A tank exploded in Boston, flooding a neighborhood with molasses and killing two dozen people.

Location: Boston, Massachusetts

Cost: N/A

Constructed: 1915

Issue: Temperature variance, untested integrity

Date of incident: January 15, 1919

In the North End neighborhood of Boston, the Purity Distilling Company stored molasses for transfer to a facility dedicated to fermenting molasses to produce ethanol. On January 15, 1919, a tank containing 2.3 million gallons of molasses burst and flooded the neighborhood.

The molasses had been warmed to reduce viscosity during transfer, but the warmer material, in addition to the rapidly warming air temperature, must have strained the tank itself. Around noon that day, the tank burst open.

The millions of gallons rushed out of the tank at 35 mph, reaching heights of 25 feet at their peak. The molasses was dense enough to push over buildings. When the molasses settled, it was waist-deep and dragged people down. Twenty-one people died, and around 150 were injured by the wave.

Residents brought a lawsuit against the US Industrial Alcohol Company, which owned Purity Distilling at the time. The company claimed the tank was blown up by anarchist because ethanol is an active ingredient in munitions, but an auditor nevertheless found the company responsible.

According to engineer Ronald Mayville, the tank was constructed poorly, with thin metal that proved brittle under certain circumstances. Additionally, the tank itself was never properly tested. According to The Guardian, the company ended up paying $628,000 in damages — the equivalent of over $9 million today.