The Great Boston Molasses Flood of 1919 killed 21 after 2 million gallon tank erupted On Jan. 15, 1919, at around 12:30 p.m., Boston Police patrolman Frank McManus was at a call box reporting back to headquarters when he heard a loud scraping and grinding noise. Pausing to figure out the source, he suddenly found himself overcome with shock. McManus managed to make out to the dispatcher: “Send all available rescue vehicles and personnel immediately — there’s a wave of molasses coming down Commercial Street," according to Stephen Puleo, historian and author of “Dark Tide: The Great Boston Molasses Flood of 1919.” The wave was 2.3 million gallons, moving at 35 miles per hour, 25 feet high and 160 feet wide at its outset, rushing through the city's crowded and densely populated North End. A massive, 50-foot-high steel tank holding the molasses had ruptured. People in its direct path were immediately swallowed, drowned and asphyxiated by the notoriously viscous substance. Within seconds, two city blocks were flooded. Puleo told NBC News that the tide of molasses ripped the Engine 31 Firehouse from its foundation, almost sweeping the building into the Boston Harbor. The brown wave busted windows, overturned railcars and flooded homes. By sunset, 21 people were dead, 150 were injured and the North End looked like it had been bombed.