It’s a call that always comes sooner than relatives are prepared for. Quitting the search is the worst part of the job for a U.S. Coast Guard Sector Commander. Loved ones were pinning their hopes on the one last flight, the Sector Commander knows it, and now he or she has to tell them that nothing was found and they are giving up.
When the Coast Guard suspends a search for a missing boater, hearts that were breaking already fully break and the news is met with more than just tears; there is often also anger, confusion. That anger can’t be helped, but the confusion can be. Most people lost at sea stay lost. It’s a harsh reality that the USCG deals with every day. So when the Coast Guard suspends a search, they aren’t ever giving up early.
The Probability of Survival Decision Aid (PSDA)
The U.S. Army is not where you might expect to find answers about sea survival, but they have done most of the work in determining just how long a person can survive in the water. A team at the Biophysics and Biomedical Modeling Division of the U.S. Army Research Institute of Environmental Medicine created the PSDA, a computer program fed by a complex model of factors on one end, and the data about each particular rescue in the other.
The tool was developed to predict survival time taking into account both hypothermia and dehydration as the two main things you need to survive. Assuming one can stay on the surface or in a raft (or aboard your boat) long enough, survival then is about staying warm first, hydrated second.
There have been improvements to the interface and the model and predictive data used grows every year, but when compared to actual cases of survival, the PSDA ranges from accurate to generous on the survival times in different situations. Which is to say, the models give survivors every possible benefit of the doubt.
You, What You are Wearing, and Wear You Are.
[Screenshot of the PSDA Tool]
Early in the search, the Coast Guard gathers data on the incident and answers questions about the person they are searching for, determines what they might be wearing, and also gathers data on the environment to feed the models run by the PSDA.
Air and water temperature, relative humidity and wind speed, age, height, weight, even your level of fitness are factored into the model. What you are wearing – drilled down to some very well-researched details – also factor into the PSDAs survival engine to crunch the data and come up with three numbers; Cold Function Time, Cold Survival Time, and Dehydration Survival Time – all measured in hours. The Cold Function Time is how long a survivor would be able to effectively move (or wave for help, or use a radio). The other two numbers are what they are.
The Navy conducted (and still does) cold survival testing using ‘Nemo’, an anthropomorphic manikin that actually sweats. When placed in cold water in different clothing and lifejackets, researchers use Nemo to determine how much protection one piece of gear provides when compared to others. So when the Coast Guard asks, “what were they wearing?” the answers fed into the PSDA draw on the Navy’s results from Nemo a well as data from actual case history to determine the survival time.
[ Nemo – doing his thing at the Navy Clothing and Textile Research Facility]
To me, the most remarkable thing about the PSDA and how the USCG makes decisions about search times is the extraordinary benefit of the doubt they give to persons in the water without a life jacket. The tool will never assume the most likely cause of death, drowning, in any search case. Regardless of how good a swimmer a person is, what kills first in almost all water temperatures, is cold incapacitation and drowning. The PSDA just assumes that won’t happen and lets the data assume a person is managing to stay afloat. Perhaps a missing person ran across something that floats, or managed to get to a life ring thrown overboard. The Coast Guard will keep searching and will assume that flotation was acquired somehow.
Hands down, the hardest thing for any of us who ever worked in search and rescue was coming home empty from the last search of a case. Invariably, we knew we were on the last search. Calling in with negative results and heading home was the worst part of the job. Still, I always knew the Sector Commander had just been given a harder one.
Telling survivors that the search is over, along with their hope, is obviously a hard thing to do. But don’t be confused, quitting isn’t a decision the Coast Guard makes without trying everything possible not to.
(First published in Soundings)