Safety Stop - 3 min or 5 min?

[Lorenzoid]

If I recall correctly, there's a study lying around somewhere with a Doppler test at the end of dives with and without safety stop (same ascent rates) and the ones without safety stop had a higher bubble level. Now we know that bubbles don't necessarily imply DCS, but I think that's one of the reasons to do it.

Yeah, these tests are discussed in the PADI Encyclopedia, which says Andew Pilmanis conducted them in 1975 and that "a stop at 3 metres/10 feet for as little as two minutes reduced detectable bubbles by a factor of five, and a 5-minute stop virtually eliminated any trace of measurable bubbles."

So, one might conclude that the difference between the bubble reduction gained from a 5-minute stop over a 3-minute stop is not enough to make the difference between DCS and no DCS. It also depends on ascent rate, of course. I think PADI bases their recommendation for a 3-minute stop on it being done in conjunction with a 30 fpm ascent rate from maximum depth. My understanding is that a safety stop is more beneficial than a slower ascent rate.

It's all voodoo science anyway. The only thing that seems beyond dispute is that a stop of 3-5 minutes at somewhere in the neighborhood of 15-20 feet is beneficial.

 

[Bob DBF]

Since I started using a computer, I gradually started following it's advice. This was assisted by diving with my daughter who was certified with the 30 ft/min and 3 min safety stop, and me not leaving my buddy. I now stretch out the safety stop if I like the view in the 15' range, or have done something stupid like wander over NDL during the dive, even though I am within NDL arriving at the stop. Although the computer warns and records violations of ascent speed, missing a safety stop, and NDL, so far it has never locked me out of my next dive. This allows me to revert to old habits, but I try to follow the computer since that is why I bought it.

When I dove the tables, I followed them. Now that I dive a computer I follow it for the same reason I followed the tables, and if it is a bit quirky in asking me to slow down I will. As for adding to the safety stop, I have no problem with that as Deco Theory allows it and on the computer I can watch the gauge moving away from NDL which, I believe, is a good thing.



Bob
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I may be old, but I'm not dead yet.

 

[oldschoolto]

I had a quick look at the US Navy Diving Manual and could not find the term "Safety Stop." It seems that decompression stops are calculated. Indeed, the no-decompression limit is defined in terms of ascending directly to the surface:

"No-Decompression (No “D&#8221 Limit. The maximum time a diver can spend at a given depth and still ascend directly to the surface at the prescribed travel rate without taking decompression stops." (Chapter 9-3).

And..

"No-Decompression Dive. A dive that does not require a diver to take decompression stops during ascent to the surface. (Chapter 9.3)."

I might conclude that according to the US Navy, safety stops are optional whether it is 5 or 3 minutes.

GJS

Don't you know the rules about talking Navy Tables.... You dive those and you'll die for sure ..

Jim....

 

[Jack Hammer]

The three minute recommendation has to do with the amount of time it takes for circulation to occur thereby allowing gas to move from the blood to the lungs to be expelled.

 

[dmaziuk]

Since I started using a computer, I gradually started following it's advice.

If I end the dive in the shallows, after some (about 10?) minutes above 30' my computer (leonardo) turns safety stop off. I remember the first time I noticed I was a bit surprised: hey, where's my safety stop counter? Made me go re-read the small print.

Computer is your friend, trust the computer. ;-)

 

[Basking Ridge Diver]

The three minute recommendation has to do with the amount of time it takes for circulation to occur thereby allowing gas to move from the blood to the lungs to be expelled.

Hmmnnn -
[SIZE=+2]How long does it take your heart to circulate the total amount of blood in your body?[/SIZE]
(Lansing State Journal, December 01,1993)

---

For a person at rest, it takes just about one minute. If you are more active, it will take less time. Exactly how long depends on several things: the rate at which your heart beats, how big your heart is, and, to a certain extent, how big you are as well. A person's heart beats about 65 to 75 times a minutes. This is called the beat rate. With each beat, the heart pumps about 60 to 70 milliliters of blood. If you multiply the two values together, you find that the cardiovascular output is just about four to five liters per minute. Can you guess how much blood an individual has?

If you exercise, your heart rate increases, and it decreases when you rest. Your body has a remarkable way of knowing just how much blood should be flowing to properly distribute the nutrients it needs. The primary means of controlling cardiovascular output is by controlling the beat rate with hormones. One, called acetylcholine , acts to decrease beat rate, when you are resting or sleeping. Another, called norepinephrine, increases the rate at which your heart beats, when you are active or excited. The balance of these two hormones helps to keep the rate of your blood flow just right.

 

[Jack Hammer]

Hmmnnn -
[SIZE=+2]How long does it take your heart to circulate the total amount of blood in your body?[/SIZE]
(Lansing State Journal, December 01,1993)

---

For a person at rest, it takes just about one minute. If you are more active, it will take less time. Exactly how long depends on several things: the rate at which your heart beats, how big your heart is, and, to a certain extent, how big you are as well. A person's heart beats about 65 to 75 times a minutes. This is called the beat rate. With each beat, the heart pumps about 60 to 70 milliliters of blood. If you multiply the two values together, you find that the cardiovascular output is just about four to five liters per minute. Can you guess how much blood an individual has?

If you exercise, your heart rate increases, and it decreases when you rest. Your body has a remarkable way of knowing just how much blood should be flowing to properly distribute the nutrients it needs. The primary means of controlling cardiovascular output is by controlling the beat rate with hormones. One, called acetylcholine , acts to decrease beat rate, when you are resting or sleeping. Another, called norepinephrine, increases the rate at which your heart beats, when you are active or excited. The balance of these two hormones helps to keep the rate of your blood flow just right.

Great response, minus the "Hmmnnn" of course. Trying to keep it simple, no need to bring diffusion, ambient, how many times blood should circulate, gradients, gas switches, etc.

There has also been changes in deco theory since safety stops were first introduced, newer findings have little to do with why it was first suggested.[emoji2]

Sent via

 

[pjhansman]

I just do 5 minutes....I'm not usually in a hurry to get to surface anyway

 

[Basking Ridge Diver]

Great response, minus the "Hmmnnn" of course. Trying to keep it simple, no need to bring diffusion, ambient, how many times blood should circulate, gradients, gas switches, etc.

There has also been changes in deco theory since safety stops were first introduced, newer findings have little to do with why it was first suggested.[emoji2]

Sent via

Hmmmnnn - meant if you knew something I did not I would like to hear it - I was curious because Diffusion, Ambient pressure, Gradients and gas switches are pretty much immediate responses. There is no lag time built in.
So where did 3 mins vs 5 mins come from?

 

[NAM001]

I do the 3 min stops because
like most other divers we do not do square dives, which should be a reason not to do them, since avg depth is less than max.
i am older ( if that makes any difference)
no one can kep up with the actual depth one is at (multi level diving)
most of my dives are 60 ft and more with multiple dives a day.
I am not the poster child for body type the rules were made around by the navy.
lastly i do a buoyancy check at the end of each dive to evaluate weighting air supply. and gear secured prior to returning to non water gravatational effects.

If i am doing 30 ft dives i do not do safety stops no matter how long i am down. (time is air limited) gear is secured at depth.
I always play the game of ascent speed control at end of dive. (skills maintenance)

a prior post on the first page cited the navy tables showing no safety stop required. A safety stop is a deco stop and the term NDL is what is being cited.
what was interesting about the post is the conditions stated. depth, time, ascent rate. most experienced divers manage this very well. those that dont need a little conservatism on thier side to cover errors.