Is Nitrox right for me?
In 1957 commercial divers began using a 50% nitrox mix to extend the time that divers could work underwater without increasing the incidences of DCS. In 1959 the US Navy began using Nitrox instead of pure Oxygen to increase the working depths of divers and reduce the problems associated with Oxygen toxicity. NOAA (National Oceanographic and Atmospheric Administration) began researching and test diving Nitrox mixtures (primarily 32% and 36%) in 1970. After thousands of experimental dives, the first Nitrox tables were created by NOAA. It wasn't until 1985 that Nitrox was introduced to recreational divers. That extremely controversial task was spear headed by Tom Mount (IANTD) and Dick Rutkowski (Hyperbarics International). These two men endured years of criticism and ridicule by many divers and most training agencies, but "science always trumps bullshit". Tom and Dick paved the way for us to enjoy these benefits. Most training agencies didn't follow suit until 1995.
Nitrox is usually promoted as "revolutionary" and "miraculous". It's all that, but is it for every dive and every diver? I have been certified for nitrox for many years, and have been teaching for many years as well, but I don't use it on EVERY dive on Guam.
Nitrox offers the most benefit if you want to maximize your number of dives within a somewhat limited depth range. Four or five dives a day in the 50 to 100 foot range (like a live aboard trip or dive holiday) is the ideal Nitrox scenario. You can even benefit from diving Nitrox on your next boat dive. If you were to dive Blue Hole and then Hap's reef, a typical boat trip, you would gain approximately 25% more no decompression time. You gain more bottom time, but you have to do more planning. You have to determine the "best mix" of Nitrox you want to dive at the site considering the depths you anticipate on diving. You also have to arrange to get the Nitrox mix you want. Sometimes that's easier said than done.
Shops like MDA (Micronesia Diving Association) and GTDS (Guam Tropical Dive Station) use partial pressure blending to make Nitrox. That's the cheapest way to make Nitrox, but also incurs the most risk. They add pure Oxygen to your "oxygen clean" scuba tank and then top off with air. The biggest problem with this method is that the pure Oxygen can react to impurities in your scuba tank causing a small fire or explosion. Obviously explosion is a hazard to the fill station operator, but the "small fire" can generate carbon monoxide (or worse if the viton o-rings burn) and injure the diver at depth. This is very rare, but you should know it. Diver's choice uses a membrane separation method to produce their Nitrox. The membrane acts like an air filter that filters out some of the Nitrogen. Using the membrane system is far safer for both fill station operator and the diver since pure Oxygen is never in contact with the diver’s equipment (yes you can put pre-mix Nitrox in any scuba cylinder without oxygen cleaning it) Getting Nitrox "on demand" has been a challenge for the dive stores on Guam also. MDA and GTDS rent Nitrox tanks and stock different mixtures, but is it the mix you want? Neither shop has done well (“in my opinion") of mixing Nitrox on demand. Divers choice also rents Nitrox tanks, but they also "bank" (store a large volume of pre-mix Nitrox so they can fill on demand just like an air fill) common Nitrox mixes. So it's getting easier to get the Nitrox you want or need.
Popular Nitrox Myths:
1) Nitrox reduces narcosis. This sounds reasonable. If nitrogen causes narcosis and you're breathing less of it, you should have less narcosis. The trouble is the depth range where you start worrying about narcosis (100 to 130 feet) is also where you have to reduce the percentage of Oxygen in the Nitrox mix because of the risk of oxygen toxicity. Dr. Peter Bennett, who co-edited The Physiology and Medicine of Diving, says the preventive value of Nitrox is "very small, so marginal that I think it should be discounted." I tend to agree with that in most cases; however an experienced diver should be able to tell the difference.
2) You'll feel better after the dive. Is it really the "feel good" gas? The theory here is that the work of off gassing nitrogen is a major cause of diving fatigue, so less of it should leave you less tired. Many Nitrox divers swear it's true, but Bennett cites a blinded study that proved otherwise. Using unmarked tanks, one group of divers was given Nitrox, another was given air, and both were asked later how they felt. "There was no difference," says Bennett. "It's a placebo effect." Again, I think this is somewhat dependant on the diver's ability to observe what his or her body is doing.
3) You'll use less gas. This sounds reasonable too. If there's more oxygen in each breath, presumably you don't have to take another one so soon and your gas consumption rate is lower. Unfortunately, it doesn't work that way because most of the oxygen you breathe is exhaled unused anyway. What drives the next breath is the need to exhale carbon dioxide, and that's not affected by what's in your tank.
4) You can dive deeper on Nitrox. Some divers think those green-and-yellow cylinders look cool and "techie", and associate that with going deep. In fact, Nitrox introduces a new depth limit that's often shallower than the 130 feet we're used to. The recommended depth limits are 110 feet for 32 percent Nitrox and 95 feet for 36 percent Nitrox. Exceeding the MOD (maximum operational depth) of the Nitrox mix you're diving can cause a convulsion resulting in your death by drowning. For example, if you were to dive Blue Hole and want to enter the side opening at 125FSW, you would have to dive a 28% Nitrox mix.
In conclusion:
Nitrox can be a very useful diving gas by extending your no-decompression limits or allowing for shorter surface intervals, but there are trade-offs. I strongly encourage you to take a Nitrox specialty course even if you probably won't dive Nitrox all the time. Increasing your bottom times on the first couple of boat trips will justify the cost of the class, and your "once in a lifetime" dive vacation will be very limited without Nitrox.
