Boston Molasses Flood

By Kristy McCaffrey

On January 15, 1919, a massive tank at the Purity Distilling Company in Boston exploded, releasing more than 2 million gallons of hot and sticky molasses. The wave of thick liquid was 30 feet tall and traveled at 35 miles per hour, destroying buildings, vehicles, and even knocking an elevated train off its tracks.

An 8-foot wave of molasses moved down a Boston street at a speed of 35 mph.
Wreckage of the collapsed tank can be seen in the background.
(Photo: Wikimedia Commons)

For residents in the immediate vicinity there was no escape and 21 people perished that day, including three firemen who were killed when their nearby firehouse collapsed. An additional 150 people were injured, and several horses were also killed. Survivors were helped by the police, a local Army battalion, the Red Cross, and the Navy, but the sticky mess hindered the response. It took four days to find all the victims, and another two weeks to clean up the syrup. Nearly a century later, residents in the area still report smelling molasses on hot summer days.

The cause of the flood was immediately linked to sabotage, but the reality was that the tank had not been well-built. The fermentation process combined with an abnormally warm day had caused a buildup of pressure. More recently, engineers have concluded that fluid dynamics played a role in the wave that caused so much devastation. When a dense fluid spreads horizontally into a less dense fluid (molasses into air), gravity currents come into play. It’s similar to how cold dense air will flow through an open door into a warm room, even if there is no wind to drive it.

Purity and its parent company were found to be responsible, and the civil lawsuit lasted until 1925. That year the company took a charge of $628,000 against its profits, reflecting settlements and legal costs related to the disaster. That’s about $8.3 million in 2013 dollars.

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