Things may be different in the US, but here it is much dangerous to drive to the dive site than to dive solo. MB.
I've said this myself, in a written report on the safety of a university dive project. Be that as it may, there will continue to be misconceptions about solo diving, diving equipment, and emergency procedures.
First, this bit about pinching off the air flow of a single-hose Low Pressure hose under a first stage malfunction. I've thought this to be bogus, but have hesitated to say so until I tested it. The reason I thought it not to be correct is that, when these LP hoses first came out in the 1960s, dive shop owners would take the hose, and challenge any diver to rip it apart after it had bit cut half in two. No one won the new regulator that was the prize. It cannot be done. One dive shop went to the trouble of towing one car with another, using the half-cut hose between chains. So tonight, I found my trusty Calypso regulator, which has on it a hose in need of replacement. I put it on my 80 ft3 tank, turned on the air, and noted the pressure (3000 psi). I then pushed the purge button, simulating an open first stage (but not fully open), and tried to crimp the hose with my right hand (the stronger one). It was a no-go. The air gushed out without any noticable reduction in flow. In less than 30 seconds, I was down 300 psi (2700 psi by the guage). You cannot pinch off a LP hose and stop the flow. Those hoses are simply too tough. Don't try, as you are wasting time better spent preparing your ascent, or buddy breathing.
Second, some thoughts on regulator reliability and solo diving. Cousteau dove two-hose, single stage regulators on the Calypso's expeditions for a reason. This is a very easily-serviced, reliable regulator. It has six moving parts, none of which is dependent upon an "O" ring. The plastic seat (teflon?) is very tough, and is not worn by simply setting unused. If it is damaged, air will flow in a constant manner though the two hoses. Cousteau's team used these regulators on some extraoridary dives, some to great depths. In his Conshelf 2 project, one of the saturation divers reached a depth of 362 feet, without using a redundant system. As a matter of fact, what was shown on their film, "World Without Sun," was one diver bringing another diver a new set of tanks, without a regulator. They took the one regulator off that they had, and put it on the second set of tanks, purged it. This was done while all the time keeping the full-face mask with communications on. As I said, the Mistral regulator was a tough, dependable regulator.
Contrast this with what is recommended in
Solo Diving, The Art of Underwater Self-Sufficiency by Robert Von Mailer. He talks a lot about redundant systems, about being self-sufficient with your diving system, shows all the possibilities, and breaks them down into "Type I, Alternate Air Supply" and "Type II, Redundant Air Supply." The Type I would include the octopus second stage. The Type II would be something like a pony bottle, Spare Air, or indepentant regulator systems. He says, concerning the Spare Air:
The Spare Air 3000 is an excellent choice for sport/recreational diving that doesn't involve overhead environments, deep water, (i.e. 80+ feet/24+ meters), or any other type of advanced, specialized situations. Not that it couldn't be included as an additional form of redundancy in such cases, but as a first line Type II EBS, it most likely would not supply the diver with enough emergency air.
Independant doubles, or duel cylinders with separate regulators, is what is said to be the best, as they are most reliable. Two different, totally independant systems, where one can be relied upon if the other fails. And I agree, wholeheartedly, with this for those situations Mr. Von Mailer states are beyond the use of a Spare Air (above).
But, I have been solo diving for decades, without incident. I have not always used redundant systems, or even an octopus. I wrote one of the first articles on solo diving for the instructor periodical, NAUI News, in the mid-1970s. This was a time when the octopus was just being adopted.
In the 1960s-1970s, I worked as a USAF Pararescueman. We wore doubles, with a single-hose regulator that had a single hose. We conducted a lot of solo dives, because when you parachute out of an aircraft from 1250 feet into the ocean, we usually did that one jumper per pass of the plane. Were we at a high risk because we didn't have a redundant system? No, these dives (to recover a parachute from the ocean, or to search, or do a swim under the waves) were usually shallow. We did have to do one shallow and one deep dive per quarter, as I recall, for currency. These were done with twin 72s, or twin 42s, and again without redundant systems. But, we kept our regs in good shape, and tested them before the dive.
I continue to dive solo at times, usually shallow (<25 feet), sometimes with only a double-hose regulator and front-mount BC (my design). Do I feel that I'm jeopardizing myself doing this? No, I don't.
Let's look at the duel cylinder system from another angle. I dove one last Spring (simply put two single 72 into a double tank band, and presto, you have the most redundant system available). It actually worked quite well, and I switched regs when I got to 1000 psi on the right cylinder. It was pretty heavy, but I enjoyed the dive. In a situation that I judge warrents this setup, I won't hesitate to use it.
But there is one other thing to consider. Each regulator has "O" rings, and these are a source of potential failure. I counted the number of "O" rings on my two regulators, and came up with 18. My book on Product Safety,
Product Safety Management and Engineering, Second Edition (American Society of Safety Engineers, 1993), by Willie Hammer shows that "O" rings have a generic failure rate of 1.182 failures per 10 to the sixth power part-hours (for gaskets and packing, the rate is 0.24; and diesel engines have a rate of 1733.1, for rough comparisons). That is quite reliable, but when you have 18 of them, you need to add the individual failure rates to see the failure rate of your system (potentially). The more "O" rings, the greater the potential for a failure, not because the failure rate is added, but because they are a point of failure in case maintenance is not consistant. In other words, if each "O" ring is replaced at the same time, and left alone, the failure rate would remain about the same. But because we are constantly tinkering with our gear, take a hose off here, putting it on there, and maybe not lubricating or replacing the "O" rings, there is a greater hazard the more there are. And, each requires its own maintenance.
As good as the "O" ring failure rate is, the orifice/seat system in the old, very reliable Mistral single stage regulator is better. It doesn't meet today's standards in many ways, but in this one it does.
Finally, there is the difference between "safety" and "reliability." Someone can be wearing the most reliable equipment, and not be diving safely. Water skills matter as much as equipment in how safe a diver is in the water. NAUI used to use the motto, "Safety Through Education." Most divers now think it's "Safety through Equipment." Many are very overweight, do not have good water skills, and limited experience. One instructor told me recently that the reason people are buying double 105s is that they have a horrendous air consumption rate; they really don't, in my opinion, know how to dive. These diving skills are what I would like to see re-emphasized, but they do not market well. Why? Because the diver has to work to attain these, whereas equipment needs only to be bought. Some instructors appear also to be reluctant to tell potential divers that they are not ready to dive yet too.
SeaRat
