On January 15, 1919, shortly after noon, a massive molasses tank collapsed on Commercial Street in the North End of Boston. The tank, standing 15 meters high, held up to 2.3 million US gallons—about 8,700 cubic meters—of molasses, enough to fill more than three Olympic-sized swimming pools. The disaster killed 21 people and injured 150 others. A 7-meter-high wave of molasses surged through the street at 55 km/h after the tank ruptured, causing widespread destruction and chaos. The tank, built by the Purity Distilling Company in 1915 near the port, was designed to store molasses arriving from Puerto Rico and transport it to a nearby plant. However, the construction was rushed and poorly executed. The steel used was 50 percent too thin and lacked manganese, making it excessively brittle. The tank was never tested with water, and the sheets used were too thin. A 2015 study confirmed these issues, noting that the steel was indeed too thin and brittle due to the lack of manganese. The site supervisor, who had no technical training, failed to read blueprints properly, contributing to the structural weaknesses. Leakage from the tank began almost immediately, with long dark streaks running down its sides. Local children even scraped the molasses off the tank with sticks, making makeshift lollipops. Despite employee reports of the tank’s instability and passersby hearing the structure groaning, management ignored the concerns and painted the tank brown to hide the stains. The weather also played a role: after a sharp cold snap, temperatures rose, and a delivery of warm molasses further increased the pressure on the already weakened tank. This combination of factors led to the catastrophic rupture. The aftermath was both immediate and harrowing. The thick molasses trapped and suffocated victims, making rescue efforts extremely difficult. Some bodies were later recovered from the Boston port months after the disaster. The situation was so unprecedented that rescuers had to adapt on the spot. Initially, the parent company, United States Industrial Alcohol (USIA), suggested the disaster might have been an anarchist attack, a theory that was widely considered at the time given the recent history of bombings in the area. However, after a lengthy legal process, the Massachusetts court ruled in 1925 that the disaster was due to the company’s negligence, not an attack. This led to compensation for the victims. The choice of location—near a poor, immigrant neighborhood—highlighted the social inequalities of the time, and the incident forced the industry to reconsider how it stored hazardous materials, long before the use of modern sensors and monitoring systems.