Solving a Mystery Behind the Deadly "Tsunami of Molasses of 1919

By ERIN McCANN NOV. 26, 2016

€œA dull muffled roar gave but an instants warning before the top
of the tank was blown into the air,€� The New York Times wrote in 1919.
€œTwo million gallons of molasses rushed over the streets and converted
into a sticky mass the wreckage of several small buildings which had
been smashed by the force of the explosion.€�

€œWagons, carts, and motor trucks were overturned. A number of
horses were killed. The street was strewn with debris intermixed with
molasses and all traffic was stopped.€�

It was January. The place was Boston. And when 2.3 million gallons of
molasses burst from a gigantic holding tank in the citys North End, 21
people were killed and about 150 more were left injured. The wave of
syrup €” some reports said it was up to 40 feet tall €” rushed through the
waterfront, destroying buildings, overturning vehicles and pushing a
firehouse off its foundation.

For the past 100 years, no one really knew why the spill was so deadly.

But at a meeting of the American Physical Society this month, a team of
scientists and students presented what may be a key piece of the
century-old puzzle. They concluded that when a shipment of molasses
newly arrived from the Caribbean met the cold winter air of
Massachusetts, the conditions were ripe for a calamity to descend upon
the city.

By studying the effects of cold weather on molasses, the researchers
determined that the disaster was more fatal in the winter than it would
have been during a warmer season. The syrup moved quickly enough to
cover several blocks within seconds and thickened into a harder goo as
it cooled, slowing down the wave but also hindering rescue efforts.

€œIts a ridiculous thing to imagine, a tsunami of molasses drowning the
North End of Boston, but then you look at the pictures,€� said Shmuel M.
Rubinstein, a Harvard professor whose students investigated the disaster.

When the molasses arrived in Bostons harbor, it was heated by just a
few degrees. The warmer temperature made it less viscous and therefore
easier to transport to a storage tank near the waterfront.

When the tank burst two days later, the molasses was still probably
about four or five degrees Celsius warmer than the surrounding air, said
Nicole Sharp, an aerospace engineer and science communications expert
who advised the Harvard students. (She runs the website FYFD, through
which she explains the principals of fluid dynamics to people outside
academia.)

The students performed experiments in a walk-in refrigerator to model
how corn syrup, standing in for the molasses, would behave in cold
temperatures. With that data in hand, they applied the results to a
full-scale flood, projecting it over a map of the North End. Their
results, Ms. Sharp said, generally matched the accounts from the time.

€œThe historical record says that the initial wave of molasses moved at
35 miles per hour,€� Ms. Sharp said, €œwhich sounds outrageously fast.€�

€œAt the time people thought there must have been an explosion in the
tank, initially, to cause the molasses to move that fast,€� she added.
But after the team ran the experiments, she said, it discovered that the
molasses could, indeed, move at that speed.

€œIts an interesting result,€� Ms. Sharp said, €œand its something that
wasnt possible back then. Nobody had worked out those actual equations
until decades after the accident.€�

If the tank had burst in warmer weather, it would have €œflowed farther,
but also thinner,€� Mr. Rubinstein said.

In the winter, however, after the initial burst €” which lasted between
30 seconds and a few minutes, Ms. Sharp said €” the cooler temperature of
the outside air raised the viscosity of the molasses, essentially
trapping people who had not been able to escape the wave.

About half the people who were killed €œdied basically because they were
stuck,€� Mr. Rubinstein said.

A firefighter who survived the initial wave managed to stay alive for
nearly two hours while he waited to be rescued, they said, but he drowned.

€œMen and women, their feet trapped by the sticky mass, slipped and
fell and were suffocated,€� The Boston Globe wrote in 1968. €œThe stronger
tried to save others, and many of them died for their heroism.€�

The exact cause of the tanks failure has never been known. Last year, a
team of engineers using modern methods to analyze the century-old
disaster blamed poorly designed steel tanks.

Ronald Mayville, a structural engineer who worked on that study, told
The Boston Globe that the tanks walls were at least 50 percent too thin
and were made of a type of steel that was too brittle.

The project at Harvard grew out of Mr. Rubinsteins class Introduction
to Fluid Dynamics, which asks students to create a final project.
€œChoose an interesting project and make an appealing video,€� he said.

Mr. Rubenstein and Ms. Sharp said they would like to eventually build an
entire course around the disaster, where students could apply what they
learn in other classes to understanding not just why the molasses
behaved the way it did, but also what other forces shaped the events of
that day in 1919.

The Boston molasses disaster, Mr. Rubinstein said, is €œa beautiful story
for teaching.€�