Question What's your safety stop depth?

Which setting would you use for your safety stop, given the choice?

  • 3 m

    Votes: 3 2.6%
  • 6 m

    Votes: 57 49.6%
  • Whatever my dive buddy uses

    Votes: 1 0.9%
  • Never mind what my computer says, I'm doing it at 5 m / 15 ft.

    Votes: 42 36.5%
  • I don't do safety stops

    Votes: 12 10.4%

  • Total voters
    115

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Cheizz

Contributor
Messages
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Location
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# of dives
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Many training agencies advocate a safety stop of 3 to 5 minutes at 5 m / 15 ft depth. Some computers give you the choice of a safety stop at 3 or at 6 minutes. Why isn't this 5 minutes if that seems to be one limit of an industry standard?

When given the choice, what would you set your dive computer to?
 
The Shearwaters credit anything between 10' and 20'. I usually hang someplace in the middle.Since they are a recommendation, not a reuirement, it's hard to talk about a "standard"
Agreed. I only call it a standard, because there seems to be a consensus amongst training agencies. For recreational diving, at least.
 
Should really be an option for "depends on what the surface is doing":)
 
Most computers give you a range from 10-20 feet/3-6 meters. Fifteen feet is just a number in the middle of that range. If you understand why, it all makes sense.

More then 100 years of research indicates that if you ascend at a safe rate of speed, you should be able to go directly to the surface on an NDL dive. The safety stop is exactly what the name suggests--an extra precaution just to make sure.

You do not want your tissue pressure to be too great in relation to the ambient pressure around you, and that tissue pressure drops as you ascend. Ambient pressure drops dramatically in the last 10 feet, so in order to be sure you are in a safe range, it makes sense not to go shallower than 10 feet for this stop.

You have a variety of tissues in your body, and they absorb and release gas at different rates. The fastest tissues had the most pressure when you began the ascent, and by doing a safety stop, you will hopefully give them enough time to off-gas to a safe level. When they off-gas, they do so until they are at equilibrium with the pressure you are under at that depth--then they stop. In the meantime, some slower tissues are still on-gassing, even during the safety stop. That on-gassing will stop when they are at equilibrium with the pressure at that depth--they will not go beyond that.

In other words, if you stayed long enough at safety stop depth, all your tissues would end up at the pressure you are under at that depth--some will off-gas to get there, and some will on-gas to get there. The good news is that research on saturation divers indicates that if you are saturated at pressures shallower than 20 feet, you can go to the surface at any time. In other words, if you stayed at safety stop depth for a week, you could still go directly to the surface.
 
The real issue is on what dives should you do a safety stop, and on what dives can you skip it. The practice nowadays is to do a safety stop on all dives, but newer computer technology may play a role in that.

When I do an NDL dive with my Shearwater computers, I leave them in tech mode, and I have the SurfGF mode open in one of them. That tells me how close I would be in percentage to the Buhlmann limits if I were to surface right away. What a lot of people are doing these days is ignoring the standard time of a safety stop and instead ending it when they see a SurfGF they like. In theory, anything under 100 should be safe to surface. An 85 should be good, and 75 should be very safe. Some will stay until it drops to 70.

When you start thinking along those lines, you look at the safety stop in a whole new way. I was just diving for 2 weeks in Roatán, and we spent a lot of time in pretty shallow water while using nitrox. I was the only one on those dives with a SurfGF feature, and everyone else did standard safety stops every time. I stayed with them regardless of what my computer told me. On nearly every dive, my final SurfGF was below 20, and it was sometimes below 10. On one dive it never got above 19 throughout the entire dive, but, by golly, we all did a safety stop. I do not believe a safety stop was necessary on any of the dives we did.
 
You missed a safety stop option which many of us practice.
"I don't stop at one depth, I spend at least 5 minutes sliding up between 30ft and the surface"
 
https://www.shearwater.com/products/perdix-ai/

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