All told, the flood killed 21 people (along with several horses) and
injured 150 others. Rescue efforts were undertaken by several cadets
from the USS Nantucket, which was docked at a local pier, as well as
police officers, the Red Cross, and Army and Navy personnel in the area.
Survivors were taken to a makeshift hospital, although the rescuers
struggled to reach victims in time because of the difficulty of wading
through the molasses. It took weeks to clean up the mess, using salt
water to wash the stuff away and sand to absorb any remaining behind.
Even so, people had tracked molasses through adjacent streets, subways,
pay phones, streetcars, even into their homes.
One of the strangest historical tragedies of 20th century America is
the Great Boston Molasses Flood of 1919, when tons of treacle from a
burst storage tank coursed through the city’s streets. The incident
reveals some fascinating fluid dynamics, according to a presentation at
the annual meeting of the APS Division of Fluid Dynamics in November
2016.
The owner of the faulty tank was the Purity Distilling Company. At
that time, molasses was a vital commodity, not just because it could be
fermented to make rum and ethanol, but also for its use in making
munitions as World War I raged in Europe. Located in the North End of
Boston, the tank was built hastily because of the war, with rather loose
regard for safety regulations. Most notably, it was never filled to
capacity to test for leakage, prior to being used to store molasses. Not
surprisingly, the tank leaked from the start, showing brownish-red
stains in stark contrast to the original blue paint job. Some people
even collected the leaked molasses for their personal use. When a few
local residents finally complained, the company painted the tank to
match the stains, in order to camouflage the leaks.
In hindsight, a catastrophic failure was inevitable, and disaster
struck on the afternoon of January 15, 1919. Witnesses heard a roar, a
rumbling sound, and then a crash and a loud bang. The the tank — which
had just been filled to near capacity a few days before — had collapsed
under the strain, and 8.7 million liters of molasses rushed into the
streets of Boston, peaking in height at 27 meters and flowing as fast as
56 kilometers per hour.
The onslaught was sufficiently powerful to flatten several buildings
and do significant damage to the girders of the nearby elevated train.
People caught in the flow struggled waist-deep in the molasses, and
contemporary newspaper accounts describe people being picked up and
hurled several feet, crushed by and drowned in molasses. Others
succumbed to injuries and infections in the subsequent weeks.
Boston residents sued Purity Distilling’s parent company, the United
States Industrial Alcohol Company, which initially claimed that the
flood had occurred because anarchists had blown up the tank as an act of
terror. This initially seemed plausible, given how fast the molasses
spread through the streets. But investigators concluded this was
baseless. In the end, the courts found the company responsible, with
survivors of the victims receiving roughly $7,000 each as compensation
for their loss. And two decades later, physicists discovered that
gravity acting on the viscous fluid provided sufficient driving force to
account for the speed of the molasses.
Several factors contributed to the bursting of the tank. Some
hypothesized that the fermentation process caused carbon dioxide to
build up inside the tank, until its rivets burst. Alternatively, a 2014
structural engineering analysis by Ronald Mayville found that steel used
to make the tank was half as thick as it should have been, given its
size, and also was far more brittle than modern steel because of the
absence of manganese. Furthermore, the rivet holes were not reinforced,
making them more likely to deteriorate under stress.
Yet nobody had really studied the fluid dynamics of how the molasses
behaved during the flood until
aerospace-engineer-turned-science-communicator Nicole Sharp teamed up
last year with Harvard graduate students Jordan Kennedy and Shmuel
Rubinstein to conduct rheological studies of the substance and model the
resulting data. Then they compared the models’ predictions with
historical accounts of the actual flood. And those predictions matched
reasonably well with the details Sharp et al. gleaned from the archives.
By doing so, they gained some insight into highly viscous spreading
flows. Molasses typically falls into the category of a shear-thinning
non-Newtonian fluid, but Sharp et al. decided to use classical fluid
models for their study because at sufficiently cold temperatures — like
those on that fateful January day in Boston — it behaves more like a
classical fluid. In other words, temperature has more of an effect on
the viscosity of molasses at very cold temperatures than deformation.
Additional research should shed light on likely convective mixing
between warm and cold molasses inside the storage tank just prior to the
structural failure, which may have also contributed to the accident.
Sharp believes that understanding the physics of the Great Molasses
Flood could provide insight onto other structural failures, such as
breached levees or industrial spills. But the flood is also a useful
interdisciplinary educational tool, incorporating fluid dynamics,
structural mechanics, and engineering, in addition to history, ethics,
and law. "We hope that, by shedding some light on the physics of a
fascinating and surreal historical event, we can inspire a greater
appreciation for fluid dynamics among out students and the public," said
Sharp.
