On 15 January 1919 the ground near 529 Commercial Street in Boston, Massachusetts began to tremble. At the nearby Purity Distilling Company, a six-story-tall iron molasses tank grumbled like a massive stomach with severe indigestion. This enormous cache of sweet molasses was awaiting transfer to a Purity processing plant, where it would then be used in the production of sweetener, drinking-liquor, and alcohol-based munitions.

Mere moments after the first distressed groan, a sound reminiscent of machine-gun fire echoed in the streets. It was the massive tank’s iron rivets buckling in quick succession. Just as bystanders began to identify the source of the alarming noises, the tank burst in a terrific explosion, throwing massive, ragged chunks of sheet-iron into the surrounding neighborhood. The blast flattened the offices of the Purity Distilling Company, and a flying section of iron crushed a nearby fire station.

Despite the force of the rupture, the meteoric remains of the iron tank only harmed a handful of adjacent buildings in the North End neighborhood. There remained, however, the matter of the molasses which was no longer contained, unleashed in every direction.

The two-and-a-half million gallon column of thick fluid collapsed instantly into the Boston streets. The smothering goo swept up and inundated bystanders, tossing and rolling men, women, and children on a wave of thick sludge. The migrating wave of brown syrup pushed buildings off their foundations and overturned wagons, carts, horses, and motorcars. It broke the girders of an elevated rail track, and tossed aside train cars. Within minutes, several blocks of Boston’s streets were buried in struggling victims, rubble of ruined buildings, a clutter of tumbled vehicles, and other assorted wreckage, all coated and mired in several feet of sweet, tacky goo.

Rescue efforts began at once, but most who ventured into the morass became mired themselves, and in need of their own rescuing. Terrified survivors ran away from the chaotic scene covered from head to toe in dark brown molasses. The USS Nantucket was anchored at the Playground Pier a few blocks away, and upon learning of the scope of the disaster, Lieutenant Commander H. J. Copeland sent over a hundred of his able-bodied sailors to lend assistance. Police officers, military personnel, and Red Cross nurses slogged through the knee-deep syrup all night long, searching for sticky victims.

In all, twenty-one lives were lost in the disaster⁠—mostly due to crushing and asphyxiation–-and 150 injuries were reported. It is said that a lawyer for Purity arrived on the scene within hours and tried to pin the disaster on anarchist saboteurs, but despite this continued insistence, the company ultimately paid out about $1 million in settlements (equivalent to about $11 million today). The nearby harbor remained brown through the rest of the winter and spring, and it took over six months to clean the structures, automobiles, and cobblestone streets of the sticky mess. By coincidence, the 18th amendment of the US Constitution was ratified the day after the catastrophe, paving the way to the Prohibition.

The molasses tank prior to the explosion
The molasses tank prior to the explosion

The exact cause of the explosion was never determined definitively, but it is generally attributed to high pressure and a defects in the tank construction. Witnesses testified that the Purity Distilling Company had neglected to pressure-test the massive vessel prior to filling it for the first time; and when it was first loaded with molasses, the outside of the tank became covered in brown rivulets from leaks. Rather than paying to reinforce and repair the inadequate tank, Purity had opted to paint the whole thing molasses brown. On warmer days the molasses would naturally ferment in the tank, increasing the internal pressure. Eventually the strain was more than the rivets could bear, and their failure ultimately resulted in the energetic rupture on that fateful day in 1919.

Although it’s been a century since the flood, they say that on a hot day the streets in some parts of Boston still bleed molasses.