Boston Molasses Tank — A Brittle Steel Tank Burst and Drowned a Neighborhood in Syrup

At about 12:30 in the afternoon of 15 January 1919, on Commercial Street in Boston’s North End, a 50-foot-tall riveted steel tank holding roughly 2.3 million US gallons of molasses split apart and discharged its entire contents in a wave that killed 21 people and injured around 150. The cause was not fermentation pressure, not sabotage, and not an explosion. It was a brittle fracture of the tank’s thin, low-manganese steel shell, initiated at the over-stressed rivet holes beside a manhole at the base, propagating at the speed of sound through plates that were never thick enough and never inspected.

The tank belonged to United States Industrial Alcohol (USIA), through its subsidiary Purity Distilling, and had been thrown up in 1915 to store the molasses that fed wartime demand for industrial alcohol and munitions. It was 50 feet high and 90 feet in diameter and held about 13,000 short tons of liquid when full. The man who ordered and oversaw its construction, USIA treasurer Arthur Jell, had no architectural or engineering training. He did not commission stress calculations, did not have the steelwork checked by an engineer, and skipped the standard practice of filling the completed tank with water to test it under load — running only a few inches of water into the bottom rather than the full hydrostatic test that would have revealed the leaks before they revealed themselves.

The shell leaked from the day it was filled. Molasses wept from the seams so persistently that USIA painted the tank brown to disguise the runs, and neighborhood children collected the drips. At least one employee warned management that the structure was unsound; the company’s response was to re-caulk. The forensic verdict, settled across a three-year court audit at the time and confirmed by modern fracture-mechanics analysis decades later, was unambiguous: the wall plates were roughly half as thick as the load required, the steel was deficient in manganese and therefore brittle, and the failure began as cracks at the rivet holes where stress concentrated. On a January day the metal was well below its ductile-to-brittle transition temperature, and a structure already loaded near its limit failed without warning and without yielding.

The disaster ended in one of the longest civil proceedings in Massachusetts history. A court-appointed auditor found USIA liable after years of hearings, and the company paid out about $628,000 in settlements — on the order of $11 million in present money. The litigation also did what the absent engineer never had: it forced the lesson into law. Massachusetts and then jurisdictions across the country began requiring that major structures be designed, signed, and sealed by a licensed engineer or architect, the regulatory ancestor of the professional stamp.