Hydro Atlantic without Helium?

[dberry]

Putting the whole helium question aside, you dove the Hydro Atlantic on Nitrox? 1.4 pO2 at MOD of 165 fsw would be only 23% EAN. Hardly seems worth it. EAN 26% for pO2 of 1.6 atm, if you want to push the boundaries.

Of course, I suppose air qualifies as nitrox; my apologies if I read too much into this.

 

[Coztick]

Would it be worth using air for the bottom and say 32% for travel, switching at MOD?

 

[boulderjohn]

Would it be worth using air for the bottom and say 32% for travel, switching at MOD?

If you are using air for a bottom gas, there is no point in using a travel gas. With a normal descent rate, you will be on the wreck in about 3 minutes, about a minute after the switch, so it would have no real benefit on descent.

On ascent it would have some benefit as the first deco gas, although it would be more efficient to use the more common 50% instead.

 

[OceanEyes]

Putting the whole helium question aside, you dove the Hydro Atlantic on Nitrox? 1.4 pO2 at MOD of 165 fsw would be only 23% EAN. Hardly seems worth it. EAN 26% for pO2 of 1.6 atm, if you want to push the boundaries.

Of course, I suppose air qualifies as nitrox; my apologies if I read too much into this.

Hello dberry. I presume that you are referring to my post, the one immediately preceding yours.

NOAA reduced the maximum PO2 from 1.6 to 1.4 in 2015. When I began diving using US Navy tables, the maximum PO2 was 2.0. Thus I’d made hundreds of air dives deeper than the Hydro, in colder water, and in a variety of conditions. The idea of diving the Hydro on air was not a terrifying concept to me, but as I had the means of choosing a slightly more suitable breathing medium, took that opportunity.

In those years my preferred fO2 for dives on the Hydro was 24%. I had been living in Florida for a few years before I made my first dive on the Hydro, and as an industry insider, had established a good relationship with many local professionals, some of whom were on the leading edge of diving practices that have come to be known as “Tech Diving.” Amongst this scurvy crew were a few who had access to gas blending supplies and equipment. It was no big deal to bring cylinders to these folks and request a custom mix. Just as an example, to achieve a mix of 24% oxygen in a tank rated for 3,000 psi, (O2 cleaned because you are blending using partial pressure), you would add O2 to an empty tank until you reached 114 psi. Then you’d top it off with air. Pretty simple, safe for a qualified blender, and not very time consuming.