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A definition of ‘industrial accident‘ is a large-scale accident that is caused by an industrial company and affects a lot of people or a large area. When you think of industrial disasters you probably think of fires or explosions. We know also that there are natural disasters like hurricanes, tornadoes and floods. But, if we hear the word molasses, we most likely think of the brown sugary liquid you enjoy on pancakes and waffles. However, my tale is about a very bizarre industrial accident. What if I told you that once there was a flood of over TWO million gallons of Molasses? Well, keep reading and you will learn of a disaster that occurred just over 100 years ago.

Historical Timeline

If you remember your history; the American entry into World War I came in April 1917, after more than two and a half years of effort by President Woodrow Wilson to keep the United States out of the war. But we did supply others with war materiel. World War I also known as the First World War or the Great War, was a global war originating in Europe that lasted from 28 July 1914 to 11 November 1918. World War I resulted in the deaths of 9 million soldiers and 7 million civilians. Many transportation systems faced disaster, including the Great Train Wreck of 1918 in Tennessee, the sinking of Princess Sophia in what is known as the greatest maritime disaster in the Pacific Northwest and the worst railroad accident in world history located in Brooklyn, New York. But the molasses storage tank we are talking about had been built quickly in the winter of 1915 to meet rising demand for industrial alcohol, which could be distilled from molasses and sold to weapons companies, to make dynamite, nitroglycerin, smokeless powder and TNT for use in World War I. The 1918 influenza pandemic (Spanish influenza) was an unusually deadly influenza pandemic, the first of the two1 pandemics involving H1N1 influenza virus. It infected 500 million people, including people on remote Pacific islands and in the Arctic. In August 1918, Boston was the first stop for the mysterious Spanish influenza which was making a deadly race across the United States. In October the Mayor closed the city in a quarantine to try to halt the spread of the flu. When the epidemic had ebbed, 6,000 Bostonians had died from the disease. With the end of the war 1919 was looking better for the people of the United States. By the time of the flood, the war was over, and the molasses inside the plant was expected to become rum in the last days before Prohibition. Prohibition became law with Nebraska’s ratification of the 18th Amendment on January 15th. At the time the US Industrial Alcohol Company (USIA), Purity Distilling’s parent company, still had a license to distill alcohol for industrial applications. For a short time, the story of the flood disaster was all anyone could talk about. Boston had seven daily newspapers at the time, and the molasses flood was huge. Although the molasses flood occurred on the night the Prohibition Amendment passed, the flood story was so big that it knocked the Prohibition Amendment off the front page. It also overshadowed the Versailles peace talks, the talks that ended World War I. In the 100 years since this disaster a lot has changed in Boston’s north end. To remind visitors of the disaster only a small plaque exists. There is nothing left from the flood. Even the smell is gone, though many old timers used to say that when they walked down Commercial St., they could smell the molasses, especially on hot humid days.

The Engineering of The Tank

USIA Molasses Tank

USIA Molasses Tank

USIA owned the tank and took regular shipments of molasses from the Caribbean and used them to produce alcohol for liquor and munitions manufacturing. The company had built the tank in 1915, when World War I had increased demand for industrial alcohol, but the construction process had been rushed and was haphazard.


The molasses tank was originally built in December 1915 under the direction of Arthur Jell, USIA’s treasurer. Arthur Jell, was not an engineer or an architect; he had no technical background. In fact, Arthur Jell, could not even read a blueprint. The tank needed to be an engineering marvel to hold all that weight, but the company never even consulted an engineer on the project. The tank was rushed to completion and was never inspected and was never filled with water as a test.


The method that was used to put tanks together in those days was by riveting, not welding. Designed to hold 2.5 million gallons of liquid, it measured 50 feet tall and 90 feet in diameter. But its steel wall thickness, which ranged from 0.67 inches at the bottom to 0.31 inches at the top, were too thin to support the weight of a full tank of molasses.


It immediately showed signs of disrepair. There were often comments made by people in the vicinity that this tank would shudder and groan every time it was full, and it leaked from day one. It was very customary for children of the North End to go and collect molasses with pails. The response of USIA to worker and community comments and complaints about the leakage was to paint the tank brown so that the leaks were less noticeable.
The tank had been filled nearly 30 times since its first use in 1916 but was near capacity only four times. The repeated use, and the added weight, probably contributed to the disaster.


The massive tank was nearly full on January 15, thanks to a recent infusion of 2.3 million gallons of molasses from Puerto Rico. When the warm molasses from the ship mixed with cold molasses in the tank, it triggered a fermentation process that produced gas. People reported hearing the tank whining and groaning. Several days later, with the almost-full tank weighing 26 million pounds and the gas inside putting pressure on the steel walls, it ruptured. 

Scientific Information on Molasses

Molasses is the active ingredient in alcoholic beverages and is also a key component in munitions. Molasses, is 1.5 times denser than water, weighing 11.46 pounds per gallon and is notoriously slow to pour. But in the flood, molasses—which is a non-Newtonian fluid2 like ketchup or toothpaste—would have moved as a gravity current, much like a mudslide, avalanche or lava flow. Scientists from Harvard University began investigating the science of this disaster again in 2016, after undergraduate students produced a video about the flood. The researchers found that at the time of the collapse, the air temperature would have been around 400 F. The molasses, however, had arrived from the Caribbean to top off the tank and was likely at 500 to 680 F when it was first delivered. After the tank collapsed, the molasses started flowing quickly over the waterfront. The researchers found that temperature can greatly influence molasses’s viscosity, or the degree to which it resists flowing. Temperatures dipped just below freezing the night after the accident. Based on the data the Harvard scientists collected, it’s possible the viscosity of the molasses increased by a factor of four or more due to that drop in temperature.
Site of the collapsed tank with molasses all around

Site of the collapsed tank with molasses all around

The Incident

The disaster occurred at the Purity Distilling Company facility at 529 Commercial Street near Keany Square. Temperatures on the afternoon of January 15, 1919, were over 400; unusually mild for a Boston winter. The pressure relief valves were closed due to the cold. On Jan. 15, 1919, shortly after 12:40 p.m. local time, the giant storage tank on Boston’s waterfront collapsed in the city’s crowded North End. Based on the chemical and physical properties of molasses, modern calculations confirmed that the initial wave could have moved as quickly as 35 mph. The resultant wave was 40 feet high and 160 feet wide at its outset as it rushed through the city’s densely populated North End. The wave of molasses buckled the elevated railroad tracks, crushed buildings and inundated the neighborhood.

Results of the Disaster

The Great Molasses Flood in Boston’s North End killed 21 people and injured 150. The Engine 31 firehouse was knocked clean off its foundation, causing its second story to collapse into its first. Horses died like so many flies on sticky flypaper. The more they struggled, the deeper in the mess they were ensnared, which resulted in the death of about 25 horses. Men and women also suffered the same fate. At least one victim was swept into Boston Harbor by the 25-foot wave. Molasses, waist deep, covered the street and swirled and bubbled about the wreckage of the elevated track and the buildings. The waters of Boston Harbor remained stained brown until the summer.

Molasses flood area map

Molasses flood area:
1. Molasses tank
2. Firehouse (heavily damaged)
3. Police station and paving department
4. Purity offices (destroyed)
5. Copps Hill Terrace housing
6. Boston Gas Light building (damaged)
7. Purity warehouse (some damage)
8. Residential area (Clogherty house destroyed)

When the tank broke and the molasses exploded, there was no outrunning it. When the wave came through, it pulverized everything. People’s bones were crushed, their bodies thrown onto buildings and train cars. Many survivors had broken backs and fractured skulls.

Observers looking at former tank site from elevated tracks

Observers looking at former tank site from elevated tracks

Collapsed elevated railroad track

Collapsed elevated railroad track

Eyewitnesses to the disaster

Harry Howe was on leave from the Navy for the weekend when the flood occurred. On a boat docked in the harbor, Howe witnessed the incident firsthand, as he recalled in a 1981 interview with the Stoneham Public Library: “We saw this big cloud of brown dust and dirt and a slight noise. And there was an arm sticking out from underneath the wheel of a truck. So, two of us got a hold of his arm and pulled and unfortunately, we pulled his arm off.” Boston Police patrolman Frank McManus was at a call box reporting back to headquarters at around 12:30 p.m. on Jan. 15, 1919, when he heard a loud scraping and grinding noise. Pausing to figure out the source, he suddenly found himself overcome with shock. McManus managed to make out to the dispatcher: “Send all available rescue vehicles and personnel immediately — there’s a wave of molasses coming down Commercial Street,” Edwards Park3 wrote of one child’s experience in a 1983 article for Smithsonian Magazine: Anthony DiStasio, walking homeward with his sisters from the Michelangelo School, was picked up by the wave and carried, tumbling on its crest, almost as though he were surfing. Then he grounded and the molasses rolled him like a pebble as the wave diminished. He heard his mother call his name and couldn’t answer, his throat was so clogged with the smothering goo. He passed out, then opened his eyes to find three of his four sisters staring at him.

Rescue Operations

First to the scene were 116 cadets under the direction of Lieutenant Commander H. J. Copeland from USS Nantucket, a training ship that was docked nearby at the pier.

During the next several days, rescue workers sifted through the ruins, shooting molasses-trapped horses and recovering bodies. The human toll eventually climbed to 21 dead and another 150 injured, but many of the deceased remained missing for several days. The remains of one victim, a wagon driver named Cesare Nicolo, were not fished out of nearby Boston Harbor until almost four months after the flood.

After the victims had been pulled from the muck, cleanup crews quickly learned that getting rid of 2 million gallons of molasses is very difficult. In his book Dark Tide (see References), Stephen Puleo wrote about one of the chief obstacles to the cleanup: firefighters couldn’t just use their hoses to blast the molasses off buildings and streets with fresh water. Eventually they realized that saltwater would cut the hardened molasses and enable them to hose it down the streets into gutters.

Rescuers sort through rubble.

Rescuers sort through rubble.

Ambulance at Boston's Great Molasses Flood

Boston’s Great Molasses Flood – Ambulance accesses flood area

The Cleanup

Over 300 workers converged on the scene in the days after the disaster to remove wreckage and debris, and firefighters later used brooms, saws and saltwater pumps to strip away the last of the syrupy residue. Wikipedia (see References) reports that: The cleanup in the immediate area took weeks, with hundreds of people contributing to the effort, and it took longer to clean the rest of Greater Boston and its suburbs. Rescue workers, cleanup crews, and sightseers had tracked molasses through the streets and spread it to subway platforms, to the seats inside trains and streetcars, to pay telephone handsets, and into homes.

The Investigation Begins

USIA was quick to blame anarchists. The company claimed that since its alcohol was an ingredient in government munitions, anarchists must have sabotaged the tank by detonating a bomb. Defense attorney Charles Choate fabricated a story blaming the disaster on Italian anarchists4 . Another theory explained that the molasses had fermented inside the tank, producing carbon dioxide, which led to an explosion.

Modern Analysis

Ronald Mayville5, a senior structural and metallurgical engineer with Simpson, Gumpertz & Heger in Waltham, MA who has researched the disaster for years in his spare time, said several design flaws led to the catastrophic failure. The steel was too thin to withstand the enormous stress of 2.3 million gallons of molasses, a weakness that the builders should have known at the time. The tank was made from a steel susceptible to fracture and was coincidentally the same type used on the Titanic. Mayville said the walls were at least 50% too thin, even by the more relaxed standards of the day. The builders at the time did not know that the type of steel used for the tank was brittle because it contained a low amount of the chemical element, manganese, making it more likely to crack. Mayville, has long held an interest in engineering disasters, but said his work received a major boost by the discovery of an archive at Lehigh University that belonged to a consultant who testified in the trial against USIA. For what he believes is the first time, Mayville analyzed the collapse using modern engineering techniques, such as finite element analysis. Flawed rivet design was another problem, according to Mayville’s analysis. Stresses were too high on the rivet holes, where cracks first formed. He found that the fracture probably began in the 20-inch manhole, and that a rivet hole directly above was highly stressed and could have deteriorated.

Legal Consequences

North End residents who had lost their homes and loved ones in the disaster predictably turned their rage toward USIA. USIA soon found itself named as the defendant in 125 lawsuits, which led to a legal battle that nearly matched the flood’s scale. The plaintiffs argued that the molasses tank had been too thin and shoddily built to safely hold its contents. Colonel Hugh Ogden was named by the Massachusetts Superior Court, as the auditor who would hear the evidence and report back on the cause of the disaster. It took Ogden nearly six years to hear testimony from 3000 witnesses. The trial gathered input from thousands of expert witnesses, producing 20,000 pages of conflicting testimony. The lawsuits against USIA were eventually combined into a mammoth legal proceeding that dragged on for five years. On April 28, 1925, Auditor Hugh W. Ogden submitted his report on the molasses disaster to the Supreme Court of Massachusetts. In the end, USIA was liable for the damage and paid around $7000 to the family of each victim.

Financial Impact

The Massachusetts Foundation for the Humanities website6 claims that the property damage totaled around $100 million in today’s dollars. A court-appointed auditor found USIA responsible after three years of hearings, and the company ultimately paid out $628,000 in damages ($9.26 million in 2019, adjusted for inflation). Relatives of those killed reportedly received around $7,000 per victim (equivalent to $103,000 in 2019).

Regulatory Impact

The Boston Molasses Disaster marked a major moment in American public policy. It led to a shift in how cities and states evaluated and regulated construction standards, first in Massachusetts and then nationwide, triggering the sudden promulgation of requirements and restrictions governing the concrete and steel used to build American cities. The Great Molasses Flood appears to have been a tragedy that could have been avoided, but the disaster really drew attention to the potential repercussions of shaky construction. The case helped prompt Massachusetts and many other states to pass laws requiring that engineers and architects inspect and approve plans for major construction projects.

In Memorial

At the present time on a small wall at the entrance to Puopolo Park there is only a small, easily missed plaque to commemorate the disaster. It was placed by the Bostonian Society. The plaque is located at the entrance to The Harborwalk, at the intersection of Commercial Street and Copps Hill Terrace and positioned along the sidewalk near the bocce ball court, between the two baseball diamonds.

Plaque commemorating the Boston Molasses Flood

Plaque commemorating the Boston Molasses Flood

The small green sign is set low into a stone wall, unnoticed unless you are looking for it. The sign location is the exact site of the outside wall of the tank. Despite its lack of grandeur, it is a sign worth seeking out, for no other reason than to stand and contemplate what was once America’s strangest disaster scene.

Bryan Webb, a civil engineer, has recently presented conceptual designs for a more fitting memorial to the victims of the disaster at the top of the Rose Fitzgerald Kennedy Greenway near the North End. Webb, 24, said the memorial, which would be part of a proposed park at the spot, would commemorate a tragic event in the city’s history, one that spurred major reforms in building standards and zoning laws.


Mark Rossow7, a civil engineer and professor emeritus at Southern Illinois University in Edwardsville, states, “There is plenty of science to explain what went wrong in the molasses flood. But the accident ultimately boils down to ethics. Most of the things I have looked at do not really have so much to do with lack of scientific knowledge so much as a lack of responsibility of the people in charge.” Amid the coverage of the catastrophe, no one documented any environmental impacts, nor does it seem anyone questioned the decision to dump the molasses into the harbor.


  1. The second outbreak occurred in 2009, influenza A (H1N1).
  2. Non-Newtonian fluids typically exhibit either shear thinning or shear thickening behavior and in some cases, exhibit a stress level which must be overcome before the fluid begins to flow.
  3. Edwards Park, “Without Warning, Molasses Surged Over Boston 100 Years Ago,” Smithsonian Magazine, November 1983.
  4. As an enormously rich and powerful corporation, USIA was a logical target for anarchists, who were opposed to all forms of government and advocated the overthrow of the capitalist system. Anarchists had indeed bombed several of the company’s facilities in New York earlier in the decade.
  5. Ronald Mayville, “The Great Boston Molasses Tank Failure of 1919“, Civil and Structural Engineer Magazine, Vol 1, No. 6, September 2014, pp. 33-37.
  6. Mass Moments: The Great Molasses Flood
  7. The Molasses Flood of 1919 and Other Ethical Failures in Engineering (PDF)

About the Author

Howard Spencer lives in Yardley, PA and holds a BS from Letourneau University, Longview, TX and a Master of Engineering from Texas A&M. He holds several certification: CSP, CHCM, and CPSI. He has 43 years of diversified experience in insurance, hospital, beverage, R&D and petro-chemical industries. He is a professional member of ASSP.

SHHS welcomes Mr. Spencer as the first volunteer author from the safety and health field to contribute an article to The Archives of Safety and Health.

Thank you very much!

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