Thank you Mike and Simon for your reply.I am aware of some of the problem related with the gas mixture. And I can tell you that I am very carefull with me sub. I made 3 dives so far and I went to 10 feet, 10 feet and 15 feet. I never intend to go under 33 feet. I have my open water padi training and I do agree with you guys that a nitrox training would be complimentary for me.
Am I right in assuming that at 33 feet, the level of PPN2 is not a factor for decompression sickness? And as long as I stay at minimum 21% O2 I should be ok?
But what happen in 1atm sub like a K-350. When they wait 2 hours to resurface? there PPO2 must be below 0.21. Is that dangerous also?
Pierre----- Original Message ----- From: "Michael Wright" <mwright@smallip.com>
To: <personal_submersibles@psubs.org> Sent: Tuesday, September 27, 2005 3:42 PM Subject: Re: [PSUBS-MAILIST] Life Support
I would strongly suggest taking a NITROX Scuba course to anyone considering an ambient Sub. They cover things Max Operating Depth for a given breathing mixture. A rebreather class would also cover useful information. TDI offers a no-dives required Nitrox Class.Here's an outline of your 66 foot depth scenario. Surface PPO2 0.21 ATA (air) 66 Feet PP02 0.63 ATA (air pressure compensation) After some time at depth letting the oxygen level drop back to 0.21 ATA 66 Feet PPO2 0.21 ATA Surface PPO2 0.07 ATAIf you keep your PPO2 constant at 0.63 at 66 feet depth you won't have an issue when you ascend. You can also use the standard Air SCUBA tables. Basically you are keeping the same fraction O2 (Oxygen) and fraction N2 (Nitrogen).If the PPO2 drops to .21 at 66 feet depth when you surface you'll have a PPO2 of 0.21/3 or 0.07 ATA, which is not a safe level.A second problem with letting your PPO2 drop in and ambient sub is Nitrogen loading and a high potential for Decompression Sickness. If you decrease the % oxygen in the breathing gas you by definition increase the % nitrogen. Nitrogen exposure is the limiting factor in SCUBA and Nitrox diving. You cannot use standard SCUBA tables to figure bottom times since you are no longer breathing regular air.Before attempting any of this you should take at least NITROX Scuba class, and probably a Rebreather class. Too low a PPO2 causes Shallow Water Blackout (unconsciousness), too high a PPO2 causes CNS Toxicity (unconsciousness). Both of these conditions lead to unconsciousness and have few if any warning signs. Becoming unconscious while piloting a PSUB is extremely inadvisable.mikeDisclaimer: Information provided is for discussion purposes only. Any person reading this is responsible for making their own decisions regarding their personal safety after receiving relevant training on the subject.On Sep 27, 2005, at 5:37 AM, Marie-Andrée et Pierre wrote:Hi Phil and others,I'm in the process of building a scrubber/O2 monitor system for my dry-ambient sub.My question is: If I stay at 66 feet for some time and monitor PP O2. Will there be a problem when I surface? The PP O2 should be like 3 times lower on surface then at 66 feet right? Will I have to have atleast 3 times the minimum PP O2 (0.21 X 3 = 0.63) before I begin to surface? Otherwise I may lack O2 in the cabin and pass-out or something?It remind me of the technique you just mentionned about raising cabin pressure in a 1atm sub. I think there could be the same issue there.Any thought? Pierre Poulin----- Original Message ----- From: "Phil Nuytten" <pnuytten@compuserve.com>To: <personal_submersibles@psubs.org> Sent: Sunday, September 25, 2005 4:04 PM Subject: [PSUBS-MAILIST] Life SupportHi, Daniel: Sunday, again - a little time to wander thru' the debbil box! Ifyou need ultra lo-cost LSS, put in an oxygen tank with a medical regulator that has a needle valve/ flowmeter on it - these are nickles and dimes on eBay - less than a 100 bucks will get you a 40 cu ft tank and reg - if you want 72 hours, get two. Get an O2 analyzer/monitor ( another 50 -100 bucksin eBay 'scuba') - buy a 10 dollar wind - up oven timer and set for 5minutes to remind you to check 02 level (buzz! /rewind) and adjust flow ( once you get it dialed in, you may only touch it a couple of times during a 6-8 hour dive) For scrubbers, get a low voltage hair dryer and snip the heating coil out of it - or a 12 volt automotive heater blower, etc, and attach to the end of a piece of 6 inch PVC pipe- or clear acrylic if you are using color indicating absorbent.Screen both ends ( 2 layers of plastic bug screen mismatched so holes dont line up!) Stuff it full of Sodasorb, Sofnolime or soda lime of choice, and there y'go ! For a passive scrubber,get some 400 foot, 16mm movie reels, make plastic snap-on plastic bug screen covers - they're good for a couple of hours each, and the center sprocket hole makes a convenient mounting point.For a virtually no-cost LSS, install a large diameter vent valve (light cracking pressure non-return valve) and instead of coming to thesurface every two hours, double your cabin pressure from your air ballast supply tank or from an interior scuba bottle after the intitial 2 hours bottom time ( if you're happy with the '2 hours before surfacing to replacecabin air' scenario) - this will halve the PP C02 and still provide sufficent 02. After another 2 hours at 33 feet cabin pressure, you canincrease it to 66 feet to gain additional time, but must be mindful of the air no-decompression limits. The excess cabin pressure will vent on ascent- or rig your hatch with a couple of bungee cords so it will burp on acouple of pounds excess pressure - if you're concerned about the vent valvesizing or your ability to make a relatively controlled surfacing.Obligatory disclaimer: Please note that I don't recommend either of these approaches, only offer this info as examples of what has been done in the past. FYI, the 02 tank/liter flow reg/oven timer/ manual adjustment was the way most commercial deep-diving subs provided LS in the 50's and 60'sand even into the 70's. The pressure-down system was used a lot during early (60's)bounce bell one-at observation dives when a lock-out wasn't contemplated, only a look-see at problem - and the bounce bells weren't fitted with scrubbers. 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