Going Deeper than 130'

[buckaltc]

I have some questions about going deeper than 130'. I really have no desire to get into advanced tech diving for it's own sake, but I do want to get to around 160' or so. I live in Michigan and there are some things in Lake Huron that I want to see one day. I am a PADI Divemaster and I work mostly with Scout groups. I did this because I felt it was a great way to dive a lot and keep the costs down but I'm not a Divemaster for a living. I'd like to learn some more and do more wreck diving and to that end I'd like some advice on which way to go. I want to keep costs down of course, but I won't cut corners on safety. I'm a little turned off on DIR right now but I could be convinced--not a slam on DIR just what I read--I don't know enough to have a real opinion.

What is the minimum/recomended level of training and equipment needed to get to 160'? And where would you go for training? I know the question is a little lame, I'm not a minimum prep guy. The goal of my post right now is only to get enough information so I can start asking better questions.

 

[Blackwood]

That's a wide open question. Some people will tell you they do it on air in a single 80. Others will tell you they do it on doubles with helium and a deco bottle.

Are you a solo diver or a buddy diver? (goes to gas supplies)
What's your risk aversion regarding narcosis? (goes to backgas contents)
How comfortable are you with long, cold exposures? (goes to bottom time and potential accelerated decompression)

etc..

Talk to some people in your area who are diving the wrecks you want to dive. Get a good picture of how various people approach them. After that, you'll likely conclude that advanced nitrox and decompression procedures courses (or equivalent) would be a good start (I certainly don't relish the idea of decoing from 160 feet on backgas in cold water).

 

[captndale]

A diver should not be doing technical diving "for its own sake" nor should he be diving to 160 feet for its own sake. A dive to 160 feet is a decompression dive and, by definition, a technical dive. Technical diving includes learning the techniques and tools necessary to do a dive to 160 feet safely. If you do such a dive without the proper training and equipment you may be lucky, but then you might not...

 

[drbill]

Captndale's words are wise and cautionary. When I used to do dives as deep as 200 ft on air, I had 40 years of dive experience, dove an HP120 with backup, and gradually acclimated myself to such depths over a period of several months.

Although some dispute this as a general statement, I found through my personal experience that by diving frequently (300-350 per year) and to depths in excess of 100 ft, my response to narcosis was minimal. I was quite functional at even the deepest depths as judged by my ability to locate subjects, frame and follow them properly as I filmed.

Once I stopped diving as frequently and remained in depths above 130 ft, I found my tolerance to narcosis decreased significantly. I was quite narced at depths of 150 ft, and even once at 107 ft. Thus, I'm not sure how well you would tolerate narcosis at such depths without conditioning.

My reason for diving to such depths was two fold. The primary purpose was to film a segment on "deep ecology" for my cable TV show. As a scientist, there was a secondary purpose... to experiment with my tolerance to narcosis at depth.

I filmed enough footage to satisfy my needs and have not descended to such depths over the past 2 years. Were I to do so after two years of relatively infrequent (100 dives/year) and shallow (above 100 ft) dives, I'm sure my results would be different.

 

[flots am]

What is the minimum/recomended level of training and equipment needed to get to 160'? And where would you go for training? I know the question is a little lame, I'm not a minimum prep guy. The goal of my post right now is only to get enough information so I can start asking better questions.

160' is a decompression dive, which means that you have a number of mandatory deco stops on the way back to the surface. In fact, a 15 minute dive to 160' on air requires more time on deco stops than you get in bottom time.

Since a large deco obligation means that you'll probably be severely injured or die if you simply surface, you'll need whatever training and equipment will allow you to handle any problem and still complete your required decompression. This generally involves redundant gas first-class equipment and a well trained buddy.

This is not something you can do with "minimum prep" unless you're willing to die for your lack of effort.

While you don't have to drink the DIR kool-aid, you do need to obtain appropriate training (You could try TDI) and equipment and a buddy, which means that "minimum prep" is pretty much out of the question unless you have a death wish.

flots.

 

[buckaltc]

Thanks Blackwood-- good things to consider!

I dive wet right now with no real problems. It's cold but not stressful for me. I suspect one day I may need to go dry, but not before I have to and I still have to get some time deeper than My current floor of 110 before I make that decision. On that note I've got 6 or so dives to 100+ with no concerns for narcosis... yet.
I currently use an AL80 but I'm likely going to a steel 120 this winter.
I won't be going solo.

 

[ianr33]

What are the water temps you will be diving in? Can't imagine many people will do 160 in a wetsuit in Lake Huron.

The minimum training you would need is Advanced Nitrox and Deco Procedures. Realistically Trimix (normoxic) would be sensible.

 

[muddiver]

A diver should not be doing technical diving "for its own sake" nor should he be diving to 160 feet for its own sake. A dive to 160 feet is a decompression dive and, by definition, a technical dive. Technical diving includes learning the techniques and tools necessary to do a dive to 160 feet safely. If you do such a dive without the proper training and equipment you may be lucky, but then you might not...

160' is a decompression dive?

It depends on what table you are using.

 

[scubadiver888]

buckaltc,

I'm assuming you are looking to figure out what you don't know. You are looking for a starting point.

First, think about how much time you have at 130 feet before you hit NDL. You would have literally seconds at 160 feet before you hit NDL. For any meaningful dive, you are going to go into deco. You need to understand what that means.

As part of your Deep training you learned about nitrogen narcosis. If you have EAN training you should know about oxtox and should be able to figure out that that EAN23 is the mix for a MOD of 160 feet. Not much better than air (EAN21). So you will be narc'd. The best way to avoid this is trimix. You reduce the nitrogen to avoid narcosis and you reduce the oxygen to avoid oxtox. But do you have enough oxygen in the mix at shallower depths? How long will decompressing take.

To speed up decompression you might want to breath 50% or higher oxygen.

At 160 feet you are at almost 6 atmospheres. What is your Surface Air Consumption (SAC) rate? If you are using 0.75 Cubic Feet per Minute (CFM) then at 160 feet you are using 4.5 CFM. With an AL80 you are going to be out of air in 17 minutes. Assume a greater depth because of the cold and we should assume it is really 14 minutes. Factor in time to get down to 160 feet (maybe 1 minutes if you are really good), time to ascend (3 minutes) plus the decompression stops (maybe 10 minutes). You would surface with an empty tank. Anything goes wrong (free flow, current, excitement, etc.) and you run out of air on the way up. By the way, we haven't even considered the air you need to put in your BCD as it compresses (remember 6 atmospheres means 1/6 of the size at depth)

What about the temperature? You will be going deeper which often means colder. You will be in the water doing decompression. You cannot leave the water if you get too cold (unless you have a chamber on the boat). Are you prepared for the cold or will you risk hypothermia?

So far, you have:

1. decompression
2. avoid nitrogen narcosis
3. avoid oxtox
4. shorten decompression
5. carrying more air
6. reduce exposure to cold

You now have to worry about more equipment. You will need to practice with the new configuration. Some training might be in order at that point. How much trimix do you need to bring? How much oxygen (50%) do you bring? Is your tank and regulators O2 clean? Maybe you can get away with EAN40 for decompressing but how much time will that add to you being in the water? More time means (a) more heat loss and (b) more gas you need to carry.

This is just scratching the surface. Bottom line, diving to 160 feet safely requires training, specialized equipment and planning.

As a PADI DM, see if you can get the handout for Tec40 (130 feet) and Tec50 (160 feet). It will give you some idea of what you need to know to do a dive to 160 feet.

 

[Blackwood]

Thanks Blackwood-- good things to consider!

I dive wet right now with no real problems. It's cold but not stressful for me. I suspect one day I may need to go dry

I suspect you're right. 50 feet deeper in a lake may prove to be substantially colder, and also conventional wisdom says that decompression is far less efficient when you're cold (which even if you aren't at 100 feet now, you may be at 100 feet coming up from colder waters).

flots am had a good post regarding handling emergencies without surfacing. Since you're diving with a buddy, that may involve shared team resources. When I dive, I maintain enough backgas to get both me and one buddy up to the next switch (either a bottle or the surface).