No deco time proximity.

[Bob DBF]

The PADI RDP was designed to make recreational diving possible. Before the PADI RDP, there was pretty much only the US Navy tables. Try to imagine what recreational diving looked like back then.

Getting a bit carried away implying recreational diving was not possible prior to the PADI RDP. I'm pretty sure diving was popular before it was released.

Before the RDP, Navy tables were used, however they were not the same as the Navy tables used now. The biggest difference on the tables was the limitation on multiple deep dives without incurring deco. I didn't have an issue with that for quite a while and the solution was was learning deco from a different set of Navy tables in the manual.

The Navy tables are the standard other algorithms are compared with because the NEDU bias been researching and revising them for over a hundred years. The only issue is that their tables are for working divers trying to maximize their first dive time, if it takes longer for a Navy diver to finish a job, you just send down the next duty diver. Not optimal for recreational divers but it worked well for a lot of recreational divers for a long time.



Bob

 

[boulderjohn]

#45

You mean this???

This has been tested. Safety stops reduce bubbling after the dive. So the divers doing the SS will have less stress. It isn’t bubble people who argue that, it is people with ultrasound machines. The integral supersaturation argument also says you are better surfacing later.

Some of the testing had slightly deeper stops, but only maybe 12m.

The bloke describing a slow ascent has something he thinks works, whether it does or not who knows, but at that depth it is unlikely to matter much.

Our question was not about doing safety stops--I support doing safety stops. The question was whether you are better off spending extra time after the standard safety stop gets you to the point of being safe to ascend in the water or going to the surface. You should notice I was pretty clear about that.

Ken also seems to be referring to the 2004 Marroni study on ascent speeds and safety stops, particularly deep stops. The results of that study have not been replicated, and other work since then has had contrary results.

 

[boulderjohn]

Getting a bit carried away implying recreational diving was not possible prior to the PADI RDP. I'm pretty sure diving was popular before it was released.

I worded my point badly. I meant that it made recreational diving as we know it today possible. Scuba was popular, but the long surface intervals were a challenge.

 

[scubadada]

IIRC the Navy tables' slowest compartment has a much longer half-time than the PADI RDP, so while they're more liberal for your first dive, they're more conservative for the following dives on the same day...

The USN tables were not designed for repetitive dives and the dives frequently included decompression. The PADI RDP was designed for repetitive, no stop dives. The USN used the 120 min compartment for the limiting half life for repetitive dives and calculation of SI credit. The PADI RDP uses the 60 min compartment for these calculations and this is the major factor determining the longer NDLs for repetitive dives.

Clearly, other modern decompression algorithms use a similar strategy and repetitive dive NDLs are similar. This is clearly shown with the Suunto NDLs supplied by @Storker, nearly identical to the PADI RDP

 

[Storker]

The USN tables were not designed for repetitive dives

Quite. While the PADI RDP was developed to allow for repetitive dives in a safe manner. IIRC @boulderjohn has posted tidbits from the history of the development of the PADI RDP several times here on SB. I encourage diving history buffs to search for those posts.

 

[scubadada]

Quite. While the PADI RDP was developed to allow for repetitive dives in a safe manner. IIRC @boulderjohn has posted tidbits from the history of the development of the PADI RDP several times here on SB. I encourage diving history buffs to search for those posts.

The DSAT Recreational Dive Planner. Development and validation of no-stop decompression procedures for recreational diving. Hamilton, et al., 1994.
Development and validation of no-stop decompression procedures for recreational diving: the DSAT recreational dive planner.
Link to the full article PDF at the bottom of the page.

 

[dmaziuk]

You mean this???


Our question was not about doing safety stops--I support doing safety stops. The question was whether you are better off spending extra time after the standard safety stop gets you to the point of being safe to ascend in the water or going to the surface. You should notice I was pretty clear about that.

How long? Is the diver surfacing after a 3-minute SS under less deco stress than the diver surfacing after 5-minute SS? There's voices advocating stretching the safety stop for as long as you can, are they trying to give themselves more decompression stress than their buddies who get out the moment their watches hit "3:00"?

 

[boulderjohn]

How long? Is the diver surfacing after a 3-minute SS under less deco stress than the diver surfacing after 5-minute SS? There's voices advocating stretching the safety stop for as long as you can, are they trying to give themselves more decompression stress than their buddies who get out the moment their watches hit "3:00"?

Let's look once again at what I said and what others have said.

Let's say that two divers on an NDL dive have the same careful ascent followed by a solid safety stop and have reached the point that they are safe to go to the surface. Diver A goes to the surface, and Diver B stays in the water for an extra 5 minutes.

When Diver B gets out of the water, yes, he will have less nitrogen in his body when he exits the water than Diver A had when he exited the water. But it's 5 minutes later now, and Diver A has been off-gassing faster while on the surface. So, at that point in time, Diver A has less nitrogen in his system than Diver B does. If they do a second dive together, Diver A will have less residual nitrogen at the start of the dive than Diver B.

Think of it like a series of decompression stops, which is essentially the same thing. Let's say you did a decompression dive, and your computer algorithm tells you to do a 3 minute decompression stop at 20 feet and a 6 minute decompression stop at 10 feet. What would be the benefit of spending an extra 5 minutes at the 20 foot stop? If you did that, your computer would add time to your 10 foot stop to make up for that extra time you spent deeper, and it would not add that extra time because you benefited from it.

 

[KenGordon]

You mean this???


Our question was not about doing safety stops--I support doing safety stops. The question was whether you are better off spending extra time after the standard safety stop gets you to the point of being safe to ascend in the water or going to the surface. You should notice I was pretty clear about that.

Ken also seems to be referring to the 2004 Marroni study on ascent speeds and safety stops, particularly deep stops. The results of that study have not been replicated, and other work since then has had contrary results.

https://www.researchgate.net/profil...dial-bubbles-after-dives-to-25-msw-82-fsw.pdf

From a 2007 paper by that author. I don't know if it is the same one. Even if you choose to ignore the 15m stops then the longer 6m stops improve bubble scores. You say it has not been replicated, but has anyone done anything similar and found bubble scores get worse with longer safety stops? Obviously bubble scores are not DCS so you might dismiss it on those grounds. These profiles are like the ones this thread is about though, so unless there is something properly wrong with the study it is probably worth keeping in mind. Looking at the later tables about saturation levels in various compartments you can see the 15m stops they are suggesting would result in a higher integral supersaturation.

 

[TrimixToo]

All computers offer an accurate gauge of your NDL time.
<snip>
May the experts correct me,
Cheers, Kevin

I'm not an expert, and I didn't stay at a Holiday Inn Express in the recent past, but I think many people confuse precision with accuracy. Computers offer a precise view of your NDL time, but for various reasons (many of which @doctormike listed) none of them can be considered accurate. Our collective hope when we all rely on them is that they are "accurate enough," and that's an important distinction in my mind.