1.5 2.0 (seconds)
V. NITROX EQUIPMENT
V. NITROX EQUIPMENT
J. Hardy: I'm going to share what I did based on the nine years and several hundred dive computers we've tested for Rodale's Scuba Diving Magazine. I've compiled a nitrox compatible dive computer list (10.25.00) of what is currently available. This list is not going to be perfect, but as of the end of last month, includes 13 different manufacturers with 35 models of dive computers. I may have missed a few in the process, but these computers have all been included in tests that we've done over the last nine years and are still in distribution.
I've noted the distributors Aqua-Lung, SeaQuest or Scubapro because of the various different brand names.
Table 1. Nitrox Compatible Dive Computers MANUFACTURER
AERIS AERIS AERIS AERIS AERIS COCHRAN COCHRAN COCHRAN COCHRAN DACOR DACOR DIVE RITE DIVE RITE DIVE RITE GENESIS SCUBA GENESIS SCUBA MARES
OCEANIC OCEANIC OCEANIC OCEANIC OCEANIC OCEAN REEF SHERWOOD SCUBA SUUNTO*
SUUNTO*
SUUNTO*
UBS UBS UWATEC**
UWATEC**
UWATEC**
UWATEC**
ZEAGLE ZEAGLE
MODEL 300G 500 AI 750GT Atmos Pro Savant Commander Commander Nitrox Nemesis +
Nemesis Ila Nitrox Equano2X
Transcend NiTek NiTek3 NiTekC Nitrox Resource React
Surveyor Nitrox Data Plus Data Plus 2 Datamax Pro Plus Datatrans Plus XTC-100 Ocean O2 Nitrox Logic
Cobra
Solution Nitrox Vyper
Chameleon Nitrox Pro2 Aladin Air X Nitrox Aladin Air Z O2 Aladin Pro Nitrox Aladin Pro Ultra Stratus I Stratus II
* Distributed by Aqua Lung & Sea Quest
** Distributed by Scubapro
Lang (ed.): DANNitrox Workshop, Divers Alert Network, November 2000
J. Hardy: It is very simple math for a dive computer to handle nitrox. It is not complicated for that microchip to do the job. What it is essentially doing, at the risk of oversimplification, is moving the no-decompression line over based on NOAA's materials. Virtually all computers say that in their literature. Most of them have a way to adjust the PO2 either on the fly or beforehand. The typical range is from .21 to 1.6 atm. Many computers will have a demarcation at 1.4 and 1.6 atm. Others must be preset before the dive. You set the O2 percentage, which can be anything from 21 (air) up to 50 percent. A few models go all the way to 99 or 100 percent. Variability comes in what the manufacturers share with us and what we're able to test, which is, what the computers track and how they track it. That is not clear among the manufacturers. You should also realize that practically all manufacturers are moving towards nitrox computers. You're going to see an era when all computers have a nitrox program. It's simply a function that you call up when you want to use it. On the face of the computer it has air and if you want nitrox, you simply punch up that screen and go with nitrox. I also predict that all dive computers will eventually interface with desktop computers.
NITROX EQUIPMENT DISCUSSION
M. Lang: As we start this discussion, I ask that you be very crisp and precise in your comments so that we can most effectively use the remaining time.
T. Mount: We're discussing something already involved in the standards. The manufacturers are producing nitrox regulators, which takes precedence to what the training agencies say anyway. IANTD says anything up to 46 percent can be used without special cleaning provided it meets the specifications of the manufacturer. We default to the manufacturer.
B. Gilliam: I agree completely with Tom that the agencies would really like to have the onus put on the manufacturers. The one thing that would help all of us is if there was consistency and common sense throughout the process. We all can see where the potential fire hazards are in the high pressure side of the first stage of a regulator. Is it necessary for us to get very concerned about the second stage where the low pressure is really not much of a fire hazard?
We get very passionate at times in these discussions about "to clean or not to clean", but nobody ever brings up the issue of cleaning the other components. If you have to clean the second stage of the regulator then you also have to clean the low-pressure inflator that inflates the BC. I don't know anyone who's ever taken that path. What about HP hoses and submersible pressure gauges? If you were ever going to have a fire, it would probably happen right there in the SPG. The whole equipment package should be looked at, which would help everybody come to agreement
B. Wienke: I agree with Jon's comment that all dive computers are probably going to be nitrox.
Some dive computer manufacturers (e.g., Suunto and Cochran) are also going to include tri- mix. The reason why they haven't gotten into the tri-mix business to date is because of liability. The technical diving community is driving that. Presently, all computers, except for a very few, are typically Haldanean models. These are dissolved gas models with M- values if they're U.S. Navy, or Buhlmann values. That's going to change in the future to dual phase models brought up on risk computers because the computing power and the memory is sufficient to perform phase calculations.
V. Nitrox Equipment Discussion
B. Wienke: On the oxygen combustion issue, it's not really hard to model with high surety oxygen combustion flows in any type of system. We have done such calculations. To do this, it's fairly easy to draw on combustion technology that is used for designing engines in Detroit and at Los Alamos National Laboratory. The whole oxygen combustion issue can be correlated with experiments to a very high degree. We can come up with probabilistic curves for ignition. Ignition doesn't always mean burn propagation, but we can come up with ignition criteria as a function of configuration whether it's a first stage of a regulator or a tank valve. The important unknown factor is the nature of the dirt that you're trying to ignite. Is it hydrocarbons, plastics, pyrotechs or rubber or do we have titanium or titanium oxide particles? The combustion chemistry is really the important consideration. We did 3D simulations with a simple configuration. An overdrive gas with a variable fraction of oxygen slams up against a stopped end. The stopped end has a hole in a model of a regulator first stage with gas flowing out of the tank tube. Viscous equations are employed. We vary the drive pressure between 50 to 5,000 psi. As this pneumatic gas slug forms in the region in and around the first stage of the regulator and the seat or the hole in the stop end, a shock pattern is generated that is strong enough to ignite some of the dust in there. The dust can be hydrocarbons, nylon or teflon, which doesn't burn very well, rubber or fabric, plastic, metal or glass. The result is shock heating plus implosive compression. The whole process is highly non-adiabatic, so there is heat transfer mainly by shock heating. We looked at dust densities between 50 and 350 mg, distributed evenly across the face or the stopped end of the regulator. These are typical dust densities that are described in the literature. With flammable dust densities around 100 mg per square foot on the regulator surface stop end, we needed 70 percent oxygen to ignite and burn the assembly. You can get a spot ignition and not necessarily have combustion waves or reaction waves propagating through the gas. If we drop the drive pressure to 2,000 psi, we need a high amount of fairly dirty dust distributed over the stopped end to get the assembly material to ignite and burn. By dropping even highly combustible dust densities below 10 milligrams per square foot, we don't get ignition even up to 99 percent oxygen. The question of metals is interesting because in this particular simulation, if you take only small titanium or aluminum particles on the order of a micron size and spread them across the stopped end, they don't necessarily ignite. However, if you ignite metal such as titanium and aluminum by impact, that's a different story. If it's pure titanium surrounded by other kinds of containment, it's not clear that you will always ignite the titanium. Igniting a local hot spot does not mean that you're going to have an explosion propagating through the gas. You could have a "whoosh" sound and nothing happens or an explosion could follow it. Calibration comes from experiments that are done in shock tubes.
The calibration is used to dial in the reaction chemistry for the combustion. The expertise for the combustion chemistry is drawn from studies and designs that are done for Detroit on combustion engines. The model there is what they call a droplet model. With fuel (gas) injection, your carburetor or igniter fires material into the combustion chamber in droplet form. That is a very good model for doing these tests.
B. Gilliam: From your experience and knowledge of the components that are being put into regulators today, do you think that we have just been lucky or are we on solid ground with the 40 percent rule?
Lang (ed.): DANNitrox Workshop, Divers Alert Network, November 2000
B. Wienke: I believe that 40 percent is quite conservative from the simulations we've done. It's like decompression sickness, it doesn't mean to say that you are not ever going to get hit.
The track record of nitrox diving is excellent and it's not just 30 to 38 percent O2. We're also talking about stage decompression diving where people are using 100 percent mixtures of oxygen and have no problems.
S. Angelini: As a manufacturer, it would be nice for us to be able to test every single configuration of regulators we have to 100 percent O2 to establish what functions at what levels. It would not be a definitive answer, but at least it would give us some kind of quantification of the risk, what we accept and what we do not. Of course, liability is always there and you only need one person to get hurt to be in trouble with a big lawsuit. At least you can show that you've done the best you can. We've done it with only a small fraction of the regulators because financially, it becomes a burden. The diving industry is not a very rich industry. The risk level that you tolerate is really what matters. There should be different standards for nitrox fillers and the scuba diver end user. As you fill, you heat up the components as the gas is flowing through. It's not the opening of the tank valve that is necessarily the most crucial moment. From the professionals in the field you can expect more rigor in what they do and more training in how they do it. On the other hand, the scuba diver does not have any technical knowledge. He faces the risk of a problem only as he opens the valve because that's when the heating taking place inside the first stage. We don't necessarily need to make it mandatory that people open the valve very slowly, although that would take away most of the problems. In most instances you would burn the seat, empty your tank and miss the dive. If you have a titanium body or some other exotic material, you may run into more problems. The bottom line is that the diver is faced with a lot less risk in the case of an ignition because it will only happen when the tank valve is opened. The diver himself does not need to be perfectly trained and knowledgeable about all these aspects, which makes this easier. You cannot expect the whole diving community to know everything. We're also talking about bagging regulators and whether the low pressure side needs to be cleaned. This is not necessary because it's not just the concentration that drives the whole process, it's also the pressure. Concentration times absolute pressure results in a partial pressure that you need to worry about. Under 500 psi it's a consensus that there's nothing happening, thus there is no need to worry about cleaning the low pressure side.
There's really no need to bag the regulator as long as you clean your dust cap and close your regulator after diving. It's very improbable that a particle of dust will travel up the second stage into the first stage. Even in a piston first stage that is not perfectly sealed, the only part that is in contact between the inside and the outside is a low pressure o-ring, at which point you've already reduce the pressure and do not have that risk. The point is that we have data that show that people don't necessarily clean their regulators and they're fine. On the other hand, we have liability as manufacturers. One of the points that Elliot made was that the manufacturers have to assume the liability. That's a big issue when you look at what the lawyers make these days, no offense.
B. Turbeville: I resemble that remark.
S. Angelini: We want to have testing to back these data, which is why we stand with 23.5 percent on anything that's not tested. The fact that people in the field use it to a higher level therefore eliminates a liability if we don't support it, but at the same time we're comfortable that we don't have a bomb out there waiting to go off. If it is going to happen, it will be at
V. Nitrox Equipment Discussion
the very beginning of opening a tank valve. The diver will be on the surface and it will very likely to fizzle into nothing.
B. Bjorkman: As an industry we have this fixation with oxygen cleaning. The overall picture emphasizes operating pressure, temperature, ignition sources, and velocity of gases. We can pour 100 percent pure oxygen through a horribly contaminated tube without real risk at all if there's no ignition source. Especially when you consider 'oxygen clean' as a transitory state.
A regulator can be cleaned thoroughly and tested for cleanliness, but how long will it remain clean while in use? It's very important for the dive shop blender to realize that if they're dealing with a horribly contaminated system that is not designed for oxygen service, they probably shouldn't be using it.
B. Oliver: I've had the misfortune to be involved in some litigation. Invariably, no matter how benign the risk might be, the plaintiffs attorney will ask whether there is a better alternative design that could be used. The cost impact of going to that alternative design puts the manufacturer in a tough spot by responding that it would cost too much to install Viton o- rings, clean the regulators and put Christolube in them when they are shipped. It's not a very defensible position. What you will see is that the manufacturers are going to start doing this to all of their regulators just to cover their bases, which is probably going to answer this 40 percent issue.
D. Rutkowski: I was pleased to hear Forsyth's and Wienke's presentations, two opposing situations. Forsyth's presentation was mainly concerned with flammability. Wienke was talking about chemical ignition. In this business we are more concerned with chemical ignition than we are with flammability. If we're talking about oxygen percentages for physiology then it's 21. If a fire started in this room, where would you rather have the oxygen percentage? Twelve, twenty-one or 40 percent? I would rather have a 12 percent oxygen mixture in this room if a fire started. History shows that it's improbable to have chemical ignition up to 40 percent O2. Forsyth authored a paper for NASA showing that pneumatic pressurization of the first stage of a regulator in 20 milliseconds, resulted no problems using up to 50 percent oxygen. If you reference OSHA 1910.430(c), that test was conducted before 1974. This community has proven by the millions of tanks that have been filled with up to 40 percent nitrox that there has not been a problem.
E. Forsyth: That paper did show, in fact, that we did not get any ignitions (see Forsyth's referenced paper first published by ASTM with some supplementary data in this volume). It puts into proper context what that particular group of tests did. Unfortunately, it's been abused in the sense that it's a test that showed no ignitions, but the scope and the applicability of that particular test needs to be taken into consideration if it's going to be used. Second of all, there is not a difference in opinion here, despite what Mr. Rutkowski said. Bruce Wienke and I are literally talking about the same thing. Ignition is different than propagation and those are the terms that are commonly used in industry. Whether you can ignite something is totally different than whether it propagates after you get it ignited. Bruce's data showed ignitions of the dust between 70 and 90 percent O2. I have some data from follow-up tests on hydrocarbon oil that show ignition down to 10 milligrams per square foot. These are levels that are quite a bit lower than what Bruce was showing with particles of dust down to 50
Lang (ed.): DAN Nitrox Workshop, Divers Alert Network, November 2000
percent oxygen. We tested that at 50 percent and 100 percent O2. It is an ignition problem, however the issue that needs to be addressed is whether it's a propagation problem. In none of those tests did we see propagation. Is ignition in and of itself tolerable? What Sergio said was very insightful regarding the differences between a high-pressure regulator and the low pressure side. There is merit in two different standards in terms of how a regulator is cleaned. To NASA's Neutral Buoyancy Lab we recommended that they fully oxygen-clean their first stage regulators used in their 46 percent nitrox systems. All the second stage equipment is still clean, but it's only done via a visual inspection. Typically, NASA does take the conservative approach because their level of risk acceptance is different from that expressed in this forum.
E. Betts: The data presented here is an illustration of what goes on in the real world of the dive store concerning cleaning low pressure equipment. The recommendation that ANDI follows is that the low pressure equipment is certainly far less of a consideration. Nevertheless, in the actual servicing procedure, it's extremely difficult for the service technician to use oxygen clean capabilities and oxygen clean lubricants on the high pressure side and then switch over to standard protocol using non-compatible lubricants and materials on the second stage. In my experience, one of the issues is cross-contamination. It becomes quite an embarrassment to see a non-compatible lubricant on significant surfaces of equipment that was intended to be oxygen clean. The simple recommendation is, if you have decided to oxygen clean a regulator and put correct lubricants in, to not use silicone grease on low pressure equipment.
This reduces cross contamination on the technician's side at the dive store level.
B. Hamilton: Let me brief this group on what the new NO A A diving Manual will say. We talked about oxygen cleaning at two levels. There is formal oxygen cleaning and informal oxygen cleaning. Formal oxygen cleaning is what Elliot referred to what CGA and ASTM want and it's mostly a matter of paperwork. There is an enormous amount of documentation involved. That's what NASA does and that's one of the reasons why it's so expensive. I used to work for Union Carbide and I know what this is all about, it was a lot of trouble. But informal oxygen cleaning is what Sergio referred to, you make sure that the regulator is clean, that it doesn't have any garbage in it and that it has a proper lubricant. That should be done with the second stage as well even though it is a very low risk area. If you're using 40 percent and clean it to the dishwasher standard, that's clean enough. That's oxygen clean, but it doesn't follow the protocol, the paperwork trail. Therefore, make it clean, inspect it and make sure that you don't contaminate it again with silicone lubricants.
T. Mount: Every training agency insists that when oxygen cleaning is taking place oxygen compatible lubricants be used throughout the regulator's first and second stages. The real problem is even if the second stage were oxygen clean, you would need oxygen compatible diaphragms, which there aren't many of on the market. There'd be no reason for manufacturing them. It would be a waste of money because it wouldn't accomplish anything.
S. Angelini: My comment earlier about not cleaning the second stage took some things for granted. What I meant is that we don't use Viton o-rings in second stages. We only use oxygen-compatible lubricants. Some of these lubricants work better than the non-oxygen compatible ones anyway. They're a little bit more expensive, but it is actually simpler having