On Jan. 15, 1919, Boston became the site of a disaster that would reshape engineering across the United States. A massive steel tank containing 2.3 million gallons of molasses suddenly ruptured in the city’s North End, unleashing a sticky tsunami down Commercial Street that crushed buildings, derailed an elevated train, and claimed 21 lives and injured 150 people. It could have been avoided. The tank, which was hurriedly constructed from steel that was too thin, leaked from the start. It was never tested at full capacity, and there was no independent oversight of its operation.
The catastrophe spurred states to establish professional engineer licensing as a safeguard for public health and safety. Throughout the 1920s and ’30s most states adopted standards requiring that critical infrastructure—including bridges, dams and tanks—be designed using scientifically validated principles rather than guessing. Additional sources: Why the Great Molasses Flood Was So Deadly, 100 years ago today: Molasses crashes through Boston’s North End.