In A Nutshell
On January 15, 1919, Boston experienced a rather unique tragedy. A large storage tank filled with molasses suddenly exploded. A wave of hot molasses obliterated several buildings, killing 21 people. Though the molasses flowed quickly upon release, it soon thickened, trapping and burning its victims. (The immediate aftermath is pictured above.)
The Whole Bushel
January 15, 1919 was an oddly warm winter day which ended up being anything but mild or pleasant for Boston. On Commercial Street sat an 18-meter-tall (58 ft) storage tank owned by the Purity Distilling Company. This tank was not in particularly good condition, having shown signs of structural instability in the past as well as leaking frequently. Nevertheless, on January 15, the tank was filled to maximum capacity with molasses. It is believed that this molasses was fermenting, increasing the tank’s internal pressure via the production of carbon dioxide.
Around lunchtime, the top of the tank suddenly exploded skyward while the sides split, firing rivets and twisted metal outward. A section of the massive tank fell on the nearby Engine 31 firehouse. The metallic debris from the tank was only the vanguard for the real calamity: 7.5 million liters (2 million gal) of hot molasses. A wave of molasses 7.5 meters (25 ft) tall and 50 meters (164 ft) wide plowed outward at 55 kilometers per hour (34 mph), essentially forming a localized, sugary tsunami.
This wave swept away several nearby freight train cars and caused massive damage to the building from which the train’s cargo was being loaded. Workers in the building’s cellar were quickly drowned and burned. Engine 31 was torn off its foundation, as were two other buildings. Two support columns for an elevated railway over Atlantic Avenue were knocked over. The molasses flowed through the streets, still chest-deep at 90 meters (295 ft) from where the tank stood. Ultimately, 21 people and a number of horses and dogs were killed by the molasses explosion, with 150 more people injured.
The United States Industrial Alcohol Company, the owner of the Purity Distilling Company, faced over 100 lawsuits for the Boston Molasses Disaster. The courts eventually held the company liable, as it had ignored numerous signs that the tank could eventually fail. Ultimately they had to pay out over $1 million.
The physics of molasses make the Boston Molasses Disaster stand out from typical industrial accidents. For one, molasses is classified as a non-Newtonian fluid; its viscosity varies depending on what other forces are acting on it. The fermenting molasses inside the storage tank would have been sufficiently pressurized to initially flow much more freely than one would expect of the normally slow, sticky goo. In other words, the molasses hit like a tsunami at first and then congealed, trapping those unfortunate enough to be caught in it.
Those caught in the wave were in a dire situation, as it is nearly impossible to swim in molasses. An object’s Reynolds number is a calculation which indicates how well it can move through a fluid, taking into account the properties of both the object and fluid. A normal adult male in water has a Reynolds number of roughly one million. In molasses, which is normally at least 5,000 times more viscous than water, that number is only 130. Normal swimming movements would not help a person to move at all. Victims caught in the molasses wave experienced a fate similar to insects caught in tree sap.