Need info for a novel (deep diving information)

[mart1]

I want to remind you oxygen is every bit as narcotic as nitrogen, and then some.
So if you calculate your END, count the oxygen in the mix in.
Just because it is fiction, does not mean we should forget the facts ;-)

ciao, mart

 

[PerroneFord]

If these divers were truly salvagers, I doubt they'd be worried much about END. They'd probably be able to afford Heliox. Obviously that's my unqualified opinion as I am not a trimix diver, but I doubt they'd be worried about the extra $30 to get rid of the nitrogen in the fill.

 

[humanphibian]

try thedecostop.com, there are a bunch of guys over there that'll help you with the info that you are looking for.

 

[TheRedHead]

I think having someone tox on Nitrox at 200 feet might be interesting in a novel. Nice way to kill off a character.

 

[Don Burke]

I'm not sure if anyone here can, or would even have the time to respond to this inquiry, or if this is the right forum topic to be posting this. I'm writing a novel and a portion of it takes place at an undersea shipwreck. I want it to have at least a basic sense of reality so I was looking for some simple tech info on deep sea salvage dives. I'd appreciate any help anyone could give me. I've done a small amount of research but I'm not completely familar with all the correct terminology so please bear with me if I get some of this wrong. And please remember, this will be a work of fiction so there is room for pushing the reality envelope to a certain degree. I'm looking for basic info pertaining to:

1) At a dive of approx 200ft, working with trimix tanks, how long could divers work and stay down safely at that depth?

The main factors are gas supply and the amount of deco that can be safely done with the weather conditions. Predicting the weather twelve hours in advance is pretty difficult in some places.

Is there a maximum safe time?

Not really.

If there is no limit, what would the answers be to the following questions based on an on-wreck time of 60 to 90 minutes? Keep in mind these divers are very experienced yet somewhat unorthodox risk-takers.

2) What would the time of ascent be with a dive like this if they stayed down the maximum safe time (or for 60-90min)?

3) How many stops on the way up would they need to make and what type of mixture level changes would they need to make during ascent?

45 minutes would be realistic based on gas that can be carried. Here is what 45 minutes means on 16% oxygen & 50% helium for a bottom mix with deco on 30% oxygen/50% helium, EAN50, and oxygen:

200 feet for 45 minutes on 16/50
140 feet for 1 minute on 30/50
120 feet for 1 minute on 30/50
110 feet for 2 minutes on 30/50
100 feet for 3 minutes on 30/50
90 feet for 4 minutes on 30/50
80 feet for 5 minutes on 30/50
70 feet for 4 minutes on EAN 50
60 feet for 5 minutes on EAN 50
50 feet for 7 minutes on EAN 50
40 feet for 9 minutes on EAN 50
30 feet for 15 minutes on EAN 50
20 feet for 19 minutes on oxygen
10 feet for 35 minutes on oxygen

That would be a total of 110 minutes of deco plus the 45 minutes of bottom time and 3 minutes of transit time. Most divers would take a little more time, so round it up to around 165-170 minutes.


If you solve the gas supply problem, here is 60 minutes:

200 feet for 60 minutes on 16/50
140 feet for 1 minute on 30/50
120 feet for 3 minutes on 30/50
110 feet for 4 minutes on 30/50
100 feet for 4 minutes on 30/50
90 feet for 6 minutes on 30/50
80 feet for 8 minutes on 30/50
70 feet for 5 minutes on EAN 50
60 feet for 7 minutes on EAN 50
50 feet for 10 minutes on EAN 50
40 feet for 13 minutes on EAN 50
30 feet for 21 minutes on EAN 50
20 feet for 27 minutes on oxygen
10 feet for 49 minutes on oxygen

That would be a total time of something like 230 minutes. The amount of deco gas required is getting rather out of hand.


Since you asked, here is 90 minutes:

200 feet for 90 minutes on 16/50
140 feet for 2 minutes on 30/50
130 feet for 3 minutes on 30/50
120 feet for 5 minutes on 30/50
110 feet for 6 minutes on 30/50
100 feet for 8 minutes on 30/50
90 feet for 11 minutes on 30/50
80 feet for 12 minutes on 30/50
70 feet for 9 minutes on EAN 50
60 feet for 10 minutes on EAN 50
50 feet for 16 minutes on EAN 50
40 feet for 22 minutes on EAN 50
30 feet for 35 minutes on EAN 50
20 feet for 42 minutes on oxygen
10 feet for 81 minutes on oxygen

That would be a total time of over six hours. The diver would be unlikely to be able to carry enough deco gas to pull this off. Perhaps a rebreather could support this. Surface supplied would be another option.

The diver in all of these scenarios would be over the NOAA limits on oxygen exposure. Make that well over for the second and stupidly over for the third.
You _did_ say they were risk takers.

4) How long would they have to wait before they could dive again to that depth, and if they did dive again, would their down time (time at site) need to be less and how would this affect their decompression ascent time back to the surface?

They could dive immediately, but the decompression obligation for a similar dive would be pretty substantial.

Waiting a few hours would help, but the second dive would be shorter or involve more decompression time or some combination of the two.

5) If someone had to do an emergency ascent, fully inflating their buoyancy compenasator, or some other means of very, very fast ascent, from approx 100ft, could they survive if the ship had a portable hyperbaric chamber on board and couldn't make it to a medical facility, and how long could it possibly take before they might regain some sense of coherent consciousness?

If it was the first dive in 24 hours or so and the diver was only down for about 20 minutes, he could smile and wave at the camera. I would not try it beyond that and could only guess at how much time at depth would result in unconciousness.

One member suggested "The Last Dive" as a reference. That would help here. "Stars Beneath the Sea" could also give you some insight into rapid ascents.

Again, remember there is room to push the reality envelope a little for this scenario.

If anyone is able to assist with any of this info, I thank you now, and if and when this gets published, a technical advisory credit would of course be given.

I would prefer not. Just tell us the name of the book when it is published and I will buy one and have you autograph it for me.




I am not an author and do not play one on the web, so take this for what it is worth:

110 feet for 70 minutes on EAN 32
50 feet for 1 minute on EAN 32
40 feet for 4 minute on EAN 32
30 feet for 8 minutes on EAN 32
20 feet for 7 minutes on oxygen
10 feet for 12 minutes on oxygen

That is plenty of deco to hurt if missed and would require no special gear. It is also enough oxygen exposure to make underwater oxtox a possibility on repetitive dives, which is pretty high drama in itself. It is also deep enough that narcosis could be a problem.

 

[my1ocean]

5) If someone had to do an emergency ascent, fully inflating their buoyancy compenasator, or some other means of very, very fast ascent, from approx 100ft, could they survive if the ship had a portable hyperbaric chamber on board and couldn't make it to a medical facility, and how long could it possibly take before they might regain some sense of coherent consciousness?

Again, remember there is room to push the reality envelope a little for this scenario.

If anyone is able to assist with any of this info, I thank you now, and if and when this gets published, a technical advisory credit would of course be given.

An emergency ascent of a trimix diver from 100ft would probably be fatal. Regardless of exhalation on ascent. Too many bubbles would form in too many places and cause irreperable damage. A normal diver could ascend from 100ft and survive with no risidual effects provided he/she exhaled and got to a chamber quickly.
However, commercial divers do surface decompressions all the time where they come to the surface with decompression requirements and get into a chamber within 5 minutes. These are typically satruation divers, but a trimix diver could do the same provided he did not shoot to the surface. Saturation divers have a prescribed ascent rate which, I appologize, cannot remember.

cheers.