What it's like to dive to 120 feet

Okay - it was really only 119 feet; the photo of my dive computer was taken just before I got to 119'.

The dive was set up as a training dive for a student who needed a deep dive (100' or deeper) for his advanced diver certification and for a woman working toward becoming a dive master. I was just along for the experience. The idea was to simulate a decompression dive, complete with safety/decompression stops, without actually going into decompression mode.

For the uninitiated, here's the thing about diving: it's all about being safe as you can be. As you descend, the pressure forces additional nitrogen into your body tissues. You don't feel it, but it's there. As you come back up, that nitrogen is released. If it is released too quickly, i.e., if you ascend too quickly, the extra nitrogen is released quickly, causing decompression sickness, commonly known as "the bends." So the plan is to ascend slowly, allowing the nitrogen to sort of bleed off. Every dive ends with a "safety stop" for 3 minutes at 15 feet. If you dive deep or stay down for a long time you need to make additional stops, called "decompression stops," on the way up to release nitrogen safely.

If you look at the picture of my computer, here's what the numbers are telling you: at the top, the large "116" is the current depth. The smaller number to the right is the maximum depth reached on this dive. The big "5" in the middle is how long I can stay at this depth without having to make an additional decompression stop. The "6" in the bottom is the running time of the current dive. (The "82" is not relevant to this discussion; it is the water temperature.)

Our objective was the buoy off Crashboat beach. The buoy sits on the bottom at about 125 feet or so. As you can see, after being down for only six minutes and with only five minutes "to deco,"the "bottom time" of deep dives is very short.

In fact I didn't actually make it all the way down to the bottom of the buoy. A minute or so after this picture was taken I reached 119 feet and my computer said, "one minute to deco." To avoid going into "deco" (which was one of the dive objectives) I had to hover at about 119 feet.

So what is it like? I've been to114' before on The Wall off La Parguera. For some reason this dive was scarier, at least at the beginning. Maybe it was decompression briefing before the dive. Maybe it was that there wasn't nearly as much to see as there was on The Wall so I was much more aware of "time to deco." I spent my "bottom time" mostly staring at my computer. Otherwise, it didn't feel much different than other, shallower dives.

The water absorbs light so there is less light at those depths than nearer the surface. Your eyes compensate for the reduced light levels but they can't compensate for the lost colors. The water filters out first the red wave lengths, then orange and yellow until all that's left is greens and blues.Wherever there is to see looks either greenish or brownish depending on it's actual color.



There is another difference on deep dives, one you don't feel but that can be seriously problematic on the way up. As you go deeper, you use more air from your tank. Under pressure, your lungs compress and it takes more air molecules to fill them. So  you suck more air from your tank. At 122 feet you use air five times as fast as at the surface. That means you have less air for those all-important safety stops.

On this dive we all did a good job of managing our air. We did our first safety stop at 65 feet for one minute and another for 10 minutes at 15 feet. We all reached the surface with a generously safe amount of air left in our tanks.

This was not the most fun dive I've ever done but it was a great training dive. And it confirmed that unless there is something really really special to see - like a wall or a wreck - there really isn't much point to diving to 100' or more.