deco myths

[txdamselfish]

enjoying this presentation by Mark Powell as a rec diver and wanted to share.

 

[L13]

Uh-Oh! Mark Powell is in the all dives are decompression dives camp.

 

[tursiops]

Uh-Oh! Mark Powell is in the all dives are decompression dives camp.

Nobody is perfect.

 

[BlueTrin]

Uh-Oh! Mark Powell is in the all dives are decompression dives camp.

It's not wrong, it is just misleading.
NDL dive allow direcct access to the suface.
Deco dives do not.
That is the difference.
Yes, you have ongassed on an NDL dive BUT not enough to harm you if you should surface.
The distinction is useful.

But that’s not what Mark Powell is disagreeing with, I think.

If I remember correctly he is mostly disagreeing with the word no-deco dive and is saying that they should be called “no stop” dives, as no mandatory stop dives.

Obviously that could confuse new divers with the only stop they know being a safety stop.

(I didn’t watch this video, I remember reading the original blog entry)

 

[L13]

It's not wrong, it is just misleading.

It's not misleading, but it is often misunderstood.

In my mind the solution to that is education, not denial. Powell's discussion of the actual fuzzy nature of the region between the two classes of dives is part of that education and should be understood by everyone.

 

[scubadada]

This has been discussed a million times. You can directly surface from a no stop dive assuming an acceptable ascent rate. You must stop to satisfy at least one decompression stop on a decompression dive. This is the commonly accepted definition. No stop or decompression dive.

 

[L13]

This has been discussed a million times. You can directly surface from a no stop dive assuming an acceptable ascent rate. You must stop to satisfy at least one decompression stop on a decompression dive. This is the commonly accepted definition. No stop or decompression dive.

Which leads to the misunderstandings that Mark Powell was trying to clear up in his presentation and why he talked about the red/green continuum in his presentation slides.

At NDL, the only difference between the second before and the second after is the procedure you apply, to surfacing. There is no significant physiological change between those seconds. If a second after exceeding NDL, you change your GF's from 75 to 85, you don't magically change the dive, you don't undo any physiological characteristics, but you went from needing a stop dive to no-stop with a recommended safety stop. The dive has not changed, but your surfacing procedure (and your risk) has.

Denying this leads people to misunderstand the physiology of diving.

The reason people occasionally get bent on No-Stop dives is exactly because they are still dives with decompression where the decompression was done too fast for the actual physiology of those dives.

Which is why I am confused by @LI-er . His endorsing your comment, and his miss-representing the video, directly contradict his mis-guided attack on @tursiops 's perfectly clear post. He harps on the danger of NDL dives, but dismisses the fact that those dangers are directly the result of instances of inadequate decompression.

 

[scubadada]

Which leads to the misunderstandings that Mark Powell was trying to clear up in his presentation and why he talked about the red/green continuum in his presentation slides.

At NDL, the only difference between the second before and the second after is the procedure you apply, to surfacing. There is no significant physiological change between those seconds. If a second after exceeding NDL, you change your GF's from 75 to 85, you don't magically change the dive, you don't undo any physiological characteristics, but you went from needing a stop dive to no-stop with a recommended safety stop. The dive has not changed, but your surfacing procedure (and your risk) has.

Denying this leads people to misunderstand the physiology of diving.

The reason people occasionally get bent on No-Stop dives is exactly because they are still dives with decompression where the decompression was done too fast for the actual physiology of those dives.

Which is why I am confused by @LI-er . His endorsing your comment, and his miss-representing the video, directly contradict his mis-guided attack on @tursiops 's perfectly clear post. He harps on the danger of NDL dives, but dismisses the fact that those dangers are directly the result of instances of inadequate decompression.

The longer your exposure the greater your risk. An individual's tolerance is exactly that. A probabalistic deco algorithm might give you some perspective.

SAUL Recreational Dive Planner | Modern Decompression

 

[inquis]

Uh-Oh! Mark Powell is in the all dives are decompression dives camp.

He also uses the phrase "deco dive" to mean one with a mandatory decompression stop, in contrast to a "no-stop" dive. (See for example, Myth #2.) In other words, he uses it both ways. It's clear from context when he uses "decompression" as a synonym for off-gasing.

 

[EFX]

He also uses the phrase "deco dive" to mean one with a mandatory decompression stop, in contrast to a "no-stop" dive. (See for example, Myth #2.) In other words, he uses it both ways. It's clear from context when he uses "decompression" as a synonym for off-gasing.

And that's the problem. Some people don't pick up context. I've said this before in another thread that the term NDL is the problem because it is misleading. It implies, if you take the term literally, that you will not decompress if you stay within the limit. I offered the term NSL "No Stop Limit". Although more accurate the term isn't complete. It should be NMSL for "No Mandatory Stop Limit". This eliminates the confusion over safety stops which are not mandatory stops.

For recreational divers the problem with deco stops besides trying to hold a fixed depth in the water is the additional gas planning involved. You have to make sure you have enough gas to complete the mandatory deco stops. Recreational divers generally do not get this training.