The Divers Alert Network (DAN) has issued a preliminary report into the tragic death of popular cave-diving expert and Dive Rite General Manager, Jared Hires, who died in Norway’s Plura cave system on 3 April.
Internet speculation has revolved around the possibility of CNS (central nervous system) oxygen toxicity, a known danger for rebreather divers should a controller failure inject pure oxygen into the breathing loop while the diver is at depths sufficient to exceed the safe partial pressure limits for oxygen.
The report states that the seizure which led to Mr Hires’ death was a medical event, however, and not a mechanical failure, most probably brought on as a result of a pre-existing medical condition. Hires had apparently suffered a similar seizure in 2023, and the family has a history of rare and unexplained seizures.
The following is taken from DAN’s blog, and is based on an interview with one of the other divers in the team who witnessed the seizure, a conversation with Mr Hires’ father, Lamar Hires, and data downloaded from the CCR controllers of all three divers who were making the dive.
Plura Cave System
The Plura cave system is the deepest cave in Northern Europe and the most popular cave diving destination in Scandinavia. In the parts of the system that are suitable for diving, accessible through the Plura river, the limestone and marble formations form some narrow and edgy, but also big passageways and rooms with visibility described as ‘as far as your light can shine’. The water temperature in the cave ranges from 36 degrees Fahrenheit (2°C) in winter to 44 degrees Fahrenheit (4-7°C) in the summer with the entrance lying under ice in the winter months.
The Dive
A team of three experienced rebreather divers planned to execute a check-up dive in preparation for a deeper dive the following day to confirm that all gear was in working order after travel. All three divers used adequate equipment that they were familiar with and wore adequate thermal protection for the dive.
It was their first dive in Plura on this trip, however, diver 1 and 3 had dived the system in previous years. Diver 1 (witness) took the lead, followed by diver 2, and diver 3 (victim) in the back. The first half of the dive was uneventful with a maximum depth of 34 m (110 ft), all three divers surfaced after 30 minutes in the air-filled “Wedding Chamber”.
The dive was planned as a circuit, but the Wedding Chamber did mark the approximate half-time point of the dive. The team briefly discussed and confirmed that all equipment was in working order and everyone was feeling well and descended again after 2 minutes at the surface in the same formation with diver 1 in the lead and diver 3 in the back. The CCR controllers logged this as a separate dive.
Consulting the logs provided by the team, the descent for this second dive was also uneventful for all three divers until minute 16, when diver 3’s log shows a sudden descent from 25 m (82 ft) to 29 m (95 ft) in less than 20 seconds. At this point, diver 1 had turned around to assist diver 2 who was deploying a backup light after their primary light had failed.
While reconfiguring their formation to put diver 2 in the lead, diver 1 witnessed diver 3’s light moving erratically and recalls hearing diver 3 screaming, potentially trying to articulate a problem. When diver 1 reached diver 3, he was already in full tonic-clonic convulsions. His loop was not in his mouth but was found to have been closed, which suggests that diver 3 had attempted to bail out but was not able to get his bailout regulator into his mouth in time before the onset of his seizures.
After unsuccessful attempts by diver 1 to secure diver 3’s airway, he proceeded to swim the still convulsing diver towards the exit, a distance of roughly 250 m (800+ ft) with several depth changes. When diver 3 had stopped seizing after approximately 3 minutes, diver 1 tried to insert a regulator into his mouth again but was not able to unclench diver 3’s jaw, so he proceeded to swim him out of the cave. He signaled diver 2 to swim ahead and to alert the surface and call for assistance. A diver at the surface was able to meet them close to the exit and assist in bringing diver 3 to the surface. Diver 1 and 3 surfaced after 31 minutes (17 minutes after onset of convulsions).
CPR was initiated immediately, and oxygen and AED were ready within minutes after surfacing and used before and in conjunction with local EMS response via ambulance and helicopter. Unfortunately, all resuscitation efforts by the team at the surface and EMS over the course of almost 2 hours remained unsuccessful.
Medical History
After communication with the deceased diver’s family, it has come to light that he had an unprovoked seizure for the first time the previous year and that there is a family history of very rare and to this date medically unexplained seizures, in these cases connected with overexertion, stress, and dehydration.
The diver told his dive partners that morning that he had slept well, was not jetlagged, and was feeling rested that day, it should be mentioned though, that the week before the trip to Norway, the diver had displayed symptoms of a viral infection with flu-like symptoms and gastrointestinal involvement, which may have added to potentially existing electrolyte imbalance and dehydration from intercontinental air travel.
Seizures During Diving
A word about oxygen toxicity and why this was most likely not oxygen toxicity:
When reading about seizures in diving, a logical first conclusion people jump to is central nervous system oxygen toxicity which presents in symptoms just as the ones described above. Plenty of literature is available on the topic and training courses as early as open water or at the very latest Enriched Air Nitrox courses cover the topic. Rebreather divers are painfully aware of the three “H”s, Hyperoxia, Hypoxia, and Hypercapnia, which each can lead to disabling injury and death/drowning while diving.
The review of the logs of this dive does not support the theory of an oxygen-induced seizure. At no point before the event did oxygen levels or cell readings spike significantly. The ppO2 very briefly (less than 1 minute) exceeded the high setpoint (set to 1.2) to 1.3. Changes in ppO2 are only seen after the event and are easily explained by the solenoid still firing and the efforts of diver 1 to vent and inflate equipment to exit the cave.
The narrative suggests that diver 3 seems to have felt the onset of a seizure, which makes an underlying medical condition more likely than an oxygen-induced seizure. These seizures rarely present with an aura or warning signs. A medical event is also more consistent with the duration and quality of the witnessed seizure, which would best be described as a Grand Mal rather than oxygen toxicity.
Unprovoked seizures can develop suddenly and at any age. The risk of recurrence of a seizure after an individual has experienced a single unprovoked seizure has been published in a comprehensive literature review in 2023 and it states that the likelihood of seizure recurrence is between 25% and 41% in the first 6 months to 2 years.
Summary
After careful review and consultation with experts in diving accident analysis, we conclude that this tragic accident was caused by a medical event and predisposition of the diver, and that neither equipment failure or error in human-machine interaction is responsible for the outcome. The diver was likely not aware of the implications that a first-time unprovoked seizure could have. The dive team did everything humanly possible in this challenging environment to rescue the diver.
In summary, we feel that it is important to educate the diving community about medical and physiological issues that, while easily manageable at the surface, can prove fatal when experienced underwater, especially in extreme environments.
