Confused: Suunto D4 Safety Stops

[MrsBBC]

Is that an older D4? I have a new D6i and in my manual it clearly shows the "stop" alert when the computer is telling you to make a RECOMMENDED or a MANDATORY safety stop. My manual indicates the only time I would get a "asc time" alert is when I go into a decompression dive (i.e., I stay down too deep for too long), so as others have said, you went into a decompression dive. However, you should also have seen the "stop" alert, which should disappear only after you make your safety stop. So I don't know why yours didn't. Can anybody answer that question? Other than maybe older versions of the D4 do not have this feature?

The ER will appear if you exceed the ceiling and you have 3 minutes to get back below the ceiling to complete your safety stop. Since you did not complete your safety stop, the computer went into permanent ER (i.e., 48 hours of ER display).

The Stop alert for the safety stop would not have shown because the 8 minute decompression stop was not completed. After completing the 8 minutes of deco the 3 minute stop would appear.
Because the dive was finished before completing the mandatory decompression stop (hence the lock out Error), clearly the safety stop was not made.

8 mins of deco, although not a lot of deco (assuming adequate gas), is a lot of deco if you do not understand how to operate your dive computer in deco.

'mandatory safety stop' is sunnto babble for a safety stop that suunto require you to complete or will penalise you for it. It is not a deco stop. Although I don't recall it ever happening to me, I see no reason why the mandatory safety stop could not follow a deco stop. But regardless, the computer does not error for missing a mandatory safety stop, only for not completing deco.

 

[DevonDiver]

...the computer does not error for missing a mandatory safety stop, only for not completing deco.

I think it does penalise on subsequent dives though?

I've only seen 'mandatory stops' as a result of breached max ascent rates... normally when I forget to take the computer off before teaching OW CESAs (Suunto is max 10mpm..students ascend at 18mpm). I remember reading that if the mandatory stop isn't completed, then the algorythm will be 'tweaked' for more conservatism on subsequent dives - someone may correct me on that.

 

[Juardis]

I think it does penalise on subsequent dives though?

I've only seen 'mandatory stops' as a result of breached max ascent rates... normally when I forget to take the computer off before teaching OW CESAs (Suunto is max 10mpm..students ascend at 18mpm). I remember reading that if the mandatory stop isn't completed, then the algorythm will be 'tweaked' for more conservatism on subsequent dives - someone may correct me on that.

No, you're correct. At least according to my manual. Subsequent dives are penalized for violating a mandatory stop, but not for violating a recommended stop. And yes, it will give you a 'mandatory stop' when you exceed 10m/min ascent over a 5 sec period. Happened to me in a 15 foot pool when I was practicing mask clearing from a nuetrally buoyant position. Since I ascended too fast, you can guess I wasn't neutrally buoyant

 

[watboy]

Two notes on Suuntos. First, a fast ascent will automatically trigger a mandatory deco stop. Its annoyingly easy to trigger the fast ascent alert by just raising your arm fast enough. Secondly, if you do anything "bad", ie go into deco, trigger fast ascent, get too close to your NDL, go deep etc, the Suunto will give you a dive warning. A Triangle with an ! in it. This alert tells you to extend your surface interval. If you go back down with the dive warning still on, the Suunto will severely reduce your NDL times, about halving the times. Annoyingly, it doesn't tell you by how much to extend your SI, just to not go back in until the warning goes away. I believe however, it maxes at 90minutes SI though.

Hi All,

I did 2 dives yesterday with about 1 hour in between. These were not deep dives, i.e. 70 feet for the first dive for about 45 minutes and 60 feet for the second for about 50 minutes.

My D4 gave the warnings that can be seen in attached images at the end of second dive. And, I got confused by these and wanted to ask:

1. According to the D4 manual, if there is a safety stop recommendation or a mandatory safety stop, it should display "STOP" there, but it only displayed CEILING and ASC TIME, and there was no STOP on the display??? What does this mean?

2. It gave 8 minutes for the ascend time at around 9 feet, which seemed a lot. My wife's oceanic gave only 3 minutes, and 8 minutes is a lot more. And, we had to finish diving due to currents after 6 minutes of a safety stop (as always, she is the master and we do what she says), and D4 errored out (it is only showing ER on screen now).

What i don't understand is that even though it did not give a stop, it kept giving warnings and errored out even though these were pretty regular dives and we did not push limits in any way.


Thanks in advance.

View attachment 106893View attachment 106894

 

[FinnMom]

2 points worth knowing for Suunto usage

* If you exceed the ceiling with less than 3 minutes left, it won't go into error. So if you really don't need to stay down to whole time, for instance if you forgot to set the computer from air to to EAN 32, you can [finally] go up once you've reached 2:59 w/o having the thing go on strike.

* If you set/enable the deep stops, the recommended safety stops option will be disabled.
Forget this fact and you might think your computer is broken. I know I did ;-)
Note: recommended=NOT mandatory; a safety stop is NOT a deco stop.

 

[DevonDiver]

2 points worth knowing for Suunto usage

* If you exceed the ceiling with less than 3 minutes left, it won't go into error. So if you really don't need to stay down to whole time, for instance if you forgot to set the computer from air to to EAN 32, you can [finally] go up once you've reached 2:59 w/o having the thing go on strike.

That might confuse people. The computer gives a mandatory deco stop - THAT YOU MUST DO - then it gives a safety stop (this is included in the ascent time). You can skip the safety stop if necessary.

However, you cannot skip the last 3 minutes of a deco stop.

Personally, I think you'd need a pretty important reason to skip the safety stop though. The fact that the computer may, or may not, lock out is irrelevant. If you choose to follow a computer to provide safety from DCS on a dive, then you should follow it​. Otherwise, just cut some custom tables.

* If you set/enable the deep stops, the recommended safety stops option will be disabled. Note: recommended=NOT mandatory.
Forget this fact and you might think your computer is broken. I know I did ;-)

Yes, it's a shame this happens. Regardless of how the algorithm works, doing an optional safety stop should remain part of the dive plan - and the computer should aid the diver in doing this.

 

[Juardis]

The Stop alert for the safety stop would not have shown because the 8 minute decompression stop was not completed. After completing the 8 minutes of deco the 3 minute stop would appear.
Because the dive was finished before completing the mandatory decompression stop (hence the lock out Error), clearly the safety stop was not made.

Not saying you're wrong, but I am saying that what you're saying contradicts what's in my D6i manual.


As this image shows, the stop indicator appears as soon as you enter the decompression dive. In this example, the diver is at 25m and is told to ascend to 3m and, if the diver ascends at 10m/min and holds a safety stop (appears to be about a 6 1/2 minute safety stop in this example), the total time is 9 minutes. So all of this shows the stop indicator well before the diver gets to the ceiling and the time includes the safety stop.

So, as I asked earlier, is that an earlier D4 than the newer D4's? Reason I asked is because I borrowed an older D6 before my D6i came in and there were differences between the newer D6i manual (other than the integrated pressure data) and what the older D6 computer could do.

 

[DevonDiver]

As this image shows, the stop indicator appears as soon as you enter the decompression dive. In this example, the diver is at 25m and is told to ascend to 3m and, if the diver ascends at 10m/min and holds a safety stop (appears to be about a 6 1/2 minute safety stop in this example), the total time is 9 minutes. So all of this shows the stop indicator well before the diver gets to the ceiling and the time includes the safety stop.

Safety stop isn't a decompression stop, and vice versa. It's important to get the terminology right, so that mistakes like the OP made are not replicated.

A safety stop is an optional stop, conducted for 3 (or more) minutes to add an element of conservatism to a dive by allowing additional off-gassing and extending the overall ascent time. The dive computer (when not in deep stop mode) provides information on the safety stop at the end of a normal ascent (within NDL) or following the end of decompression. It is simple 'bolt-on' conservatism. It is not mandatory to complete this, but the scuba industry does recognise the benefits of completing safety stops.

In contrast, a deco stop is a mandatory stop, conducted at a varying depth for a varying amount of time - as dictated by the theoretical nitrogen loading of the diver; which is calculated by the computers' algorithm based on dive depth and time. It occurs when the diver over-stays their no-decompression limit and has too much saturated nitrogen in their system to allow a direct ascent to the surface. The word 'ceiling' is used to describe a minimum depth that the diver must not ascend above, without exaggerated risk of DCS susceptibility. When conducting decompression, the existence of a ceiling creates a much more critical relationship with the divers' remaining gas supplies. The ceiling should be considered an overhead environment and just as inviolate as being in a cave or in a wreck.. it may be an 'invisible' ceiling, but it should be treated as if it was very solid. In order for the diver to more easily recognise that relationship, the computer will provide an overall 'ascent time' to the surface - thus making any 'on-the-fly' analysis of remaining gas volume, SAC/RMV and deco time easier and more obvious. Rather than just give the information in terms of 'stops' - it provides a total time that must be spent submerged so that the diver has adequate and obvious warning for their gas planning.

 

[CuracaoJ]

what's in my D6i manual.

That's an interesting pic from the manual, and as near as I can tell, it is completely erroneous. In my family we have an old D4, D6, and D9. I also have the new D6, and the new D9. I have dove all of them, and have had all of them in DECO. With all of these watches in the screen shot that is in the manual the 9 minutes would roll off, the arrows and the ceiling would disappear and then the 3 minute, non mandatory safety stop timer would appear. I just had my new D9 in DECO last night (4 minutes at a Superior Producer night dive here in Curacao), and it worked exactly like that -- the four minutes came off, and then 3 minutes appeared. It might be worth linking this over in the Suunto forum, because either they have a mistake in their book or I have 5 broken computers!

 

[DevonDiver]

Two notes on Suuntos. First, a fast ascent will automatically trigger a mandatory deco stop.

Pleeaasseee... let's try not to confuse the duck out of newbies by using ghastly inaccurate terminology.

A fast ascent won't trigger a deco stop. Deco triggers a deco stop. It will, however, apply a mandatory safety stop.

Yes...it's still a 'stop', but the mechanics are very different (see below).

Its annoyingly easy to trigger the fast ascent alert by just raising your arm fast enough.

Yes, it will warn you. BUT.. it only applies a mandatory safety stop for extended violations of ascent speed. Your arms are probably not long enough to attain that.....

5 second duration violation, in excess of 10mpm = you need to travel at least 84cm whilst in violation of the ascent speed. Short enough to give you quick warning, but long enough not to penalise you for arm movements.

Secondly, if you do anything "bad", ie go into deco, trigger fast ascent, get too close to your NDL, go deep etc, the Suunto will give you a dive warning. A Triangle with an ! in it. This alert tells you to extend your surface interval. If you go back down with the dive warning still on, the Suunto will severely reduce your NDL times, about halving the times. Annoyingly, it doesn't tell you by how much to extend your SI, just to not go back in until the warning goes away. I believe however, it maxes at 90minutes SI though.

Stick is sometimes better than carrot


For reference:

5.10.2. Mandatory Safety StopsWhen the ascent rate exceeds 10 m/33 ft per minute continuously for more than 5
seconds, the microbubble build-up is predicted to be more than is allowed for in the
decompression model. The Suunto RGBM calculation model responds to this by
adding a Mandatory Safety Stop to the dive. The time of this Mandatory Safety Stop
depends on the severity of the ascent rate excess.
The STOP sign appears in the display and when you reach the depth zone between
6 m and 3 m/20 ft and 10 ft, the CEILING label, ceiling depth, and the calculated Safety
Stop time also appear in the display. You should wait until the Mandatory Safety Stop
warning disappears. The total length of the Mandatory Safety Stop time depends on
the seriousness of the ascent rate violation.

You must not ascend shallower than 3 m/10 ft with the Mandatory Safety Stop warning
on. If you ascend above the Mandatory Safety Stop ceiling, a downward pointing arrow
will appear and a continuous beeping starts. You should immediately descend to, or
below, the Mandatory Safety Stop ceiling depth. If you correct this situation at any
time during the dive, there are no effects on the decompression calculations for future
dives.



If you continue to violate the Mandatory Safety Stop, the tissue calculation model is
affected and the dive computer shortens the available no-decompression time for your
next dive. In this situation, it is recommended that you prolong your surface interval
time before your next dive.