Reported Story

I was recently certified on a closed-circuit rebreather system. It feels very different than open circuit, so I was trying to get comfortable using it while on a trip to Bahamas.

I carefully transported my gear, and on the night I arrived I painstakingly set it up for diving. On the first dive the next day, my buddy told me that I had a small leak coming from my over-pressure valve. He tried to troubleshoot it underwater. No dice. He asked if I wanted to continue the dive or abort. I opted to continue and planned to have a closer look at the valve back at the dock. I finished that dive without further issue.

At the dock later that day, I took out the valve to inspect it visually for cracks and found none. My buddy put a bit of plumber's tape on the threads and reinstalled it for me. I headed back out to dive. I did not closely inspect the valve once it was replaced — mistake No. 1. When I put the unit back on, I reached behind me and turned my cylinders on, one small twist each — mistake No. 2. The oxygen cylinder requires only one small twist, but the diluent cylinder is the same as your 80-cubic-foot open-circuit tank. This cylinder must be opened up wide to allow for any flow at all under pressure.

I splashed first and began my swim toward the anchor line. Suddenly I realized two things at once: I was taking in water through my mouthpiece, and I felt like Wile E. Coyote when someone hands him an anvil. I have never felt so heavy! As I plummeted toward the bottom, I switched to open circuit via my bailout valve. This is a device mounted on the mouthpiece of the loop. With one 90-degree twist, the user can switch back and forth between open-circuit and closed-circuit modes. In the open-circuit mode, I was drawing directly from my diluent bottle — you know, the one I had failed to open all the way. Nothing happened.

In closed-circuit mode I got water. In open-circuit mode, I got nothing at all. While my mind was ripping through possible causes at a mile a minute, I realized that I didn't have flotation either. The diluent cylinder is plumbed into the BCD and supplies gas for flotation the same as it does on open circuit. As I descended uncontrollably, something to breathe became a secondary problem, and I swam for the anchor line with all my might.

When I finally reached the line and arrested my descent, I was able to ditch my loop and switch to my open-circuit bailout cylinder. This is a standard part of every rebreather diver's gear. It is an entirely independent cylinder, usually slung on the side of the diver. It provides backup gas in case it should become necessary to abandon the closed loop. Now I was breathing and got instantly engulfed in clouds of bubbles from my exertion and heightened anxiety level.

I pulled myself up the line, trying to calm down and troubleshoot at the same time. I knew that I had turned on my diluent. I could remember doing it. Why couldn't I access it? I pulled myself hand over hand to the surface. As my head broke the surface of the water, the divemaster on the boat asked me if I was OK. I shook my head no.

The waves were still breaking over my head, and I was not willing to part with my regulator yet. When I brought myself under control I realized that I would have to let go of the line to swim to the ladder. Nothing doing! I still had no flotation. I seriously considered ditching my unit when I decided to try opening my diluent valve further. The sea state was about six feet, so it took me a minute of fighting to let go of the line with my left hand, make a space between my bailout cylinder and myself, find the valve and open it. Now I had flotation. I was able to inflate my BCD, let go of the line, make my way to the ladder and board the boat. When I broke down the unit, I found the scrubber canister and breathing hoses flooded.

Diver’s Comment

I was quiet and introspective for the rest of the day, scrutinizing what had happened. I can only surmise that the over-pressure valve had gotten stuck down or cross-threaded during reinstallation. I should have made a close visual inspection of it, but, more important, I should have performed positive/negative pressure checks again. These checks are done before the first dive of every day and whenever the loop seal is broken for any reason. They are designed to show the diver that the system is truly closed and ready to dive. I also realized that while I had turned on my diluent, I only opened it by half a turn, making it no good to me under pressure for bailout gas or flotation.

I never anticipated having two dramatic problems at once. Having no flotation and nothing to breathe at the same time is not fun. I did learn, though, that it does not have to kill you. My training kicked in as it was designed to do. Although I admit I was scared, I did not panic. I knew what I had to do. I had been trained to handle a flood, and I did it. Admittedly, I was never trained to handle a scenario with no gas plus no flotation. I had to improvise a few protocols on my own.

I took away some very important lessons with me that day. The buddy checks that were so important when I was sport diving had faded to the background when I began technical diving. Those checks should be more important than ever now. I have more gear and more technology on me than I used to. Two sets of eyes should make sure that everything is good before I splash. I need to take the time to inspect all my gear thoroughly and make sure it all passes the predive checks before getting in the water. I need to set up my unit the way I was taught to do before every dive — with the diluent all the way on!

I also learned what I had done right. I did not panic. I retained my ability to think and reason through the situation instead of giving way to animal instinct. I attribute my ability to handle the situation to the fact I had such good instruction. We had reviewed the flood drill more than any other skill in the class. As a result, I had the knowledge and ability to handle a real situation. Since these drills were so fresh in my head, I did not hesitate to carry them out. If it had been years since my training, the outcome might have been very different, reinforcing the theory that it is necessary to practice all life-saving skills on a regular basis.

I assume all responsibility for what happened that day. I know the entire incident was because of user error. I know now what I will and will not do again. I also take credit for a successful self-rescue. It gave me confidence in my instructor, my training, myself and in the system. I can confirm that what you are taught truly does work and might save your life.