Blunt Avenue Quarry, Knoxville, TN
SEP95-An experienced, mix-trained cave diver and dive software developer grabbed the wrong tanks and suffered a CNS convulsion at depth during a 200 f/ 61 m body recovery. He was brought to the surface unconscious, resuscitated, and evacuated to a chamber where he suffered massive heart failure and died. The independent double cylinders contained EAN 34 (34% O2, bal. N2) with a maximum operating depth of about 108 f/33 m.
The diver, who was the only member of the local Sheriff’s Volunteer Rescue Squad trained for depths beyond 130 f/ 40 m, had slept only three hours before receiving an early morning call requesting his help in recovering a drowned swimmer’s body from the 300 f/ 92 m quarry. It was reported that he regularly used the same sets of doubles for air, EAN, and trimix, never labeled his cylinders or used contents tags, and did not own an analyzer. Instead relied on his excellent memory much to the consternation of his friends. The diver apparently grabbed the doubles containing EAN instead of air and arrived at the dive site.
It is believed that the diver descended breathing off one of his stage bottle containing EAN 23, and switched to his doubles containing EAN 34 at depth (PO2=2.4 atm @ 200 f/61 m). A second member of the recovery team was breathing air. The two found the body approxi-mately XX minutes into the dive and tied it off at about 200 f/61 m. The rescue team signaled to surface. Just then the partner reported hearing the diver moan and start kicking hard for the surface. The partner tried to stop the diver to no avail, and followed him up. The diver was found face down with his regulator out of his mouth at 170 f/52 m. His partner began to haul him up and handed him off to support divers at about 110 f/ 34 m who then got him to the surface. The diver regained consciousness briefly as he was being evacuated to a chamber, where he died of heart failure. Sadly the use of content tags on his cylinders would likely have prevented his death. Damn.
AUG95-A diver decompressing at the 20 f/6 m stop suffered an oxygen convulsion and was rescued successfully on a dive on the Lusitania by the Starfish Enterprise.
Although the Starfish operations are with-out doubt high-risk ventures, as a technical diving operation this one appears to be exem-plary, and this incident bears that out. The group was correctly criticized for not having an onboard chamber, but it should be pointed out that their dives, conducted over two seasons, have something sorely lacking in most other open sea technical operations: an organiza-tional structure and an operations plan.
Briefly, Starfish uses two standby divers, one in the water and one on deck, and has a second chase boat which tends to offset the use of a small dive boat as the main platform. The divers take their oxygen decompression while hanging on a semi-rigid "station," so all can drift as a unit. This minimizes the problems of fighting current, and reduces the wind chill factor. A chase boat makes drift decompression a new ball game.
The divers used a profile generated ("cut") with MigPlan. The important issue here is the actual profile, which shows the diver deeper than 287 f/87 m for 16 min (maximum depth 307 f/93 m) after a 3-min descent. He made planned stops while ascending to 20 f/6 m, switched to air at 170 f/51 m and to EAN 50 at 70 f/21 m. After 14 min at 30 f/6 m, he con-vulsed. His partner and another diver were not successful in putting an air regulator into his mouth. His head was tilted back, his eyes were closed, and blood came out of his mouth. He still had a tight grip on the john line. They tried to force gas out of his chest but saw none escape, and took him to the surface.
He was given some meaningful expired-air resuscitation while still partly in the water, his BC and tanks were removed, and he was hoisted on board. It took about 2 min to get the diver onto the deck. A helicopter was called.
He looked dead and he did not appear to be breathing. His mouth was open and his tongue protruded about half an inch. His mask was full of vomit, and some light pink fluid, not frothy, escaped from his mouth. His neck seal was cut away, and resuscitation was continued. Within moments he began to breathe on his own. He was placed on a dry, warm, engine hatch cover which had been cleared in advance for just such an event. A constant flow oxygen mask with a good seal was used at first while his breathing was weak; as it became stronger, he was switched to a demand mask set for slight positive pressure. He recovered consciousness and was given a quick neurological check, which showed no DCI abnormalities. A support diver gathered up the records and his dive computer. The helicopter picked him up 50 min after he surfaced, and in another 15 min, he was at the chamber, disoriented but with few other DCS symptoms. He was given a Table 6 (RN 62) about an hour later; no oxygen toxicity symptoms were noted. He was hospitalized for two days.
The diver does not remember anything from the time he felt the convulsion coming on until the arrival of the helicopter. He will not be allowed to dive for three months, but no residual effects are expected.
From the point of view of non-commercial diving operations, the rescue and resuscitation were classical.
Several points are worth noting. There was some, but not much warning of the impending seizure. It was impossible to reinsert the mouthpiece; this is to be expected, and further points up the value of a full-face mask.
There is always concern about embolism when ascending a convulsing diver. This team tried to expel air out of his lungs, a sensible move. Although embolism from such ascents is relatively rare, ascending is the better alterna-tive if drowning is the other. If the diver is able to breathe, then ascent should be delayed until the diver is breathing regularly.
Because there were standby divers to take over, the dive partner went only part way to the surface with the unconscious diver (because of his own decompression obligation). To surface for a minute or two after being several minutes at the 20 f/6 m stop on oxygen is acceptable for lifesaving efforts and entails very low extra risk as long as the obligated decompression is completed. If more than 2 or 3 min-utes are spent at the surface it would be advisable to add some oxygen time, as a guess about three or four times as much as the time spent at the surface, plus any remaining obligation.
Constant-flow oxygen is normally not ideal for surface treatment of DCI, where the patient needs to receive 100% oxygen; a demand sys-tem is better. In this case, constant flow was appropriate when the diver was not breathing strongly. Having another diver accompany a diver going for treatment is highly recommend-ed. Although it is desirable to make an immed-iate switch to air or a lower-PO2 mixture, in the event of a convulsion, this need not be done if it requires unusual effort or risk.
At this point, we have no clues as to why this diver convulsed. He had made over 100 similar trimix dives, so had been exposed to substantial oxygen profiles before. He was not taking medications, got sleep the night before, his equipment seemed to be functioning normally, and he was not exercising or doing anything else known to cause a CO2 buildup. The highest PO2 on the bottom was 1.24 bars, and on decompression was 1.56 for only 3 min; the diver was at 1.61 during the oxygen breathing for 14 min, and had used about 50% of his allowable exposure (by at least two widely used methods against the NOAA 1991 limits). He normally takes his oxygen in cycles, but in this case had not even used one cycle. He had no toxicity symptoms during the Table 6 (RN 62) two hours later. At this time we have no confident explanation. This shows the fickle nature of CNS oxygen toxicity, and highlights the need to have rescue capability. This incident further shows the value of a strong organization, especially when it results in two standby divers.