Deco + safety stops?

[grassybreakfast]

Maybe I’ve misunderstood something in the original post but before trying to optimize GFs, I think it's important to sort out a fundamental distinction.

We conduct a safety stop on a recreational dive.

We conduct one or more decompression stops on a known or anticipated decompression dive regardless of maximum depth and duration of time obligation at the required stop. If we incur a decompression obligation, then we have a decompression obligation.

I don’t intend to be contentious or adversarial but this notion of “light deco” that pops up on ScubaBoard always comes from those who aren’t, frankly speaking, practicing technical divers. I think being a “dabbler” is a slippery slope towards cutting corners in planning and execution. That doesn’t mean those who like that phrase need to go knock out some long Trimix dives in order to hang out with upper classmen and be cool…not at all. It just means using a distracting term is unhelpful for anybody - themselves, seasoned technical divers and those wanting to learn and train beyond the recreational rubric.

Like others have said, listen to your body and add on some more time at your final stops (likely 6m and 3m at your current stage of experience) if necessary.

Learning to crawl to the surface is a matter of proper weighting and proficiency in buoyancy control. We get that sorted with time underwater and with specific configurations. If I can do it, you can, too.

Since you intend to dive with increased volume that allows you to really start exploring, I applaud your intention to take additional BSAC training.

Thanks.

Yes, I am aware of the distinction between safety stops and deco stops. Safety stops are stops that are not necessary according to the deco model, and deco stops are ones that are. Or maybe it's more helpful to think of safety stops as non-mandatory deco stops, since the goal is still to deco, it's just that the model doesn't think it's necessary.

The question pertains to the seemingly inconsistent application of the safety stop (stop beyond what the model requires) on NDL dives, but not on deco dives, after the mandatory deco stops have been cleared. In fact, if anything, as alluded to by steinbil's reply above (#5), on a longer and deeper deco dive, if you only just clear the deco stops according to ZHL-16, you are actually at a higher risk of DCS compared to a recreational dive just inside of NDL.

If anything, extra conservatism on top of the model (at least with ZHL-16) is warranted more for deco dives than for NDL dives, even though people do safety stops on NDL dives, but not on deco dives, which seems like a curious contradiction.

I put "light deco" in quotes exactly because I know the use of the term is controversial. In my mind, deco is deco. "Light" is just an adjective like "shallow" or "short". A 5 minutes deco on back gas is obviously not the same as a 2 hours accelerated deco with multiple mixes, and they also have different training requirements. If "light deco" is such a loaded term, maybe "short" deco is more descriptive?

In terms of what I am happy to do, there is really no slippery slope here. At my certification level I'm trained and allowed to do back gas deco, and that's all I'm (going to start) doing. It may just be a bit confusing because I understand that many agencies don't introduce any deco before "tech" levels.

 

[J-Vo]

@grassybreakfast
For me, my GF settings are already way more conservative than standard for recreational PDCs, so if my PDC says no deco than a safety stop is likely not warranted.

Also, technical divers are expected to be way more controlled and typically don't need to target safety stop depth to prevent themselves from popping to the surface uncontrolled.

Also, Also, DCS risk is roughly proportional to how long a tissue stays super saturated, so GF99 of 90% on a 15 minute tissue is less risky than the same on a 60 minute tissue. Technical dives load the slower tissues more, so surfacing with the same GF as a recreational dive actually has more risk.

 

[dmaziuk]

The question pertains to the seemingly inconsistent application of the safety stop (stop beyond what the model requires) on NDL dives, but not on deco dives, after the mandatory deco stops have been cleared.

They are optional in both cases. No-stop divers are trained to do the optional stop, technical divers are trained to follow their planned deco schedule. Everybody dives within their training -- very consistently.

 

[Wibble]

For me, every dive is a deco dive and planned accordingly. I have my personal Gradient Factors (50:75) and use those for all dives. I always make a slow ascent from the last stop and am not in any hurry to reach the decompression ceiling on the initial deeper stops. I frequently extend the decompression based on feeling, there should be no rush to get back on the boat — a sign of poor planning or not sticking to the plan.

I so rarely do dives without decompression that safety stops just aren’t an issue. However, as above, there’s never a rush to the surface, so maybe that is the definition of a safety stop.

Recently did some warm water diving that was very much the epitome of NDL resort diving. The safety stop with the group was interesting as I seemed to be the only horizontal diver and the slowest to ascend from 6m/20ft as per above. They were all very serious about doing precisely three minutes then rushing back to the boat.

 

[steinbil]

If anything, extra conservatism on top of the model (at least with ZHL-16) is warranted more for deco dives than for NDL dives, even though people do safety stops on NDL dives, but not on deco dives, which seems like a curious contradiction.

However, if you consider that (a) technical divers will often slowly crawl to the surface after last stop and/or add some time/hang out at last stop depending on circumstances and that (b) many experienced divers will dive with preferred GF settings and not do any safety stops on NDL dives, there really is no contradiction. Safety stops are most common among less experienced divers or those diving on guided dives following a DM.

I put "light deco" in quotes exactly because I know the use of the term is controversial. In my mind, deco is deco. "Light" is just an adjective like "shallow" or "short". A 5 minutes deco on back gas is obviously not the same as a 2 hours accelerated deco with multiple mixes, and they also have different training requirements. If "light deco" is such a loaded term, maybe "short" deco is more descriptive?

In terms of what I am happy to do, there is really no slippery slope here. At my certification level I'm trained and allowed to do back gas deco, and that's all I'm (going to start) doing.

Some may disagree, but for me, the slippery slope starts when doing deco without deco gases. A proper technical deco dive requires more planning and more gear. However, with "back gas deco" it's very easy to start incurring a few minutes of deco here and there without necessarily planning a deco dive. Doing NDL dives and pushing into mandatory stops is not the same as planning a deco dive properly, and it's very easy to stretch the limits too far because of normalization of deviance. You might not do this, but I know many divers that are in this category.

 

[Blackcrusader]

I wrote before that I use SurfGF as a guide for safety stops. Here is more on that process.

I made the mistake of mentioning this on ScubaBoard, and someone made a big deal about it, calling for me to be banned for advocating people doing decompression dives without training or equipment. To get to the end of the story, I change my GFs for NDL dives so that no one gets excited about me going into deco on an NDL dive. You never know when some dimwit is going to have a hissy fit about it.

Don't worry, I have had people diving with the DC's ( mostly SUUNTO ) sometimes Peregrine which they have never look at settings point at me on dive then after the dive telling the guide I must have gone into deco. Then I ask them what are your GF settings? What's that they ask?

My reply you don't even know your own DC's setting then tell people I went into deco? lol
I did on my second last dive last vacation get to 0 NDL. Saw a nice frog fish decided to get a photo in. Rather naught but my guide was at less than 10m depth above me as he ran out of NDL a long time before me on his Suunto lol
Closest to a square profile I get to from a multilevel dive.

SURF GF

1% lol

 

[Blackcrusader]

They were all very serious about doing precisely three minutes then rushing back to the boat.

On my last trip my guide said to me that I am the slowest person to the surface he has seen in a long time.
He will give the thumbs up and head to to surface and I take more than a minute from 5m depth.
I just tell all the other divers I am older and slower lol.

 

[grassybreakfast]

Thanks for your replies everyone. I think the original question has been answered. Here's my summary of (what I believe to be) the good answers (some of the points have been made by more than one person, so apologies for lack of attribution):

* People use lower GF high on deco dives than equivalent on NDL dives.
* Part of the reason for the safety stop is to compensate for mistakes like ascending too quickly, that deco divers (or really, more experienced divers) are less prone to.

Some may disagree, but for me, the slippery slope starts when doing deco without deco gases. A proper technical deco dive requires more planning and more gear. However, with "back gas deco" it's very easy to start incurring a few minutes of deco here and there without necessarily planning a deco dive. Doing NDL dives and pushing into mandatory stops is not the same as planning a deco dive properly, and it's very easy to stretch the limits too far because of normalization of deviance. You might not do this, but I know many divers that are in this category.

Are these people trained for back gas deco? I feel like maybe introducing deco earlier in training would help with this kind of situation. Many people would like to be able to spend say 10 minutes at a 35m wreck but don't want to go any further. Do they really need several tech courses and spend thousands of $/£/€ to be able to do that? It's really not that difficult to plan for short back gas deco. Guesstimate emergency SAC rate, decide on a max TTS (say 10 min), calculate min gas, and have a plan for loss of gas. Then NDL+10min is the new limit. 10 min not enough? Just plan for a longer limit instead (assuming sufficient gas).

The only bit that requires significant training is redundant gas, if required. That would depend on individual risk profile. Our club's policy is max 1 min deco without redundant gas.

 

[NothingClever]

I think what you laid out above takes “light deco dabbler” to a new level.

While I recognize value in your confidence, I don’t think it has the right underpinning. You’re rationalizing matters rather than deviating from a position of competency with technical knowledge and skills.

I encourage you to get more training.

 

[Wibble]

I encourage you to get more training.

And practice. Lots of practice.

Even in a shallow 10m/33ft lake (near Heathrow ) you can practice decompression ascents. Just do stops every metre/3ft. Platforms have their uses too as you can do some skills & drills whilst hovering a couple of feet from the edge (some lakes have crap visibility!). If you can hold that position for 10 minutes using the platform as a reference, you're well on the way to good decompression skills.

Caveat: the sea doesn't have still water nor conveniently located 6m/20ft platforms! Your main reference is your SMB reel/spool bouncing up and down in the waves.