“Fish on!”
It sounds like a call from one friend to another while bobbing on a lake in northern Canada on a summer afternoon. In northern Thailand, in the summer of 2018, these words had a more profound meaning – they were the code words used by the rescue team when one of the trapped soccer players was secured to the last stretch of line, ready to be hauled the final distance to safety.
By the time the players had reached this point, they had travelled through cold water for about two hours. Without protection, a healthy person in water at 5 ⁰C has about 30 minutes before exhaustion and possible unconsciousness. That’s because body heat is quickly transferred to surrounding water molecules through the skin, much more quickly than to the less dense air. And, although these boys were incredibly strong, they had been starving in a cave for almost two weeks – their reduced body fat meant they would lose heat to the water at a dangerously high rate.
Water has very high ‘thermal conductivity’, especially compared to air, which is why jumping in a lake on a hot summer day feels so refreshing. When our body temperature is higher than the surrounding medium, heat moves from hotter to colder at a speed that depends on the temperature difference between the two objects but, just as critically, on what materials the heat is moving through. Here’s an example that my daughter noticed at home: our dog, Cleo, loves to chomp on ice cubes. Fragments scatter everywhere and slowly melt to create little puddles to step in on the kitchen floor. Mara noticed that pieces that landed on the ceramic tile melted MUCH faster than similar-sized pieces that landed on Cleo’s rubberized mat under her water bowl. Here’s a video of thermal conductivity in action, sped up a little for effect. (The full video runs for 2.5 minutes.) On the left, the ice cube is placed on a block of aluminum. On the right, the ice cube is placed on a block of plastic. The coated metal has much higher thermal conductivity and the ice cube is almost entirely transformed into water by the end, while the ice cube on the insulating plastic is almost entirely still intact.
This is why you should NEVER lick a metal pole in the winter time – please don’t EVER try this. The metal is such a great conductor that it pulls the heat out of your tongue almost instantly, turning the moisture in your mouth to ice and attaching it firmly to the icy pole.
Creatures in extreme climate conditions have evolved to manage thermal conductivity really well. Polar bears in the far north have two layers of fur and a very thick layer of fat (depending on the season); a combination that prevents almost all heat loss from their warm bodies to the frigid surrounding air, water, or icy ground. They also have black skin, believed to help them absorb more energy from the sun more efficiently to replace the heat they do lose to their surroundings. Animals in hot climates have the opposite problem – they need to enhance their ability to lose excess heat so creatures like the jack rabbit or African elephants have evolved very large ears that have a lot of blood flow in them in order to do just that.
The solution for the soccer players trapped in those underwater caves? Wetsuits. Wetsuits are made of an insulating material that slows down the transfer of heat from hot to cold. Wrapping the soccer players in wetsuits made of a layer of Neoprene foam, which is a synthetic rubber with nitrogen bubbles inside, would slow down their heat loss. These suits need to be snug, letting in as little water as possible. Just a little too loose and cold water will continuously sneak in, completely sabotaging the Neoprene. In the case of the underweight soccer players, this was yet another worry for the rescue team. But the repeated cry of “Fish on!” in those muddy Thai caves proved that the insulation provided by even ill-fitting wetsuits was good enough to bring the entire team home safely to their families.
Image Citations
“Stay clear fishing lines” by macrophile is licensed under CC BY 2.0.
“Wes Jumping In Lake” by Martin Cathrae is licensed under CC BY-SA 2.0.
Video provided by the author, edited in Microsoft Clipchamp
“winter-1799288” by exit78 is marked with CC0 1.0.
Elephant image – “Axel Tschentscher”, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
Jackrabbit image – Don McCullough from Santa Rosa, CA, USA, CC BY 2.0 <https://creativecommons.org/licenses/by/2.0>, via Wikimedia Commons
Thai soccer team – Casa Rosada (Argentina Presidency of the Nation), CC BY 2.5 AR <https://creativecommons.org/licenses/by/2.5/ar/deed.en>, via Wikimedia Commons
Wonder Why 
