[PSUBS-MAILIST] onboard gear

Tue Apr 23 21:25:45 EDT 2019

 I have been following this thread with interest because it is highly relative to me.  The R300 if an operational, one atm boat with a maximum operating depth of 300 ft.  NOP calls for not operating the boat where bottom is deeper than 300 ft.  I have a flowchart that is accessible from pilot HMI to the help pilot make a bailout no bailout decision.  Key is bailout is last resort if :1) boat is flooding2) there is fire on board3) CO2% is greater than 1% (10,000 PPM) 4) O2%< 13%5) Cabin pressure is >18psia and climbing6) Atmosphere is toxic7) Depth is less than 450 ftThese criteria came out of a US Navy safety document for the Steinke hood. 
Because I have a small sub, I don't have room for any of the mixed gas options being discussed.  I do have a BIBS.  Given the stress the operator would be under, I think Sean calls out the only practical solution for my boat which is buoyant emergency ascent.  If I have to bail, I have a Steinke hood on board.  The calculations for a 300 ft bailout for my boat with a 1" NPT  scuttle valve (ball type) is that the water level in at boat will reach chest level in 64 seconds with the pressure at that point being 44 psia.  At 94 seconds the pressure in the boat has equalized and the hatch will snap open.  The ascent rate for the Steinke hood from US Navy documentation is 425 ft/min for a fully inflated hood.  In a perfect world I would have 100% O2 on surface.  
The specific steps I would take on making the decision to bailout are:            1.     Releasehatch latches.            2.     Turnon the dive light attached to life jacket.           3.     Locate“Steinke hood”, set snorkel valve to “open position” and place hood over headand bite down on mouth piece.
            4.     Orallyinflate the “Steinke hood” ballast chamber.

            5.     Turnoff both the master switch and the circuit breaker.
            6.     Fullyopen scuttle valve.         7.     Whenwater level reaches level A (approximately chest level), repeat oral inflationof Steinke hood ballast chamber, close snorkel valveon Steinke hood and grip hatch handle.            8.     Whenhatch opens, launch yourself upwards through the hatch. Breathe normally during ascent to prevent lung over inflation.          9.     Onsurfacing, open snorkel valve to breathe surface air then inflate (embedded CO2cartridge) life jacket to increase buoyancy. If calm sea state, remove Steinkehood.

I like Sean's caveat and agree completely,  "To be clear, an emergency escape from a disabled submarine at these depths is not even remotely a good idea - it is simply a marginally better idea than dying on the bottom.
I am going to get narced badly and I am probably going to burst my ear drums during ascent but given the relatively short exposure time to air at depth, I don't think decompression sickness will be my top concern.
What I would really like to do is do a training bailout at this depth in a controlled environment with safety divers on hand to see how bad the nitrogen narcosis is at 300 ft.  My only experience with nitrogen narcosis was as part of my Advanced Open Water PADI certification.  
Cliff

    On Tuesday, April 23, 2019, 5:52:11 PM CDT, Sean T. Stevenson via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

 There is a significant difference between submarine escape and a planned SCUBA dive with regard to both the dive profile and the equipment that you can reasonably carry.  An escape is more akin to what is known as a buoyant emergency ascent in recreational diving, where you need to get to the surface yesterday and all other considerations are secondary.  In this specific case, trying to keep to a slow ascent rate would significantly increase the incurred decompression obligation that you must necessarily then blow off as you ascend through the shallows, introducing an even greater risk.  You also have the hypothermia issue to deal with if you are not equipped with exposure protection specifically intended for submersion at depth. Being cold reduces decompression effectiveness. In order to keep to a target ascent rate or perform decompression stops, you would need diving instrumentation (depth gauge and timer), would need the skills and experience to perform gas switches and hold stops, and would need significantly more bulky equipment to have enough gas to perform a proper decompression (slow ascent, gas switches, etc.).

When I dive to these depths on SCUBA, I wear twin cylinders (>100 cu. ft. each) on my back with the bottom gas (10/70 or whatever for the planned depth and time), plus three or four off-board cylinders (80s) carrying the decompression gases (typically 21/35, 35/25, EAN50 and oxygen), plus a small bottle of argon for drysuit inflation.  Obviously, as an escapee you are not so equipped.  Far better to lockout as quickly as possible and rapidly ascend (with buoyant assist) to get clear of those depths where you are ongassing the most, and if at all possible, to slow the ascent as you approach the surface, and then have your surface support or emergency responders administer oxygen as transport is arranged to recompression.  To be clear, an emergency escape from a disabled submarine at these depths is not even remotely a good idea - it is simply a marginally better idea than dying on the bottom.

To illustrate, if you were to attempt a continuous ascent from 300 fsw, the average depth is 150 fsw, which is about 5.5 atmospheres absolute.  If you assume a surface air consumption rate of 1 cu. ft. / minute (high, but typical of a diver who is stressed or working hard, which is inevitable in a submarine escape scenario), that corresponds to 5.5 cu. ft. / min at the average depth of the ascent.  At a 30 ft/min ascent rate, that's 10 minutes, or 55 cu. ft. of gas consumed just for the continuous ascent with no decompression stops, without consideration for the gas consumed while blowing down and locking out.  You can judge for yourself the practicality of carrying an 80 on a PSub sized vessel just for emergency escape purposes.

Sean

‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
 On Tuesday, April 23, 2019 12:32 PM, David Colombo via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Hi Guys, This topic is fascinating and scary at the same time. Accent rates form the old Navy logs had 60ft / minute max with a recommended max accent rate of 30 ft/ min. At 300ft escape depth, what volume of mixed gases would you need for a 10 minute accent assuming you choose not to swim 60ft/min.

Best Regards,
David Colombo

804 College Ave
Santa Rosa, CA. 95404
(707) 536-1424
www.SeaQuestor.com

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