The Great Molasses Flood occurred on January 1919 in Boston when a five-story-tall vat of molasses exploded and filled the streets with two million gallons of the thick, heavy substance. Twenty-one people died and another 150 were injured in the unexpected and traumatic event.
The surge of molasses was 15 feet at its highest point and oozed through the streets at around 35 mph. The high-viscosity liquid ripped a local firehouse from its foundation, nearly derailed a train, drowned 12 horses and took out several buildings and electrical poles along the way. In total, the damages caused by the 160 foot-wide wave would have amounted to around $100 million in today's economy.
The vat, which belonged to the Purity Distilling Company, was nearly full on the day it burst open. The unusually warm temperatures in Boston that January combined with the vat being at capacity may have contributed to the explosion. Fermented molasses produces carbon dioxide, which would have created additional pressure within the vat. However, the tank had always had deficiencies; locals were aware of the vat's tendency to leak years before the tragedy occurred.
Clean-up efforts continued for months. While the heaviest damage was done in the neighborhood around the distillery, visitors to the area would inevitably end up with molasses on their shoes and clothing, which then transferred to public phones and trolley platforms throughout the city.