A Straight Dope Classic from Cecil's Storehouse of Human Knowledge

Was Boston once literally flooded with molasses?

December 31, 2004

Dear Cecil:

My girlfriend told me that on a recent walking tour of Boston the guide told her about the Boston molasses disaster of 1919. Seemingly a huge tank of molasses crumbled under the tremendous weight, sending a "tidal wave of molasses traveling 35 mph" down the street, where it proceeded to kill tens of people and many horses. A little research on the Internet uncovered that such an event seems to have occurred, but even the most skeptical of Web sites still relates that the molasses moved at 35 mph. In January, no less. My question is: In 1919, how could they have possibly measured that speed? Is it simply another exaggeration in this already hyperbolized story? Is any of it to be believed?

Cecil replies:

Oh, the great molasses flood definitely happened. Twenty-one people died, 150 were injured, and nearby buildings were reduced to kindling. Molasses traveling at 35 mph in January is impossible, you say? If photos of the aftermath and eyewitness testimony don't change your mind, you can do like me and check with a professor at the Massachusetts Institute of Technology. After reviewing four pages of calculations, I'd say it's clear that when a 50-foot-tall tank of any liquid gives way, the contents are going to do more than just ooze.

The blackstrap deluge was no laughing matter at the time. As the story is told in Dark Tide: The Great Boston Molasses Flood of 1919 by Stephen Puleo (2003), the sticky liquid was stored in a massive dockside tank in Boston's crowded North End. Ninety feet in diameter with a capacity of 2.3 million gallons, the tank had been hastily constructed in 1915 by a subsidiary of the United States Industrial Alcohol Company. The firm shipped molasses, a by-product of sugar refining, from Caribbean ports to plants in the U.S., where it was distilled into alcohol, used back then in the manufacture of gunpowder and other munitions. Demand had increased sharply with the outbreak of war in Europe, and USIA hoped to cash in.

Construction of the tank had been overseen, or more accurately gazed stupidly at, by Arthur Jell, a bean counter with no technical background who was unable even to read blueprints. Anxious to complete the tank in time for the arrival of the first molasses shipment, Jell forwent the elementary precaution of filling it first with water to test for leaks. Once molasses was pumped in, the tank leaked so copiously at the seams that neighborhood kids collected the drippings in cans. When an alarmed employee complained, Jell's response was to have the tank painted brown so the leaks wouldn't be so noticeable.

With the war ending and demand for industrial alcohol plummeting, USIA decided to distill molasses into grain alcohol for liquor before Prohibition killed the market for good. On January 12 and 13, 1919, a tanker filled the huge vessel almost to the brim. Two days later, at about half past noon, the tank gave way with a roar, sending a wave of molasses variously estimated at 8 to 15 feet high in all directions. Many nearby were drowned or crushed when buildings fell on them. A massive hunk of the steel tank was flung into an elevated rail line, collapsing the tracks only seconds after a train had passed. Rescuers were hampered by the knee-high tide of congealing goo; the last victim, a deliveryman, wasn't found for 11 days — he and his truck had been swept into the harbor. For decades afterward it was claimed that central Boston smelled like molasses.

How fast did the initial surge of molasses travel? Experts and eyewitnesses agreed on 35 mph, but we needn't take their word for it. I consulted with Gareth McKinley, professor of mechanical engineering at MIT, and established that the theoretical maximum rate of flow for a (roughly) 50-foot column of liquid, ignoring density and viscosity, was 38 mph. Surprisingly, molasses's stiffness would have slowed things only a bit — making certain assumptions about Reynolds number and whatnot that I expect some gratitude for not sharing, the flow rate would have been mostly a function of inertia (i.e., mass) rather than viscosity. Bottom line: 35 mph was a pretty good guess.

An inquiry found the disaster was due to inadequate construction; USIA paid out more than $600,000 in damages — at least $6.6 million in today's money. The timing gives one pause, though. In September 1918, a few months before the flood, the Red Sox won the World Series, an event that, in light of its subsequent rarity, surely constituted a major disturbance in the force. Now the Red Sox have given fate the finger once more. Come January, Boston fans noticing a distant rumble and a funny smell will have to wonder: Is that just the subway, or is it payback time again?

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