The Dangers of Narcosis | Scuba Diving

The Dangers of Narcosis

Phil was diving deeper and farther than most divers ever got to go. He was going deeper than he had ever been before as well. He had just entered the world of technical diving — newly certified in the special techniques and practices it took to make a successful dive beyond recreational depths — and he was close to 170 feet deep. He was thrilled with this new experience and the freedom it gave him. He couldn’t wait to tell all of his diving friends and convince them they needed to seek out the training as well. And then he inhaled, but nothing came.

The Diver

Phil had been diving recreationally for years. He dived in the local lake and took a trip or two each year to resort destinations with his family. The entire time, though, he wanted more. Wanted to see more, do more and go to more places. Finally, the world of technical diving was opening up new opportunities for him. He had recently completed his technical training, but hadn’t done much diving beyond recreational limits yet. He had also just purchased a complete set of technical gear and was itching to put it to use.

The Dives

The shipwreck rested at nearly 200 feet and was about an hour-and-a-half boat ride offshore. Phil had wanted to make a dive there ever since he saw it profiled in a dive magazine. It had become one of his goals as he learned about technical diving. He made the trip alone and found a dive buddy on the boat, learning they both had the same goals. Phil’s buddy was a bit more experienced than he was, but they figured their diving would be compatible enough, so they planned to make the dive together. Both divers were carrying three gas mixes on the dive. They would use one mix, their travel gas, on the descent to the bottom. It was simply “air” in a smaller tank Phil had mounted on his left side. The second was for the actual dive, called a bottom mix. This was trimix, a specially combined mixture of nitrogen, oxygen and helium. This mixture (40 percent nitrogen, 17 percent oxygen and 43 percent helium) would give them adequate oxygen without becoming toxic at depth, along with minimal narcotic effects from the nitrogen and ease of breathing from the helium. Both divers carried the trimix on their back in a set of twin tanks called doubles. The third gas they carried was 80 percent oxygen, which they planned to use during their decompression near the surface. Phil carried the oxygen in a tank hanging from the right side of his dive rig. According to the dive plan, when the divers reached the top deck of the wreck at around 150 feet, Phil would switch to his bottom mix. He would continue the dive using the gas on his back until he reached his planned time, or remaining pressure, and then he would begin his ascent. He was to switch to the decompression gas when he reached his stop depth and complete a series of stops that would allow the nitrogen to escape from his body. The dive was planned to exacting detail using special decompression software.

The Accident

When Phil and his buddy began their descent, Phil realized they weren’t as compatible as he thought they might be. They used different hand signals as soon as they dropped below the surface and Phil didn’t quite understand what his buddy meant. They hadn’t discussed hand signals on the surface before they began. Phil’s new buddy descended much faster than he was ready to go. Within just a few short minutes, Phil lost track of his new buddy altogether. That didn’t matter though, because at the same time he realized he was on top of the wreck, the place he had dreamed about for years. He noticed his buddy’s bubbles on the stern so he decided to swim toward his partner, following along the contours of the wreck. Between the narcosis brought on by breathing air at that depth and his excitement at reaching his goal, he forgot to switch to his bottom gas. His travel gas for descent was intended for only a short duration, and he quickly ran out of his supply. He went from euphoria to panic in just a moment, and the only option in his mind was to swim for the surface, but he never made it.


Technical diving requires a tremendous amount of equipment to ensure a safe dive, as evidenced by the three different gases Phil carried on this dive. Each gas had at least one, if not two regulators that would provide backup in case of failure. But buying all the equipment in the world doesn’t take the place of training, experience and following a well-crafted dive plan. Phil had a dive plan. But he failed to follow it, allowing the narcotic affects of nitrogen at depth to cloud his judgment along with the excitement at reaching a goal for the first time. Nitrogen narcosis has varying effects on different people, and even different effects on the same people on dive days. But there is no question that air becomes narcotic at depth, especially at a depth of six atmospheres (165 feet) or more. It can become so narcotic, in fact, that some people become almost catatonic. In Phil’s case, he forgot all about switching to a breathing gas with a reduced concentration of nitrogen that would have helped him keep his head at depth. One reason for the use of trimix is to avoid nitrogen narcosis. Had he remembered to make the switch, his head would have cleared almost immediately. The most important thing about that switch, though, was that he had his bottom gas in much greater supply than he did his travel gas. He quickly breathed through his travel-gas supply during the descent and while swimming after his buddy, and ran out of gas. Even then, if he would have had the presence of mind to switch to his bottom gas, he would have been fine. The combination of the nitrogen narcosis from the depth and suddenly running out of air limited his options dramatically. It’s not possible to know exactly what went through Phil’s mind when he took his last breath. Probably he panicked, leading to perceptual narrowing and a fight-or-flight response that would cause Phil to attempt to flee to the surface. The only thing known is that he drowned at depth. When his body was recovered, the tanks on his back holding his bottom gas were still full and his travel gas was empty. Phil’s dive buddy didn’t realize Phil was missing until he began his own decompression stops. There was nothing he could do at that point, having more than a half-hour of obligated decompression before he could reach the surface and alert the dive boat. It took searchers two days to find and recover the body.

Lessons for Life

1. Seek training. Before attempting any new type of diving, you should seek appropriate training. The more complex the diving technique, the more time you will spend in training.
2. Have a dive plan and follow it. It’s important to understand the limitations of your dive and follow your plan.
3. Stay with your buddy. Diving is a social sport and the shared experience is what makes diving exciting. Buddies can also help should you get into trouble on a dive.
4. Discuss details like appropriate communications with your dive buddy. When you are diving with a new buddy, you should always discuss diving techniques, planned descent speeds and communication techniques.
5. Don’t let a goal cloud your judgment. No dive is worth dying for. Use your head when making a dive. Don’t let your desire to achieve a goal get in the way of making a safe dive.

Eric Douglas co-authored the book Scuba Diving Safety, and has written a series of dive-adventure novels and short stories. Check out his website at