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A photo showing the aftermath of the molasses flood in Boston’s North End (Boston Public Library)

A new research study on the Great Molasses Flood of 1919 in Boston’s North End says that January’s cold weather made the molasses extra deadly. The cooling effect increased the thickness of the sweet syrup, making it incredibly hard to escape. A huge wave of the syrupy brown liquid moved down Commercial Street at a speed of 35 mph over two blocks destroying all in its path.

A Harvard team of fluid dynamics experts recently presented their findings after studying the tragedy that killed 21 people and injured another 150 when a faulty tank ruptured and exploded onto Commercial Street January 15, 1919.

Leader of the Cambridge fluid dynamics team, Nicole Sharp, explained that the phrase “slow as molasses in January” is not necessarily true since the molasses wave initially moved at a speed of 35 miles per hour. But it was the cooling process of the molasses after the initial wave that probably increased the death toll. In a CBC interview, Sharp said:

For the first 30 to 60 seconds or so, according to our calculations, that wave would have moved a lot like a tsunami, if you could imagine that. In that moment, what mattered about the molasses was its weight and heavy density. So, for that initial minute, you just have this massive wave of heavy fluid that’s crashing through everything. After that first minute or so, that’s when the fact that it’s molasses, and molasses is incredibly viscous, so it’s really thick and it likes to try to resist flow, that’s when that starts coming into play. Then you go from being a sort of tsunami to being like a seeping. It’s a seamless transition between those, but the longer you go after that first minute the more the viscosity of the molasses matters and the more it’s going to kind of seep through the neighborhood and creep.

When the warm molasses was exposed to the January air, the cooling of the molasses thickened it to the point where those engulfed by the non-Newtonian fluid found it very difficult to escape. The thickening of the syrupy mess also complicated rescue efforts.

Just two days before the spill, the faulty tank on Commercial Street was topped off with molasses from the Caribbean that had not yet cooled down to the outside temperature. The study implies that if the accident had happened in the warmer weather, the death count would have been significantly lower.

Purity Distilling Company built the tank, 50 feet high and 90 feet wide, in the North End’s densely populated neighborhood of mostly Italian immigrants at the time near where the bocce courts are located today at Langone Park. Despite many warnings that the tank was faulty, the molasses company ignored the welfare of the North End’s Italian immigrant population.

The disaster brought nationwide attention to the lack of industrial safety standards. Cracks and leaks in the tank were literally covered with brown paint by the company that initially said anarchists blew up the tank. Later, a lengthy class action lawsuit brought forward damaging evidence resulting in a settlement of $600,000 (~$11 million in today’s dollars). Although Purity used the molasses for industrial alcohol, some hypothesize that the tank was overfilled because of the the prohibition threat for possible use later to distill rum.

Neighborhood folklore has it that you can smell the ill-sweet remains in the summer’s hottest weather.

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