The study’s purpose is to determine the causes and risk factors associated with snorkel-related fatal and non-fatal ocean drownings in Hawai‘i and develop appropriate safety messages.

Drowning historically means death due to submersion in and inhalation of water—this is drowning by aspiration. In 2005, the World Health Organization developed an additional definition: “Drowning is the process of experiencing respiratory impairment from submersion/immersion in liquid.” A person rescued while drowning is an example of a non-fatal drowning.

It is not at all unusual to find a snorkeler who has drowned motionless, in calm conditions, sometimes even close to shore, often not very long after entering the water. Usually there are no signs of distress or known causes.

By far the most important finding of the Snorkel Safety Study is the confirmation that Rapid Onset Pulmonary Edema (ROPE) is the trigger leading to hypoxia in some, possibly most, fatal and non-fatal snorkel-related drownings. This phenomenon, while identified in other activities such as SCUBA and swimming, has not before been associated with snorkeling. Yet the evidence is indisputable. It is supported by physiology, case studies, medical records, and first hand accounts. ROPE explains previously mysterious fatal and non-fatal snorkel-related drownings.

ROPE is an acronym that stands for Rapid Onset Pulmonary Edema. While the mechanics of ROPE are technical and complex, the concept is simple. When inhalation is impaired, as can happen when breathing through a narrow tube, lung pressure is reduced. This is called negative transthoracic pressure (NTP). As a consequence of NTP, the lungs become infused with edema (pulmonary edema) causing a loss of oxygen (hypoxia), which can happen in a matter of minutes and leads to death.

Yes, very different. Drowning by ROPE does not necessitate either submersion in or inhalation of liquid. Rather, it is a respiratory impairment that can be triggered by snorkeling. Its progression is quick and quiet. In either case—drowning by aspiration or ROPE—death is by hypoxia, a lack of sufficient oxygen, but the path to hypoxia and the person’s experience is very different. Externally, the primary difference is the presence or absence of struggle. Rescue can happen almost anywhere along either of these trajectories resulting in a non-fatal drowning.

The snorkel is a narrow tube, which generates resistance to inhalation. If the resistance is strong enough, and if it persists, it will result in reduced pressure in the lungs—NTP—which can lead to ROPE. This is an established physiological phenomenon.

Yes. Visitors to Hawai‘i are 10 times more likely than residents to drown while snorkeling. Statistics also show that older people are far more likely to develop ROPE, and that men are more vulnerable than women. This is consistent with a clear relationship between cardiovascular problems and developing ROPE.

Typically, the snorkeler first experiences shortness of breath due to hypoxia (lack of oxygen). If the snorkeler increases exertion, hypoxia is hastened. Insufficient oxygen causes loss of muscle strength, confusion, and harbingers of death. The heart tries desperately to pump oxygen. Loss of consciousness and clinical death ensue.

The correlation between heart conditions, specifically elevated left ventricle end diastolic pressure (LVEDP), and ROPE was confirmed in both autopsy reports and case studies. In several cases, the condition was not diagnosed until after the incident itself. Heart disease, especially LVEDP, is a likely risk factor that can lead to ROPE. LVEDP is common in older age groups and is most often asymptomatic when not severe.

The demographics of snorkel-related fatal drownings in Hawai‘i show that visitors are at least 10 times more at risk than residents. Rescue personnel have identified a lack of swimming ability on the part of many visitors as a major factor in this disparity. It may also be true that recent and prolonged air travel is relevant. There is evidence that exposure to altitude can alter permeability of the lung’s mechanisms, which normally blocks development of ROPE. Most visitors to Hawai‘i have spent at least five hours on an airplane at cabin pressure equivalent to up to 8,500 feet elevation. The Snorkel Safety Study is exploring this hypothesis.

Snorkel design ranges from a simple basic tube to those with pleats, purging valves, pinched tubes, wet/dry apparatus and, more recently, masks with integrated snorkels, known as full-face masks. Generally, the simpler the snorkel the less resistance it generates. However, other factors, sometimes not visible, such as the size at the narrowest opening or the design of the valves, make visual determination of resistance unreliable.

Full-face masks pose no inherent advantage or disadvantage compared to other devices in terms of resistance to inhalation of air. However, there are several features of FFMs to be aware of when choosing equipment:

• Cannot assess their resistance by visual inspection
• Cannot be removed easily in urgent situations even with quick release features
• Cannot “spit out” mouthpiece in urgent situations
• Cannot clear water from tube with sharp expiratory force maneuver
• Cannot dive beneath the surface safely
• Valve malfunction may lead to serious aspiration consequence

Attention has been given to the possibility that CO2 accumulation in the mask/snorkel and then the blood causes the snorkeler to become unconscious. CO2 buildup is not a physiologically viable explanation of snorkel-related drownings.

Yes, the Hawai‘i State Department of Health has comprehensive data at:

https://health.hawaii.gov/injuryprevention/home/drowning-prevention/information/