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That might not be enough for some critters. I just found out from a fisherman yesterday why I have so much trouble getting a decent picture of a spadefish. The guys who do well on spades use black hooks since the shine spooks them. Just dragging a spoon through a school of spades can start a stampede. Imagine me coming up to them with the d-rings, buckle, manifold and whatever winking at them while a stream of nice shiny bubbles is coming from both sides of my head. I can cover the buckle and d-rings easily enough and put some sort of sleeve over the shiny parts of a single reg and valve. Redirecting the exhaust won't be rocket science either. If that's not good enough, I'll go to VIMS or the Marine Science Museum and buy a damned picture. Don ----- Original Message ----- From: Ed Street <blacknet@ph*.ne*> To: Don Burke <donburke56@ne*.ne*>; <techdiver@aquanaut.com> Sent: 08 July, 2001 18:27 Subject: RE: What Are the Circumstances where a rebreather is appropriate? Was RE: This is inspiration diving and people are supposed to die > Hello, > > Well for nature photography it's cheaper, simpler and safer to put a > diffuser on the exhaust of an OC unit ;) Besides your not fooling no one, > aquatic animals have eyes and can plainly see you. With the diffuser your > exhaust is re-directed behind your head out of your field of vision, the > bubbles/noise is seriously reduced. > > Ed > > > -----Original Message----- > From: Don Burke [mailto:donburke56@ne*.ne*] > Sent: Sunday, July 08, 2001 3:04 PM > To: techdiver@aquanaut.com > Subject: Re: What Are the Circumstances where a rebreather is > appropriate? Was RE: This is inspiration diving and people are supposed > to die > > > Hi Joe, > > Comments scattered within. > > From: Joe W <arizonajeep@ho*.co*> > > > Could someone or a few someone's list the circumstances where using a > > rebreather is appropriate? > > I only have two: > > 1. Dives where gas volume requirements can't be met by open circuit or > surface supplied rigs. > > 2. Dives where stealth is a go/no-go issue such as some nature photography, > military missions, law enforcement, or criminal activity. > > > Let me also add, as an electrical engineer who worked for NASA for 6 > years: > > > > It is entirely possible to build an electronic rebreather who's combined > > component failure rate is less than that of any currently existing > > open-circuit SCUBA assembly. > > For the electronic box itself, no doubt. > > However a valve assembly as reliable as the best open circuit regulator is a > pretty tall order. It can probably be done, but not by much. > > The O2 sensors are going to be the deal breaker. Under the best conditions, > they are unreliable. When you start varying the pressure and temperature, > look out. I don't think you can get there from here. You need a technology > breakthrough for this. > > > In fact; it will most likely look very similar to the life support systems > > worn by astronauts when going EVA. > > At one point, NASA took advantage of a property of space that divers do not > have access to, the lack of pressure. The early suits ran pure oxygen at a > reduced total pressure. This meant the wearer was getting the right amount > of gas, too much, or too little. A fault was pretty easy to diagnose. > > They might still do it that way. I know I would. > > > I'd be happy to entertain a public discussion with anyone who believes > > otherwise. > > The problem goes beyond the raw fault rate. > > In open circuit systems, the diver is getting the right amount of gas, too > much, or too little. The failure modes are easily identified with no > instruments (although a pressure guage will help you work out the details) > and the responses are easily drilled. > > In a rebreather, the unit can provide the wrong gas mix. That isn't always > easily picked up without instruments. Someone on the list said you've got > three breaths to figure it out and do something about it. My opinion of > that statement is meaningless, but I'll take it at face value. A > catastrophic scrubber failure or failure (open or shut) of the valve that > adds oxygen will make life complicated in a hurry. > > If the failure rate of a super rebreather was two per billion and the > failure rate of open circuit was ten per billion, there is a pretty good > chance that the death rate for open circuit would be lower than the rate for > the rebreather since the detection and response to the faults would come > into play. > > For many missions, the US Navy uses rebreathers which use a variation of the > NASA trick in that they work on pure oxygen and add only oxygen for depth > changes. Those units are very reliable since they have a limited number of > failure modes. The price of this is a shallow depth limit and a time limit > based on oxtox. > > IMNHO, the best idea I have seen is the semi-closed unit where the gas used > to keep the oxygen level up is actually trimix or nitrox with a PPO2 that > can be breathed undiluted on the bottom. Since there is "inert" gas added > along with the oxygen, the stealth of these units suffers since bubbles are > released. That probably isn't an issue for most of us. > > v/r > Don Burke > > > NetZero Platinum > No Banner Ads and Unlimited Access > Sign Up Today - Only $9.95 per month! > http://www.netzero.net > -- > Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. > Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'. > > NetZero Platinum No Banner Ads and Unlimited Access Sign Up Today - Only $9.95 per month! http://www.netzero.net -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. 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