Why IANTD Uses EANx80 article
From SubAqua UK
Why IANTD Uses 80/20 as a Deco Gas
By Tom Mount, posted to techdiver, 14 May 1998
Bill
I would like to take a moment to clarify a couple of issues with you on IANTD's recommendation of the use of EAN 80 in TRAINING PROGRAMS. I will not go into detailed history on how we evolved to the use of EAN 80 as I have already explained that.
When you did your training we were (if I remember correctly) still using oxygen on deco.
Over time I witnessed as did other instructors some (only a few, but still important to safety) divers develop oxygen toxicity symptoms on oxygen at the 20 foot stop. This included one diver who like all of us had been using oxygen for several years as a deco gas.
Following these occurrences we looked into several alternatives for screening or avoidance. We considered the use of an oxygen tolerance test, only to be told by the Navy and others that it really is not a reliable index except in the event of someone highly reactive to oxygen, plus we had the additional problem of chamber availability and the cost of doing a tolerance test. From Navy Days and while at the UM RSMAS I was involved in oxygen tolerance testing we (UM RSMAS) for several years conducted the Coast Guard test we never had anyone on the DRY (dry is much different than wet) testing on a 60 foot one hour exposure have a problem. This is fairly consistent with dry chamber runs such as treatment etc. In over 100 treatments I only witnessed one oxygen problem and that was pulmonary not CNS. So for a variety of reasons we decided that oxygen tolerance testing was not feasible and really would not provide reliable data. Check with about any physiologist and they will almost always agree with the reliability issue of tox testing. Combined with the cost and availability of chambers it is a poor option at best for a screening requirement.
Based on the point that a few people had exhibited in water symptoms we felt it was not a good policy to REQUIRE the use of oxygen at 20 feet (1.6PO2) So the big issue for us in training in regard to oxygen decompression is the 20-foot stop exposure.
Then of course there is the additional problem in open sea (caves have more stability and fresh water a slightly lower PO2) decompression as divers tend to vary a couple of feet even with good buoyancy control due to changes in body attitude, waves passing overhead, or when on down lines not being able to get to the exact 20 foot stop even with the use of John lines in current (every one does not have the freedom of being able to hang neutral with a drift line, or ride on a deco station, such as in NE hanging on a line in the current.) plus in open sea one is never completely at rest as in a cave type deco environment. Also some divers occasionally vary more than a couple of feet at some point during a deco schedule. AGAIN another reason for looking closely at the 20 foot oxygen stop in a training program where the student is being taught all these procedures
Options then became:
1. design in a 15 foot stop for the use of oxygen
2. Look at a EANx mixture for the stops that is significantly higher than the bottom mix and one that will also allow a faster decompression schedule to reduce the hypothermia and dehydration problems as well and still provide good off gassing
After reviewing these options and discussing them with several hyperbaric physicians and physiologist we elected to go to a high EANx mixture. Thus EAN 80 was selected. Two sets of tables in a variety of mixtures both Nitrox and trimix were designed Based on either EAN 75 or 78 with the intended gas being EAN 80. One set begins the EAN 80(75) at 20 feet the other begins at 30 feet So all current IANTD tables offered feature these mixes in technical programs. In recreational Advanced EANx we use EAN 50 for safety or required stops in the process of acquainting divers with the advantage of having more oxygen in the safety or real stop gas than what is in the bottom mix. In the intermediate trimix program we have a set of tables with one gas switch. The switch on that table is to EAN 70 at forty feet. The intent of these tables is to eliminate a need for a diver to be exposed to a PO2 of 1.6 and also to stay within the oxygen exposure limits.
As stated these tables were developed for training program use. Even the trimix tables stay within the confines of two gas switches and do not involve bottom times such as encountered on exploratory dives. No one has stated that EAN 80 is a better choice for a deco gas, it is one we think is more suitable for divers in a training program where they are involved with learning a lot of new skills and both gas and equipment management techniques
Based on Doppler testing I have done it appears that there is very little difference in bubbles detected on EAN 70 starting at 40 feet, EAN 80 starting at 30 feet and oxygen starting at 20 feet. However with mixtures less than EAN 70 there is a significant increase in the bubbles detected. It would be great to actually have some large-scale scientific studies on this; maybe someday funding will be available to do this. It is for these reasons that IANTD endorses EAN 80 as a training deco mix.
Interesting some major expeditions have opted for eAN 80 as well due to logistics and other reasons including risk exposure these include the Britticana, and the Atlanta both 400 foot dive profiles. These expeditions were completed with no incidence of DCS
On tables IANTD looked at the following models (all haldian this will most likely change as more new concepts are put into practice in validated decompression models)
1. USN tables we felt that these offered the least amount of safety as the stops begin to shallow and they act rather like doing a treatment for bubbles that are formed
2. DCEIM again we felt that the stops begin to shallow and we also felt that the stop times were excessive
3. Bulhman The stops were deeper than the other tables, it has more diving history (validation) worldwide than the other tables, at the time we were advised that it was more in tune with current theories, most dive computers use this model thus it can be used in conjunction with computers in some instances, most decompression soft ware is based on this model. We realize the Bulhmann model is not perfect but it seemed to suit our needs better than all other existing validated models. Recently in our newer tables that are available we have actually incorporated some deeper stops concurrent with what we believe will, be the trend in future tables.
(Bill if you remember back to when you were doing your course I presented material, Just as I still do, by Hills and Fife on thermodynamic models solely because they did endorse the deeper stops. Even when I was at the UM RSMAS we used to present This in our classes during the mid 70's)
Now you brought up the boat emergency gas, IANTD does not endorse EAN 80 as an emergency gas for the boat use, we think all boats should have oxygen available for emergency use. While its is important for both recreational and technical diving it is especially true for recreational diving where the risk and occurrence of AGE is greater than in technical diving. I repeat it is IANTD's opinion that charter boats should have 100% oxygen available as an emergency gas for diving accidents.
Now on deco bottles they must be labeled per IANTD standards
This is direct from our standards
C. LABELING EANx MIXTURES WITH LESS THAN 41% OXYGEN
1. Cylinders already painted yellow must be labeled with a 4 inches (10 centimeters) green band. The band must wrap around the tank starting at the flat of the cylinder. The label must state "Enriched Air Nitrox" (or an applicable acronym). IANTD has EANx decals available for labeling tanks.
2. Cylinders painted with colors other than yellow require a 6 inches (15 centimeters) Enriched Air Nitrox band (decal) with the top 1 inch (2.5 centimeters) and the bottom 1 inch (2.5 centimeters) yellow. The middle of the band (decal) should be printed with a green background and the message, "Enriched Air Nitrox" (or an applicable acronym) printed in yellow for easy identification.
3. Note: Scuba tanks without a green and yellow label with suitable contents description-wording to identify Nitrox, EANx or an equivalent acronym must not be filled by IANTD Facilities. Any color-coding other than yellow and green violates community standards, IANTD Standards and International practices.
4. Nitrox (EANx) cylinders must have Cylinder Contents Labels affixed to them. The Contents label must state the oxygen percentage currently in the cylinder and the Maximum Operating Depth (MOD). The label must be dated and signed by the person who purchased (or requested) the mix (verifying he/she confirmed the O2 percentage).
5. This label may be a separate label, or part of the EANx band. IANTD has waterproof, reusable Cylinder Contents labels and cylinder content tape available for order.
6. Nitrox (EANx) cylinders must have a current Visual Inspection (VIP) decal stated that oxygen-compatible lubricants have been used in the system (valve, tank neck, and/or cylinder). EANx cylinders used with EAN 41, or greater, or for direct partial pressure blending use, must have an Oxygen Service Rated VIP decal. IANTD has VIP decals (which also cover both tank and valve inspections) available for order.
D. LABELING EANx (GREATER THAN 40%) AND OXYGEN (GREATER THAN 91%) MIXTURES
1. Cylinders containing oxygen levels of 91% or greater must be painted either green or white, or have a 10 inches (25 centimeters) long by 4 inches (10 centimeters) wide green adhesive band decal with the word "OXYGEN" clearly and prominently printed in white on it. IANTD has waterproof Oxygen Cylinder Decals available for order.
2. Cylinders should not be painted in common sport diving colors such as black or red as underwater these are hard to read the oxygen label.
3. Regulators used with tanks containing high levels of oxygen must also have green or white second stage covers and/or hose wraps or other means of identification as oxygen service regulators, leading to the second stage. Alternatively, the second stage purge buttons may be green or white.
4. Cylinders containing EAN 40 to 90 must have a color-coded "oxygen green" and white label decal boldly stating, "Decompression Mix EAN* _____." or a Breathing Gases other than air decal that is red and white. This label must be 10 inches (25 centimeters) long and 4 inches (10 centimeters) wide. IANTD has Cylinder Contents labels available for order. * Or, equivalent acronym.
F. LABELING TRIMIX MIXTURES
1. Cylinders containing Trimix must be labeled with either the word, "Trimix", or "Breathing gas other than air". A Cylinder Contents Label reflecting the percentages of Oxygen, Helium and Nitrogen must be affixed to the tank.
Again IANTD is a training organization and our standards are based on and continually updated on those things we feel will provide the maximum safety to the students in a course.
Bill I have explained some of the process of why we recommend and cut tables with EAN 80 in training (some of our instructors do use oxygen) and also why we elected to use bulhman tables. I really do not care if you approve or disapprove of EAN 80 in training nor do I care if you think the bulhman model provides "weenie decos" In fact the answer is for the benefit of those who may be interested in the logic behind our deco gas selection and the tables we use.
These tables were not designed nor intended for use in dives of the magnitude of the dives preformed by the WKPP We have not and would not recommend our tables for WKPP type projects. Dives of this magnitude requires custom tables and your liability issue as regards a validated table are not the same as a training agency.
Even the Hamilton tables you have and the ones Billy and I have differ as yours were created to your specifications, and ours were simply ones Bill developed for what he felt would provide us with his standard Decap safety.
Tom Mount
