No Such Thing As "Safe" Air?
Ed.'s note: This regular column presents the anatomy of a diving accident and the lessons to be learned from it. The incidents described are real. Names of locations and people have been changed or deleted.
Setting the StageHe had been diving all over the world and made many deep technical dives. He regularly pushed the limits on wreck dives and mixed-gas dives. He was a strong diver and a risk taker who often ignored the rules and recommendations of recreational diving. He had little formal training beyond the basics, but he blended his own gases and believed that the limits concerning oxygen toxicity were not meant for him. The dive sites on this occasion were to be deep offshore wrecks. The trip was sponsored through his local dive store and was made up of regular customers of the dive store, as well as store and boat dive pros.
Dive DetailsBecause he had blended his own nitrox at home, no one from the dive store or boat knew the oxygen content of his tanks. When asked before the dive what gas he was diving, he brushed off the question, saying, "the usual." The dive was on a wreck in 135 feet of water. His descent and initial exploration of the wreck were apparently uneventful; he was observed by other divers to be actively swimming about hunting for lobsters.
Rescue AttemptDuring the dive, one of the dive professionals who was also exploring the wreck observed him not moving, went to him, got no response and proceeded to take him up the anchor line. Arriving in shallow water, the dive pro--knowing the dive boat was immediately above them and that he had to make a decompression stop--inflated the victim's dry suit and sent him to the surface. There, he was immediately spotted by another dive pro who towed him the short distance to the boat, where CPR was performed to no avail.
Investigation and Legal ActionAnalysis of the diver's breathing gas found an oxygen content near 39 percent. The depth of the dive was 125 to 135 feet. It was also discovered that the victim was not trained in deep, decompression, wreck, nitrox or technical diving. On this dive and on other dives before this, he dived beyond 130 feet, used mixed gases he had prepared himself, made required deco stops, penetrated wrecks, did not plan his dives, did not use complete equipment, dived alone and did not keep a log. An estranged family member brought a legal action against the boat, store and dive pros. The insurance company settled out of court, so there was no trial and no legal ruling.
AnalysisThe accepted limits for oxygen partial pressure are 1.4 to 1.6, depending on how conservative you wish to be. The higher limits, if used, are more often for short periods during emergencies or for decompression. On this dive, oxygen partial pressure was near 2.0. This diver was also engaged in heavy work, which increases the impact of the oxygen and the likelihood of oxygen toxicity. He did not understand or respect well-established oxygen limits. The maximum operating depth for this gas mixture should have been 102 feet using an oxygen partial pressure of 1.6 or 85 feet using 1.4.
There is no such thing as safe air or a safe procedure or a safe piece of dive equipment. There are ways of doing things that are safer than others, but no absolute guarantees. Degree of safety is determined by how individuals behave given certain variables--equipment, environment, experience, fitness, procedures, skills and the actual conduct of the dive. This diver clearly suffered oxygen toxicity that led to convulsions, drowning and gas embolism. He put himself above reasonable conduct and paid the ultimate price. The dive community then paid a financial price for his behaviour. Much of what we all shell out for scuba diving products and services goes toward insurance.
Lessons For Life
- Training in specialty diving activities greatly increases the effectiveness and safety of such diving.
- Mixed gases should be prepared by reputable businesses that have the training and equipment to do so properly.
- The maximum operating depths for nitrox mixtures are based on significant medical research, are reasonable and need to be followed.
- By diving with a buddy, you will have a person to provide assistance or help and, in a worst-case situation, a person to perform a rescue.
- Part of what divers learn in training is that proper, complete, well cared for dive gear increases the safety of diving.