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March 2018    Download the Entire Issue (PDF) Available to the Public Vol. 33, No. 3   RSS Feed for Undercurrent Issues
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75 Hours Afloat At Sea and Survived!

an unplanned feat of endurance and lessons learned

from the March, 2018 issue of Undercurrent   Subscribe Now

Every diver's worst fear is surfacing and finding there's no dive boat to be seen. And then drifting aimlessly at sea.

In Undercurrent September 2016, we recounted the stories of divers getting lost near Malpelo in the Pacific and at Mauritius in the Indian Ocean during the same week. Clearly, every diver needs an effective surface signaling device such as a large surface marker buoy or even a large flag on an extending pole. At night, you should carry a fully charged back-up flashlight that you've not used during the dive. Moreover, you should consider high-tech solutions, such as the Nautilus Lifeline Marine Rescue radio beacon or the McMurdo Smartfind.

New Zealander Robert Hewitt had none of those when he went diving near Mana Island (Cook Strait) in New Zealand in February 2006. An experienced Navy instructor, he became separated from his buddy but continued diving alone. He had intended that instead of returning to their boat, he would swim to the shore 220 yards (200m) away.

However, when he surfaced in a strong current, he found himself several hundred yards from where he expected to be, and the dive boat with his buddy had moved on. Wearing a farmer-John wetsuit and jacket, with a hood and gloves, he was alone in the ocean while his friend, noting eventually he hadn't made it to the shore, and unable to find him, raised the alarm.

A Scientific Case Study

Physiologist Heather Massey from the University of Portsmouth (UK) has studied what happened to Hewitt, his progressive deterioration over the following four days and three nights that he floated, how he survived and how he eventually recovered after his rescue.

Water conducts heat around 20 times faster than air. Hewitt floated in 61F (16C) water, well below his body temperature. Physiological models have determined that the median survival time for a lightly dressed swimmer is roughly between 4.8 and 7.7 hours. Hewitt spent 75 hours in the water, drifting more than 40 miles before he was spotted and rescued.

Even so, his rescue was only by chance. The intensive air and sea search had proved fruitless, but he was finally stumbled across by two police officers in a Zodiac. He was pulled into an inflatable, alive but hallucinating, before being transferred to a larger police patrol vessel.

Cold water immersion produces a four-stage response. First, there's that familiar cold shock that induces gasping, hypertension and increased cardiac workload. Hewitt's properly fitted 5mm wetsuit saved him from that, and as an experienced diver, he was used to diving fully clad in cool water. However, many people drown when falling into cold water, because the shock both induces heart arrhythmia and causes them to inhale water.

In the next stage, one loses muscle power, thanks to peripheral muscle cooling, and gradually becomes weaker. Hewitt did lose the ability to swim and even lost consciousness at times, but his inflated BCD kept his head above water and prevented him from drowning. Retaining his fully inflated BCD extended his survival time.

The third stage is deep body cooling, which affects both physical and mental functions. When he was rescued, he likely was at the edge of hypothermia, but nobody took his temperature before he was wrapped in blankets and given warm drinks, so that cannot be confirmed. His first recorded body temperature reading was 99.5F (35.7C), which suggests that he was able to generate and store sufficient heat keep his body temperature above the level considered to be hypothermic.

One factor that staved off hypothermia, besides his wetsuit, was that Hewitt was large and muscular -- 5'10" (1.8m) tall and weighing around 220 pounds (100kg). Every one-percent increase in body fat is thought to slow the rate of heat loss by 0.18F (0.1C) per hour, which adds up when applied over 75 hours. This gave him a better chance of surviving heat loss than a leaner person. His high level of aerobic fitness would have enabled him to generate heat for prolonged periods of time by swimming. Exercising while wearing a wetsuit reduces deep body cooling. He also tried to maintain a fetal position at other times to minimize heat loss.

The final stage of response can happen at the time of rescue. Evidently, it's common for people to collapse due both to a change in pressure as they move from water to air and a strong nervous system reaction to being rescued. This was discovered during rescues of yacht crews during the 1979 Fastnet Race disaster in the UK, hit by a Force 10 gale. Helicopter crews found that some of the sailors who had been safely plucked from the sea died during the ride back to land. Lifting the winched sailor from the sea in a vertical position caused disastrous blood pressure drops. Nowadays such casualties are kept horizontal. With this in mind, Hewitt's rescuers kept him horizontal and gave him verbal encouragement to fight for his life.

Heat Loss Is Not The Only Problem

Heat loss from immersion is not the only problem faced by a diver lost at sea. Dehydration can be as serious a problem. We divers know how immersion stimulates urination, which is not good when you are already dehydrated. Hydrostatic squeeze, peripheral vasoconstriction, and a tight wetsuit cause increased diuresis. The wisdom is that, if marooned in this way, you should avoid drinking any fresh water you might have for the first day so that hormone changes are triggered in the body, and you naturally start to conserve water.

Hewitt used his mask and wetsuit jacket to collect rainwater when he could, but not enough to equal the minimum volume his body would have required. After he was rescued, he drank a liter-and-a-half and then received another six liters of water intravenously. Starvation is less of a threat than dehydration. Hewitt had previously been collecting crayfish (spiny lobster), and he ate his catch. However, limiting food consumption, especially protein, while not a long-term survival plan, can assist with water conservation.

His wetsuit also began chafing his softened skin, and his rescuers found him to be covered in sea lice that were feeding on him, which they hosed off with fresh water. His face and lips were sunburned.

Next comes the impact phase when a person realizes their life is under threat and they are struck by fear. A recoil phase is when the survivor starts to show a gradual return of awareness and cognitive function. During his time alone as he drifted, he prayed and recited the names of his family members.

Reciting prayers and mantras enhances and synchronizes inherent cardiovascular rhythms and suppresses worrying thoughts, leading to a reduction in anxiety. Practicing routine tasks serves to increase the amount of spare capacity in working memory for planning and decision-making. Hewitt repeatedly and systematically checked all his gear.

Eventually, one reaches a psychological low in the struggle to survive, and by the third day, Hewitt had suicidal thoughts.

While he might easily have given up hope, he had the training, knowledge, and skills to establish a psychological state of preparedness for an emergency.

Clearly, it is a miracle that he survived his ordeal and was rescued. It took him several months to return to normal physical and psychological functioning, but he did recover fully.

What can we divers learn from Hewitt's awful experience?

Wearing a thick wetsuit and having plenty of body weight helped him, but that's often not a choice one can make beforehand. Staying in the fetal position or 'heat escape lessening posture' is a good idea. Keeping his BCD inflated kept him afloat and safe from drowning when he went unconscious.

But, the best idea is to avoid the circumstances that may lead to you getting lost. Take an effective signaling device. A low-tech one that needs no batteries, such as a marker buoy or extending flag, is best. Once darkness falls, a fully charged flashlight will give rescuers a fighting chance of finding you. Expect the unexpected.

(Massey H, Leach J, Davis FM, Vertongan V. Lost at sea: the medical, physiological and psychological factors of prolonged immersion. Diving and Hyperbaric Medicine. 2017 December;47(4):239-247. doi10.28920/dhm47.4.239-247)

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