Dives and dive time

[DevonDiver]

+1

Wreck dives are typically the most square-profile dives you can do...

 

[boulderjohn]

Marc, I think the reason we are having trouble seeing eye to eye on this is because I am having trouble understanding your point. I'm surprised, because you usually come across crystal clear to me.

Why 30fpm if we no longer care about the table instructions?

The PADI tables were researched when 60 FPM was the norm, and all numbers are based on that. It is also the recommended rate for the CESA, although I was told in my IE that it is likely and acceptable that a diver doing a CESA will go faster than this. The standard for the skill in both CW and OW classes is distance, not time.

I agree with John and Andy about the efficacy of stops. What I don't like is the mixed bag. Follow these instructions and you'll never get into a situation where you can't CESA. Oh and BTW if you have to CESA, you may be unable to follow the full instruction set.

You can always do a CESA if you follow the instructions not to get into an overhead environment. The RDP table instructions are not related to it.

I was taught that a basic purpose of PADI's dive system is to guarantee that, barring medical issues or entanglements, a diver can always safely CESA. This is accomplished by *drummroll* The Table *horns blowing and angels floating*.

The CESA has nothing whatsoever to do with the tables. It was not invented by PADI. It was a standard process before the tables were created. It has been used by people escaping submarines at great depths. There is no guarantee that doing a CESA will not get you into DCS problems. The primary purpose of the skill is to avoid a lung overexpansion injury by making sure you exhale throughout the ascent. It is an emergency process to get an OOA diver to the surface under any circumstances (other than obvious problems like entrapments or overheads.)

 

[Blackwood]

John -

In my class, I distinctly remember being struck by what was contradictory information, namely that the table is used to guarantee that CESA is always an option without inviting elevated risk of DCS.

I'm willing to suggest that my class was perhaps not representative, or that I remember it wrong.

I also recognize that the instructions I'm at odds with ("A safety stop for 3 minutes at 15ft is required any time the diver comes up to or within 3 pressure groups of a no decompression limit and for any dive to a depth of 100ft or deeper") are independent of the actual time/depth matrix displayed.

 

[boulderjohn]

In my class, I distinctly remember being struck by what was contradictory information, namely that the table is used to guarantee that CESA is always an option without inviting elevated risk of DCS.

I'm willing to suggest that my class was perhaps not representative, or that I remember it wrong.

Or maybe something in between.

In theory, if one is diving within the PADI NDL's and has to do a CESA, there should be little risk of DCS. But the tables were not planned for that purpose. They tested many, many divers on many, many dives, none of whom were doing CESAs, to find safe and effective limits to ending a dive safely with a direct controlled ascent to the surface. This does describe a person doing a CESA, but it is more of a happy coincidence than a goal.

The confusion, IMO, comes from the language--and it really is confusing--about requiring a safety stop. To me, that is like calling it a required option--an oxymoron if there ever was one. To me this means a safety stop at those depths and times is a more important measure of safety than at other depths and times, but a direct ascent to the surface at a safe ascent rate is still most likely to yield no harmful effects.

That is how I have always understood it, and it is what I tell my students.

Of course, we can always go over to the Ask Dr. Decompression forum and ask Michael Powell, who helped develop the program, for an authoritative explanation.

 

[BrotherBear]

He did say we would get hit by the boat.

In my opinion, the divers on the surface are more likely to be hit than someone 15 feet underwater, laying on the bottom. I guess if he hit us he would be running the boat up on the sand and dead coral. we were laying on.

Haven't posted on SB in a while, been lurking plenty but for now I'm back...

I'm amazed no one else seems to have picked up on this (emphasis mine). I vote with those who say the the safety "stop" was done while swimming back to the boat, they were sitting on the bottom in 15 feet of water?. If I had to guess (as everyone else is doing anyway) mine would be that the OP misunderstood the DMs frustration and anger...I would bet he was trying to tell him you don't have to actually stop swimming to do a safety "stop", none was needed because they finished so shallow anyway.

I can't comment on the rest of it as I wasn't there but I've dived just about every site in Aruba, which one was this? There are only a couple with the moorings that shallow and I don't think any are walls so a shallow swim of at least three minutes at the end of the dive is almost certain.

I've also dived with Mermaids once, they are a bit rough around the edges...not what I would describe as familly friendly, but I found them pretty safety minded overall. Go back and reread the article about the accident where a diver was hit, she corked due to bouyancy issues...could have easily been directly in front of the boat where she couldn't have been seen. Has anyone found any result of the investigation? The time I dived with them was 3 months later and all seemed to be fine.

 

[DandyDon]

Whether or not the rental computer was zeroed out, it's the instrument calling the limits, and if it was beeping, then went to ERR, sounds like a Deco dive. That applies to the buddy pair, not just one diver.

I wonder if computer should ever be rented to vacation divers? If you don't know what it's telling you, it's worthless.

A lot will depend on the brands, whether snturner's computer went into Deco too, but getting more information on this thread seems difficult.

 

[DevonDiver]

Whether or not the rental computer was zeroed out, it's the instrument calling the limits, and if it was beeping, then went to ERR, sounds like a Deco dive.

Without further information, it's hard to say. I've only ever seen computers go into ERR mode for 3 reasons:

1) Missed Deco
2) Unresolved Ascent Rate Violation (fast ascent + missed mandatory safety stop)
3) Battery Failure

I wonder if computer should ever be rented to vacation divers? If you don't know what it's telling you, it's worthless.

I agree 100%. Rental computers should come with a comprehensive briefing and/or instructions. I've never seen that happen... at least not to a level where deco mode etc were explained.

 

[MauiScubaSteve]

Every group of divers from the boats I have worked on is briefed on procedures for the end of the dive. If there are divers using our rental computers the guide explains basic computer information.

On the Gekko/Zoop that would be; top two numbers are max depth and current depth (bigger number is max depth), bottom two numbers are temp and running dive time, (not really important on our set profile guided dives), and the big number in the middle is the NDL at whatever depth you are at, until you get above 20 feet deep, when it turns into the safety stop countdown. We tell every diver in every group to not let the NDL time on their computer get below 5 minutes, explaining that all you have to do is dive 10 feet shallower and your NDL time will get longer.

We are not conducting deco dives so why brief people on deco?

The instructions for the dive are to not dive deeper than the guide and not spend too much of the dive at the max depth. If the divers follow the plan, there will be no deco. If the guide is at 20 feet deep or less for the last 5 minutes of the dive and the guest follows the plan, the SS is complete.

 

[DevonDiver]

We are not conducting deco dives so why brief people on deco?

For the same reasons that deco mode is on the computer in the first place... or why students are taught emergency deco procedures for recreational tables.

Contingency..

 

[MauiScubaSteve]

The use of Suunto's is our contingency