The Great Molasses Flood , 1919

The Great Molasses Flood, also known as the Boston Molasses Disaster or the Great Boston Molasses Flood, occurred on January 15, 1919, in the North End neighborhood of Boston, Massachusetts, in the United States. A large molasses storage tank burst, and a wave of molasses rushed through the streets at an estimated 35 mph (56 km/h), killing 21 and injuring 150. The event has entered local folklore, and for decades afterward residents claimed that on hot summer days the area still smelled of molasses.

The disaster occurred at the Purity Distilling Company facility on January 15, 1919. The temperature had risen above 40 °F (4.4 °C), climbing rapidly from the frigid temperatures of the preceding days.

Molasses can be fermented to produce rum and ethanol, the active ingredient in other alcoholic beverages and a key component in the manufacturing of munitions. The stored molasses was awaiting transfer to the Purity plant situated between Willow Street and what is now named Evereteze Way, in Cambridge.

Modern downtown Boston with molasses flood area circled
At about 12:30 in the afternoon near Keany Square, at 529 Commercial Street, a molasses tank 50 ft (15 m) tall, 90 ft (27 m) in diameter, and containing as much as 2,300,000 US gal (8,700 m3), collapsed. Witnesses reported, variously, that as it collapsed, they felt the ground shake and heard a roar, a long rumble similar to the passing of an elevated train, a tremendous crashing, a deep growling, or a thunderclap-like bang! and, as the rivets shot out of the tank, a machine-gun-like rat-tat-tat sound.

The collapse unleashed a wave of molasses 25 feet (7.6 m) high at its peak, moving at 35 miles per hour (56 km/h).The molasses wave was of sufficient force to damage the girders of the adjacent Boston Elevated Railway's Atlantic Avenue structure and tip a railroad car momentarily off the tracks. Author Stephen Puleo describes how nearby buildings were swept off their foundations and crushed. Several blocks were flooded to a depth of 2 to 3 feet (60 to 90 cm). Puleo quotes a Boston
Molasses, waist deep, covered the street and swirled and bubbled about the wreckage ... Here and there struggled a form—whether it was animal or human being was impossible to tell. Only an upheaval, a thrashing about in the sticky mass, showed where any life was ... Horses died like so many flies on sticky fly-paper. The more they struggled, the deeper in the mess they were ensnared. Human beings—men and women—suffered likewise.

Damage to the Boston Elevated Railway due to the flood
The Boston Globe reported that people "were picked up by a rush of air and hurled many feet." Others had debris hurled at them from the rush of sweet-smelling air. A truck was picked up and hurled into Boston Harbor. Approximately 150 were injured; 21 people and several horses were killed—some were crushed and drowned by the molasses. The wounded included people, horses, and dogs; coughing fits became one of the most common ailments after the initial blast. In a 1983 article for Smithsonian, Edwards Park wrote of one child's experience:

... Anthony di Stasio, walking homeward with his sisters from the Michelangelo School, was picked up by the wave and carried, tumbling on its crest, almost as though he were surfing. Then he grounded and the molasses rolled him like a pebble as the wave diminished. He heard his mother call his name and couldn't answer, his throat was so clogged with the smothering goo. He passed out, then opened his eyes to find three of his four sisters staring at him.


Several factors that occurred on that day and the previous days might have contributed to the disaster. The tank was constructed poorly and tested insufficiently. Due to fermentation occurring within the tank, carbon dioxide production might have raised the internal pressure. The rise in local temperatures that occurred over the previous day also would have assisted in building this pressure. Records show that the air temperature rose from 2 to 41 °F (−17 to 5.0 °C) over that period. The failure occurred from a manhole cover near the base of the tank, and it is possible that a fatigue crack there grew to the point of criticality. The hoop stress is greatest near the base of a filled cylindrical tank.

The tank had been filled to capacity only eight times since it was built a few years previously, putting the walls under an intermittent, cyclical load. Several authors say that the Purity Distilling Company was (or may have been) trying to outrace Prohibition in the United States; the Eighteenth Amendment to the Constitution of the United States was ratified the next day (January 16, 1919), and would take effect one year later

An inquiry after the disaster revealed that Arthur Jell, who oversaw the construction, neglected basic safety tests, such as filling the tank with water to check for leaks. When filled with molasses, the tank leaked so badly that it was painted brown to hide the leaks. Local residents collected leaked molasses for their homes.

An investigation first published in 2014, applying modern engineering analysis, found that the steel was not only half as thick as it should have been for a tank of its size, even with the lax standards of the day, but it also lacked manganese, and was made more brittle as a result