Black tide rising

Above: An elevated view of the flood's destruction. Source:  Boston Public Library 

From the Boston Tea Party to Bill Buckner’s  game-losing blooper  in the 1986 World Series, the city of Boston is the home of infamous spills. But few Beantown incidents have captured the public’s fascination quite like the Great Molasses Flood of 1919. Certainly none are more bizarre.

Shortly after lunchtime on January 15, 1919, a 50-foot-tall storage tank in Boston's North End neighborhood suddenly burst with a rending groan, disgorging 2.3 million gallons of molasses into the surrounding streets.

As the claggy syrup spouted from the tank in all directions, it formed a formidable wave that reached 25 feet high and traveled at speeds of up to 35 miles per hour, destroying nearly everything in its path. Buildings were lifted from their foundations, streetcars were flung from their tracks, trucks were swept into the nearby harbor, and an elevated railway collapsed.

In a matter of minutes, the wave of molasses devastated a half-mile swath of the Boston waterfront. Eyewitnesses claimed that the scene resembled a bombed-out war zone. So catastrophic was the damage that in the immediate aftermath, local newspapers speculated that an explosion must've caused the collapse.

But the worst was yet to come. As day turned to night, the molasses gradually cooled and thickened, hindering rescue efforts and entombing many victims in place.

The flood ultimately left 21 people dead—many of whom perished hours after the initial wave—and at least 150 injured. Cleanup efforts took months to complete, and locals reported that the sweet fragrance of molasses lingered for decades after the incident.

As day turned to night, the molasses gradually cooled and thickened, hindering rescue efforts and entombing many victims in place.

Today, a small plaque sits near the site of the tank, solemnly commemorating the victims of the incident. It is the sole physical reminder of that dark day on the waterfront. But the Great Molasses Flood is forever enshrined in the city's collective memory.

It’s hard to ignore the cruel irony of the incident: Molasses is typically regarded as a benign substance, more apt to wreak havoc on one’s teeth than a city neighborhood. But on that fateful day in 1919, the substance’s unique physical properties actually contributed to the tank’s collapse—and to the ensuing wave’s shockingly destructive force.

On January 14 (the day before the incident) the tank received a fresh batch of molasses, which had been warmed for transfer. But the tank already contained several hundred thousand gallons of cold, thick syrup. As the two batches mixed, the reaction induced fermentation, which in turn produced gas. The tank was already filled to capacity with liquid molasses, and this excess gas increased the tank’s internal pressure to extreme levels. It's possible that this pressure ultimately ripped the tank open from the inside out.

Once the floodgates opened, the principles of fluid dynamics took over. Molasses is a non-Newtonian liquid, meaning that its viscosity can change when force is applied, and that it stores much more potential energy than water. Ketchup and toothpaste are non-Newtonian fluids.

When the tank ruptured, the molasses rushed out with the force of a mudslide or avalanche, rather than that of a tidal wave. Had the tank been filled with water, the damage likely would have been far less severe.

Several months after the disaster, victims united together to jointly file a class-action lawsuit against U.S. Industrial Alcohols (USIA), the company that owned the tank. The 129 plaintiffs claimed that USIA had ignored engineering standards when constructing the tank, and once the structure was complete, it repeatedly had flouted concerns raised by the tank’s own operators. USIA, meanwhile, claimed that the tank had been sabotaged by Italian anarchists—a sensational explanation, but one favored by the media.

The trial stretched on for nearly five years, and featured testimony from over 1,000 witnesses. Although USIA maintained its innocence throughout the proceedings, the weight of evidence pointed toward the company’s culpability.

The tank was hastily constructed in 1915, from low-quality materials, in order to meet wartime demand for industrial alcohols. (Throughout World War I, the United States distilled molasses into ethanol, which was then used in the manufacture of dynamite and other military-grade explosives.) The entire structure was built from the same brittle steel as the Titanic, which famously sank after striking an iceberg less than a decade earlier.

Additionally, construction workers testified that its walls were 10% thinner than designed—a cost-cutting measure devised by the company’s treasurer, Arthur Jell, who oversaw the tank’s construction despite having no background in engineering.

The tank’s frailties were evident from the start. According to site manager Isaac Gonzales, the tank leaked from every seam every day—so much, in fact, that neighborhood urchins would fill their pails with the sweet syrup oozing from its seams. When Gonzales registered his concerns with Jell, the company simply painted the tank brown to conceal the fissures.

In 1925, a state auditor concluded that USIA was responsible for the tank's failure, and ordered the company to distribute $628,000 in damages—about $30 million today. 

But more importantly, the ruling prompted the Boston Building Department to implement engineering certification laws, which required all architectural plans and calculations to be signed by an engineer before a building permit could be issued. The rest of the nation soon followed suit; today, this case is regarded as a turning point in construction regulation. Moreover, it was the first time that members of the public successfully challenged the actions of a major corporation in court—and won.

Although the Boston Molasses Flood is remembered primarily for its sheer absurdity, the incident left a lasting impact on civil society: No longer was big business allowed to operate unrestricted—and no longer was it immune from consequence.