Why is deep technical diving complicated?
Technical diving is more complex, risky, and expensive than recreational open circuit scuba diving and is not for someone who wants to simply jump in the water. I am well aware I am a high maintenance diver and I don’t like people touching my equipment. When your life depends on a specifically tailored set-up you can’t take deep diving lightly as there is little room for error to avoid potentially dangerous and deadly accidents.
Below is a dive profile for a December 2014 101m multi-level dive on the Gulf Fleet 31 wreck. I was in the water with six cylinders all containing different gas mixes tailored for specific purposes or depths. Two cylinders attached to my rEvo rebreather provided my breathing gases and contained 10/58 trimix (10% oxygen, 58% helium) as my diluent and 100% oxygen; a small independent third air cylinder was used to inflate my wing. I carried three 12 L bailout cylinders containing 10/60 trimix, 15/50 trimix, and 50% oxygen. Bailouts are only used in an emergency and positioned tightly to my body to avoid drag and are rotated to different positions during the dive. I also dive with four technical dive computers: one Shearwater attached to my rebreather reading three oxygen sensors, one independent Shearwater as my backup, and two rEvo Dreams which read independent oxygen sensors. I dive with a PPO2 (partial pressure of oxygen) set point of 1.3, bumping it up to 1.4 around 18m to speed decompression provided the CNS (warning for oxygen toxicity) doesn’t rise too high.
Dives are planned based on how much bailout you can carry because if you don’t have enough bailout gas to get you to the surface in an emergency you either shorten your dive time and/ or depth. With this in mind for the dive profile above I planned a 12 minute bottom time at 100m with a move to 85m for 8 minutes for a 20 minute total bottom time (if I stayed at 100m I would only have an 18 minute bottom time and I wanted an extra few minutes in deep water). We didn’t reach the wreck at 101m until minute 6 and I was up to 85m at minute 12. At minute 20 we ascended at a rate of 10m a minute for our first decompression stop at 45m which was precisely at 24 minutes into the dive. You must stick to the dive plan or you may end up with a much longer dive than planned and not have enough bailout gas in case of emergency. For example, an extra five minutes at 100m adds about one hour to your total dive time. This 101m dive had a total dive time of 141 minutes, with 60 minutes spent decompressing at 6m.
As you can see from this dive profile, you have very little time at deep depths and must be super efficient with the job at hand (for me that is finding interesting species and setting up photographs correctly) while keeping a close eye on dive computers and making sure PPO2 doesn’t go above 1.4 among other issues that can arise. For the 101m dive I was photographing with two cameras and my main camera lost most function as the buttons on the housing were depressing from the pressure. I deal with it efficiently and work with what is functional, always knowing my safety takes priority above all else.
Here is another dive profile from July 2014 for a 76m dive with a bottom time of 25 minutes and total dive time of 146 minutes. We were on the bottom by minute 3 so I was happy to have 22 minutes to settle in and find species to photograph. With the 10m/ min ascent rate we were at our first deco stop at 39m by minute 29, and we spent 60 minutes decompressing at 6m. My diluent gas was 9/59 trimix and three bailouts were 12/60 trimix, 20/30 trimix, and 50%.