gas faster than expected are especially susceptible.

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.

 

[JamesBon92007]

My apologies. I am not aware of either "bandwagon fallacy" or "argumentum ad populum," although I can discern the meaning of the latter Latin term. Realize that you are talking to a multitude of people here, and in my own case, you are talking to a 70 year-old. Thanks for the explanation; I am still learning.

SeaRat

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