Freediver Experiences Shallow Water Blackout

By Stephen Pacetti

After scuba diving for nearly 18 years, I began freediving, hoping for a new challenge. As a teenager I had been a competitive swimmer and found I still had some of my earlier stamina. There was also spiritual appeal to freediving; it was like underwater meditation.

During Labor Day weekend I planned to spend three days on a live-aboard off San Clemente Island, California. As usual, I didn't sleep well the first night on the boat. Despite feeling tired and not particularly energetic, I ate a little and decided to go freediving.

My buddies were getting ready to make their first dive so I entered the water with them. This was my second mistake. Even though I was diving near others, I was essentially diving alone. Scuba divers cannot look out for a freediver.

I took a few deep breaths and piked down. At the outer edge of the kelp bed I grabbed my buddy Dave's console: it read 67 feet. At this point they started heading back toward the boat.

Then I made my third mistake. I usually have no distractions when I freedive. Between dives I rest on the surface and don't move at all. While on the bottom I just observe, swim very little and pay attention to how I feel. Here, I was swimming on the surface through thick kelp. Once on the bottom, I would catch up with my buddies and swim with them. On the fourth or fifth dive I finned down about 50 feet and swam alongside Rich, the leader of the group. This was my fourth and final mistake. I was showing off and trying to impress my buddies. Tiring, I grabbed Rich's first stage to hitch a ride. After a while I let go and headed up.

I saw a large clearing in the kelp canopy and rose toward it. The surface was very calm; the sun, still low in the sky, highlighted the movement of the water. It moved slowly, a liquid mirror. I'll never forget the way it looked.

The next thing I remember I was lying flat on my back on the deck of the boat. People were holding my arms and legs down. I was fighting to get them off. I lurched, trying to sit up but was pushed down. Confusion, panic and anger at being held down welled up inside me. My vision was blurred, just shadows. An oxygen mask was pressed onto my face. I wanted to speak but everything was slurred and uncoordinated. My mouth and tongue hurt and my tongue had swollen to fill the back of my mouth. However, I could hear Rich saying, 'Take it easy man' over and over. My head pounded and I was very nauseous. I could sense the anxiety in the people around me. I wanted desperately to tell them I would be okay, to give me time, to leave me alone but I couldn't.

I had experienced shallow water blackout. To keep up with my buddies I was hyperventilating on the surface. This artificially lowers the carbon dioxide level in the body and it is the carbon dioxide that gives you the urge to breathe. I was also not resting fully between dives. Another interesting phenomenon is the effect of pressure. As you descend the air in your lungs compresses and your lungs get smaller. Consequently, the partial pressure of oxygen in your lungs is raised. Hemoglobin in the blood is oxygenated according to the oxygen partial pressure. During freediving you can use this to extend your bottom time. Even though the percent of oxygen in your lungs is low, the depth makes the partial pressure high. However, you pay a price for this. On the way up, the pressure drops. The oxygen level drops quickly and you black out. On the last dive I don't remember really hurting for air. As I rose, things just moved slower and slower.

Apparently, on the surface, even though I was not breathing my heart kept beating. It is a good thing I was weighted lightly.

After I had been breathing oxygen for more than half an hour, the U.S. Coast Guard arrived and my panic lessened. I simply felt embarrassed.

After evacuation by helicopter, I spent a day and night in intensive care, followed by another day and night in a regular hospital room. Monday morning, reasonably sure that there were no permanent effects, I walked out of the hospital and flew home to San Jose, California.

I learned many things from this experience. I learned that I had been too carefree in the water for some time. On many occasions I had gone freediving alone. I was very lucky, my story could have been very different, with a very different ending. To this day, I am still astonished it happened. I plan on sticking to scuba diving as I'm not sure I can trust myself freediving. In all my years of scuba diving, I have never had a problem.

If you are drawn to freediving, do it with a buddy or at least have someone watch your ascents. Don't do it when you are tired and don't hyperventilate on the surface as I suspect I was doing. Know what your limits are or someday your limits will find you.