Standard Gases by JJ

Before I begin any discussion of the specific gasses I chose for GUE I want to reiterate a few aspects to standard gas selection. I recognize that this may appear to be old hat but some of the concerns seem best answered in this format. Please recognize that the constituents of a particular set of standard mixes are less important than the utility of standard mixes in general. In other words you can always find a "better" mix at a given depth; this is also true for a range of depth segments.

The more you obsess about the "perfect" mix for a given depth the more you reduce the utility of standard gasses; in this case you are migrating toward a "best mix" philosophy. For those not familiar with this convention it selects a given PO2/END (ie 1.4/100) and adjusts the mix to maintain these parameters. There are a range of reasons that we went away from this paradigm, not the least of which involves our assessment that this strategy promotes false benefits while ignoring more relevant risks. In other words we came to believe that it was not useful to run one's PO2 in the elevated range (for some time it was common to set between 1.4 and 1.6 if not higher); likewise we determined that it was detrimental for both deco and safety to maintain high END depths. More importantly, we came to see that using a set of standard gasses greatly enhanced our ability to intuitively run our dives ie"deco on the fly" or "ratio deco" or any of the conventions we have used to discuss developing an understanding of the way in which one's deco follows an anticipated curve.

 These issues together with the wide range of safety, mixing, marking, convenience and team issues make standard mixes (regardless of their particulars) incredibly powerful. When selecting standard gasses there a variety of nuances that one might preference but in general simplicity and safety remain priorities. While selecting standard mixes it is also important to frame gas selection with consideration to the sort of dives done at various depths ie time, exertion etc. Within the WKPP our inclination was to utilize rather low PO2 levels with reasonably high He levels. Within those mixes we had to recognize that most of our diving was deep and that even dives that were planned for shallower depths could easily go quite a bit deeper (because of the common depth of the region); longer dives further increase the risk of oxygen problems when diving elevated PO2. Therefore, the longer the dive the shorter the PO2 considered reasonable. In selecting GUE gasses

I was hoping to select gasses that had notable utility across a broad range of diving, thereby increasing the benefit of standard mixes in general (because they would become somewhat ubiquitous). As a set of mixes becomes utilized by a greater number of people than it becomes easier to integrate teams, locate desired mixes in a given region, justify banking mixtures that are regionally appropriate etc. I tried to weigh the various issues from safety and convenience to efficiency and simplicity. Of course there are always going to be particular dives for which the selected paradigm is less ideal. However, I would argue that the vast majority of scenarios find little benefit from tinkering with Standard Mixes. Speaking directly to GUE's mixes I chose a ROUGH guideline of 1.3PO2 and 70'/21m END. In the shallower range of the mixes I kept the PO2 a bit lower as the benefit to higher PO2 has to be weighed against the increased likelihood of longer bottom times. Likewise for deeper dives (250 +) that are likely to accumulate a greater total oxygen load, the PO2 is relatively lower across the working range of the mixture.

There is no question that several dives would not be "ideal" with any standard gas mixture. However, that contention largely misses the point of standard gasses. Certainly there are potential dives in which one needs to use some common sense while planning a dive. For example, a very long dive in the mid range, a very deep dive for long periods, a very long shallow dive etc. Likewise, divers may choose to bump a mixture to the next  standard gas ie diving 18/45 instead of 21/35. From my perspective more He is generally better and less O2 rarely problematic. Of course there are always exceptions to any rule. However, one usually discovers that perceived exceptions bring marginal benefit thereby reducing if not eliminating any real benefit to custom mixes. GUE mixes represent an effort to weigh these various issues. Of course we could use 23/35 instead of 21/35 (to bring the PO2 more in line with the other mixes); there are no legal or other over riding issues promoting 21%.

This is true at least outside of this gas facilitating lower O2 at the shallow range with a reasonable END while also falling into the general 50' 3%O2 drop used to demarcate these gas segments. However, we create minimal if any benefit while migrating away from the benefits found within the standard gas paradigm. With respect to the WKPP mixes there are some inconsistencies but please recognize that the goal of those mixtures is different and are regionally specific; notice that there are really only two bottom mixes 0-190 and  190+. The GUE mixes are designed to work for a larger audience with a greater diversity. Of course one might choose to create a set of standard mixes for their region but they do lose some of the benefit found in a larger  audience of divers that are on the same page so to speak. For example, these divers have a smaller audience of fellow divers with whom to compare various experiences, questions, or patterns within the deco. In short, the more divers use a well established common standard- one with a proven track record- the more synergy exits within a team and among various teams.

Best, Jarrod Jablonski
President/Director of Training Global Underwater Explorers