dive computers and reverse profiles

[PBcatfish]

SSI has some things out of date, such as quarter turn back for valves, in their open water materials. There is a video in their dry suit course which shows a diver in doubles and a snorkel.

I don't know the process of an agency in when/how they update all their training materials.

Please pardon my ignorance, but what is the problem with the 1/4 turn?

 

[tursiops]

Please pardon my ignorance, but what is the problem with the 1/4 turn?

1) it is unnecessary with modern valves
2) people get confused, and can turn the valve off, then back on 1/4 turn. There will still appear to be a gas flow, but it will be restricted and can be insufficient at depth.
3) people get over-exuberant and turn the valve on, and turn it back WAY more than just a 1/4, which can also leave the valve in a a compromised, not-fully open position.

 

[Subcooled]

Maybe you shouldn't be diving, then.

Always a safe option, but not that fun

A) Ratio deco

I do not oppose ratio deco as a method. Everyone chooses what style of diving they do. Even if there might be some decompression algorithm out there that is slightly more conservative, there may be other factors in your style of diving and life that outweigh this small difference. As I am not using ratio deco, I have the option to choose some other deco procedure, having agreed on it with my team.

B) Reverse diving profiles

Reverse profiles do not seem to be that bad, according to DAN, and I do reverse dive profiles myself when I need to... but little bit of extra deco is always relaxing and can't hurt (on any dive), water termperature permitting. Asymptomatic damage is damage is my personal belief, but everyone has their own beliefs and chosen levels of conservatism.

With regard to reverse diving profiles one could even ask which one of these is better:
- an inexperienced diver (bad buoyancy control especially in the shallows) doing a deep dive first and then, with some residual nitrogen (closer to NDL), a shallower yoyo-profile
- or the other way around

I do not know the answer.

Anyway... back to the topic. Reverse diving profiles seem to be OK.

 

[Subcooled]

Please pardon my ignorance, but what is the problem with the 1/4 turn?

An old scuba instructor and diving history expert told me that the quarter turn was used because in the old days valves got stuck open because of their construction. The quarter turn helped to mitigate that. I do not know the details. This is just what I was told.

The following scenario:
1) You open the the cylinder valve
2) You close it a quarter of a turn
3) Someone else checks your cylinder; decides to open it; uses #1 and #2 but turns the valve in the wrong direction
- or maybe you do it yourself accidentally while having other things to worry about; it happens.
4) Now your cylinder (or both!) is a quarter of a turn from closed but you do not notice it on the surface
5) At depth breathing gas flow is restricted.
6) Accident

People have died because of this.

There was a fatal diving accident on 10th of August 2019 in Finland at the lake Iso-Melkutin. The cylinder valve was nearly closed. I have no detailed information but this. Hence, I cannot confirm whether it was exactly quarter turn related or not, but it confirms the steps 4 > 5 > 6

Related discussion on Scubaboard: Lake Iso Melkutin fatality - Finland

 

[BlueTrin]

An old scuba instructor and diving history expert told me that the quarter turn was used because in the old days valves got stuck open because of their construction. The quarter turn helped to mitigate that. I do not know the details. This is just what I was told.

The following scenario:
1) You open the the cylinder valve
2) You close it a quarter of a turn
3) Someone incompetent messes with your cylinders; decides to open them; uses #1 and #2 but turns the valves in the wrong direction
- or maybe you do it yourself accidentally while having other things to worry about; it happens.
4) Now your cylinders are a quarter of a turn from closed but you do not notice it on the surface
5) At depth gas flow is restricted and you experience an OOA-incident.

People have died because of this.

This scenario happened to me last year when I was on a single cylinder on holiday. It became harder to breathe at 15m. I managed to get the DiveMaster attention and he fully opened the valve for me.

Someone admitted to touching my valves after the dive while I was getting something in the van. Also I remember that the SPG needle didn't flinch during the buddy check (or at least that's how I remember it)

Since then, I always do a valve check when the cylinder is on my back or right before to put it on my back. I will get also very annoyed at anyone who touches my valves as well.

 

[tbone1004]

Please pardon my ignorance, but what is the problem with the 1/4 turn?

The Quarter Turn That Kills - Cave Diver Harry

 

[Steve_C]

statistics showing that most DCS incidents happen on the first day of a trip, and on the first dive of the day, and not on the last dive of the last day as you'd expect if DSC stress "accumulated" like Wienke says.

It is also possible that the increased DCS incidence was due to equipment maintenance or skills. Looking over the times I have had a buddy have an issue - regulator, pull dump failure, etc. they have usually not been diving for a while and/or were diving equipment that had not been serviced for a while. These were casual but experienced divers so they handled it. But I can see where an out of practice diver with equipment issues is much more prone to a rapid ascent and DCS.

Your statistics are only relevant if you separate out the incidents due to a problem from those that occur during normal diving.

 

[dmaziuk]

Your statistics are only relevant if you separate out the incidents due to a problem from those that occur during normal diving.

This may be Dr. Doolette's or Dr. Pollock's statistics, I forget whose, but thank you for re-stating my point: there's mounting amount of evidence against bubble theories, but a lot of it can be argued six ways from Sunday.

 

[Subcooled]

there's mounting amount of evidence against bubble theories

Against RGBM and VPM with default settings, you mean?

Bubble theories have a ton on paramaters. Maybe those need adjusting?

Bubbles, unfortunately, are what kills us.

 

[BlueTrin]

Against RGBM and VPM with default settings, you mean?

Bubble theories have a ton on paramaters. Maybe those need adjusting?

Bubbles, unfortunately, are what kills us.

I think bubble theory is not only about bubbles it is about preventing to have too many asymptomatic or silent bubbles by having deeper stops rather than trying to use supersaturation more efficiently.

My understanding is that the current trend is to not do deep stops.

Please correct me if I made a mistake.