Much of the credit for the recent widespread adoption of enriched air nitrox in the scientific diving community goes to NURC/UNCW. Gas Verification — The operation must be able to demonstrate regular analysis of the air used for mixing enriched air.
NITROX OPERATIONAL DATA A. Nitrox Certification Data
Probably the only caveat is that the number of instructors only represents nitrox instructors and nitrox instructor trainers. In order to gain some validity of the data, because that is what we are looking for, it would be fair to comment that there must be a huge number of duplicate certificates. While this may be true at the instructor level, I think the other numbers are quite difficult.
We thought we might be able to get a good handle on the number of nitrox dives that actually occur among captive live diver populations. The next option I pursued was to try to get an idea of the number of nitrox dives by overlaying a formula on the cubic footage of oxygen consumed; however, several liveaboard operations use gas separation membranes so we could not answer how many 80 cu.ft. Their numbers were underreported because only eight of their 13 vessels could report, so their number of divers would be higher.
Nitrox Dive Data
I'm not sure if we'd be talking about the number of dives or the hours we spend in spacesuits. From my own experience, at least about half of nitrox dives are done in the US. The majority of our business is in the nitrox market and this is the largest database we have.
Obviously, you're going to see more DCS in the extended range type programs than the others, but the numbers are still very small. Gilliam: In the case of the SEA HUNTER fleet, their use of nitrox is almost 100 percent. In the case of the Aggressor fleet, this is trending towards 70 percent and is likely to increase.
Nitrox Training Requirements
Shreeves: PADI recognizes the track record of the 40 percent guideline, but we adhere to the manufacturer's recommendation. Bjorkman: For those teaching outside the United States, do these values apply to international communities? The greater density of the mixture and the greater work involved in inhaling it promote hypoventilation and the build-up of CO2 (see below).
There is individual variability in the ventilatory response to all 3 factors and the actual degree of hypoventilation resulting from their combination is subject dependent. Special equipment required includes a wet pressure chamber and a rapid response CO2 analyzer or, better yet, a mass spectrometer to accurately measure end-tidal CO2 tension instead of the more important arterial tension. Group mean end-tidal PCO2 was not significantly higher in the latter, demonstrating the dominance of an individual trait unrelated to depth in determining the degree of hypoventilation.
CORRELATION BETWEEN MIXED-EXPIRED AND END-TIDAL Pco 2 : 1 ATA AIR
NITROX PHYSIOLOGY
Discussion of Kerem paper
There were people for whom, at 1 atm of air, the CO2 retention did not even exist. You would probably want to say that it was the increased density caused mainly by depth. Maan: Well, almost all the data in the literature is based on end-tidal CO2.
It's going to affect them both the same way, isn't it, because they're the same densities. Vann: Alessandro, regarding your question about deep air diving, there are a number of reports in the literature. I also saw a case in the lab of people going to sleep only at 150 to 180 feet and there were a number of deaths there.
Maximum PO2 Limits Discussion
One of the things you want to ask yourself in this discussion of oxygen toxicity, it seems like the probability of having a problem at 1.6 atm oxygen partial pressure is very low. Again, I'm asking for someone to enlighten me as to why we think we have a problem at 1.6 atm. We set it at 1.4 atm for recreational divers as a safety margin for diver error.
You don't give up much when you lower the oxygen limit from 1.6 to 1.4 atm. Hamilton: This was a hit after a three-mix dive, breathing pure oxygen at 1.6 atm during decompression. Ed, you made a bunch of pretty sweeping statements about why the Navy chose 1.3 atm.
Testing Nitrox as a Product
If you're willing to accept that half a million clean dives are proof that 1.6 atm is okay, then by all means feel free to do so. Most of the knowledgeable people say there is no difference, but we haven't tried that test yet. Our first consideration of the thermal balance aspect is that there are so many other variables that we cannot distinguish it.
Kerem: It can probably be done in a blind or preferably a double-blind trial. You could have people breathe from a nitrox container labeled as nitrox and have 22 percent, almost air, and an even higher percentage of oxygen, and then test them underwater with a psychological performance test for narcosis. At the end of the dive, give them a fatigue rating questionnaire and compare it.
Nitrox Mix Analysis Discussion
- NITROX RISK MANAGEMENT
None of the individual users analyze the gas or log it at any time. You have one of the best calibration gases in the world right here, 20.94% O2 in this atmosphere. Many of the diving tables are cut off at the borders so that the diver cannot exceed the tables.
Gilliam: I agree with Tom that the move to nitrox tables provides a quick reference that eliminates most of the math calculations where people will make mistakes given a chance. Richardson: I would predict that if we did a proper educational research study, assuming they mastered the performance objectives, we would have a similar outcome. Language: The first discussion will be a brief overview of the OSHA nitrox variance for recreational nitrox instructors.
OSHA Recreational Nitrox Variance
The first discussion will be a brief overview of the OSHA nitrox variance for recreational nitrox instructors. The second example is a more interesting, technical tri-mix dive where it clearly exceeded the scope of the variance or the original exemption for sport diving. They talked to the owner of the store and in January 1998 they knew that there was an employer-employee relationship.
I have to say from a legal perspective that if you are outside the variance parameter and you are teaching nitrox diving in an employer/employee relationship, you may be outside the parameter. OSHA has always recognized part of the goal as that Divemaster working in the same safety envelope; it provides education and information about the environment. Turbeville: This brings us to the point of administrative and prosecutorial discretion, which is that while there may be a strict reading of the rule, noncompliance may not allow surveillance of recreational divers.
Nitrox Community Standard Of Care
The Navy Diving Manual is a Navy publication required by law to be made available as a public document. Emmerman: To explain the comments on the TWA dive, the Navy divers used mixture. I think we still have the naval standard out there and it's still an issue that we have to deal with.
Thalmann said that as a sport diving community we have to say that the Navy standard is their standard, it's not our standard. In fact, Wells and I have been on NEDU teaching courses for the Navy four years ago. I don't see how you can justify going to Navy Manual 1.3 atm when all their stuff is operational air diving, not nitrox itself.
Nitrox Legal Considerations
- Divemaster duties
- Buddy system
- Diving deeper than 130 feet
- Decompression diving
- Waiver and release forms
- Dive briefing
- Personal responsibility
- NITROX TRAINING CURRICULUM
This diver was also engaged in heavy work, which increases oxygen exposure and the likelihood of oxygen toxicity. The primary duties of a divemaster are to assist the divers and the captain of the vessel in conducting dive operations. Forsyth shows that the probability of ignition and combustion in the presence of an oxygen-rich environment is highly dependent on the device configuration and system operating pressure.
Most companies still limit the use of their equipment to a maximum of 40 percent oxygen. Use history is considered at each step of the risk management approach and is discussed below. But as the model shown above shows, usage history is only a small part of the risk management approach.
Results of pneumatic impact tests of diving equipment and contamination assessments have been previously reported (WSTF, 1997) and are summarized below. The results of tests performed in 100% oxygen and 50% nitrox are summarized in Table 2.
1.5 2.0 (seconds)
NITROX EQUIPMENT
We can all see where the potential fire hazards are in the high pressure side of the first stage of a regulator. If you need to clean the second stage of the regulator, then you also need to clean the low pressure inflator that inflates the BC. The important unknown factor is the nature of the dirt you are trying to ignite.
It is not the opening of the tank valve that is necessarily the most decisive moment. One of the points Elliot made was that producers need to take responsibility. Betts: The data presented here is an illustration of what goes on in the real world of the dive shop regarding cleaning low pressure equipment.
FINAL DISCUSSION AND RECOMMENDATIONS
Long: Do we agree that there should be a redundant chain of testing the gas? Did we also agree that there should be a redundant analysis of the gas on the pump side and on the end user side? Gilliam: Let me imagine that we're peeling back the layers of the onion quite a bit now.
Moon: Oxygen analysis of the breathing gas must be performed by the dispenser and verified by the end user. Saying that the end user must authenticate puts some of the burden on the end user, but not all of it. Oxygen analysis of the breathing gas must be performed by the blender and/or dispenser and verified by the end user.
Notes
