So why is it a bad idea to go back to do a safety stop if you blow it?

[boulderjohn]

Isnt it In-water Recompression?

Yes--my bad.

 

[farsidefan1]

As one who has spent soem time in a chamber I have found this to be a facinating thread. Mine was an "unexplained hit" where symptoms occurred hours later so I didn't have to consider the return to water option. I remember that the reason the other guy had to be in the chamber with me (I felt sorry for the guy, he had nothing to do for nearly 6 hours the first time and 3 hours the second time) was in case of convulsions. For this reason I would have given this as the major reason for not returning to the water. I mean, convulsions, even at safety stop depths would have a bad outcome for the diver. I was not aware of the "time before bubbles form factor". I must admitt that initially I thought Danvolker was an idiot (gratefully I kept reading the thread instead of responding in ignorance) now I am appreciative of his insights into factors I was unaware of. I thought the damage would have already been done. I think the OP has the technical reasons for why not to return to the water and hopefully will never have to choose amongst the options discussed. JUST DON'T BLOW THROUGH FROM DEPTH. In my limited experience I have (knock on wood) never seen anything like this or an equiipment failure as discussed by Dan occur. Hope I never do. Lots of food for thought, Thanks again

 

[Levigarrett]

The idea of blowing the stop from 130 feet as the OP "fabricated" for this discussion, and to go back down---is NOT a safety stop discussion, it is a decompression discussion...and all stops on ascent are deco stops, as you know well... for all of us...Calling them "safety stops" I imagine was to take the dangerous or techy sound out it
In any event, this deco discussion is exactly on point for the OP discussion, and in the context of possibilities for a fairly new diver, this is actually something they SHOULD be reading and trying to figure out their own way of handling if such an issue occurs for them.

Agreed! I'm a relatively inexperienced diver and I have not and will not perform anything remotely resembling a deco dive profile yet I'm enjoying this thread immensely. It's been a great read thus far....please continue!

 

[captain]

I think PADI misrepresents what is a NDL dive by inserting a "mandatory safety stop". Basically they are using the old 60 FPM rate and making a mandatory stop to slow it down, kind of like why the safety stop was originally designed to do under the old 60 FPM rate. The no D limit for 130 is the same as the old Navy table, all they did is chop up the SI into a bunch of smaller increments compared to the Navy table.

 

[VooDooGasMan]

Farside, one reason would be out of gas, therefore you need to head to a chamber, or know that the obligation you blew off, is not all that much. Either way, if you do not dive much, always know your dive profile for a safe decision.

I believe some things in this thread could happen, yet, I have went back down, and went diving the next day. Plus after deep dives everyday, I would go out and do a long shallow, start out at around 100' slowly to 40' then slowly make it to 30' and while at 20' and under, spend more time, 30 or so mins.


Now while spearfishing, I will come up no safety at all, and go back down to get another, depends if sharks are around, my last time up Ill do a stop.

Breathing oxygen is a very good thing to have.

Always know your profile, ascend safely, have plenty of gas in your tank, and stop and enjoy a shallow stop.

 

[boulderjohn]

I think PADI misrepresents what is a NDL dive by inserting a "mandatory safety stop". Basically they are using the old 60 FPM rate and making a mandatory stop to slow it down, kind of like why the safety stop was originally designed to do under the old 60 FPM rate. The no D limit for 130 is the same as the old Navy table, all they did is chop up the SI into a bunch of smaller increments compared to the Navy table.

PADI's creation of the RDP (a project in which SB's Doc Decompression, Michael Powell participated) was more complicated than that. They did a lot of actual original research on divers using Doppler bubble imaging. They created a very different set of tables from the old Navy tables. The navy tables then in use had much less research behind them. Here the critical differences:

1. In general, they used shorter maximum bottom times for first dives than the Navy tables, creating a more conservative first dive. Part of the thinking was to shorten the SIs so that recreational divers could get back into the water without as much of a delay.

2. The Navy had added a 120 minute compartment to the old Haldanean set of compartments and decided to use it as the controlling compartment for planning purposes. This leads to a 12 hour washout (6 x 120 minutes). PADI's research indicated that although that might be good for hard hat divers doing extremely long working dives, it did not relate to typical recreational dives. Their study indicated that the 40 minute compartment was the controlling compartment for typical recreational dives, but they decided to use the 60 minute compartment, just to play it safe. That leads to a 6 hour washout (6 x 60 minutes). The result is shorter surface intervals for recreational divers.

3. For divers who are doing dives that more closely resemble the dives for which the Navy tables were designed, they created the WX and YZ rules, which require longer surface intervals for repetitive dives approaching NDLs.

Whatever the origin of safety stops, subsequent research (see DAN) has indicated that they are more important than previously thought and are, in fact, more important than the ascent rate.

 

[HattDiver]

I'm often guilty of the opposite. Hanging for as long as I can, way past needed stops, and enjoying the blue water and barracuda that come up off the wrecks to "join" us. The boat I dive with has a regulator on a 15-foot rig so I never worry about air. Always go to the ladder with 500psi anyway. Best things I can think of is to stay fit, relax underwater, and enjoy yourself. Safety first, if for no other reason to be able to dive again!

 

[norcal_diver]

Safey stop in PADI's recreational trainin is almost always optional. If you blow it, it isn't too bad. If you push the PADI RDP to a point a stop is necesary, then it is actually a deco stop. A few problems with this so called "in water recompression" for recreation divers: 1) what makes you think they can hold the top when they go back in? (if they already blow it the first time). 2)With single tank, if a diver can manage to hit NDL, gas in tank is most likely running low too. Maybe not have enogh gas going down to 15' to complete the stop. 3)if thing happen after a diver blow a mandatory deco, he is better to be on surface when syndrome kick in.

Overall, before anyone even thinking of going into tech or any dives with mandatory stop(s), he/she better be damn good about buoyancy control even when task loaded. Too bad, these days not too many agencies and instructors emphasize such a basic skill anymore.

 

[norcal_diver]

Safey stop in PADI's recreational trainin is almost always optional. If you blow it, it isn't too bad. If you push the PADI RDP to a point a stop is necesary, then it is actually a deco stop. A few problems with this so called "in water recompression" for recreation divers: 1) what makes you think they can hold the top when they go back in? (if they already blow it the first time). 2)With single tank, if a diver can manage to hit NDL, gas in tank is most likely running low too. Maybe not have enogh gas going down to 15' to complete the stop. 3)if thing happen after a diver blow a mandatory deco, he is better to be on surface when syndrome kick in.

Overall, before anyone even thinking of going into tech or any dives with mandatory stop(s), he/she better be damn good about buoyancy control even when task loaded. Too bad, these days not too many agencies and instructors emphasize such a basic skill anymore.

 

[DevonDiver]

Safey stop in PADI's recreational trainin is almost always optional.

Any safety stop is, by definition, optional. Any stop that imposes a rigid 'ceiling' on the diver is no longer a safety stop - it becomes a deco stop.

PADI confuse the issue by specifying that for certain deep dives/pressure groups the safety stop becomes mandatory. That is what confuses people, because you cannot have a mandatory 'safety' stop.

Safety stops are recommended for one reason: increased conservatism. PADI tables are calculated based upon 3 primary factors (yes, 3). Depth, duration (bottom time) and ascent rate. Adding a safety stop allows further tolerance to account for individual physiological variances, different diving/water conditions etc. The safety stop also acts as a safeguard to ensure that the 'time to surface' ascent rate (which the tables rely upon) is within the correct parameters. However, the safety stop itself is not of calculated duration, nor does it factor within the off-gassing equation/model that forms the PADI table.

Safety stops also play an important role in ensuring (novice) diver safety by creating a pause in their ascent, where they can confirm that NDLs haven't been exceeded, moderate their buoyancy, check for overhead boat traffic and prepare for egress from the water etc. In that respect, they have nothing to do with off-gassing... but play a more general role in diver safety.

In contrast, deco stops are imposed as a necessary part of the off-gassing equation. If you breach the depth ceiling you are at a significantly higher risk of DCS. The mathematics is saying that if you breach the deco stop, you will still be super-saturated beyond the pressure gradient at which bubbles may form.

Now... the PADI 'mandatory' safety stops confuse this differentiation. They aren't a mathematically modelled requirement for safe off-gassing. They are simply an expression of PADI applying a principle of more rigid conservatism to deeper, more aggressive, dive profiles. Thus we get this wierd scenario of a mandatory-recommended stop. It remains, however, a method of imposing conservatism, rather than a requirement dictated by mathematical bubble modelling.

As such, the mandatory safety stop, should always be treated as a conservatism measure. It should be planned into the dive, but may be aborted if more critical factors subsequently pose safety risks to the diver.

If you blow it, it isn't too bad.

That depends on how you blow it. Ascent rate is a primary factor in determining the DCI consequences.

If you push the PADI RDP to a point a stop is necesary, then it is actually a deco stop.

Incorrect. The PADI RDP demands a safety stop in 3 instances. If you exceed 30m max depth, if you will end the dive within 3 pressure groups of an NDL... or if you are in the final pressure group/NDL for the dive.

As explained, those instances of mandatory safety stops are still not deco stops.

A few problems with this so called "in water recompression" for recreation divers:...

There's more than a "few" problems with attempting in-water re-compression. In fact, there are so many potential problems and drawbacks that in-water re-compression is simply not a viable option unless a considerable amount of logistical and medical planning/preparation has been conducted in advance. It is a majorundertaking, well beyond the capabilities of any recreational dive charter. If a technical charter/expedition wished to provide re-compression, it'd probably be simpler and more effective to just get a portable hyperbaric chamber on their vessel.

There are already some very informative threads on this subject already. However, as a very basic run-down; here are some considerations:

1) In-water re-compression typically takes many hours
2) The casualty needs to be delivered with pure O2
3) The casualty needs to be rapidly hydrated
4) The casualty needs medications (immuno-suppressants, anti-inflammatories etc)
5) The casualty needs treatment for shock and/or may lose consciousness
6) The casualty needs continual monitoring, including neurological assessments
7) The casualty needs to be maintained at an optimal temperature

...the list goes on.