This article helped tip the scales in what was the biggest controversy in diving at the time; Nitrox for recreational use. At the time we published this article, the Cayman Islands had completely banned the use of Nitrox, and Skin Diver Magazine came out with an unprecedented four editorials in one issue, each written by a different expert, all against Nitrox.
Alex Brylske was able to present the pros and cons of Nitrox in a balanced way, and his article played an important role in the efforts to take Nitrox mainstream.
— Mark Young, Publisher
Content below originally published in Dive Training, July 1992.
To Breathe or Not to Breathe: Exploring the nitrox controversy
By Alex Brylske
The issue of recreational nitrox diving has been at the forefront of the diving community for the past several months. There are no shortages of opinions about the topic but there seems to be very little objective information about the subject. This article is a milestone in that it addresses both the pros and cons of the activity in an objective and straightforward manner.
When we originally planned a nitrox article for Dive Training, we envisioned it as a two-part series, much like the trilogy published about the dive tables. However, we felt a two-part series increased the chances of confusion, and opted for a single, comprehensive report. We hope you will enjoy the results.
Recently an increasing number of recreational divers have begun purposely altering the air they breathe. Instead of using special gas mixtures to attain certain advantages while diving. These exotic mixtures go by such names as heliox, trimix, and nitrox. By far, the most common alternate breathing mixture is nitrox.
Some of you maybe already know about nitrox diving. Others perhaps have heard about it, but know very little. Even if you’ve never heard of nitrox diving, you certainly soon will. Industry estimates are that from 1985 to 1991, recreational divers engaged in 30,000-50,000 nitrox dives. And the numbers are growing. As altering the diver’s breathing mixture involves serious practical and legal questions, nitrox diving is becoming a hotly debated topic. In this article we’ll examine the issues involved I this new and controversial form of recreational diving. Hopefully, we can put the subject into perspective.
It is not the position of Dive Training to either advocate or discourage the use of nitrox. In a free society, that choice is left up to each individual. The choice, however, should be an informed one. The purpose of this article is to present the facts and explain the status of nitrox in the recreational diving community. It’s up to you to decide whether or not the benefits of enriched air are worth the problems, expense and risks.
A MATTER OF TERMINOLOGY
The concepts involved in nitrox diving are not complex, but they do require an understanding of certain terminology. To begin, the term nitrox itself refers to any breathing mixture composed of nitrogen and oxygen – such as our own atmosphere. Specifically, a breathing medium with normal atmospheric levels of gas – 79 percent nitrogen and 21 percent oxygen – is called normoxic nitrox. In commercial and scientific diving, nitrox usually refers to a breathing mixture with less than 21 percent oxygen. Such mixtures are used in commercial and military diving to avoid certain physiological disorders.
Any breathing mixture with an oxygen component greater than 21 percent is called enriched air nitrox (EAN) or simply enriched air. The term “enriched air” or EAN is preferable to nitrox because it more accurately describes the breathing mixture, and it avoids confusion with mixtures with less than 21 percent oxygen.
WHY USE EAN?
Why, you might ask, would divers want to alter the air they breathe? After all, humans have been breathing what Mother Nature has seen fit to provide us with for millions of years. Theoretically, the answer is simple. For land-based animals who breathe at normal atmospheric pressure, good ol’ regular air does the job of sustaining life quite well. But, when we venture either to altitude or underwater, there are certain disadvantages to regular air. At altitude we’re all aware that the reduced atmospheric pressure robs us of precious oxygen. This is why pilots must breathe oxygen when flying at high altitudes and why the cabins of jet aircraft are pressurized.
When we venture underwater, air continues to have certain limitations. But these limitations have less to do with the oxygen component of air than the nitrogen. It all centers around a topic we have explored extensively in past issues of Dive Training –decompression. The length of time a diver may remain at depth, or the amount of decompression he must undergo if exceeding the no-decompression limits, depends upon the amount of nitrogen absorbed. If a diver breathes air, he breathes a gas mixture containing 79 percent nitrogen. In an EAN mixture, oxygen is used to replace some of the nitrogen. So, instead of breathing a mixture containing 79 percent nitrogen, an enriched air mixture might contain only 68 percent to 64 percent nitrogen. Therefore, as the diver is breathing a gas containing less nitrogen, he absorbs less nitrogen in his body. This means both an extension of the decompression limits and –if required—reduced decompression time. Reduced decompression time is the primary—though not the only—benefit of using EAN.
Before exploring other theoretical and practical matters in more detail, let’s put the issue of EAN diving into a historical context. Although most recreational divers view EAN diving as some brand-new form of “high-tech” diving, this really isn’t true. The idea of enriched air diving has been around for as long as scuba. In 1943, Dr. Chris Lambertsen of the University of Pennsylvania first proposed the idea of reducing the diver’s decompression obligation by replacing some of the nitrogen he breathes with additional oxygen. By 1959, EAN diving was standardized for military scuba operations, and procedures appeared in the U.S. Navy Diving Manual. In 1962, the Navy began using enriched air in the Mark V (hard hat) diving system.
Enriched air has been used in military, commercial, and medical applications for more than 30 years. But the organization most responsible for EAN diving practices is the National Oceanic and Atmospheric Administration (NOAA). Under the guidance of Dr. Morgan Wells, NOAA’s director of diving operations, EAN was first used to support scientific diving operations in the early 1970’s. By 1978, NOAA published the first standardized procedures for decompression using EAN. Today, NOAA’s experience with EAN has played such an important role that many of their guidelines and procedures have become standards for the EAN recreational diving community.
An example of NOAA’s continued influence in the EAN filed is seen in the gas mixtures used by recreational divers. A standardized mixture called NOAA Nitrox I (NNI) contains 32 percent oxygen and 68 percent nitrogen. As these are the most commonly used mixtures for EAN diving, NOAA has also developed standardized decompression tables for enriched air based on the Navy air tables.
Although some recreational divers have been using enriched air for many years, it didn’t become popular until the mid-1980s. Dick Rutowski of Hyperbarics International at Key Largo, Fla., set up the first organized EAN program for recreational divers. (Before starting Hyperbarics International, Rutowski was NOAA’s deputy diving coordinator for more than 30 years.) He also founded the International Association of Nitrox Divers (IAND). The use of EAN by recreational divers has been growing ever since.
THE ADVANTAGES OF USING EAN
As in most human endeavors, there is an up side and a down side to the EAN issue. Let’s examine the advantages before looking at the problems. As stated previously, the greatest advantage of using EAN is the extension of no-decompression limits for three of the most popular air dive tables, along with the limits for NOAA Nitrox I and II. As you’ll see, EAN can often more than double the no-decompression limits of the air tables.
Additionally, using EAN can shorten the required surface interval between repetitive dives. Or the diver can make a longer repetitive dive with the same surface interval as a comparable air dive. Either option is possible, again because the diver absorbs less nitrogen than on a comparable air dive.
While the extension of no-decompression time can be a real benefit, it is not—in the opinion of this writer—the primary advantage of using EAN. The real advantage of enriched air is that it can provide recreational divers with an additional safety margin when used with regular air dive tables or computers. Air tables and computers assume the diver will breath air containing 79 percent or 64 percent nitrogen. This means the diver actually absorbs far less nitrogen than the air tables or computer calculates. Thus, the diver’s actual nitrogen absorption will be far below what the tables or computer shows.
Using EAN in this way can be an ideal method of automatically building In the conservatism so many authorities advise when using tables and computers. It might also be a way of overcoming the risks from such unquantifiable factors such as age, obesity, cold, fatigue, and dehydration. In addition, susing EAN with air tables could help decrease the decompression sickness (DCS) rish among dive professionals—instructors and divemasters—who dive continually as part of their duties. Some diver resorts, who maintain EAN filling stations, have already implemented the policy of having their dive guides use EAN for an added measure of safety.
While using EAN with air decompression schedules offers great promise, it’s not a panacea for DCS. We still know far too little about the disorder to make any solid claims about the certainty of avoiding the bends.
Other advantages of EAN have been reported, but haven’t yet been fully scientifically documented. The first involves nitrogen narcosis. The theory is this: The breathing mixture contains less nitrogen than normoxic air, and nitrogen is responsible for narcosis. Thus, as the diver breathes less nitrogen, he is less susceptible to nitrogen narcosis than when breathing air at the same depth. Many EAN divers have confirmed this hypothesis, while others have seen no noticeable difference between air and EAN.
Another benefit experienced by many EAN divers is what can be called the “feel goods.” Quite often divers who use EAN report noticeable lack of post dive fatigue. In many cases, excessive post dive fatigue is attributable to what is termed “sub-clinical” DCS. The theory is that the higher percentage of oxygen in EAN reduces or eliminates these symptoms. The “feel goods” might also result from better oxygenation of the tissues by the enriched air-breathing environment.
A final benefit of EAN, oddly enough, is assumed to occur if a diver is stricken by decompression injury. Because the breathing gas contains a higher-than-normal level of oxygen, it’s theorized that tissues affected by these disorders will survive longer than if the diver was breathing air. Evidence also suggests that breathing EAN can help significantly reduce asymptomatic or silent bubbles after a dive.
THE PROBLEMS WITH BREATHING EAN
EAN is not a magical answer to the physiological problems facing divers. For instance, EAN divers are still subject to the same effects of Boyle’s law – squeezes and lung overexpansion. And while the reduced percentage of nitrogen will increase no-decompression time, EAN divers are not immune to DCS. In addition, EAN creates a few unique problems of its own.
We have known since the late 18th century that humans cannot tolerate breathing pure oxygen at high pressure with eventually falling victim to a disorder called central nervous system (CNS) oxygen poisoning. The symptoms of this disorder include: tunnel vision, ringing in the ears, nausea, facial twitching, irritability, and dizziness. But the most serious effect of CNS oxygen poisoning is the onset of epileptic-type convulsions. Normally, convulsions are not a life-threatening event—if they occur on land. A diver who convulses underwater, however, could drown. Thus, divers must avoid any circumstance where convulsions might arise. (This is why people with seizure disorder are usually disqualified as candidates for diving.)
A complicating factor is that individuals vary greatly in their susceptibility to CNS oxygen poisoning. Even the same individual can vary in his own susceptibility from day to day. Based on years of experience and tens of thousands of dives, both the U.S. Navy and NOAA long ago determined specific oxygen tolerance limits. The modern EAN diving community has followed suit and also adopted these limits. Recently, though, some authorities have recommended a reduction in these limits for recreational divers.
The current recommended oxygen tolerance limits for diving are determined by calculating the partial pressures of oxygen breathed under pressure. These tolerance limits are established in order to prevent divers from encountering CNS oxygen poisoning at depth. You’ll remember that, according to Dalton’s law, each gas within a gas mixture exerts a pressure proportionate to the surrounding pressure. This explains why as a diver descends, the partial pressure of oxygen he is breathing increases. If the diver continues his descent, oxygen toxicity, due to increasing partial pressures, will occur. The depth at which CNS oxygen poisoning occurs is directly related to the amount of oxygen in the diver’s breathing gas. The more oxygen in the mix, the shallower the depth for the oxygen tolerance limit.
When using normal air, the oxygen toxicity limit has no impact on divers who restrict their diving to 130 feet or less. This is because the partial pressure of oxygen in normal air does not reach toxic partial pressures until depths of more than 210 feet. However, EAN mixtures, because of their increased oxygen content, reach this limit at much shallower depths. The chance of CNS oxygen poisoning, therefore, becomes a very real concern even at recreational diving depths. For example, the Maximum Operating Depths (MODS) for NOAA Nitrox I and NOAA Nitrox II are 130 and 110 feet respectively. Exceeding these depths exposes divers to the same risk of oxygen poisoning as breathing air beyond 210 feet!
Oxygen tolerance is the reason for one of the most important rules when using enriched air: “The diver must closely adhere to depth limits.” As you’re aware, the maximum depth for recreational diving is 130 feet. This is because of the possibility of severe nitrogen narcosis beyond that depth.
However, it’s the onset of CNS oxygen poisoning that determines the depth limit for EAN, not the effect f nitrogen. Unlike nitrogen narcosis, CNS oxygen poisoning does not always come about gradually. While the diver might experience minor symptoms before convulsions occur, convulsions often begin with no prior symptoms!
Dr. Lee Sommers, diving safety coordinator at the University of Michigan, sums up the matter quite well. He states in an article in the recent issue of NAUI (National Association of Underwater Instructors) journal Sources, “I suggest that, unlike nitrogen narcosis, which appears to manifest itself progressively from mild to severe impairment, oxygen toxicity can be a much greater threat to the diver. The simple fact that the onset of oxygen-induced convulsions with no preceding symptoms is possible adds another unpredictable dimension to (enriched air) diving. Oxygen may prove to be far less forging than nitrogen!”
The conclusion is both harsh and simple: While a diver breathing air might get away with exceeding the recreational diving limit f 130 feet, it’s unlikely he’ll live to tell about it if he exceeds the depth limits using EAN.
THE PROBLEMS OF HANDLING EAN
Many problems associated with EAN don’t come from breathing it, but mixing it. Because it must be mixed correctly, there are problems in the handling and storage of the gas. This makes the process of filling cylinders with enriched air more complex than filling cylinders with regular air. In addition, all mixing procedures involve some degree of danger. And regardless of the method of mixing EAN, all are far more expensive than filling cylinders with compressed air.
Handling pure oxygen is risky because of the potential for explosion. And all methods of mixing EAN involve handling pure oxygen at some point in the process. This makes safety the most critical concern in mixing EAN. Many believe the safest way of mixing enriched air is by continuous flow blending, which requires an expensive oil-free compressor. The advantage of the blending method is that it keeps the gas mixture below 40 percent oxygen. Gas handling standards require that once a gas mixture exceeds 40 percent oxygen, all equipment used to store, compress, or transport the gas must be “oxygen-clean and compatible.”
Cleaning equipment for oxygen service involves a special and meticulous disassembly and cleansing process. It removes all petroleum-based oil residue, solvents, and any other hydrocarbons that might burn in an enriched oxygen environment. Oxygen compatibility refers to the ease with which something might ignite. For example, items such as Teflon tape, silicon grease, and even some types of O-rings—commonly used in high-pressure air systems—could easily ignite in an oxygen enriched environment. Only with special care to ensure all equipment is both oxygen clean and compatible can the potential for an explosion be minimized. This adds significantly to the cost of maintaining an EAN fill station.
Another method of mixing EAN is by partial pressure, also called “cascading.” The most common method of mixing EAN, cascading involves adding a predetermined amount of pure oxygen to a scuba or storage cylinder, then diluting it with normal compressed air. Some authorities believe this method is more dangerous than blending. But, with special care and meticulous attention to maintenance, many professional facilities have shown cascading to be a safe method of mixing.
Unfortunately, the cascading method is sometimes misused by irresponsible or untrained EAN divers. Sloppy or improper mixing by cascading can result in accidents not only to the person using the cylinder, but to anyone filling it as well. The most dangerous practice is “home brew” enriched air. Home brewing involves a diver filling his cylinder with a small, predetermined amount of oxygen. He then completes the filling process by taking the cylinder to a dive center. The problem arises when the dive center isn’t told the cylinder contains pure oxygen. Since the center’s fill station is probably not oxygen-clean and compatible, oxygen from the cylinder could back up into the compressor system, causing an explosion. To avoid this situation, some dive centers in areas where EAN diving is popular have made it a policy to first fully drain all cylinders before filling them.
A recent development has occurred that might help solve the gas mixing dilemma. Based on requests made by the enriched air diving community, commercial gas suppliers are looking at the feasibility of providing premixed EAN to dive centers and other facilities. This will completely avoid the need to deal with pure oxygen at the local fill station. The drawback is that this method of delivering gas is likely to be more expensive than mixing at the fill station.
Regardless of the mixing method, the cylinder must be analyzed to confirm the exact percentage of oxygen in the mixture. Without such analysis, there is no way to know the breathing mixture’s actual oxygen content. An EAN mixture with a higher oxygen percentage than assumed will expose the diver to oxygen poisoning at a shallower—depth than expected. A standard practice in the EAN diving community is to analyze the mixture at least twice. First analysis is usually done by personnel at the fill station. The second analysis is done before the dive and conducted by the diver planning to use the cylinder. This procedure requires expensive and sophisticated oxygen analyzers. Ideally the use of at least two inline oxygen analyzers is advised to ensure an accurate analysis. Some fill stations use three or four analyzers.
EAN cylinders should never be confused with cylinders containing regular compressed air. Therefore, EAN cylinders must be clearly labeled and dedicated exclusively to holding enriched air. Here, too, most EAN fill stations follow NOAA’s labeling standard. Accordingly, a properly labeled EAN cylinder is yellow with a 4-inch-wide green band at or near the neck. In addition, the “NITROX” should appear prominently on the side of the cylinder in large print. Finally, the fill station should attach a label to the cylinder documenting information such as the date of the fill, the percentage of oxygen, whether and by whom the first analysis has been conducted, and the MOD (Maximum Operating Depth) of the mixture.
There are two particularly important considerations concerning EAN cylinders. First, never fill an uncleaned, unlabeled cylinder with EAN. This places an unknowing diver using the cylinder (and assuming it is air) at risk. It also increases the chances of an explosion, particularly if it’s filled by the cascade method. Secondly, never fill a dedicated EAN cylinder with regular compressed air from an air system not designed for oxygen service. If this happens, have the cylinder recleaned before filling it again with EAN.
Some in the EAN diving community advocate the use of dedicated regulators as well as cylinders. But as enriched air mixtures never exceed 40 percent oxygen at the time the cylinder is actually used, this practice is uncommon. Some equipment manufacturers, however, are considering providing oxygen-clean and compatible regulators. In the mean time, it’s important to understand that scuba equipment produced for recreational diving is not designed for oxygen service. And even equipment that comes right out of the box isn’t oxygen0-clean.
The final problem with EAN is its cost and availability. Setting up and maintaining a complex fill station and oxygen analyzers is an expensive undertaking. So expect to pay more for EAN than a regular air fill. The actual cost of an EAN fill will depend on the amount of gas you purchase and the exact oxygen content. Currently the price ranges between $8 to $15 per fill. In addition, there are now only about two or three dozen facilities throughout North America that can provide EAN, although, as EAN diving becomes more popular, this number will certainly grow.
There are two organizations that specialize in training and certification for EAN diving. These include the American Nitrox Divers Inc. (ANDI) and International Association of Nitrox Divers (IAND). (See the side-bar for more information.) Both organizations provide a full range of programs from basic EAN diving through instructor training. If you take an EAN course—even at the basic level—expect it to be a bit more “academically intensive” than most scuba courses.
ANDI offers two student-level courses—the “Limited User” and the “Complete User.” As the name implies, the Limited User program gives a certified diver the basic knowledge and skills needed to use EAN only under specific circumstances. Although the program addresses the important concepts of EAN diving, it does not require a lot of complex computations. The course involves about four hours of classroom theory and one open-water diver. The minimum prerequisite for taking the course is an Open Water scuba certification. The Complete User course is much more in-depth and geared toward the true “technical diver.” The program is math-intensive and requires 10 classroom hours and two open-water dives.
IAND has a similar course structure, calling their programs “Nitrox Diver” and “Nitrox Technical Divers.” Unlike ANDI, however, IAND requires an advanced scuba certification for all courses, and they offer training in both EAN and other forms of mixed-gas diving, such as trimix (a gas mixture of nitrogen, oxygen and helium).
Both EAN training organizations discuss similar topics in their basic diving courses. In the classroom you can expect to learn about the history of EAN diving, review basic decompression theory, EAN decompression procedures, oxygen physiology, tolerance limits, and diving physics (especially Dalton’s law of partial pressures). During open-water training you’ll learn about gas handling and safety procedures, along with how to conduct an oxygen analysis of an EAN cylinder.
Currently the only traditional scuba certification agencies that recognize EAN diving are the National Association of Scuba Diving Schools (NASDS) and the National Association of Underwater Instructors (NAUI). Through a cooperative agreement, ANDI and IAND instructors who are affiliated with NASDS can offer an NASDS certification in “Enriched Air Diving.” But, rather than encouraging extended no-decompression limits, NASDS advocates the use of air tables only. ANDI and IAND instructors who are affiliated with NAUI can have their programs authorized as an advanced instructor-specified specialty course. (A mre thorough explanation of NAUI’s EN policy, along with PADI’s policy, is detailed in the sidebar.)
IS EAN WORTH IT?
Some in the recreational diving industry vehemently opposed the proliferation of EAN diving. The reality is, however, that this is like trying to push water uphill. The question is no longer should recreational divers use nitrox; the fact is that they are using it. ANDI and IAND have, to date certified almost 300 instructors and more than 4,000 divers. Furthermore, authorities expect this number to double within the next year! These figures, of course, don’t account for those using EAN who have not been formally trained to do so. How many divers this involves is difficult to determine.
Rather than trying to resist the inevitable, it’s more useful to ask the question: Are the advantages of EAN worthwhile given the problems it presents? Frankly, this depends on the type of diving one does and how EAN is used.
For divers of less than 60 feet, there really is no particular advantage to using EAN over air—if increasing your no-decompression time is what you’re after. Although EAN will theoretically extend the no-decompression limits greatly, this has little practical effect. Unless a diver wears double tanks, he’d run out of air long before he reached the EAN no-decompression limits.
For dives below 130 feet, EAN provides no advantage to recreational divers. In fact, because of the increased partial pressure of oxygen, NOAA Nitrox I cannot be used safely below 130 feet. And NOAA Nitrox II can’t be used safely below 110 feet.
The advantage of using EAN to extend no-decompression time, as Table 1 shows, occurs on dives in the 60- to 130-foot range. EAN probably gives a significant enough advantage to consider its use in this depth range if you’re properly trained and closely adhere to EAN diving procedures. (See the “EAN Do’s and Don’ts “sidebar.)
Still, the primary benefit of using EAN is that it can probably enhance diving safety considerably when used in conjunction with air tables or computers. For this reason alone, enriched air deserves a close and thoughtful examination by all divers.
WHAT THE FUTURE HOLDS
In the mid-1980s, many viewed the EAN diving community as dare-devils or lunatics. But things have changed greatly since then. In addition to the creation of two high-quality certification organizations, a less volatile EAN dialogue is blossoming in the recreational diving community. One example of cooperation rather than confrontation was an EAN diving workshop organized by the Scuba Diving Resources Group, the technical diving journal AquaCorps, Hamilton Research Ltd., and Reimers Engineering. Held at Houston, Texas, in January 1992, the workshop brought together most of North America’s leading EAN diving experts. Representatives included individuals and organizations from the recreational, commercial, and scientific diving communities.
The program chairman was dive table designer Dr. R.W. “Bill” Hamilton. A summary report from the workshop was recently released. It stated: “This report is neither a detailed proceedings nor a strict consensus, but—with the help of chairmen, organizers, and others—it is an honest attempt to reflect the general opinion of the highly qualified group of specialists, experts and experimental practitioners as they address the major issues.”
While not a consensus, this report is likely t become an important document in guiding the direction of EAN in the recreational diving community. Those interested in obtaining a copy, should contact the Outdoor Recreation Coalition of America, P.O. Box 3229, Boulder CO 80307.
EAN diving is also gaining recognition among dive computer manufactures. One Company, Quatic Ltd. Of Great Britain, is producing a dive computer called the “Ace.” It allows the user to select a program to calculate EAN decompression schedules. Although no other company now offers this option, it’s probably only a matter of time before they do. But, as with all new technology, expect to pay the price. With the module needed to run EAN decompression calculations, the Quatec Ace costs about $1,700.
Some believe EAN holds promise in helping solve the problem of multi0day repetitive diving. Evidence from the Divers Alert Network (DAN0 suggests that multi-day diving—like that done while vacationing at a dive resort—could subject divers to an increased risk of DCS. (See “Ascent Rates Safety Stops,” June 1992 Dive Training, for more on this subject.) EAN advocates say that this risk could be reduced by having divers use enriched air instead of regular air and dive in accordance with regular air tables. Those who hold this view claim there has been a drop in DCS accidents among resort-based divemasters and instructors who use EAN with regular air tables.
MAKING THE CHOICE
As mentioned at the onset of the article, choosing EAN for your diving adventures is a personal decision. Perhaps you think nitorx diving is an activity you wish to pursue. Then again, you may decide that you’re content with what recreational divers have been using for more than 30 years—“God’s own nitrox.”
The author would like to thank Dr. Dudley Crosson for his technical review and commentary. Special thanks to Billy Deans and Mark Nease of the Key West Hi-Tech Diving Center and Mike Menduno of AquaCorps for their advice and insight in preparing this article.
DO’s and DON’Ts of EAN DIVING
Be trained and certified for EAN diving: Never dive with enriched air if you haven’t completed a sanctioned course. The dangers of enriched air are both subtle and insidious. Also, certified EAN divers should never encourage friends who are not EAN-certified to use enriched air without proper training
Secure EAN from a reputable source, and never dive using a “home brew”: All divers must be certain of the quality of their breathing air. For EAN diving this means not only avoiding contaminates, but also verifying the mixture’s oxygen content. Ask whomever is providing your fill to give you a tour of the compressor/storage system, and ask them to explain the operating procedures and safeguards in place. Above all, never try to mix your own EAN.
Always personally analyze your gas before use: Only an analysis can confirm the actual percentage of oxygen in an EAN mixture. Never use a cylinder containing enriched air unless you analyze it first. And be sure to use at least two in-line analyzers. Multiple analyzers validate the results of one another.
Never exceed the Maximum Operating Dept (MOD) for the mixture you are using: The maximum depth for using EAN is not approximate or flexible. Remember, convulsions from CNS oxygen poisoning can come without warning. Know the Maximum Operation Depth for the mixture you’re using and don’t dive beyond that limit.
Use only dedicated oxygen clean and compatible cylinders: Use of non-dedicated cylinders results in a high risk of explosion, and could subject an unknowing diver to oxygen poisoning. Follow the proper labeling procedures.
DIFFERENT VIEWPOINTS ABOUT EAN: FROM TWO OF THE CERTIFICATION AGENCIES
National association of Underwater Instructors: NAUI’s director of training, Jim Brown, says: “The use of enriched air nitrox for recreational diving is permitted, provided formal training has been obtained through a nitrox diving program which meets NAUI approval. The procedures used in such diving should follow those detailed in this training program.
“Active status NAUI instructors who are currently recognized as EAN instructors and authorized to award certifications through the International Association of Nitrox Divers (IAND) or American Nitrox Divers Inc (ANDI) may apply for authorization to teach an advanced instructor-specified specialty course in the recreational use of enriched air nitrox.”
Brown also mentioned that NAUI’s professional liability policy provides full coverage for their instructors who teach EAN courses.
Professional Association of Diving Instructors: PADI’s vice-president for training and education, Drew Richardson, says: “At this time, PADI does not feel that the proper infrastructure of industry controls is in place to safely support a broad application for recreational diving, as it is for the well-controlled and specialized applications of Enriched Nitrox in scientific and commercial communities. As a result, there are many safety concerns that exist with regard to popularizing Enriched Air Nitrox for use by recreational divers at large.”
“Some of the safety concerns resulting from the lack of an infrastructure within the recreational community include: proper supervision, gas mixture, training, dive planning, equipment considerations and equipment capability, control of partial pressures of oxygen, depth and table considerations, etc. PADI does not sanction gas mixtures other than air for recreational diving at this time.
“We wish to make clear that PADI is not against Nitrox diving, but simply that PADI’s educational charter, to date, has focused on the training of air diving techniques. Our training materials and standards were constructed based on air diving and to date we have little or no provisions for mixed gas or Enriched Air Nitrox diving. As a result, PADI certification and course sanctions apply to air diving only.
“However, we have no conflict with certain qualified PADI-member dive centers or instructors offering Enriched Air Nitrox courses or Nitrox diving if the instructor and /or dive center is properly trained, qualified, and equipped to do so. We do require that the use of Enriched Air Nitrox be kept clearly separate from any PADI course or program. This is consistent with our philosophy and policy in other areas of technical diving, such as cave training. While we realize there are some individuals and operations within the technical community that do have proper infrastructure in place, the overall recreational community has no such infrastructure present/existing.
“PADI remains objective and open to the development of equipment and technology in our educational offerings to the general public…and to this end we are presently researching and collecting member opinions and views regarding Enriched Air Nitrox diving.”
Regarding insurance coverage, Richardson added, “Presently, the professional insurance policy that is offered through PADI by Vincencia and Buckley for supervisory and instructional liability insurance does not cover the use of Enriched Air Nitrox or other gas mixtures other than air. Our store insurance policy offered through Vincencia and Buckley does provide coverage for operational activities, like tank fills, repairs, and sold products, at this time and makes no distinction between use of air and Nitrox. Therefore, the use of Nitrox associated with these activities does not diminish coverage as is the case in our professional liability policy.”