A Century Later: Reflecting On the Great Boston Molasses Flood

Posted by Ronald Mayville on January 16, 2019
Boston Molasses Flood

On 15 January 1919, a tank holding more than 2 million gallons of molasses burst in Boston’s North End, sending a sticky flood through the streets – killing 21 people and severely damaging surrounding buildings and infrastructure. This tragedy caused quite a stir at the time, as engineering experts were not able to agree on why the tank failed.

The case has remained an engineering mystery all these years later. No one knows the exact cause of the failure, but historians and engineers continue to examine the story. I have researched and analyzed this topic in my spare time for many years, applying modern engineering techniques like finite element analysis to this 100-year-old problem, and believe there are several reasons we can point to for this disaster.

One thing is clear: the tank was under-designed and did not have adequate thickness to withstand stresses from the molasses. On top of that, it seems that the method the designer used to make the rivet holes – tanks were riveted in those days, not welded – was substandard, which may have created small cracks. Builders should have recognized these issues at the time, but it seems the project was rushed along because there was an impending shipment of molasses. 

Secondly, and with the benefit of hindsight, we now know that the steel used for the tank was brittle, making it more susceptible to cracking. The tank’s designer would not have known this at the time, but it surely increased the likelihood of collapse. 

These design flaws and elemental challenges played key roles in this strange disaster. While we still do not have a full picture of the decision-making and construction practices that went into the tank, new research efforts continue to piece the information together and help inform current engineering decisions. 

I recently spoke with the Associated Press about the effects of the disaster. This story is also covered in recent articles by Civil + Structural Engineer, History Channel, and WBUR.

Categories: Points of View