A warming life jacket

Sometimes the biggest threat from a boat sinking isn’t the accident itself. It’s not even the sharks that might be swimming nearby. It’s a life-threatening loss of body heat from remaining too long in cold water. Now, a South African teen has invented a heat-producing liner for life jackets. It could help delay injuries — or death — until a rescue is possible.

Normal body temperature for people is around 37° Celsius (98.6° Fahrenheit). But when the core body temperature falls below 35° C (95° F), people suffer from something called hypothermia. When this occurs, the body doesn’t function quite the way it should, says Danielle Mallabone. She is a 17-year-old junior at St. Teresa’s High School in Johannesburg, South Africa.

With mild hypothermia, blood vessels just beneath the skin shrink. This restricts blood flow to help cut the loss of heat from blood. (As blood cools, it speeds the cooling of internal tissues.) Hypothermia also triggers shivering. Those muscle contractions help generate heat to somewhat boost the body’s internal temperature, she notes.

During severe hypothermia, things get much worse. People become confused and uncoordinated. They also have difficulty speaking. Eventually, major organ systems such as the heart will fail. This can lead to death.

The body’s temperature can drop to dangerous levels even in relatively warm water, explains Mallabone. That’s why she designed a heat-producing liner for life jackets. Pockets in the liner hold a powdered chemical called calcium oxide, which gives off heat when it gets wet.

That heat-producing, or exothermic, reaction warms the water between the life jacket and someone’s body. This might stave off severe hypothermia long enough to allow for a rescue.

Mallabone tested her own invention by jumping into 50°C water. Each test lasted an hour. The first version of her life jacket liner included only 50 grams (about 1.8 ounces) of the calcium oxide, she notes. “But that amount didn’t provide enough heat, and my body temperature dropped to 35° C after just an hour,” she says. So the next version included 1 kilogram (2.2 pounds) of the heat-producing chemical. In her test using that liner, her body temperature stayed above 36.1°C.

The chemical reaction between calcium oxide and water generates heat slowly. The reaction began producing heat after 5 minutes, Mallabone found. The liner produced the most heat about 25 minutes after the life jacket was first immersed.

The teen presented her findings May 13 in Phoenix, Ariz., at the Intel International Science and Engineering Fair. The Society for Science & the Public, which created the fair in 1950, still runs the competition. (SSP also publishes Science News for Kids.)

Overall, Mallabone’s tests suggest there’s no risk the jacket liner will explode or heat up so much that it risks causing burns. The reaction also doesn’t produce acidic byproducts. And because calcium oxide doesn’t react with humidity (water vapor in the air), the liners can be stored for long periods and still work when needed.

Power Words

calcium oxide A substance that gives off heat as it chemically reacts with water. Its chemical formula is CaO (which means each molecule is made up of one calcium atom and one oxygen atom).

exothermic reaction A chemical reaction that generates heat as it proceeds. (In Greek, “exo” means outside and “therm” means heat.)

hypothermia A life-threatening medical condition in the core (internal) body temperature falls below 35° Celsius (95° Fahrenheit). (In Greek, “hypo” means under or lower than normal, and “therm” means heat.)