On January 15, 1919, Boston's North End experienced one of the strangest industrial disasters in history: the Great Molasses Flood. A massive steel tank holding 2. 3 million gallons of crude molasses burst, unleashing a 25-foot wave traveling at 35 miles per hour.
While the initial blast caused immediate destruction, it was the bizarre thermodynamic conditions following the explosion that turned rescue and cleanup into a logistical standstill. Just before the explosion, Boston experienced an unseasonably warm thermal shift. Temperatures rose rapidly from freezing to over 40 degrees Fahrenheit in less than 24 hours.
This warm liquid expanded inside the poorly constructed steel tank, increasing internal pressure while accelerating fermentation gas build-up until the structure catastrophically failed. However, as millions of gallons of warm molasses flooded the streets, the weather abruptly inverted again. A arctic cold front slammed into the city, plunging temperatures back below freezing within hours.
Molasses is a fluid whose viscosity is hyper-sensitive to temperature. At warmer temperatures, it flowed like heavy oil; at sub-freezing temperatures, it transformed into a tar-like, semi-solid goo almost as tough as asphalt. Emergency crews and firefighters tried using salt water from harbor hoses to wash away the sludge, but the freezing air combined with cold ocean water caused the molasses to congeal even faster.
Instead of diluting the mass, the water created a slippery ice-and-sugar crust over buried wreckage. It eventually required steam hoses, sand, and over 80,000 man-hours of manual scraping to clear the city streets.