For the study 49 snorkels – 16 simple tubes, 29 tubes with additional wet/dry apparatus and four full-face masks – were tested for resistance using an invention of Dr Foti’s, a Snorkel Airway Resistance Analyser (SARA).
Generally, the simpler the snorkel design the less resistance it generated, and the more exertion on the snorkeller’s part, the greater was the resistance.
The conclusion seems to be that snorkellers need to be selective when choosing a breathing device, just as scuba-divers need to take care when picking a regulator. However, as the researchers soon found, trying to determine the resistance of a product through a cursory visual inspection proved unreliable.
It could be the size of the tube at the narrowest point, at the bend near the mouthpiece or the design of a valve that caused the problem.
The report that first drew attention to potential pitfalls for snorkellers.
The study stressed that, based solely on these experiments, full-face snorkelling masks had no inherent advantage or disadvantage in terms of resistance.
That wasn’t to say they were off the hook. The researchers drew attention to other drawbacks inherent in full-face designs, and there would seem to be enough of these to make potential purchasers at least pause for thought.
They couldn’t be removed easily in an emergency, including those with “quick-release” features; the mouthpiece couldn’t be spat out; water couldn’t be cleared from the tube by blowing sharply; the user couldn’t dive beneath the surface safely; and valve malfunction could lead to serious consequences for breathing.
Evidence of the supposed CO2 accumulation that had previously been advanced as a possible explanation for at least some snorkel-related drownings could not be found in the tests.
But it’s worth noting that of those survivors who contributed to the survey, no fewer than 38% had been using full-face masks – and 90% of them believed it had been a factor in their experience.
In the initial report, wet/dry snorkels were not singled out for any particular criticism. These have a float valve to seal the tube if it becomes submerged, so they’re designed for people who might have trouble blowing water out of the tube, for whatever reason. But the valve could be a risk factor if it caused any constriction in the tube.
The team reviewed coroners’ reports on the snorkelling victims, and found that it was not possible to differentiate between drowning by aspiration of water and by IPO. In both cases the lungs ended up full of liquid, causing death by hypoxia.
But of 32 deaths closely analysed with all other factors taken into account, no fewer than 15 were judged to be “very likely” the result of hypoxia due to an IPO, and 14 considered as likely to be due to either cause.
The post mortem reports also indicated a promising avenue to explore further. They pointed to a “significant correlation” of the drownings with cardiac disease, in particular Left Ventricle End Diastolic Pressure (LVEDP), which is more common in older people. There are often no symptoms with this condition.
Among the survivors, of 31 respondents who had a pre-existing condition, 84% had high blood-pressure or heart issues.