An Open Letter of Personal Perspective to the Diving Industry by NetDoc

[tursiops]

Indeed, and the ratio without a pool session is 1:1.

Well, not exactly. Pool and "confined open water" are both 4:1 (if an instructor is leading), but the Confined Open Water is clearly defined:
"Confined water is a general term that refers to either a swimming pool or confined open water.
Confined open water is an open water site that offers swimming-pool-like conditions with respect to clarity, calmness, and depth.
It has both shallow water and water sufficiently deep to allow student divers to meet all skill performance requirements.
Evaluate confined open water conditions carefully before each dive because a site may qualify as “pool-like” on a given day under
certain conditions, but not qualify under others."

The 1:1 you speak of is from:
"If participants will go on an open water dive, and shallow water for skills practice is inaccessible, an instructor
conducts the skills session from a boat, dock or other surface support station by using a descent line, horizontal
bar or platform that is within 2 metres/6 feet of the surface. The ratio is 1:1 when using the descent line option."

According to the reports just posted, there was apparently shallow water for a skills session in "confined open water", but I certainly doubt if the viz was "swimmjng-pool-like with respect to clarity," so the shallow-water session did not qualify as a confined open water site.

 

[The Chairman]

So, you disagreed with me to point out that I was right? OK.

 

[redacted]

I do open water dives in fresh water with students in 7mm suits, but not FJs. We use aluminum tanks. I would start someone that size with about 10 pounds. I used to work for a shop that used 7mm FJs. I don't remember us ever using more than about 24 pounds on a full sized adult with an aluminum tank.


Once the initial diver bolted to the surface, which would have taken a couple of seconds from 15 feet, that episode was over. The instructor had to go to the surface to make sure he was OK, but it would not matter if he arrived a hair later, the amount of time needed to show the two other divers the thumb and get them to ascend with him.

Don't forget that the altitude also makes the wet suit more buoyant, like 20% more at 0.8 ATM. One of my dive buddies had a new adult large 7mm FJ that weighed in with 30 lb of buoyancy in my pool. It is my impression that the victim was probably not grossly over-weighted.

I agree that taking all to the surface would probably have been a better plan (although still a standards violation in this case). But remember, the 2nd Dr's statement suggested that if the cause of death was as he hypothesized, the child should be expected to suffer the same problem. I believe he suggested that even surfacing along the line may have resulted in the same result.

---------- Post added January 2nd, 2015 at 03:30 PM ----------

According to the reports just posted, there was apparently shallow water for a skills session in "confined open water", but I certainly doubt if the viz was "swimmjng-pool-like with respect to clarity," so the shallow-water session did not qualify as a confined open water site.

According to tourist propaganda, Bear Lake is "Known as the "Caribbean of the Rockies" for its intense turquoise-blue water". But I suspect the bottom is like many lakes that silt out when disturbed.

 

[boulderjohn]

Don't forget that the altitude also makes the wet suit more buoyant, like 20% more at 0.8 ATM. One of my dive buddies had a new adult large 7mm FJ that weighed in with 30 lb of buoyancy in my pool.

I would like to see that.

I recently did OW dives at about the same altitude for some students who were wearing 7mm suits (not FJs) and using aluminum tanks. One of them, a small adult male at about 150-160 pounds (larger than this boy), told me that he had intentionally used a 7mm suit for his pool work so that he would know what he needed in the OW dives. He said will full confidence that he needed 22 pounds--that's what the instructor who did his pool work assured him he would need for the OW dives. I talked him into doing his first weight check at 18 pounds, and that check showed him to be badly overweighted. By the time we were done with the class, he was doing the dives with 10 pounds. If he had used a steel tank, he would have needed less weight. When I did these dives with 7mm FJs, I never saw anyone of any size who needed 30 pounds, and that was with aluminum tanks.

 

[The Chairman]

Don't forget that the altitude also makes the wet suit more buoyant, like 20% more at 0.8 ATM.

If it were only made of air, then sure, it would have %20 more buoyancy. Say the voids accounted for %50 of the material, which I think would be high. If that were the case, then the max would be a %10 swing, but only at the surface. At three feet the buoyancy would be the same as at sea level.

FWIW, I've seen the same deep blue here in Florida. We are a limestone state and our springs have their origin in limestone. That doesn't change the specific gravity of our water much at all.

 

[redacted]

I would like to see that.

I recently did OW dives at about the same altitude for some students who were wearing 7mm suits (not FJs) and using aluminum tanks. One of them, a small adult male at about 150-160 pounds (larger than this boy), told me that he had intentionally used a 7mm suit for his pool work so that he would know what he needed in the OW dives. He said will full confidence that he needed 22 pounds--that's what the instructor who did his pool work assured him he would need for the OW dives. I talked him into doing his first weight check at 18 pounds, and that check showed him to be badly overweighted. By the time we were done with the class, he was doing the dives with 10 pounds. If he had used a steel tank, he would have needed less weight. When I did these dives with 7mm FJs, I never saw anyone of any size who needed 30 pounds, and that was with aluminum tanks.

I measure the buoyancy of all my neoprene in a pool and log it so I can easily make adjustments as I make thermal protection changes. I attach a mesh bag to the garment and add lead until it sinks. As I get close, I shake out any remaining air bubbles. Then I check it by removing a pound any see if it floats again. We did each piece of his suit and did not believe the results so we did it again. It was a real cheap suit and I guess they can be even more floaty than those with higher quality neoprene.

I am a little skeptical about a number of points such as why he would sink from just below the surface yet the body was found "floating" with only the fin tips touching the bottom. I would have expected the change from .8 ATM to about 1.3 ATM to have caused enough compression to become quite negative.

In any event, I no longer believe that over-weighting was a contributing factor to this accident.

---------- Post added January 2nd, 2015 at 04:44 PM ----------

If it were only made of air, then sure, it would have %20 more buoyancy. Say the voids accounted for %50 of the material, which I think would be high. If that were the case, then the max would be a %10 swing, but only at the surface. At three feet the buoyancy would be the same as at sea level.

FWIW, I've seen the same deep blue here in Florida. We are a limestone state and our springs have their origin in limestone. That doesn't change the specific gravity of our water much at all.

The rubber in neoprene has a density quite close to water, so a proportional approximation should be a pretty good estimate. They are basically little balloons.

 

[tridacna]

Nice to see that everyone is so comfortable with the boy's weighting. I'm not so sure that this was true earlier in the thread. LOL.

Names have been redacted...(This is a small selection).

· The 120 pound boy had been given weight of 30 pounds for a five mil suit and steel cylinder.

Nice to see a more objective account of what happened. I'm 250# and I don't wear 30# of lead in a 5mm.
+1 for drBill. Also #250.. and I wouldnt wear 30# with a drysuit and wintergarments...
I'm speechless.
I'm not even a DM and 30lbs + steel tank is about what I use with my drysuit + thermal fusion and is ~2lbs over weighted....in a 5mm....I'm 160 and in my 5/4 I used 16lbs with an al80...
Most people should agree the kid had too much weight
The 30 pound dilemma is a direct descendent of the stupid way IDCs and IEs are setup for most recreational agencies.
I can understand that grossly over weighting a kid is negligent and stupid
Not only overweighted, but all that weight was in fresh water.
... and a steel tank to boot!!! It simply boggles the mind.
If they were properly weighted, it would have been an easy, easy swim
At 120lbs/30lbs the boy was well over 25% weighted -not a good start....

 

[The Chairman]

yet the body was found "floating" with only the fin tips touching the bottom.

Where did this information come from? The testimony of the guy who found the body indicates that he had to remove all of the gear to get the body off of the bottom. I'll have to go find it again and reread it to be sure. I certainly don't remember this testimony from him.

The rubber in neoprene has a density quite close to water, so a proportional approximation should be a pretty good estimate. They are basically little balloons.

You missed the point. Neoprene is filled with voids and rubber. If it were a perfect balloon (no neoprene) then it would be a twenty percent increase. But there's a lot of neoprene in there giving the suit weight and structure. The less rubber, the more floaty the material and greater the compression with depth. Also, the Sheriff's report indicates it's a 5 mil, not a 7. Which is right?

 

[cerich]

I start a cave dive in freshwater with Worthington Lp 85 (at rated -7.1lbs each) pumped to ~3400 so say -10ls each, a can light giving another say 4lbs negative in a drysuit and I am always quite negative at the beginning of the dive and even with thick undergarments I am negative at the end with approx 1/3's left in the cylinders. I am 6 ft 240lbs ( need to lose the weight again)

 

[Zippsy]

I am a little skeptical about a number of points such as why he would sink from just below the surface yet the body was found "floating" with only the fin tips touching the bottom. I would have expected the change from .8 ATM to about 1.3 ATM to have caused enough compression to become quite negative.

Now there is some gosh darn healthy skepticism! Now if you were on the TV show CSI (or NCIS, which everyone knows is a much better show), would you trust the eye-witness or physics?