Mandatory safety stop vs. deco

Linus Torvalds torvalds at
Mon Sep 9 08:50:03 UTC 2013

On Mon, Sep 9, 2013 at 8:21 AM, Miika Turkia <miika.turkia at> wrote:
> It was a surprise that warranted a bit of digging to find out what is going
> on, why the deco. This also seems to depend on the Suunto model whether you
> get mandatory safety stop or not. My Stinger didn't mind the ascent...

The suunto model isn't just about saturation, they talk a lot about
their "microbubble" modeling too. That's what the warning triangle you
so often get after a dive means, and is why Suunto computers get *so*
unhappy if you have lots of surf and end up bouncing up and down by
3-5m when you are nominally at 10m depth (been there, done that, my
HelO2 went absolutely nuts).

Also, the notion of being in deco is not entirely black-and-white. The
dive computer wants to give you reasonable bottom time, so generally
it assumes some aggressive but sane ascent rate to the surface. For
example, you should not think that it's safe to just ascend at max
possible speed from 30m just because your computer said you're not in

So I'm sure there isn't a "right" answer. I think the Suunto
"mandatory safety stop" is somewhat different from their normal "deco"
thing in that it probably means that you had more microbubble issues
than actual nitrogen saturation issues. Regardless of the reason, your
suunto thought that there was a reason for it not being safe to ascend
directly to the surface.

Of course, suunto is famous for that. I put mine in the "yes, I will
die" mode (suunto calls it "50% RGBM") because otherwise it is too far
off any other computers I carry (or other people carry).


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