Continue dive?

[man_water]

Hmmm.... Some seem to have taken them as separate questions...

Let's see. I've seen people do this: Go down, set the dive flag or boat anchor, come up, and go down with a group. And this: Come up from the last dive and go back down to pick up the flag anchor.

If you've been diving at say 30 feet and come up reasonably slow, say even the recommended 30 fpm, is there more risk of DCS to go back down to 30 feet assuming you're way under the table limits? If there's more risk of DCS by doing this, is the risk the same as if you're at 70 or 100 feet?

 

[The Iceni]

man_water once bubbled...
. . . I've seen people do this: Go down, set the dive flag or boat anchor, come up, and go down with a group. And this: Come up from the last dive and go back down to pick up the flag anchor.

Why is this ever necessary?

There is little doubt that the decompression penalties (and added risks of DCI) are increased by such practices.

In the UK it is almost unheard of for someone to make an initial recce down the anchor chain. A decent shot line (on a wreck) located by the means of an echo sounder almost guarantees hitting the target without the need to send any diver down.

As for the ascent, routinely the last buddy pair attach a lift bag to the anchor/shot before surfacing on their DSMB - the boat following with the current.

Thus we all have nearly square profile dives.

 

[TheDarknessLord]

I don't understand pretty much the word float in your question, but anyway I will try to explain what you have to do if a diver, for any reason, has an emergency under the water and the only way to get out is going up very fust.

1st - if you need to go up very fast, never hold your breath. if you have to go up, and you hold your breath you are going to damage your lungs, and it could be fatal.

2nd - never go back again. Go to the nearest hospital and find for a diving doctor or specialist.

Decompression Illness is very common in deep diving avoid that kind of activities unless you have the right training!

 

[getwet]

Maybe we should treat the situations separately?

Coming to the surface while not having any emergency, not having exceeded the no-decompression limits, and following the right ascent speed should not be a real problem. Based on almost every dive table, if you remain less than 10 minutes at the surface, it's not considered as another dive (except for the DCIEM, where the time is 15 min). In that case you should avoid going deeper, and you have to add the time you've been at the surface, to your bottom time.

Now, if you surface because you have an emergency.... well, that's something completely different. Even if you make it to the surface without barotrauma or any DCI symptons, you can't be sure you won't have any problems (remember symptons can show up even a long while after you ended your dive). Then, considering the "10 minutes rule" here would not be something very smart... I'd definitely keep myself out of the water, get some oxygen -if avail, and go straight to a hospital.