Alan,
Your ambient sub will definitely be unique and have several complications that are not encountered in a typical ambient PSUB. You are going against convention in the technical diving community in that for all practical purposes you will have a rebreather without a means to monitor your oxygen levels. You have much more to worry about than just fire. While I admire your computations, I do not believe that they are as straight forward as you lay out. In reality, when you look at your proposed life support system, it would be termed a feed-and-bleed case and these are governed by a differential equation vice a linear decrease in the oxygen level. As it has been many years since I have had to contemplate this particular type of equation used in this manner, I will leave it to you to conduct further mathematical research.
You should do a literature search on Dr. Bill Hamilton and oxygen tolerance. The onset of oxygen toxicity can be rapid, with little forewarning, and have tragic results. There are two types of oxygen toxicity, one due to high partial pressures at depth and the other due to length of exposure. And since most ambient subs involve some parts of the body being immersed in water, you need to take in to account thermal exposure. Something many people do not consider is that an exposure to 72 degree Fahrenheit water for an hour will put most people mildly hypothermic…with this comes a significant decrease in mental acuity and muscle strength. Don’t remember where you plan on operating but exposure can be a significant factor.
R/Jay
Resepectfully,
Jay K. Jeffries
Andros Is., Bahamas
Save the whales, collect the whole set.
From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of Alan James
Sent: Tuesday, August 11, 2009 10:30 PM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Ambient running on nitrox
Thanks for your reply Jay these emails can take some time.
Thought I had you on the regulator issue.
As said on my initial post, I'd have to think on restricting myself to the dive time tables for air & the dive depth for nitrox as there would be a dilution of the O2 content.
However at say 99ft the O2 in a hull with an air volume of 200 liters would be 312 liters with a 39% nitrox mix. This would give me 144 liters of O2 before I
got down to the 21% O2 mark. This is 9.6 hrs at .25 liters per minute consumption. Not to mention the air at 39% O2 replacing it to keep the sub ambient.
Quite a safety margin seeing I'm restricted to decompression times. Also no need for a dedicated O2 feed.
I'll be using a scrubber & for the ambient system, a pipe open to the sea, comming up through the hull with probes down it leading to a solenoid valve.
As the water level increases it hits the probes wich activate the solenoid valve letting air in to equalize. Excess pressure bubbles out the pipe.
Like a dive, it will need planning & building in margins of error.
My main concern that I'll look into at depth is the fire risk.
Thanks for the shared experience of the moisture vulnerable O2 monitors.
I won't be trusting one with my life.