Confused: Suunto D4 Safety Stops

[Juardis]

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.

Thanks for the clarification Devon. My manual did not delineate between mandatory stops and deco stops, at least when it came to terminology. So if I understand you, there are 3 separate stops.

Recommended Safety Stop - no penalty for violating
Mandatory Stop - penalizes subsequent dives if violate and violations can occur for ascending to fast
Deco stop (your terminology) - computer goes into ER mode unless and until you complete the deco stop time. After the deco stop time it transitions to a mandatory stop

So when does the stop indicator appear if my manual is wrong? Going back to the OP and his jpegs, my manual appears to be wrong and MrsBBC is correct.

 

[watboy]

Apologies for not being precise. However, if you find suunto beeping and its giving you a ceiling, how do you know if its a mandatory safety stop or a deco stop? Assuming you were completely oblivious to how you were diving.

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).



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.



Stick is sometimes better than carrot


For reference:

 

[TT_Vert]

Disregard, I misread that.

 

[DevonDiver]

Assuming you were completely oblivious to how you were diving.

Well, there's your problem.

It would mean;

1) You didn't know if you had exceeded an ascent rate (even with the audible and visual alarm).
2) You didn't know your NDL (either planned before the dive and during the course of the dive from the computer).
3) You didn't know your dive time/depth and outline profile during the dive - and how that related to your NDL.
4) You hadn't read the computer's instruction manual.
5) You hadn't monitored your computer over the dive.

Assuming you were completely oblivious to how you were diving - knowing the difference between a mandatory safety stop and a deco stop would be the least of your concerns.

Luckily, Suunto seem to account for such ineptitude - and give a series of simple instructions to get the diver out of trouble, rather than bother to differentiate such things. Darwin's Law is accounted for - hence the lockout (which seems to be the main precursor for initiating many questions on Scubaboard, rather than any worry over potentially breached deco)

 

[watboy]

So, purely looking at the suunto screen, you have absolutely no way of knowing if the stop it is giving you is a mandatory safety stop or a deco stop. I've never been fully clear on how mandatory safety stop relates to an optional safety stop and mandatory deco stop. Optional and Safety seem to go together, as does mandatory and deco.... so mandatory safety means?

Well, there's your problem.

It would mean;

1) You didn't know if you had exceeded an ascent rate (even with the audible and visual alarm).
2) You didn't know your NDL (either planned before the dive and during the course of the dive from the computer).
3) You didn't know your dive time/depth and outline profile during the dive - and how that related to your NDL.
4) You hadn't read the computer's instruction manual.
5) You hadn't monitored your computer over the dive.

Assuming you were completely oblivious to how you were diving - knowing the difference between a mandatory safety stop and a deco stop would be the least of your concerns.

Luckily, Suunto seem to account for such ineptitude - and give a series of simple instructions to get the diver out of trouble, rather than bother to differentiate such things. Darwin's Law is accounted for - hence the lockout (which seems to be the main precursor for initiating many questions on Scubaboard, rather than any worry over potentially breached deco)

 

[Bubbletrubble]

So, purely looking at the suunto screen, you have absolutely no way of knowing if the stop it is giving you is a mandatory safety stop or a deco stop. I've never been fully clear on how mandatory safety stop relates to an optional safety stop and mandatory deco stop. Optional and Safety seem to go together, as does mandatory and deco.... so mandatory safety means?

@watboy: "Mandatory Safety Stop" is Suunto language that is defined explicitly in the dive computer instruction manual.
For my Suunto Mosquito, the manufacturer lays it out quite clearly on page 35 of the manual...

3.2.1.4.2. MANDATORY SAFETY STOP
When the ascent rate exceeds 12 meters/min [40 ft] momentarily or 10 meters/
min [33ft] continuously the micro-bubble build-up is predicted to be more than
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 will depend on the severity of the ascent rate excess.

The STOP sign will appear in the display and when you reach the depth zone
between 6 m to 3 m [20 ft to 10] also the CEILING label, ceiling depth and the
calculated Safety Stop time appear in the display. You should wait until the
Mandatory Safety Stop warning disappears (Fig. 3.13.).

The Mandatory Safety Stop time always includes the three minute Recommended
Safety Stop time. The total length of the Mandatory Safety Stop time depends on
the seriousness of the ascent rate violation.

Put simply, an ascent rate violation causes the computer to specify a "mandatory safety stop."

 

[DevonDiver]

S Optional and Safety seem to go together, as does mandatory and deco.... so mandatory safety means?

I'd imagine that it's mandatory primarily due to legal reasons. Suunto has to justify its algorithm against DCI risk. If the user violates the parameters of that algorithm, then Suunto need to be black and white about the situation. If they had an optional safety stop for violation of ascent speed, then there could be legal cases?

 

[watboy]

I'm not that well versed in the different decompression model theories. But, is micro build up related/a precursor to DCS in the RGBM model? I would assume then that skipping the mandatory safety stop has a material increase in the chance of a DCS? I guess what i'm asking is how does a mandatory safety stop differ from a mandatory decompression stop in reducing the chance of a hit. Or is it the same, the difference being one is to reduce risks arising from fast ascent and the other from too much nitrogen loading?

@watboy: "Mandatory Safety Stop" is Suunto language that is defined explicitly in the dive computer instruction manual.
For my Suunto Mosquito, the manufacturer lays it out quite clearly on page 35 of the manual...


Put simply, an ascent rate violation causes the computer to specify a "mandatory safety stop."

 

[redacted]

Is this thread really an advertisement for Oceanic computers?

 

[Juardis]

I'm not that well versed in the different decompression model theories. But, is micro build up related/a precursor to DCS in the RGBM model? I would assume then that skipping the mandatory safety stop has a material increase in the chance of a DCS? I guess what i'm asking is how does a mandatory safety stop differ from a mandatory decompression stop in reducing the chance of a hit. Or is it the same, the difference being one is to reduce risks arising from fast ascent and the other from too much nitrogen loading?

To my simple understanding (as I understand my manual), a Mandatory Safety Stop is actuated when you ascend too fast. There is a slight chance for DCS. Consequently, if you violate the Mandatory Safety Stop, you're penalized on your subsequent dives by having your no-deco dive time shortened. However, since the chance is slight, the computer will let you dive again (again, my simple understanding).

A Mandatory Deco Stop is actuated when you stay down too deep for too long. Now the risk of DCS is greatly increased UNLESS you stop at the ceiling and off gas for the specified period of time. IF you choose to ignore the Mandatory Deco Stop, or cannot complete it for some reason, then your computer will error out and not allow you to use it again for 48 hours.

I guess one way to tell the difference between a Mandatory Safety Stop and a Mandatory Deco Stop, assuming you were oblivious to your entire dive up until the time you hit the ceiling, is to ascend above the cieling and see if you get the ER indication. If you see that, you know you're in a Deco Stop and you have 3 minutes to descend back below the ceiling to complete your stop.