The Explosion and Ensuing Flood
The explosion occurred at around noon on January 15, 1919. Survivors recall the day as being unseasonably warm. The epicenter of the disaster was the Purity Distilling Company, a firm whose specialty was the production of ethyl alcohol. Ethyl alcohol and rum can be made from the fermentation of molasses; the molasses in the tank that exploded was intended for distillation into ethyl alcohol. Though Prohibition was about to take hold in the United States, Purity Distilling Company was free to produce alcohol as it was a component of munitions of the day.
At the time of the explosion, workers would have been enjoying their lunch breaks. No one, therefore, was watching as the molasses tank exploded. Many heard the explosion, though; they described the noise as resembling a machine gun. This machine gun-like roar came from the rivets that held the tank together bursting apart. As the tank came apart, witnesses reported that the ground shook as if from the passage of a nearby train.
The reason for the Boston Molasses Disaster's destructiveness was the sheer size of the molasses tank that exploded. The tank, which stood at 529 Commercial Street (by Keany Square), was 50 feet high and had a diameter of 90 feet. At the time of the disaster, the tank was nearly full; it held 2.3 million gallons of molasses.
With the rupture of the tank, a wave standing as high as 15 feet was unleashed, sweeping outward onto the streets. Contrary to molasses' slow-moving reputation, the wave sped outward at an estimated speed of 35 miles per hour. The high density and viscosity of molasses contributed to the massive destructive power of the molasses wave, which exerted a pressure of around 2,000 pounds per square foot (about twice atmospheric pressure).
This high pressure, in addition to the wave's immense speed, destroyed just about everything in the immediate vicinity. Girders on the nearby elevated rail platform were mangled; meanwhile, a train was lifted off the tracks. The wave also knocked a number of houses off of their foundations, and crushed others. One woman, Bridget Clougherty, was killed after her home collapsed on her. Further away, a truck was tossed into Boston Harbor.
The wave was made up of more than just molasses. It also carried large shards of metal from the ruptured tank along with it, which wreaked havoc as the wave spread outward. One such shard took out a freight house on its journey, killing several workers who had been inside it.