It’s a call that always comes sooner than hopeful relatives are prepared for. Loved ones pin their hopes on one last flight, and the U.S. Coast Guard sector commander—the man or woman responsible for calling off a search—knows it. He or she has to tell the family that nothing was found, and that the Coast Guard is giving up.
Deciding to quit a search is the worst part of the job. When the Coast Guard suspends a search for a missing boater, hearts that were breaking now fully break, and the news is met with more than tears. There is often also anger and confusion. The anger can’t be helped, but the confusion can be eased.
Most people lost at sea stay lost. It’s a harsh reality that the Coast Guard deals with every day. But families should know that when the Coast Guard suspends a search, it is never giving up early—and it is using advanced computer technology to make sure of it.
The U.S. Army has done most of the work in determining how long a person can survive in the water. A team at the Biophysics and Biomedical Modeling Division at the U.S. Army Research Institute of Environmental Medicine created the Probability of Survival Decision Aid, or PSDA. It’s a computer program that combines a complex model of factors with data about individual rescues, and that predicts survival time by taking into account hypothermia and dehydration. Survival is about staying warm first and hydrated second.
The predictive data that are used increase every year, but when compared to actual cases of survival, the PSDA ranges from accurate to generous on the survival times. Early in a search, the Coast Guard gathers data on the incident and the lost person. Then it gathers data on the environment to feed the PSDA. Factors include air and water temperature, relative humidity and wind speed, age, height, weight, the person’s level of fitness and what he is wearing. The PSDA comes up with three numbers: cold function time, cold survival time and dehydration survival time, all measured in hours. (Cold function time is how long a survivor should be able to effectively move, or wave for help or use a radio.)
Some of the data in the PSDA comes from the U.S. Navy, which conducts cold-water survival testing using “Nemo,” an anthropomorphic dummy that actually sweats. When placed in cold water in different clothing and life jackets, Nemo shows how much protection one piece of gear provides compared with others. So when the Coast Guard asks, “What was he wearing?” those answers are fed into the PSDA and draw on the Navy’s results from Nemo, as well as data from actual case history, to determine the survival time.
The most remarkable thing about the PSDA is the extraordinary benefit of the doubt it gives to people 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 the person is, what kills people first in almost all water temperatures is cold incapacitation and drowning. The PSDA assumes that won’t happen; perhaps the missing person ran across something that floats and the Coast Guard will assume that flotation was acquired.
Hands down, the most difficult part of search and rescue is coming up empty after the last search of a case. Calling in with negative results and heading home is the worst part of the job. Still, when I was a rescue swimmer, I always knew the sector commander had just been given a more difficult task.
Telling a lost person’s loved ones that a search is over is a hard thing to do. But know that the call to quit isn’t a decision the Coast Guard makes without exhausting every
This article originally appeared in the November 2019 issue.