Oxygen toxicity, CO, or narcosis? The fatal Maldives dive disaster differential
Industry Buzz
As you start to go deeper, that narcosis effect potentially could create panic, but also would make them less likely to be able to find their way out.
—John Volanthen, British Cave Rescue Council diving officer
Five Italian divers entered the water near Vaavu Atoll in the Maldives last Thursday and did not come back. []
What began as a deep cave dive has become one of the country’s most serious diving disasters, with four bodies later found deep inside the cave and a fifth—the group’s diving instructor—recovered earlier outside it. []
A Maldivian military diver also died during the recovery effort, reportedly from decompression sickness, underscoring how dangerous the site remained even for rescuers. []
Related: Minnesota family physician dies after medical emergency while scuba diving in MexicoWhat went wrong?
The biggest question now is: Did the divers run out of gas, or were they inadvertently breathing toxic air?
An underwater and hyperbaric medicine expert told ANSA English that investigators will need to examine the divers’ tanks, wrist computers, and autopsy findings to understand whether an incorrect breathing-gas mix, human error, or some combination of factors contributed to the deaths. []
Why the cave setting matters
The divers were exploring a cave system near Alimathaa Island. [] Officials have said the recreational diving limit in the Maldives is 30 meters, while the bodies were found at approximately twice that depth, in the cave’s innermost area. [] Recovery teams described poor visibility, strong currents, rough weather, and hazardous terrain. []
Four of the bodies were reportedly found close together, a detail that may matter to investigators because clustered deaths can point toward a shared environmental or equipment-related problem—but it can also reflect group behavior in an overhead environment where one emergency rapidly becomes several. []
When air becomes toxic
For physicians, the “wrong gas” theory branches into several possibilities.
One is oxygen toxicity. Oxygen becomes more physiologically potent as ambient pressure rises. A breathing mixture that is safe at one depth can become dangerous at another if the partial pressure of oxygen climbs too high. []
Divers Alert Network describes 1.4 ATA as a common upper “green light” oxygen partial pressure for open-circuit scuba. On a deep dive, an enriched-oxygen mixture intended for shallower depths could push a diver into central nervous system oxygen toxicity territory. []
Clinically, CNS oxygen toxicity is alarming because it presents so abruptly. Symptoms may include vertigo, nausea, tunnel vision, twitching, seizures, or loss of consciousness; underwater, a seizure can quickly become drowning. []
MSD Manuals note that divers using inappropriate oxygen concentrations during deep dives are at higher risk, and that seizures or fainting can result in drowning. []
Another way diving air can be contaminated
A second possibility is carbon monoxide contamination. This can happen when breathing gas is contaminated during filling—often due to a compressor malfunction or exhaust exposure. []
Carbon monoxide is especially treacherous in diving, as depth increases the partial pressure of inspired gas. A contaminant that might cause vague symptoms at the surface can become much more consequential underwater. []
Carbon monoxide contamination manifests via headache, confusion, weakness, impaired judgment, and loss of consciousness. [] In a cave, where ascent is not vertical and immediate, even mild impairment can be catastrophic.
Nitrogen narcosis and the cognitive hazards of depth
A third possibility is narcosis caused by high nitrogen pressure, which is not a tank-filling error but a depth-related effect of breathing nitrogen under pressure. []
At 50 meters, narcosis can impair judgment, coordination, and situational awareness. In open water, that is dangerous; inside a cave, it can be lethal. Panic, silt-outs, entanglement, current, equipment failure, and gas-management errors can cascade quickly when divers cannot simply ascend. Divers use cylinders, which may contain compressed air, enriched-air nitrox, trimix, oxygen for decompression, or other mixtures depending on the dive plan.
“As you start to go deeper, that narcosis effect potentially could create panic, but also would make them less likely to be able to find their way out,” John Volanthen, a British Cave Rescue Council diving officer, told CNN. []
Investigators will likely focus on several data points: residual gas analysis from recovered cylinders; dive computer logs showing depth and timing; autopsy findings consistent with drowning, barotrauma, decompression illness, or toxic exposure; and witness accounts from the boat and surviving members of the expedition. Tank analysis, wrist computers, and anatomic-pathologic findings are critical. []
Evidence points to a broader chain of risk
The recovery itself has complicated the investigation. Search operations were suspended after the Maldivian military diver died, then resumed with Finnish technical cave divers using advanced systems, including closed-circuit rebreathers, which recycle exhaled gas and remove carbon dioxide to permit longer, complex dives. []
So, were the cylinders filled with the wrong gas? Right now, that remains unproven. It is a plausible line of inquiry, not a conclusion.
The known facts support a broad differential: gas mix error, gas contamination, oxygen toxicity, narcosis, panic, current, entrapment, poor visibility, or a chain reaction involving several of these factors.
In diving, fatal accidents are often less like a single diagnosis and more like a perioperative disaster: multiple safeguards fail, and each failure narrows the chance of rescue.