Two-thirds of victims in the more than 300 snorkelling and freediving deaths in Australia this century were overweight or obese – and almost half of them had underlying health conditions that would have predisposed them to cardiac arrhythmia-related incidents.
These and other worrying statistics have emerged from what could be the largest dataset of snorkelling- and freediving-related deaths ever analysed, in a new review of 317 fatalities recorded in Australia between 2000 and 2021.
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Designed to identify more exactly the causes of death and counter-measures, the survey was carried out by diving-medicine specialist Dr John Lippmann, founder of DAN Asia-Pacific and holder of an Order of Australia award for services to scuba-diving safety, resuscitation and first aid.
The review is based on data held by the Australasian Diving Safety Foundation, of which Lippmann is chairman and CEO, and the National Coronial Information System. Monash University’s public health & preventive medicine department and the Royal Lifesaving Society were also involved in the study.
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Earlier reports from the study have already considered data from 2001-2013 and 2014-2018 to determine trends during those periods.
While an estimated 88,000 Australians aged 15 and above snorkel or freedive every year, locations such as the Great Barrier Reef (GBR) and Ningaloo also attract hundreds of thousands of international visitors. 56% of all the deaths occurred in Queensland because, for many middle-aged or older overseas tourists, “surface snorkelling” on the GBR is a bucket-list pursuit.
The analysis also covers the generally more experienced freedivers and spearfishers who died taking part in competitive underwater sports or practising breath-holds.
Of all the recorded deaths, 198 victims (62%) were likely to have been predominantly surface snorkellers while 113 (36%) were carrying out some form of breath-hold diving.
Mainly male
Victims were overwhelmingly male – 88% of them, with a median age of 48. Females tended to be older with a median age of 60, while freediving men had a median age of 35 and women 58.
Many of the snorkelling fatalities were men aged 50 or more. They were frequently overweight, inexperienced snorkellers with pre-existing medical conditions that could have led to incidents of cardiac arrhythmia (irregular heartbeat).
Freedivers, in contrast, were typically relatively young, healthy and experienced but with potential to succumb to primary drowning, often following from apnoeic hypoxia (low blood oxygen).
44% of all victims were overseas tourists with a median age of 60; 8% were Australian tourists and the rest Australians diving locally. 15% had never snorkelled before, 24% were inexperienced and 33% were reportedly experienced (expertise was not specified in other incidents).
34% of victims had been snorkelling with commercial operators (mainly on the GBR), 63% were sightseeing, 20% spearfishing and 11% diving to gather shellfish and/or crustaceans.
State of health
Post mortem examination reports were available in 92% of cases, with body mass index (BMI) recorded for 248 victims. Mean BMI was 27.5, with 41% of victims classified as overweight (BMI 25-29.9) and 26% obese (BMI above 30).
Pre-existing health conditions found in almost half of the fatalities included ischaemic heart disease (IHD) and left ventricular hypertrophy (LVH), both of which would have predisposed the victim to arrhythmia-related snorkelling incidents.
A third of the victims were probably disabled by cardiac arrhythmias and at least 137 deaths were from primary drowning, 34 of these following apnoeic hypoxia.
IHD and LVH predispose many older people to death while snorkelling, and crucially Lippmann observes that this risk could be “somewhat mitigated” through targeted health screening.
Up to 11% of all victims drowned following apnoeic hypoxia from extended breath-holding, eight in pools and six with other people nearby but not monitoring them closely. 32% were freediving solo and only 25% died in the presence of another person.
The report says that to mitigate risk, freedivers need to practise in a controlled environment and focus to a greater extent on effective buddying and improved supervision, especially if inexperienced.
Predisposing factors in freedivers include poor fitness, pre-existing medical conditions, inexperience, adverse sea conditions, inadequate supervision and seafood hunting or harvesting in areas frequented by large predators.
From disease to crocodiles
The pre-existing health-related conditions thought to have contributed to 48% of all deaths were most commonly cardiac (112), particularly moderate-to-severe IHD, LVH and/or an enlarged heart (cardiomegaly) (73). 56 victims had both substantial IHD and LVH/cardiomegaly.
At least 101 of the fatalities had already received medical care for their identified or a related condition. 33 were being treated for hypertension (24 of these turned out to have LVH and/or cardiomegaly), eight for asthma, eight for diabetes and six for seizures. Alcohol or drugs contributed to or caused five of the deaths.
Poor planning – mainly deciding to snorkel alone, wander away from a buddy or set out in adverse sea conditions – likely contributed to 43% of deaths. Poor skills and inexperience were probable contributors to at least 26%, while higher-risk activities such as extended apnea without adequate supervision led to 15%.
One freediver suffered a cerebral arterial gas embolism after diving and breathing from a friend’s scuba unit before ascending (without adequate exhalation).
Trauma deaths resulted from shark encounters (9), boat impacts (5), crocodile encounters (3), sting ray injury (1) and, in one case, hitting rocks in rough seas.
Drowning and arrhythmia
Drowning has traditionally been recorded as the default cause of death when someone is recovered from water with non-specific effects on the lungs and no other obvious cause.
The difference between the 61% of snorkellers for whom drowning was given as cause of death and the 43% in which asphyxia was cited might reflect the number of cases in which drowning was secondary to a cardiac arrhythmia, according to the report.
Surface snorkellers were more likely to be disabled by a cardiac event than freedivers (50/15%) and less likely to be disabled by primary drowning (41/61%).
It might seem surprising that for all the discussion about immersion pulmonary oedema (IPO) or “drowning from the inside” in recent years, this was identified as the cause of death in only four incidents. However, the condition can be so difficult to distinguish from drowning that it is likely to go unidentified in many cases, as Lippmann acknowledges.
Cardiac arrhythmias can be precipitated simply by immersion or submersion, the review explains. As buoyancy counters the effects of gravity, it encourages redistribution of venous blood from the limbs to the thorax, causing a substantial increase in cardiac workload.
This loading can then be boosted further by factors including exercise, anxiety, cold-induced vasoconstriction (blood-vessel narrowing), respiratory resistance and elevated heart-rate.
Breath-holding can also precipitate arrhythmias, especially in cooler waters, however young and healthy the individual, but there is no definitive post mortem test to determine whether this has occurred, says Lippman.
His study suggests that “cardiac arrhythmias were the likely precipitant of many of these often silent deaths” which is why, he says, scuba divers aged 45 or more are advised to undergo a diving medical examination with a focus on cardiovascular assessment.
“Since many of the potential cardiac triggers described above are common to scuba divers and snorkellers, it seems prudent that older active or potential snorkellers should also discuss their cardiac health with their doctors,” concludes the report.
Enhanced supervision
Lippmann further suggests that if snorkellers who know they have a relevant medical condition plan to join a commercial snorkelling excursion, they should declare their condition so that the operator can offer safety measures such as enhanced supervision, a coloured tag on the snorkel or a flotation aid.
With many snorkellers being weak swimmers, he says it would help if they learnt to adhere to the buddy system, especially bearing in mind that appointed look-outs are sometimes expected to oversee more snorkellers at once than is practical.
Commercial snorkel operators should also be required to carry appropriate first aid equipment, including oxygen, defibrillators and have staff trained in their use.
”Despite its great opportunities, snorkelling isn’t a benign activity and folks should be aware of the potential challenges and adverse predispositions and manage them accordingly,” Lippmann told Divernet. His Also read: $5m lawsuit brought after snorkel deathin the International Journal of Environmental Research & Public Health.
Also on Divernet: SNORKEL-DEATHS REPORT QUESTIONS IPO FINDINGS, RED FLAGS FOR SNORKELLERS: HOW TO STOP THE QUIET DEATHS, THE JOY OF SNORKELLING
