Triggers of Dive Accidents

[TSandM]

DBailey, I think you have hit the other half of the solution to the original problem. Teach people how to plan their gas on land, and how to adjust that plan in the water -- and teach them to check their gas supply at regular intervals. The latter is a part of diving situational awareness that can be started right at OW, and this is one of the places where I think having a wrist gauge or timer is REALLY useful -- because the diver can constantly see the elapsed time, and say to himself, "Ah, five more minutes have passed, need to check pressure." If the timer is on a console, it's easy to get distracted, either by the mechanics of diving or by the environment, and simply be unaware of the passage of time. I've been diving for five years, and diving a lot, and I'm still surprised at how short a time an hour underwater can be, especially if it's a good dive full of things to see

 

[Mr Carcharodon]

Dan,

Do the WKPP tables give an ascent profile that looks like VPM for shape and duration? That is an oblique way of asking if they shorten deco time by using deep stops to prevent bubble formation. Or is there something else going on?

A.

 

[danvolker]

Dan,

Do the WKPP tables give an ascent profile that looks like VPM for shape and duration? That is an oblique way of asking if they shorten deco time by using deep stops to prevent bubble formation. Or is there something else going on?

A.

There is a deep stop....see http://www.frogkick.nl/files/george_irvine_dir_articles.pdf page 10 for how George explained this several years ago.....GUE/WKPP have refined this a little since, and there is an "evolved" variation of this now....but George's explanation is still excellent for what you want.

Regards,
Dan


p.s.

I am discussing this bubble and deco issue because of the part of the thread Spoolin started on the "mandatory" nature of stops and the meaning of the tables.
I would not suggest recreational divers try switching to WKPP tables, or that they should attempt to shorten their stop intervals.....
What I did, what George and Bill and all the WKPP guys did, was act as Lab Rats , or maybe Test Pilots ( sounds better). We did this because we were in the beginning of an adventure sport ( tech and deep cave diving) and changes had to be made....we had a lot of resources, and a lot of talent to utilize for all phases of this....
So you have Test Pilots, and you have Pilots.....recreational divers need to be either Pilots or passengers...the Test Pilot stuff is not to be advocated...it was a necessary evil for us, in our quest to find bigger adventures. Out of all our testing, can come good ideas for recreational divers....the new way GUE is putting out Ratio Deco, could be a good thing for some people here, at least for the conceptual part of what it represents. I may ask Errol to write up an article on how Ratio Deco should have meaning to an advanced recreational diver.

Regards,
DanV

 

[Garth]

Thanks Ken for your replies. You cleared things up for me to understand what you were saying. Appreciated.

 

[danvolker]

Dan,

Do the WKPP tables give an ascent profile that looks like VPM for shape and duration? That is an oblique way of asking if they shorten deco time by using deep stops to prevent bubble formation. Or is there something else going on?

A.

I just asked Errol ( a dive buddy of mine who is a GUE instructor here in South Florida) if he would write something up on the GUE concept of this....
Here is Errol Kalayci's explanation: ... " If one accepts that every dive done is a decompression dive as some amount of on gassing will occur when you descend, then you have taken the first step towards understanding “Minimum Decompression”. Minimum Decompression may be understood that for any dive, not requiring staged decompression, you should ascend in a controlled horizontal position at the prescribed table rate (usually approximately 30fsw/minute) up to your first stop. The first stop is set at 50% of depth. Your stops are all one minute in length and occur from that point, then every 10fsw up to the surface. By example, on a dive to 100fsw, a diver following Minimum Decompression would stop at 50fsw for 1 minute, then 1 minute at 40fsw, 1 minute at 30fsw, 1 minute at 20fsw, 1 minute at 10fsw. Which if you look at the profile what you see is that the typical 3 to 5 minute “safety stops ” are really just spread across the water column.
Why are “Minimum Decompression” profiles different then the Haldane type models suggesting the “Safety Stops”? Because “Minimum Decompression” is based on newer thought such as Varying Permeability Models that consider other factors and the cost of reducing pressure gradients as quickly as possible. VPM considers the bubble growth formation possibilities of rapid reductions of pressure in Haldane type thinking and tries to mitigate it by decreasing the bubble formation throughout the decompression rather than “treating” it during the “Safety Stops”. Obviously, no one is certain what decompression model is best or how it really works for that matter. Ask yourself if you are happy with how you feel after a dive with safety stops or if you are tired. Then try Minimum Decompression as see how you feel. The results should be enough to spur you into signing up for a GUE class and learning a new, holistic and I believe better way to dive. " [end of Errrol's letter to this thread].


I am going to be helping Errol and a few other GUE instructors, to create DIR Vacation "Experiences" here in South Florida. In other words, not the full blown Fundimentals classes, but dives with these guys where you still get vacation level fun, but also get to learn alot about the GUE/DIR ideas ( including the deco concepts) and techniques, and put this into use for the dives here.....and certainly, doing these trips with Errol or one of the other guys, would be a big head start for someone who decides to do a Fundies class afterward/sometime later.

Anyone interested should let me know!
Regards,
DanV

 

[knowone]

So with my limited math ability and due to all the buzz about PSI and SPG monitoring I have calculated that
it is far safer to be surfacing with 500psi in a 63cf tank than with 250psi in a 125cf tank?

Contents are the same.

 

[knowone]

That doesn't always give you sufficient information to know when it's time to ascend.

An SPG is like a gas gauge in your car ... all it gives you is a relative indication of how full your tank is. To extend the analogy, let's say you know you're 60 miles from the nearest gas station ... to relate this back to diving, let's say that "gas station" is the surface.

You need two other pieces of information in order to know whether or not you'll make it there before you run out of gas.

- you need to know how much gas your tank holds
- you need to know how many "miles per gallon" you get

Without that information, reading your gauge really doesn't really give you enough information to tell you whether or not you're going to make it.

... Bob (Grateful Diver)

Contents and PSI are not the same.

 

[dumpsterDiver]

DBailey, I think you have hit the other half of the solution to the original problem. Teach people how to plan their gas on land, and how to adjust that plan in the water -- and teach them to check their gas supply at regular intervals. The latter is a part of diving situational awareness that can be started right at OW, and this is one of the places where I think having a wrist gauge or timer is REALLY useful -- because the diver can constantly see the elapsed time, and say to himself, "Ah, five more minutes have passed, need to check pressure." If the timer is on a console, it's easy to get distracted, either by the mechanics of diving or by the environment, and simply be unaware of the passage of time. I've been diving for five years, and diving a lot, and I'm still surprised at how short a time an hour underwater can be, especially if it's a good dive full of things to see

I think that an air integrated computer might be the fastest method to allow a diver to teach themselves about time/depth/air consumption and deco status relationships..while on the fly and underwater.

 

[dumpsterDiver]

I lump this into Gas Management. I know there are many people on this board that preach up and down about Gas Planning. There are even some great articles on this board about how to plan your gas.

But...

After reading those guide, I can't remember any of them really explaining how often your air pressure should be checked underwater. Sure, veteran divers don't need to check their air very often because they know how they breathe. Newer divers don't have a firm grasp on that yet.

Give me a tank with a random amount of air in it. I can attach my gear and enter the water without any gas planning. No matter what the volume of air is in the tank, I can guarantee you that I will make it back to the exit point safely and with some air to spare. Why? I monitor my air while underwater.

If you monitor your air underwater, there is never a reason (short of unexpected equipment failure) that you should ever be surprised by the amount of air left or ever run out of air.

Even most of the text books (from all agencies) gloss over this fact. Sure they mention "check your pressure gauge", but they never go into the frequency of checks.

This is one thing that I try to beat into the heads of my students. If you are monitoring your air, then you should never run out. It is plain and simple. There should never be a point for a new diver that they look down and see "OMG, I am at 500 PSI". Somewhere along the way they should have noted that they were at 2000, 1500, and 1000.

I do teach gas planning, but I spend more time on gas monitoring. I teach they should check their air pressure after any significant event. Gear up - check air. Hit the water - check air. Having problems clearing your ears - check air. Reached our depth - check air. Look at shark - check air. Water in the mask - check air (after clearing). Had to dump some air from the BC - check air. Checked out the seahorse - check air. In class, I want them to check their air each time the successfully complete a skill.

If the student is properly geared and streamlined, it should take mere seconds to check the air pressure. Nothing is being missed on the dive by frequent pressure checks.

Back to the question, most people don't teach any kind of air monitoring. The students are taught that a certain signal from the instructor means report your air pressure, but they are not taught to self monitor their remaining air.

I don't think this is the best way to teach awareness of air pressure for recreational divers. What I taught was that, all good divers know pretty much EXACTLY how much air they have at all times. BEFORE looking at the guage, they need to mentally estimate the pressure, THEN check to CONFIRM their guess is correct. If their guess is off more than 200 psi, then they are NOT checking it often enough. Narced, deeper, distracted, breathing too hard.. etc. the reason doesn't matter, but they need to be able to self correct their lapse of situational awareness. This kind of ability may save more lives than being able to maintain perfect horizonatal trim.

Inexperienced divers need to check their pressure all the time, and experienced divers need to do it less often. On the first night of the scuba class, i would ask everyone how much gas was in the tank of their car. Most everyone knows within 1/8 to 1/4 tank how much gas they have in their car, even if they don't conciously realize it. This little demonstration for the drivers helps to give them the appropriate miindset of always knowing how much air they have in their tanks. Plus it will give you some insight into the occasional REALLY dull student who is clueless about such things early on.

 

[DBailey]

Contents are the same.

Assuming you have an accurate way to measure the 250 psi in the larger tank. As mentioned above, the potentail inaccuracy of pressure gauges at the extreme ends is an issue.

On paper they are (close) to the same, but in reality, your mileage may vary.