Why do people add a few minutes to their last deco stop?

[tursiops]

No one has called decompression modeling pseudoscience - that term which seems to be taking things off the rails was introduced as a rebuke.

Not so. The message to which I originally objected was this one:

Deco plans are "best pseudo-scientific guesses for you" even on perfect days.

 

[scubadada]

Why is this question so difficult. You add time to your last deco stop to lower your surfacing GF to lower than your GF high. Less nitrogen exposure is a lower risk of DCS.

 

[lermontov]

Why is this question so difficult. You add time to your last deco stop to lower your surfacing GF to lower than your GF high. Less nitrogen exposure is a lower risk of DCS.

I think we understand the mechanics behind it -the OP asked why not just set the GF to a different setting ( in the first place) to which @rjack321 gave a good answer

Sometimes people might have one plan but end up working harder, being colder from sweat or a minor drysuit leak, feeling ache-y on the lower stops, or feeling "dry" on the actual dive. (Looking at the DT guys here) and those are all good reasons to adapt on the fly and add more time. Or maybe just cool fish keep swimming by.

I realized that one of the reasons for that is that after more than 100 years, the science is considered pretty much settled.

is it? it's not that long ago people were ( and still are ) advocating deep stops and ratio deco - arguaments are still ongoing in that regard as to what is effective and what is not

We have reached the point that people who dive within accepted guidelines are pretty darn safe, with only a very tiny percentage getting DCS.

or we have enough data to give us some reasonable parameters

 

[boulderjohn]

is it? it's not that long ago people were ( and still are ) advocating deep stops and ratio deco - arguaments are still ongoing in that regard as to what is effective and what is not

If you check my context, you will see that I was specifically referring to decompression on NDL dives. Yes, there is still a lot of work to do on decompression dives.

One of the confusing things about all of this is that there's a lot of misinformation out there. Start a thread on ScubaBoard asking about current thinking on deep stops, and you will quickly learn that the trend is going against them on decompression dives, and there is no well-regarded evidence in favor of them on NDL dives. If instead you do a Google search on the World Wide Web, the first 100 sites you run into will have you convinced that doing deep stops, both on decompression dives and NDL dives, is the latest and greatest idea in scuba.

 

[tursiops]

is it? it's not that long ago people were ( and still are ) advocating deep stops and ratio deco - arguaments are still ongoing in that regard as to what is effective and what is not

There are still flat-earthers, too, but that does not change the shape of the planet. Some things are best ignored.

 

[dmaziuk]

is it? it's not that long ago people were ( and still are ) advocating deep stops and ratio deco

There's nothing wrong with ratio deco, provided that for some reason you want to only dive specific gas mixes to specific depths instead of just buying a ~$300 watch.

 

[Moerae]

I feel like a lot of people have missed the point of OP's question.

"What are some reasons to pad deco sometimes" is not the question that OP is asking. They aren't asking about waiting for a friend, or being cold, or having worked hard. They aren't asking people what the point of more conservatism is or why someone would want to be extra careful.

They are asking why people consistently pad deco instead of just lowing their GF High, which is effectively the same thing.

Even answers like "you can monitor your surf gf" still miss the point. You can do that either way so that's still not an explanation for why you would set your computer to be less conservative than your actual plan. And unless you have a computer that locks you out you can also monitor your surf gf to decide to leave at a less conservative number if there was a problem. "The algorithms are just guesswork" also misses the point because if you set yours to 50/80 and always add a couple minutes your fundamentally still following the algorithm and if you set it to 50/70 you'd be doing almost the exact same stops.


The only decompression related answer would be "lowering your GF high might also add a minute or two to your 30ft stop and they only want to pad their last stop".

I pose the answer to OPs question is most likely behavioral and not related to decompression: "It's pointless but makes people feel better to set gf high higher and then pad it rather than just lower it to match their plan", or "People want to set their GFs the same as their buddies or what's commonly accepted but would rather actually dive a lower GF High", or "People think they are comfortable with less conservatism but then when faced with actually surfacing, decide they want to be more conservative".

In addition to actually answering OPs question, I think that's an interesting discussion and I'd be curious what other's thoughts are on that behavior.

 

[SlugLife]

(edit, I misread, disregard this post)

 

[dmaziuk]

I won't post the question because it'll get modded away, but the answer is: "because it can".

 

[grantmac]

Running a higher GF high will let the watch show you an absolute TTS which is helpful for contingency planning.
Do you surface at a GF higher than preferred but still safe if you're starting to go hypothermic etc.