A 50-foot-tall molasses tank containing as much as 2.5 million gallons of molasses exploded. The explosion was of sufficient force to cut the girders of the nearby elevated railroad and lift a train off the rails. Some nearby buildings were also collapsed by the blast. The molasses flowed out in a wave between 8 and 15 feet high, moving at 35 miles per hour and exerting a force of 2 tons per square foot. Twenty-one people were killed and 150 injured as the hot molasses crushed, asphyxiated, and cooked many of the victims to death. It took over six months to remove the molasses from the cobblestone streets, theaters, businesses, automobiles, and homes. Purity Distilling paid $1 million in damages.
The cause of the accident is not known with certainty. It is thought the tank may have been overfilled due to the impending passage of Prohibition, or it may have burst due to fermentation occurring within, or by the unusual increase in the local temperatures that occurred over the previous day (the air temperature rose from 2°F to 40°F over that period).