One question

[lessthanjoey]

So, what does multideco give you for the Navy table NDL limit of 25 minutes for a dive to 100 feet?

Of course it gives even more mandatory deco (as would anything else running Bulhmann)

30/85:
40' 1m
30' 1m
20' 3m
10' 5m

100/100:
10' 3:30m

Wouldn't you agree that it's not a great idea to dive to navy tables though? I also realize that PADI isn't necessarily more aggressive than others, just that diving to table limits is pushing things relatively hard compared to "standard" acceptable surfacing GFs using Bulhmann. I've always assumed that this was partially due to assuming someone didn't sit right at that depth for a perfectly square profile and therefore kept some margin.

Would you happily dive to 100' for 20min or 25min and then ascend at 60fpm without a safety stop? I'd do it if I had no choice but I'd rather not end up in that situation.

EDIT: Obviously I'm a little off-topic here, but I find the question interesting, and like I mention above, I think it's splitting hairs to call these mandatory safety stops not mandatory deco.

 

[boulderjohn]

What you have to realize is that the PADI tables did not come out of thin air. They were done after extensive research on real divers doing real dives. The data indicated that those dives are very safe--the DCS rate is extremely low. The fact that another program's algorithm provides a different plan does not change the results of that research.

If a driver goes though a neighborhood at the posted 25 MPH speed limit, we say he is safe. If another diver then goes through at 20 mph, it does not mean the first driver was unsafe.

 

[lessthanjoey]

What you have to realize is that the PADI tables did not come out of thin air. They were done after extensive research on real divers doing real dives. The data indicated that those dives are very safe--the DCS rate is extremely low. The fact that another program's algorithm provides a different plan does not change the results of that research.

If a driver goes though a neighborhood at the posted 25 MPH speed limit, we say he is safe. If another diver then goes through at 20 mph, it does not mean the first driver was unsafe.

Fair enough.

EDIT: Just to confirm, you wouldn't feel good about skipping the "mandatory safety-stop" though, right? I'm guessing PADI's data always included those for where it's listed as mandatory.

 

[TMHeimer]

I'm not sure I understand your question correctly, so please help me if my response is not appropriate.

Whenever you are in the black/gray area of the RDP the supposedly optional safety stop becomes mandatory. I am pretty sure I understood that part.

It is the second question I am fuzzy on. From your wording, it seems to me as if you are questioning a rule about a mandatory one hour surface interval following a dive in which you did a safety stop that was less than the required 3 minutes. I am not aware of such a rule. The only rule I know about requiring a minimum one hour surface interval comes if you are doing 3 or more dives in a day and you end one of them in either the W or X pressure group.

Side question--The only time I recall hearing of a required 1 hour SI was in between two nitrox dives. I rarely dive nitrox--am I correct?

 

[NAM001]

NOW YOU GUYS GOT MY CURIOSITY UP. What is this mandatory stop about. Is it the 3min that you can skip and then 3min turns to 5 min is you are 10% of ndl or below 60'????? If so I thought those stops were still optional. This is why I thought so. Rec divers do not do dives with hard or soft overheads. mandatory stop is a soft overhead. Hard or soft overhead is in the tech arena. Now to reopen an old wound about ow's and 6o' limits. doesn't this idea of a mandatory stop put new OW's in mandatory deco stops???????? Requireing them to hold depth if no down line is available. A skill few have at that training level. Computers I have read about discuss the 3 min stop and it can be passed up with out violation, The books also say if you pass 60 ft or get 10% of ndl the recommended 3 minute safety stop is extended to 5 minutes, but still a safety stop. So what is it safety or mandatory stop?

 

[RJP]

Side question--The only time I recall hearing of a required 1 hour SI was in between two nitrox dives.

Never heard such a thing as a "requirement."

I think SDI recommends no less than 30min minimum, with at least 60min being preferred. But a SI of at least 60min is "preferred" by most agencies between any recreational dives.

Perhaps back when EANx was considered voodoo gas there was a belief that you needed "an air break" between "high O2 percentages" found in 32% and 36%?

---------- Post added September 9th, 2015 at 10:24 PM ----------

NOW YOU GUYS GOT MY CURIOSITY UP. What is this mandatory stop about. Is it the 3min that you can skip and then 3min turns to 5 min is you are 10% of ndl or below 60'????? If so I thought those stops were still optional. This is why I thought so. Rec divers do not do dives with hard or soft overheads. mandatory stop is a soft overhead. Hard or soft overhead is in the tech arena. Now to reopen an old wound about ow's and 6o' limits. doesn't this idea of a mandatory stop put new OW's in mandatory deco stops???????? Requireing them to hold depth if no down line is available. A skill few have at that training level. Computers I have read about discuss the 3 min stop and it can be passed up with out violation, The books also say if you pass 60 ft or get 10% of ndl the recommended 3 minute safety stop is extended to 5 minutes, but still a safety stop. So what is it safety or mandatory stop?

As John mentioned, it's a nomenclature thing.

One is a "mandatory safety stop" while the other is a "required decompression stop."

Since the diver in question is not "in deco" the mandatory safety stop isn't a decompression stop.

 

[lessthanjoey]

That's an arbitrary semantic line. Unless padi's tests were with skipping the safety stop to me this is a required stop. All dives are decompression dives (well, ignoring ultra shallow ones), although ndl dives clear you with a slow ascent, leaving an optional safety stop.

The PADI rdp is very clear that all dives to 100' incur a mandatory 3 minute / 15' stop, as do those at shallower depths that come close to the "ndl".

Like I mentioned above, if I dive my petrel's default recreational settings I'm clearly in "mandatory deco" at 100'/20 minutes and wouldn't personally ascend directly to the surface.

Sent from my Nexus 5 using Tapatalk

 

[Frosty]

NOW YOU GUYS GOT MY CURIOSITY UP. What is this mandatory stop about. Is it the 3min that you can skip and then 3min turns to 5 min is you are 10% of ndl or below 60'????? If so I thought those stops were still optional. This is why I thought so. Rec divers do not do dives with hard or soft overheads. mandatory stop is a soft overhead. Hard or soft overhead is in the tech arena. Now to reopen an old wound about ow's and 6o' limits. doesn't this idea of a mandatory stop put new OW's in mandatory deco stops???????? Requireing them to hold depth if no down line is available. A skill few have at that training level. Computers I have read about discuss the 3 min stop and it can be passed up with out violation, The books also say if you pass 60 ft or get 10% of ndl the recommended 3 minute safety stop is extended to 5 minutes, but still a safety stop. So what is it safety or mandatory stop?

THAT is exactly what I was thinking. What was going through my head is that the moment the word MUST or mandatory gets used then it is no longer a safety stop.
I fully understood/understand that its very very very (add lots of verys) strongly recommended but that's not what the question asked and not the answer it wanted to get.

 

[NAM001]

Thats a definite maybe. I use that time obligation process my self. deeper dives i do longer safety stops.

One is a "mandatory safety stop" while the other is a "required decompression stop."

Since the diver in question is not "in deco" the mandatory safety stop isn't a decompression stop.

 

[boulderjohn]

Never heard such a thing as a "requirement."

I don't have the current PADI materials with me at the moment, but the old materials on which I was certified for nitrox did indeed recommend a minimum one hour surface interval for all nitrox dives. I don't know why. My guess is that it relates to the old idea of "voodoo gas" and the general fear of nitrox. Remember that all talk of nitrox was once forbidden at DEMA because of those supposed dangers. Agencies like IANTD (the International Association of Nitrox and Technical Divers) and ANDI (American Nitrox Divers, Inc) were formed to teach about the safe use of this dangerous gas in large part because the mainstream agencies refused to have anything to do with it. My original PADI training was much, much more involved and technical than today's course, and the dramatic change reflects the realization that those early fears were so very much overblown.