Proper rate of descent?

[ScubaInChicago]

Another factor to consider (maybe not for your local diving conditions) is the water temps. If the water is cold and you're using a long burst of air to control your buoyancy at your destination, the inflator valve could freeze open. This could also cause the inflator quick disconnect to become frozen leading to more problems.

 

[TSandM]

An uncontrolled rate of descent can led divers into rapid breathing that causes CO2 levels to increase.

Honestly curious why you feel this would happen? I can see it with an unintended rapid descent, and a frightened diver. But if it is someone's intent to descend rapidly, why would their respiratory rate increase?

 

[SCUBASailor]

Honestly curious why you feel this would happen? I can see it with an uninended rapid descent, and a frightened diver. But if it is someone's intent to descend rapidly, why would their respiratory rate increase?

Because he's having fun!

On the serious side, even though I feel I have a firm grip on my descent, I do see the issue of not staying close enough to my dive partner. From now on, I will do a conservative descent unless conditions require otherwise. The descent proceeds at the rate of the slowest team member. Sounds like a rule to live by.

 

[deich]

if you find yourself in a mushroom cloud when you hit bottom that may be to fast....

 

[rmc77]

Honestly curious why you feel this would happen? I can see it with an uninended rapid descent, and a frightened diver. But if it is someone's intent to descend rapidly, why would their respiratory rate increase?

It will increase your respiration rate regardless, maybe not as much but it will. Even during normal conditions our respiration ration increases during the descent, doesn’t it?
The respiration rate may increase because you're afraid (in case the rapidly ascend was not intended) or because you're excited (especially if you like fast descends). It's a natural response of our body, mainly due to all the adrenaline that will be poured on the blood stream. How much increase in respiration rate will be a concern with CO2 buildup issue? Well, that depends.

I do agree that this is most likely to be an issue for an unintended rapid descent. Nonetheless, it’s good to have on the back of our minds that the descent rate can affect you, not as much as the rate of ascent, off course, but to an extent that dropping to the bottom as fast as you can, depending on the kind of diving you’re doing, perhaps is not the best answer.

 

[SCUBASailor]

if you find yourself in a mushroom cloud when you hit bottom that may be to fast....

Back in the seventies, I had friends who often found themselves in mushroom clouds. Oh, wait...that's not what you meant.

 

[Walter]

There was a discussion about this not too long ago, in which Walter offered that somebody (but I don't remember who) prescribes a maximum descent rate of 60 fpm.

Close, but no banana. The US Navy recommends a max descent rate of 75 ft/min.

 

[Sas]

When I plan my dives, descent is planned at 20m/minute - I find that comfortable but if a buddy is not descending as fast as that I will slow down for them as I don't like the idea of meeting on the bottom (where I dive viz can be crap sometimes so it might not be practical as it is easy to seperate). I tend to add air as I am descending but whatever works for you, really.

 

[boulderjohn]

IMHO, CO2 build up is the main concern here.

An uncontrolled rate of descent can led divers into rapid breathing that causes CO2 levels to increase. CO2 buildup is accepted in the literature as one of the factors that can intensify narcosis and O2 toxicity.

Honestly curious why you feel this would happen? I can see it with an uninended rapid descent, and a frightened diver. But if it is someone's intent to descend rapidly, why would their respiratory rate increase?

It will increase your respiration rate regardless, maybe not as much but it will. Even during normal conditions our respiration ration increases during the descent, doesn’t it?
The respiration rate may increase because you're afraid (in case the rapidly ascend was not intended) or because you're excited (especially if you like fast descends). It's a natural response of our body, mainly due to all the adrenaline that will be poured on the blood stream. How much increase in respiration rate will be a concern with CO2 buildup issue? Well, that depends.

I think that if you have planned your dive well and are confident in your abilities and the abilities of your team, you will not experience those symptoms.

What I was once told about CO2 buildup on rapid descent and narcosis was that you could get CO2 buildup if you physically work to get a fast descent, as in swimming downward. That makes sense to me.

I personally like to get down pretty fast because if I am going deep enough that I will have limited bottom time, I want to spend as little of that time in transit as possible. I do that, however, by a natural drop, with no muscle effort. If I am properly weighted in a single tank and a wet suit, it is not going to be all that fast.

On the other hand, when I am at the beginning of a dive using steel doubles, I will start dropping very quickly if I am not careful. In that case, by golly, I will be going back and forth adding little spurts to my dry suit and my wing continually. As Rob said, you do want to be able to stop when you need to. I once had my dry suit inflator become disconnected during a rapid descent, and although I was able to arrest the descent pretty quickly with the wing, it still took enough time for me to get some mild bruising from the dry suit squeeze.

 

[Diver0001]

I personally like to get down pretty fast because if I am going deep enough that I will have limited bottom time, I want to spend as little of that time in transit as possible. I do that, however, by a natural drop, with no muscle effort. If I am properly weighted in a single tank and a wet suit, it is not going to be all that fast.

Last week I did two dives to 45 metres. On the first dive we descended to about 20 metres and swam along for a few minutes before swimming over a drop-off and making the descent just on gravity. The narcosis was pretty mild considering the depth and we all felt good.

A few days later we made another dive to 45 but this time we dropped off the zodiac and swam down at about a 30% angle to get to the bottom. The descent involved more effort and was very quick. By the time we got to 45 I was sure if I went any further I would be cross-eyed narced so we moved up to 30 again without spending much time at depth.

I've noticed this before, which is that the harder you work and the faster you descend, the bigger the narc. Ideally, if you're diving deep you really should try to float down like autumn leaves falling from the trees...

R..