Molasses Flood Alarm – Is That a Thing?

It sounds like a joke, but on January 15, 1919 – 100 years ago today – there was a flood of molasses in Boston that killed 21 and injured 150. Buildings were ripped from their foundations, railroad cars were shoved off their tracks, and several city blocks were left flooded to a depth of two to three feet.

Molasses tank before the flood
50 feet tall and 242 feet in circumference, the tank held 2.3 million gallons of molasses.

The flood came from a massive storage tank that was improperly designed and poorly built. 50 feet tall and 242 feet in circumference, the tank held 2.3 million gallons of molasses. It was built with walls 10% thinner than were specified and assembled with poor materials. Thousands of rivets held it together, all installed in a rushed manner with no inspection and overseen by a person who had no technical, architectural, nor engineering experience. The tank, once built, leaked immediately and was painted brown to conceal the site of molasses oozing down its sides. Modern studies show the tank walls were only half as thick as they should have been for one of that size and made from brittle steel.

It sounds baffling that there should be a tank holding 2 million gallons of molasses for any reason. The viscous fluid is a byproduct that comes from refining sugarcane or sugar beets into sugar and not only can be distilled to produce rum, it can also be converted to ethanol and used in the production of munitions. The tank was built in 1915, one year after World War 1 broke out.

Two days prior to the disaster, warmer molasses had been added to the tank, topping it to near capacity, which had multiple effects. First, this addition to the cold, thick molasses already in the tank created a fermentation process that produced gas. This gas collected in the near-full tank, increasing pressure against the walls. Second, the warmed contents were more viscous than they otherwise would have been. When the tank structure failed, this allowed the spilling fluid to spread further and more quickly than it otherwise would have, in a wave as high as 25 feet and moving at 35 miles per hour.

The disaster took place in Boston’s North End which was very congested at the time with 40,000 people in just a square mile of space. It was an extremely busy commercial neighborhood along an equally busy shipping waterfront. A Boston police patrolman reported he heard the sound, like that of a machine gun rattling followed by a deafening grinding. He looked towards the tank which disintegrated as he watched, spilling a huge wall of dark liquid.

The wave of molasses stretched on for three-quarters of a mile, collecting debris as it moved like a tsunami. The fluid cooled quickly as it spread due to the winter temperatures and quickly became thicker, ultimately hampering efforts to free victims before they suffocated. In addition to the deaths and injuries, the accident caused $300,000 in damage, the equivalent of over $9 million today.

The aftermath of the Great Molasses Flood
The wave of molasses stretched on for three-quarters of a mile, collecting debris as it moved like a tsunami.

The cleanup was difficult as water proved ineffective at washing away the mess. In the end, salt water from a fire-boat in the harbor was needed. Cleanup took weeks and the harbor water was brown until summer. Cleanup in the rest of Boston took longer as people unintentionally tracked molasses to subway platforms, trains and streetcars, pay telephone handsets, and into their homes. For decades after the event, residents claimed they could smell molasses on hot summer days.

After the flood, the Boston Building Department began to require that all calculations of engineers and architects had to be filed with their plans and that stamped drawings be signed. This practice became the standard all across the country. This influenced the adoption of engineering certification laws in all states and a requirement that all plans for major structures be sealed by a registered professional engineer before a building permit will be issued.

This disaster did for building construction regulations nationwide what the subsequent Boston disaster of the Cocoanut Grove nightclub fire died for fire code laws.

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