Diving with gradient factors for a new recreational diver

[boulderjohn]

It's taught that way though, hell even on the damn dive table cards it's all blacked out like... > "death is waiting".

Yes, I believe standard training makes people too much afraid of violating NDLs, to the point that people who suddenly realize they are near NDL will risk an arterial gas embolism by sprinting to the surface to avoid violating NDLs. (Yes, I have seen it.)

 

[dmaziuk]

You're not out of line at all. The most recent number I saw from DAN was that 80% of the DCS cases they saw were for people diving within the limits.

Just like the other popular statistic: % of dead divers who didn't ditch their weights, this one may not mean what you think it means.

 

[Subcooled]

After about 30 dives I've fallen in love with diving and want to pursue the hobby more actively. Unfortunately, I'm a worrying personality, risk averse, and despite being a decent swimmer and a triathlete, I'm not a natural when it comes to diving and buoyancy control. I want to find ways to enjoy the sport more safely, especially as it relates to DCS risk.

DAN vignettes, ScubaBoard (especially advanced scuba), and talks like Pollock's and Marroni's have been invaluable in my safety pursuit. Most recommendations are fairly straightforward and applicable on all/most dives. As I read through the forums and research articles, however, I come to the conclusion that using conservative gradient factors with multiple stops instead of the popular 3 minute safety stop at 5m (15ft) is a good idea for minimizing risk. But is it practical to do, especially for an inexperienced diver without a regular dive buddy?

So here we go:
Do the safety benefits of multiple safety or deco stops (and diving with conservative gradient factors) outweigh the awkwardness and inconvenience of having to do them on recreational dives? Is it practical?

The pros:

1. safety - deeper than 5m stops seem to reduce bubble and DCS risk in recreational dives (somewhat significantly).
   FWIW, I don't want the discussion to get mired in whether deep stops are good or bad, but my reading of the journals is that while "too deep" is not good, some deeper than 5m stops are good for reducing bubbling in recreational divers. FWIW, for most recreational dives these seem to be at the deepest in the 12 to 9 meter (40-30ft) range depending on the dive profile and gradient factors chosen.

The cons:

1. Different (i.e. more conservative) safety / decompression protocol that (almost) everyone else in a real life recreational dive group
   1. stops different that the 5m / 3 min safety stop - both deeper and shallower stops
   2. longer total stops time
   3. (with conservative factors) high likelihood of decompression time while everyone else is in NDL
   4. (with conservative factors) lack of clarity how to handle emergencies while having deco time while others are in NDL
2. Having to convince the group to follow a different more conservative protocol - not very likely or practical
3. Separating from the group by a few meters for a stop - I guess this is an outright bad idea for a new diver, a diver without a regular buddy, might be against the manual, and I don't expect it would be tolerated by many dive masters
4. A more expensive dive computer
5. Complexity

What do you kind and knowledgeable folks recommend for someone in my situation? Is it a bad idea for a newbie diver to try to dive with multiple stops and conservative gradient factors?

Short answer:

You need a slow and controlled ascent to give time for N2 to escape. Slow down even more near the surface. Stops is just one way of achieving moderately slow ascent speeds, but a safety stop is great practise plus it gives you time to look up, locate your boat, avoid surface traffic etc. Because of this the safety stop is worth it (plus it's required if your dive is close to NDL). I have also found that an excessively slow ascent from safetystop to the surface results in a nice relaxed feeling, so I'd say it's worth it.

Long answer:

On longer deeper dives it gets complicated (mandatory decompression stops, lots of planning and contingency planning), but generally you would want to get to 6m / 18ft reasonably fast: you should make a slow and relaxed ascent to this depth but not spend a lifetime at greater depths.

Spend your extra time there at 6m / 18 ft. Swim around. You are still diving and you can enjoy the stop. It's constant depth, not fixed position. Sometimes there might not be things to see (@open sea) but it can be relaxing nevertheless. Things change if the seas are rough.

Then make a slooooooow ascent from 18ft to the surface.

Avoid excessive excertion after the dive and drink some water. Sweating in a steam bath would be a bad idea, you should drink water instead. Same applies to extended hot showers. Or alcohol. Or especially the gym or any lifting of heavy burdens. You should give time for your body to recover. This is not important after ONE recreational dive, but if you do 20 of them on a liveaboard or if they require decompression stops, then it is.

Remember that decompression = ascent, decompression stop = fixed depth, offgassing = N2 leaves, but it's not yet gone. Offgassing continues on the surface, so you should take it easy especially after dives that are not within NDL.

 

[wnissen]

Just like the other popular statistic: % of dead divers who didn't ditch their weights, this one may not mean what you think it means.

Not to get too much into the Bayesian probabilities of it all, but it is true that is tricky predicting a rare event like DCS. That goes double when the vast majority of divers stay within the NDLs, often well within. (Thinking of my dives this weekend which will have a hard bottom at 11m and an NDL of 147 minutes, which is probably still very conservative). But the point is to take into account the broader risks, and not ignore the symptoms if you do get them.

 

[dmaziuk]

Good deco models are designed to consistently produce X incidents of clinical DCS in Y dives; read DSAT report for how and why. The fact that 80% of bent divers were bent within the limits of their deco models means nothing without knowing how those 80% fit within the "X in Y" design specs.

So yes, if you knew that, and could use it for your prior, you'd probably find that those DCS incidents happened exactly when they were expected to happen. Or, as that chapter of the DSAT report is titled, "DCS is not an accident".

 

[lowwall]

I don’t see any harm in practicing stops at various depths as long as you stay inside your NDL and can make a slow assent to the surface if you get fed up. But there’s no need to plan them.

This could be a buddy problem though. The OP said he doesn't have a regular buddy (and he isn't a solo diver). He would need to explain ahead of time and get the buddy's assent. Even then, it would be kind a jerk thing to ask of an insta-buddy.

That exact question was a lot on my mind with conservative profiles and with regards to computer selection. Thank you for helping me understand how to think about this. Indeed, I do want a computer that can show SurfaceGF so that I can make rational & informed decisions should I want or need to deviate from the original plan. Though, I think I'd still choose a more conservative high GF for planning and setting the dive profile, and just monitor SurfaceGF closely should I deviate for any reason.

Just a note that while SurfaceGF is a very nice tool, you don't need a computer that shows SurfaceGF (aka Shearwater) to track gas loading. The NDL number tells you the same thing. If you are deep, you can watch it get larger as you ascend even a couple of feet. The number continues to get larger for a while if you ascend to and then pause at intermediate depths - say 35-60 feet. This is often the top of coral formations so is a lovely place to hang out for awhile. If the NDL number begins to fall at these depths, you should take it as a hint to move up to safety stop depth.

...I feel tired after diving (probably related to decompression stress), I've never had clinical DCS symptoms, but I also don't have a baseline for what's normal.

When I started diving, I would also get very fatigued after a dive. What helped me (and my wife) was spending more time at an intermediate depth and taking it very slowly from the safety stop to the surface. I really think that quickly moving through pressure levels is stressful on either the nervous system or some combination of tissues and that leads to the excess fatigue.

Eventually we got nitrox certified and that helped as well. Combine all three and I have done 5 dives a day on a liveaboard and been less fatigued than I used to be after a 2 tank dive trip.

 

[Wibble]

The dive where my buddy got bent...

I'd dived with him quite a few times. Fit bloke, younger than me, does lots of sport. We did a lovely wreck dive to 30m/100ft to 35m/115ft for an hour on the bottom (therefore a decompression dive == technical dive). Was a nice wreck where we were having fun inside, both of us separately took the same wrong turn inside and had to back out... oh the fun of wreck diving


Anyway it really was uneventful. A simple dive with both of us on rebreathers where we both ascended together slowly with a max decompression ceiling of 9m/30ft which was 6m/20ft by the time we got there. Stayed at 6m/20ft until it cleared for both of us and slowly ascended to the surface over another 5 mins with 1m/3ft a minute ascent so doing 5 minutes more decompression than was required.

Calm steam back to port on the boat, couldn't have been a nicer day.

My friend went home but developed a skin rash; called the dive doc and ended up going to the decompression chamber for a series of 5 days of recompression treatments to clear it. Subsequent doctor prodding and poking revealed he's got a PFO (Patent Foromen Oviale -- aka hole in the heart). He'd been diving uneventfully for some time until that day when the fickle finger of fate decided it was his turn. He will have it fixed and has now been cleared for shallow diving with no decompression.

Crap happens. You won't know it's your turn until fate points its fickle finger at you. Until that day you make sure you learn, practice, plan and mitigate risks.

 

[tursiops]

The dive where my buddy got bent...

I'd dived with him quite a few times. Fit bloke, younger than me, does lots of sport. We did a lovely wreck dive to 30m/100ft to 35m/115ft for an hour on the bottom (therefore a decompression dive == technical dive). Was a nice wreck where we were having fun inside, both of us separately took the same wrong turn inside and had to back out... oh the fun of wreck diving


Anyway it really was uneventful. A simple dive with both of us on rebreathers where we both ascended together slowly with a max decompression ceiling of 9m/30ft which was 6m/20ft by the time we got there. Stayed at 6m/20ft until it cleared for both of us and slowly ascended to the surface over another 5 mins with 1m/3ft a minute ascent so doing 5 minutes more decompression than was required.

Calm steam back to port on the boat, couldn't have been a nicer day.

My friend went home but developed a skin rash; called the dive doc and ended up going to the decompression chamber for a series of 5 days of recompression treatments to clear it. Subsequent doctor prodding and poking revealed he's got a PFO (Patent Foromen Oviale -- aka hole in the heart). He'd been diving uneventfully for some time until that day when the fickle finger of fate decided it was his turn. He will have it fixed and has now been cleared for shallow diving with no decompression.

Crap happens. You won't know it's your turn until fate points its fickle finger at you. Until that day you make sure you learn, practice, plan and mitigate risks.

I gotta say, a story like this does not make me think the deco algorithms are wrong. It makes me think some people are wrong to be diving, The algorithms were not designed for people with PFOs.

 

[doctormike]

The algorithms were not designed for people with PFOs.

You probably know more about this than me, but I would disagree with this statement.

The algorithms came from clinical data. 25% of humans have PFOs. Since of the early studies that established the correlation between degrees of overpressure and clinical DCS could not specifically exclude people with PFOs, I would say that some of that excess risk is accounted for.

Of course, maybe that's where "undeserved" hits come from!

 

[Wibble]

I gotta say, a story like this does not make me think the deco algorithms are wrong. It makes me think some people are wrong to be diving, The algorithms were not designed for people with PFOs.

You probably know more about this than me, but I would disagree with this statement.

The algorithms came from clinical data. 25% of humans have PFOs. Since of the early studies that established the correlation between degrees of overpressure and clinical DCS could not specifically exclude people with PFOs, I would say that some of that excess risk is accounted for.

Of course, maybe that's where "undeserved" hits come from!

Unqualified opinion alert...
The algorithms cannot cater for external circumstances. They do have some conservatism built in which would mitigate a certain degree of 'inefficiencies' with physiology. Seems that PFOs sometimes appear and get worse -- have heard of a few people saying they'd been diving for a while then got an 'undeserved' bend which lead to the discovery of a PFO. Even heard of exceedingly experienced divers getting DCS (there's a well known cave explorer diver who now cannot dive as he keeps getting DCS).

The algorithms are just that; mathematical models. They don't know what state the diver's in and there's no magical fiddle-factor to cater for unknown issues.

All I know is that I utterly rely on those algorithms to keep me fit and healthy after a dive. Hopefully my body does the rest and works like the model predicts.