Rock bottom, 500 PSI, or something else?

[Lorenzoid]

Is GUE advocating 10 ft/min as a normal ascent rate?

An ascent from a no-deco dive (or "minimum deco" ascent as GUE calls it) is to ascend at 30 fpm to half your maximum depth, then 10 fpm to the surface, executed as 30 second stops every 10 feet, taking 30 seconds to ascend to the next stop.

 

[seeker242]

Is GUE advocating 10 ft/min as a normal ascent rate?

Normal rate is actually 30ft/min to 50% of max depth. 10ft/min thereafter, divided into a 30 second stop, followed by a 30 second ascent, every 10'. Minimum gas is calculated at just 10ft/min.

 

[boulderjohn]

An ascent from a no-deco dive (or "minimum deco" ascent as GUE calls it) is to ascend at 30 fpm to half your maximum depth, then 10 fpm to the surface, executed as 30 second stops every 10 feet, taking 30 seconds to ascend to the next stop.

Can you supply the research upon which the 10 FPM ascent rate is based? In the only research I know on the subject of ascent rates found for recreational diving found that 30 FPM was superior to 10 FPM.

 

[tbone1004]

Can you supply the research upon which the 10 FPM ascent rate is based? In the only research I know on the subject of ascent rates found for recreational diving found that 30 FPM was superior to 10 FPM.

I think the rock bottom uses 10fpm since they don't have any stops in there so it makes the math a bit more simple. From 100ft, you have 4ata/2=2ata, 2 divers at 1.0cfm=2cfm, 100ft at 10fpm=10mins, 10*2*2=40cf for rock bottom. Doesn't mean it's the way you're going to do your ascent, but it's a quick way to calculate it on the boat deck if your depth changes.

To break it out:
2 minutes at the bottom is 2min*2cfm*4ata=16cf
30fpm ascent is 4min*2cfm*2ata=16cf
3min safety stop is 3min*1.5cfm*1.5ata=7cf
Total is 39cf which is close enough to 40cf for me. I may choose to add some more time at depth if on a big shipwreck or if I know that I have to traverse somewhere before I can ascent which is my call, but 2 minutes gets you close to 100ft of travel time with situation resolution, and if I'm on something like the Vandenberg which is massive, AND is in high current, then I will likely give a big ass pad to my bottom time, but it's a general rule of thumb that gets you "close enough" without doing a lot of steps

 

[Lobzilla]

Can you supply the research upon which the 10 FPM ascent rate is based? In the only research I know on the subject of ascent rates found for recreational diving found that 30 FPM was superior to 10 FPM.

Please let's not turn this into another deep vs. shallow stop debate.

The challenge for open water divers is the lack of skills to control their ascent rate if panic sets in. The "Controlled" in the ControlledEmergencySwimmingAscent that is one pillar of open water safety is IMO wishful thinking for most novice divers.

The typical "death by drowning" is not drowning from ascending too slowly, it is death by OOG, then shooting to the surface like a Poseidon missile, then embolizing, and then drowning.

After peripherally witnessing an Out-Of-Gas emergency that ended in the death of the open water diver due to PBt/AGE as a result of an out-of-control panic ascent, I demonstrated several times that even an "empty" AL80 has enough gas left in it to make a GUE type ascent from 80' (i.e. 1 min@ 40', then 30 second slide, 30 second stop every 10' to surface. This ascent pattern is IMO largely a training step for future Tec diving, not necessarily the most efficient NDL ascent strategy.)

Let's not forget that every(!) dive is a decompression dive. Recreational open water divers decompress during a controlled(!) ascent and possibly/preferably a safety stop. There is no point in becoming another casualty by exceeding the physiological limits as a result of unnecessary panic.

If you run out of gas -which should never, ever happen- and you cannot get gas from your buddy -which should also never happen-, I would suggest to ascend expediently but to keep breathing the gas that the diminishing external pressure will allow to flow from the tank. Slow the ascend down to a sane rate and do a safety stop. Be prepared to orally inflate the BC on the surface.

Disclaimer: Do not try this at home without understanding of what you are doing and without a solid "plan B". I demonstrated this in a team, with double tanks that I isolated, which means I had plenty of reserve gas around me. After turning my doubles into two separate tanks by closing the valve connecting both tanks, we continued the dive until my right tank was "empty" and breathing from my primary regulator became very hard. I then thumbed the dive and ascended continuing to breathe from my right ,"empty" tank, did the GUE stops, and even inflated the wing enough to (barely) float at the surface. During all that I had a backup second stage hanging under my chin, connected to about 70 cuft of gas in my left tank. Plus two well trained team mates with tons of gas at arm's length. So, there was no need to panic. But in the extremely unlikely case that the same thing ever happens to me while diving a single AL80, I will respond exactly the same way. Start an immediate ascent, keep breathing, and use all the time left in the tank for "deco".

 

[Ayisha]

Can you supply the research upon which the 10 FPM ascent rate is based? In the only research I know on the subject of ascent rates found for recreational diving found that 30 FPM was superior to 10 FPM.

In the shallowest 50% of a Minimum Deco dive (referred to as a No Deco Limit dive by some other agencies) to recreational depths (considered to be 100 feet by GUE)?

 

[boulderjohn]

In the shallowest 50% of a Minimum Deco dive (referred to as a No Deco Limit dive by some other agencies) to recreational depths (considered to be 100 feet by GUE)?

No, it was a talking about a straight 10 FPM ascent.

But as long as you are talking about it, what is the scientific basis for the min deco ascent profile?

 

[Ayisha]

No, it was a talking about a straight 10 FPM ascent.

But as long as you are talking about it, what is the scientific basis for the min deco ascent profile?

Actually, the person that you quoted and posed the question to, above, as well as the other person who responded, both stated "to half your maximum depth" or "to 50% of max depth", not a "straight 10 FPM ascent". See quotes below:

An ascent from a no-deco dive (or "minimum deco" ascent as GUE calls it) is to ascend at 30 fpm to half your maximum depth, then 10 fpm to the surface, executed as 30 second stops every 10 feet, taking 30 seconds to ascend to the next stop.

Normal rate is actually 30ft/min to 50% of max depth. 10ft/min thereafter, divided into a 30 second stop, followed by a 30 second ascent, every 10'. Minimum gas is calculated at just 10ft/min.

Regarding your question to me, I'm not privy to that. I believe @Dr Simon Mitchell posted something to the effect in previous deep stop threads that half-depth stops or slower ascent rates are insignificant at recreational depths, but I don't want to misquote him, so perhaps he'll clarify. In this case, GUE minimum deco dives are to a maximum of 100 feet, so the 10 FPM begins from a maximum depth of 50 feet.

 

[JohnnyC]

But as long as you are talking about it, what is the scientific basis for the min deco ascent profile?

I don't know where the GUE min deco ascent profile came from, but there's a study quoted in Deco for Divers that tracked bubble scores from divers that did various ascent profiles from direct ascent, 3(?) minute safety stop, 5(?) minute safety stop, and staged ascent. I don't remember the exact name of the study or the specific times/scores listed since my copy is in a box somewhere, but I distinctly remembering that the group that did the staged ascent had lower bubble scores.

Whether or not this correlates to a GUE min deco schedule in any way I don't know, but it does demonstrate that benefit of a staged ascent within recreational diving. The min deco table I have seen floating around is:

40ft/12m - 1 minute
30ft/9m - 1 minute
20ft/6m - 3 minutes
10ft/3m - 3 minutes

I need to find my copy of the book, I'd really like to give more specific info.

 

[seeker242]

No, it was a talking about a straight 10 FPM ascent.

No. It was talking about a straight 10 fpm in order to calculate min gas reserve.