"Accidental" Deco

[Bubbletrubble]

what is the approach? what is the approach? I really want to know. I will look up ratio deco just to understand it in case if I need it. I don't plan to do deco dive. In fact, recreation dive (<=100ft)with GUE min gas requirement and EAN32, one would never go into deco with a single tank setup.

But I still want to know what is the approach for "accidently deco".

I would leave the "ratio deco" method to the courageous souls who don't mind being guinea pigs.

A straightforward approach for a recreational diver who finds himself in an unintentional deco situation without a functioning computer to help direct his stop schedule prior to surfacing is to conduct an extended stop at depth of 15 fsw for 15-20 minutes or until tank pressure falls to 300 psi or until the diver becomes unable to remain in the water (too cold?). This assumes that the diver is aware of the deco situation prior to surfacing and that he didn't incur a ridiculous amount of deco. Obviously, if the diver's computer is still functioning and giving reasonable deco instructions, those instructions should be followed. If the diver's computer isn't working, then his buddy's computer should be consulted. Arguably, the most conservative method would be to simply do the best you can with the gas supply remaining, i.e., extend the shallow stop until gas supply dwindles to approx. 300 psi. I'm sure that others will share their own rules of thumb.

If you're curious, a nice read is the US Navy recommended course of action for "omitted decompression."
In the 2008 USN Dive Manual, it's illustrated in Table 9-3. Here's a download link to the entire 2008 US Navy Dive Manual (size ~20MB).

I think we can all agree that the best course of action for a diver not trained in deco procedures is to avoid crossing the line into deco in the first place.

For what it's worth, I've had a number of discussions with divers trained to conduct deco dives and actively doing them who have a...let's just say...rather simplistic understanding of deco theory. Perhaps I was just unlucky enough to encounter folks who were rusty on their "book knowledge" or received their training prior to the advent of current "best practice" procedures.

But then again, I'm just a dumb recreational diver, so what do I know?

P.S. It's certainly possible to adhere to Rock Bottom, stay shallower than 100 fsw, breathe a 32% nitrox mix, and have enough of a gas supply to exceed NDLs.
Check my math...
Given: Dive to 90 fsw with a SAC/RMV of 0.5 cuft/min breathing 32% mix with no prior dives
90 fsw = 3.73 ata
3.73 * 0.5 cuft/min = 1.87 cuft/min (gas consumption rate at 90 fsw)
Equivalent air depth of breathing 32% nitrox at 90 fsw = about 73 fsw
Consulting the PADI air dive tables, at 80 fsw, NDLs = 30 min.
1.87 cuft/min * 30 min = 56 cuft.
Rock Bottom for 90 fsw = about 31 cuft.
With a HP100, a diver would have enough gas to go into deco at 90 fsw without violating Rock Bottom reserve.

My typical SAC/RMV is around 0.4 cuft/min, so theoretically on 32% nitrox I could exceed NDLs with an AL80 while still adhering to Rock Bottom reserve.
3.73 * 0.4 cuft/min = 1.49 cuft/min (gas consumption rate at 90 fsw)
1.49 cuft/min * 30 min = 45 cuft.
Rock Bottom for 90 fsw = about 31 cuft.
FWIW, my typical tank is a HP100.

 

[gsk3]

I would leave the "ratio deco" method to the courageous souls who don't mind being guinea pigs.

A straightforward approach for a recreational diver who finds himself in an unintentional deco situation without a functioning computer to help direct his stop schedule prior to surfacing is to conduct an extended stop at depth of 15 fsw for 15-20 minutes or until tank pressure falls to 300 psi or until the diver becomes unable to remain in the water (too cold?).

There's nothing less guinea-piggish about your suggested profile. Even the navy tables you posted imply that flying up to 15 feet is not ideal (look at the second big row, where it talks about >30ft omitted stops).

 

[Bubbletrubble]

There's nothing less guinea-piggish about your suggested profile. Even the navy tables you posted imply that flying up to 20 feet is not ideal (look at the second big row, where it talks about >30ft omitted stops).

Please read the Navy tables more carefully. They assume that the diver had a decompression plan and that he is aware of missing a deco stop deeper than 30 fsw. Furthermore, the diver was probably using the Air Decompression Table (Table 9-9) to plan his dive.

The plan I described was a last resort, simple contingency plan for recreational divers who accidentally go into deco. Feel free to share whatever other stops you want. The plan I described is easy to comprehend, straightforward to carry out, and gets the diver closer to the surface.
From what I understand, some people actually use ratio deco as a primary method for calculating decompression schedules based on depth averaging. Doing complicated calculations in an unintentional deco situation will only add to the task-loading of managing the ascent for a recreational diver who has already gotten in over his head. Also, I'm not so sure that ratio deco calculations should be applied to non-optimal bottom mixes or deep air diving. What kind of gas does the typical recreational diver use?

How many recreational divers who accidentally go into deco are required to do a deco stop deeper than 30 fsw (according to how the majority of recreational-oriented dive computers handle situations where NDLs are exceeded)?

 

[RTee]

what is the approach? what is the approach? I really want to know. I will look up ratio deco just to understand it in case if I need it. I don't plan to do deco dive. In fact, recreation dive (<=100ft)with GUE min gas requirement and EAN32, one would never go into deco with a single tank setup.

But I still want to know what is the approach for "accidently deco".

If all else fails, I would suggest you open the little booklet that usually comes with every dive computer and familiarize yourself with the content. If you don't have one, most companies provide electronic copies on their site.
For my Suunto Vyper, I find all sort of cautions including...you may still experience DCS even though you follow to the letter the instruction provided by your computer as diving is not yet an exact science. It also covers the difference between a safety stop and a deco obligation including what you should do if you do encounter such an obligation as well as post-dive recommandation. The booklet also mentions that by not respecting these (including sustained ascent rate exceeding their recommended 10 m per min) it will lock my computer with an ERR message for 48 hours

 

[gsk3]

I read the tables more closely. The discussion, as I understood it, was what to do when underwater if you miss a stop. The table you posted is what to do if you surface while still having missed a stop. So it doesn't really apply.

Your earlier criticism of ratio deco was that it was untested. Now it's that it's too complicated. The latter, for most recreational divers, I mostly agree with.

As for whether a recreational diver needs stops deeper than 30fsw, I submit that physiology does not differ based on what plastic one carries in one's wallet. Therefore, if someone has racked up the 15-20 minutes of deco obligation that your plan calls for, they are likely better off doing a proper ascent. It is well known that "the majority of recreational-oriented dive computers" have somewhat antiquated deco algorithms, which often call for old-school 'bend and mend' profiles, with stops only at shallow depths.

Here's what V-Planner (VPM-B +2) would have to say about an "oops" recreational Caribbean-style dive (120ft for 22 minutes): 1 min @ 50ft, 1 @ 40ft, 2 @ 30ft, 4 @ 20ft, 7 @ 10ft.
The dive time and depth were picked to illustrate a diver who goes just a little bit deeper and a little bit longer than they intended, and racks up the 15-20 minutes of deco in your example.

 

[Rhone Man]

If all else fails, I would suggest you open the little booklet that usually comes with every dive computer and familiarize yourself with the content. If you don't have one, most companies provide electronic copies on their site.

Well to be fair, the difference is that if you skip a deco stop your computer will usually stop talking to you. The guidance in the US Navy Manual (which is similar to that provided on TDI course manuals) is still better than folding your arms and waiting to see what happens. Especially for short "accidental decos" that we are considering.

 

[DevonDiver]

That rather begs the question about how they should do that. I'd offer a ratio deco approach but what is your approach?

I think there is a big gulf between teaching how to do deco... and teaching how to conduct emergency deco.

Prevention is better than cure, so a firm message that avoiding deco through conservative diving practices, proper planning and evolved situational awareness should always be the primary approach. That said, including emergency deco (i.e. 'how to survive over-reaching your NDL') procedures within OW, or at least AOW, training would be a good start.

Whilst entry-level courses (i.e. OW) do deal with emergency deco, they only do so in respect of tables (i.e. PADI RDP emergency deco guidelines). People don't tend to exceed NDLs with tables - they do so primarily with dive computers. Consequently, having some education on the use of dive computers in respect of emergency deco would be a good approach.

I work with students to explain how their dive computer will manage a deco situation. In particular, how the computer will communicate critical information to them... and what that information actually means to them. Every dive computer user should understand their deco screen, along with terms such as 'ceiling', 'time to surface' and a brief intro to deco theory....so much that they understand how their recent dive history will impact on the accumulation of deco obligation, on-gassing / off-gassing and the relationship to depth and ascent rate.

In addition, some basic tuition in how to maintain a precise stop... especially stressing the need to maintain accurate stop depth and not exceed obligated ceilings.

The ability to compare deco obligation with remaining gas time is also a good idea... so gas management skills come into the picture too. I advise divers to never go below 10 minutes NDL, unless they are prepared to construct an effective gas management plan, which will include planning for an emergency deco scenario within their 'rock bottom'.

 

[Bubbletrubble]

I read the tables more closely. The discussion, as I understood it, was what to do when underwater if you miss a stop. The table you posted is what to do if you surface while still having missed a stop. So it doesn't really apply.

@gsk3: The US Navy table that I shared applies if the diver surfaces and his computer stops functioning.
I provided the chart in case eelnoraa was curious about contingency planning.

Your earlier criticism of ratio deco was that it was untested. Now it's that it's too complicated. The latter, for most recreational divers, I mostly agree with.

Both arguments have merit.

If you have received training in ratio deco, I recommend that you contact your instructor, present to him/her the scenario being discussed, and request his/her recommendation for the best course of action.
I'd be very surprised if your instructor advocates use of ratio deco to plan the diver's ascent schedule...even if the diver has some practice with calculating average depth.

As for whether a recreational diver needs stops deeper than 30fsw, I submit that physiology does not differ based on what plastic one carries in one's wallet. Therefore, if someone has racked up the 15-20 minutes of deco obligation that your plan calls for, they are likely better off doing a proper ascent. It is well known that "the majority of recreational-oriented dive computers" have somewhat antiquated deco algorithms, which often call for old-school 'bend and mend' profiles, with stops only at shallow depths.

Here's what V-Planner (VPM-B +2) would have to say about an "oops" recreational Caribbean-style dive (120ft for 22 minutes): 1 min @ 50ft, 1 @ 40ft, 2 @ 30ft, 4 @ 20ft, 7 @ 10ft.
The dive time and depth were picked to illustrate a diver who goes just a little bit deeper and a little bit longer than they intended, and racks up the 15-20 minutes of deco in your example.

So you are suggesting that the recreational diver, who exceeds NDLs unintentionally, should do a series of stops during his ascent. In the moment, do you think that such a diver will have the mental capacity to formulate such an ascent schedule and ensure that his gas supply will be sufficient to do all of those stops? Bear in mind that this is a diver who has already failed to watch his computer/gauges carefully.
I won't dispute that a series of stops during the ascent might produce a "better" off-gassing profile.

 

[gsk3]

So you are suggesting that the recreational diver, who exceeds NDLs unintentionally, should do a series of stops during his ascent. In the moment, do you think that such a diver will have the mental capacity to formulate such an ascent schedule and ensure that his gas supply will be sufficient to do all of those stops? Bear in mind that this is a diver who has already failed to watch his computer/gauges carefully.

I think we're disagreeing on the scenario being presented on two points:
-You're reading it as the diver having surfaced and I'm reading it as their not having yet surfaced.
-You're reading it as you choosing how to guide another diver through their profile and I'm reading it as what profile would I choose for myself.

I won't dispute that a series of stops during the ascent might produce a "better" off-gassing profile.

So why the snipe about "untested"? The point is, RD produces a profile that's closer to matching the best algorithms that we have. But being somewhat bent and on the surface is better than being unbent but drowned. So it depends on the circumstances.

Taking your modified scenario, in which you're guiding someone up who's gone into deco accidentally:
-If I'm guiding someone up who is calm and who seems to have reasonably buoyancy control, I'd likely attempt some short stops starting at half of max depth if gas reserves looked adequate then long stops at 20ft and 10ft. Note this is not what RD would predict (from what I've read about RD; I don't have training in RD) but rather the minimum deco profile, extended somewhat. I believe RD would begin stops at 80% max depth.
-If the person seems panicked, or gas reserves look scant, I'd likely bring them up to 20 feet and keep them there for as long as possible. That way if they further panic and bolt to the surface they're less likely to embolize, and since divers tend to congregate at 20ft near the dive boat there's more of a chance of recruiting more gas for a longer stay or higher FO2 mixes to accelerate deco. The risk here is that they blow past their 20ft stop straight to the surface, so I'd likely keep them ascending very slowly, even if we don't stop until 20ft.

During the shallow stops on either profile, we could pull out wet notes and have a chat about exactly what their profile was, to get a sense of reasonable deco. But rather than come up with rules of thumb about how long to stay at 15-20ft (which may be too long or too short) I'd rather calculate it based on the actual profile. If you don't have enough gas to make it through the required stop time, then you wait as long as you can and ascend (or recruit more gas if you can). If you do, then they ascend when the calculation says they can (and you along with them).

And if they have a computer, just follow that.

 

[Bubbletrubble]

I think we're disagreeing on the scenario being presented on two points:
-You're reading it as the diver having surfaced and I'm reading it as their not having yet surfaced.

To clarify, I included the USN table as "extra" info in case the diver surfaces without fulfilling his deco obligation.
I did offer up a suggestion as to how the diver might conduct an extended shallow stop (prior to surfacing) if he didn't have a functioning computer to guide him.

-You're reading it as you choosing how to guide another diver through their profile and I'm reading it as what profile would I choose for myself.

Fair enough.
So it sounds like you must play around with V-Planner or HLPlanner before every dive to generate contingency ascent schedules in case of going into accidental deco (and not having a working computer?). That's great. The vast majority of recreational divers out there don't do that.

So why the snipe about "untested"? The point is, RD produces a profile that's closer to matching the best algorithms that we have. But being somewhat bent and on the surface is better than being unbent but drowned. So it depends on the circumstances.

Because ratio deco is untested, relatively speaking. The strength of any deco algorithm is that others have used it to complete dives safely without a DCS incident.
Ratio deco appears to be a derivative method that generates ascent schedules that are similar to what other established deco algorithms might offer.
The strength of VPM-B is that people have been logging their dive profiles in a fairly sizeable database.
Are ratio deco users doing the same thing? Hopefully, they are. That would be meeting the empirical test of a "safe" deco algorithm.
I'm not really sure how you are defining "best" when referring to the various algorithms out there.

Taking your modified scenario, in which you're guiding someone up who's gone into deco accidentally:
-If I'm guiding someone up who is calm and who seems to have reasonably buoyancy control, I'd likely attempt some short stops starting at half of max depth if gas reserves looked adequate then long stops at 20ft and 10ft. Note this is not what RD would predict (from what I've read about RD; I don't have training in RD) but rather the minimum deco profile, extended somewhat. I believe RD would begin stops at 80% max depth.
-If the person seems panicked, or gas reserves look scant, I'd likely bring them up to 20 feet and keep them there for as long as possible. That way if they further panic and bolt to the surface they're less likely to embolize, and since divers tend to congregate at 20ft near the dive boat there's more of a chance of recruiting more gas for a longer stay or higher FO2 mixes to accelerate deco. The risk here is that they blow past their 20ft stop straight to the surface, so I'd likely keep them ascending very slowly, even if we don't stop until 20ft.

During the shallow stops on either profile, we could pull out wet notes and have a chat about exactly what their profile was, to get a sense of reasonable deco. But rather than come up with rules of thumb about how long to stay at 15-20ft (which may be too long or too short) I'd rather calculate it based on the actual profile. If you don't have enough gas to make it through the required stop time, then you wait as long as you can and ascend (or recruit more gas if you can). If you do, then they ascend when the calculation says they can (and you along with them).

And if they have a computer, just follow that.

I'm not guiding anyone up from depth. I merely made a suggestion on how to conduct an ascent if a recreational diver unintentionally crossed into deco and, for whatever reason, could not follow his computer's instructions on managing the ascent.

FWIW, your world seems to be far more ordered (wet notes, "conversations" underwater) than what I've witnessed in the average recreational diver.
I'm more than a little surprised that you seem to be advocating to put the diver on higher FO2 mixes to accelerate deco at 20 fsw. How many recreational divers are trained to do that?

I think we are in agreement that the diver should follow his computer (if available) and make the best possible use of his remaining gas supply prior to surfacing. In the couple of times that I've seen recreational divers inexplicably surface without fulfilling a deco obligation, the divers had plenty of remaining gas to do an extended shallow stop. Both times the divers admitted not being familiar with the deco mode of their computers. In both cases, the divers surfaced prematurely because other divers were exiting the water -- monkey see, monkey do.