Forced descent in Blue Hole

[Valwood1]

In other words the dive op has planned and worked out the dive for you so it's a trust me dive that usually doesn't kill anyone. The DM is doing the diving and the tourists are just along for the ride. As long as the tourist doesn't mess up too badly the DM will complete the dive as planned.

This reminds me of the waiver I signed before skydiving. It said essentially "This is really dangerous, but you're going to have a great time. Of course, you're going to die, and it's not our fault when you do. Enjoy yourself. It's a thrill. But you're going to die." And then you felt grateful when you didn't.

 

[NCSCUBADOOBA]

Dandy Don,
I did NOT do the blue hole. You guys all convinced me NOT to. The girls we dove with on other dives did it and reported the forced descent back to us. They said 'you would've totally freaked out' but they did compliment me on my first dive post certification. I did just fine, equalized great, took pictures, never sunk or shot up to the top and had a blast!!!! Oh, another thing was that they said the Blue Hole was really really murky...
So, I behaved!!!!!!!!!
Angela

 

[NCSCUBADOOBA]

Oh... the dive shop that took them out was not ADM or Protech.
Angela

 

[DandyDon]

Dandy Don,
I did NOT do the blue hole. You guys all convinced me NOT to. The girls we dove with on other dives did it and reported the forced descent back to us. They said 'you would've totally freaked out' but they did compliment me on my first dive post certification. I did just fine, equalized great, took pictures, never sunk or shot up to the top and had a blast!!!! Oh, another thing was that they said the Blue Hole was really really murky...
So, I behaved!!!!!!!!!
Angela

Yeah, my misreading was pointed out to me later in this long thread.

Glad you had a good trip...

 

[lakewinni]

I personally wouldn't want to do this dive on a single alum80 but just to everyone that was saying that its crazy, its really not if you have an excellent buddy, plan your dive and stick to that plan. If you calculate it out 30 cft is enough to provide you and your buddy ascent to the surface from 130 ft at an ascent rate of 30 ft/min with a sac of like .7ish. If you calculate a turn pressure off this, then do something like a 12 min dive total including decent you should be all set. Just make sure you have a good unified buddy team with excellent fundamental skills and even if you have a catastrophic failure you'll be getting out fine.

 

[c555]

Some people have been talking about running short on air to the blue hole. I look at it like this: if a diver has a .7 cfm consumption this is his air breakdown.
average descent deapth: 65' = average breathing rate of 2.1 scf/m
4 minute descent= 8.4 cubic feet
132 average botttom deapth= 3.5 cf/m air consuption
10 min bottom time (i know its a lot)= 35 cf used
4 min ascent @ average depth of 65 ft= 8.4 cf
5 min safety stop @ 15' = 7 cf
total air used = 58.8 subic feet
this leaves over 20 cf foor your buddy, which is enough for the ascent and safety stop. The only reason not to do this dive is if you are not cofortable with the deapth. Air sould not be an issue, if you have at least an O.K. breathing rate.

 

[DandyDon]

I just did not see much margin for problems. One diver had her air turned all the way off, then back on 1/2 a turn by the Aqua Dive deck hand - but got it turned on for her when she ran out. :11:

I think there were about 15 in my group, escorted by 3 local DMs, 2 Texas Inst from the group, 2 Texas DMs, but I was the only one carrying a pony.

 

[D_O_H]

Some people have been talking about running short on air to the blue hole. I look at it like this: if a diver has a .7 cfm consumption this is his air breakdown.
average descent deapth: 65' = average breathing rate of 2.1 scf/m
4 minute descent= 8.4 cubic feet
132 average botttom deapth= 3.5 cf/m air consuption
10 min bottom time (i know its a lot)= 35 cf used
4 min ascent @ average depth of 65 ft= 8.4 cf
5 min safety stop @ 15' = 7 cf
total air used = 58.8 subic feet
this leaves over 20 cf foor your buddy, which is enough for the ascent and safety stop. The only reason not to do this dive is if you are not cofortable with the deapth. Air sould not be an issue, if you have at least an O.K. breathing rate.

The problem is that when your catastrophic failure occurs at 132', your sac rate, as well as your buddies', probably shoots through the roof. At a minimum, it's going to go up.

I haven't run (and honestly am probably not mathematically capable of running) the numbers, but I suspect things would work out just fine with a lower .45ish sac for the normal part of the dive and a 1.something if the sheezie hits the fan.

 

[mudchick]

I would like to the the OP and all the responders on this thread. This was very educational for me. While I recently was deep diver certified, I haven't yet done any deeps recreationally and between doing the dives to 130 ft and reading this posting, it opened my mind to the idea that if I'm going to do deeps on a regular basis for my sake and more importantly for the sake of my buddy I should get trained in carrying a pony bottle. I would not be real comfortable doing that Blue Hole dive with out a good redundant system or certainly not until I was better at controlling my air consumption which I'm always working on. I was amazed at my last deep that my instructor came back from 131 ft. with almost 1200 psi on his tank! That's my goal.

 

[lamont]

Some people have been talking about running short on air to the blue hole. I look at it like this: if a diver has a .7 cfm consumption this is his air breakdown.
average descent deapth: 65' = average breathing rate of 2.1 scf/m
4 minute descent= 8.4 cubic feet
132 average botttom deapth= 3.5 cf/m air consuption
10 min bottom time (i know its a lot)= 35 cf used
4 min ascent @ average depth of 65 ft= 8.4 cf
5 min safety stop @ 15' = 7 cf
total air used = 58.8 subic feet
this leaves over 20 cf foor your buddy, which is enough for the ascent and safety stop. The only reason not to do this dive is if you are not cofortable with the deapth. Air sould not be an issue, if you have at least an O.K. breathing rate.

you are at 130 fsw. if something goes wrong, its likely that one or the other of you are going to start rapidly breathing and start taking a CO2 hit. i'd use at least a combined SAC rate of 2.0 for an emergency event. its much more likely you'll actually hit that rate at 130 than you will at only 80.

now, to take 1 min at the bottom to sort out the issue, 4 mins to ascend, and 3 mins of stops, you'll be taking 8 mins to ascend at an average ATA of around 3.0, which is: 8 * 3 * 2 = 48 cu ft of gas. that's how much you need to reserve at least on an Al80 it comes out to 1800 psi.

with a SAC rate of .75, you'll be burning about 300psi/10 min/ATA or almost 1500 psi / 10 mins. that means you'll go through your 1200 psi of available gas in under 10 mins.

the thing that terrifies me about the average diver doing this is that i've gone through training to get off the bottom and move up in the water column promptly. the average diver hasn't. you won't understand this until you've actually been put into a situation where you've been task loaded on ascent and watched yourself fiddle around for 5 minutes at depth. 5 mins at depth on an Al80 at 130 burns another 750 psi, which is nearly 1/2 your reserve. the clock is running very fast down there and with the combination of lack of traning and CO2 narcosis, i expect that most of the divers doing that dive are very overconfident. for example, i doubt that if they were at the limit of their gas and they or their buddy had a free-flow that they would be able to sort the problem out and get moving off the bottom before the tank was drained, which is just going to waste time.