Why a freak tidal wave of molasses drowned people in Boston in 1919

At the start of the twentieth century, molasses was an important economic resource as both a food product and an essential ingredient in manufacturing.

It was shipped from the Caribbean to American ports like Boston, and it became a key ingredient in the production of rum and, during wartime, a key form of industrial alcohol.

That alcohol was especially important for munitions manufacturing, particularly the production of cordite, a smokeless explosive used extensively in World War I. 

Because of the high demand, companies like the United States Industrial Alcohol Company (USIA) began constructing large storage tanks to hold imported molasses.

One such tank, built in 1915 by USIA’s subsidiary, the Purity Distilling Company, stood near Boston’s waterfront on Commercial Street.

The tank, which had stood about 15 metres tall and had been able to hold roughly 8.7 million litres of liquid, had been put into use without pressure testing or safety approval.

In fact, no qualified engineer had ever reviewed the design. The steel that was used in its construction had measured just 0.31 inches thick in places and had contained too little manganese, which had made it especially brittle in cold temperatures. 

From the beginning, locals had observed serious problems. Neighbours and workers had complained that the tank had groaned under pressure and had leaked syrup from its seams.

Children had even collected molasses in cups from rivets that were leaking.

Instead of repairing the issue, the company had reportedly painted the tank brown to mask the leaking molasses.

At the time, the surrounding neighbourhood contained crowded tenements, a firehouse, a railway siding, and industrial workshops.

This meant that many people lived or worked within only a few hundred metres of the nearby structure. 

On the day of the flood, Boston experienced a sudden change in weather. After a stretch of freezing temperatures, a sudden warm spell caused the temperature to rise above 5°C.

As a result, the molasses inside the tank began to expand, which increased pressure against the tank’s thin steel walls.

Some reports suggested that fermentation inside the tank may have produced carbon dioxide gas, which may have further strained the container and caused it to exceed its limits. 

Just after 12:40 pm, the tank exploded. Some witnesses later described hearing a sharp cracking sound followed by the roar of rushing liquid and the screech of twisting metal.

Some even compared the noise to a machine gun as rivets blasted from the tank.

What followed was a wave of hot molasses that was estimated to be over 7 metres high and that was estimated to have moved more than 50 kilometres per hour.

It smashed through buildings, destroyed the nearby firehouse, and knocked out the support columns of the Boston Elevated Railway. 

In only seconds, entire blocks were submerged beneath a thick tide that moved quickly.

Carts, freight wagons, and people were swept away, while the wave pushed wooden buildings off their foundations and flattened smaller structures.

One train barely avoided disaster when the driver stopped the carriage just before the damaged rail line collapsed.

Horses drowned, pedestrians disappeared, and heavy debris from splintered buildings crashed down on those trapped beneath the syrup. 

Because the molasses had quickly begun to cool, its thickness increased within minutes and, once thickened, the fluid trapped victims where they had fallen.

Anyone stuck inside the wave found it almost impossible to move or breathe, and some suffocated before help could reach them.

The molasses wave was estimated to have weighed over 13,000 tons and it spilled all its contents in less than two minutes. 

After the rupture, rescue workers arrived almost immediately, but the scene that they encountered was chaotic and dangerous.

Firefighters, police, and Red Cross staff tried to search for survivors, yet the depth and stickiness of the molasses severely hindered their progress.

Each step required effort, and the syrup stuck to their uniforms and equipment, which made it nearly impossible for them to maintain speed or coordination. 

Over the following hours, rescuers used ropes, planks, and makeshift rafts to move across the flooded area.

As they reached collapsed buildings, they found people trapped beneath fallen walls and twisted metal.

In many cases, only their heads or arms were visible above the surface. To free them, workers who waded chest-deep in syrup used saws, shovels, and crowbars.

Some rescuers reportedly had to cut victims free with knives when limbs became glued to wreckage.

The risk of exhaustion and hypothermia grew as the day wore on. 

In the days after the flood, workers began the difficult task of recovering the dead and clearing the area.

Seawater from Boston Harbour was pumped into the streets to break up the hardened molasses, and sand was spread across surfaces to absorb what remained.

As people resumed travel through the area, sticky footprints spread molasses across sidewalks, public transport, and staircases.

Weeks after the cleanup began, the smell of molasses still drifted through the air, especially on warmer days.

Some locals later claimed that even decades afterward, the smell sometimes lingered during the summer. 

The final death toll was recorded at twenty-one, with over 150 more injured. Most of the victims had either drowned in the molasses or been crushed beneath collapsed buildings and debris.

Recovery teams found many of the bodies coated so thoroughly in syrup that identification became difficult.

The last body was not located until May 1919, after it had washed into the harbour and had been pushed back ashore by the tide. 

Among the dead were children, factory workers, and residents of the nearby tenements.

Ten-year-old Antonio Di Stasio, who had been playing with friends, was thrown into a pole and killed instantly.

Pietro Gonella, a blacksmith working nearby, died in his workshop when the building collapsed.

Firefighters inside Engine 31 also perished after their station crumpled under the pressure of the wave. 

As the wave cooled, its thickness increased rapidly, creating a situation in which victims could neither escape nor call for help.

Many died within minutes, and survivors described how they were dragged, trapped, or suffocated by a substance they could not fight against.

The disaster ultimately killed more people than the Great Boston Fire of 1872. 

In the aftermath, public outrage grew and the United States Industrial Alcohol Company attempted to shift blame by accusing saboteurs of blowing up the tank, but investigators dismissed that theory.

Families of the victims and residents who were injured soon filed legal claims against the company.

In response, the court combined the cases into a single lawsuit, Dolan v. United States Industrial Alcohol. 

During the investigation, the company’s carelessness became clear. Testimony showed that USIA had never properly tested the tank and that its designer, Arthur Jell, lacked any engineering qualifications.

He had approved the structure without calculations or pressure tests. Multiple witnesses confirmed that the tank had leaked and had groaned for years before the collapse, but the company had taken no meaningful action to repair or reinforce it.

The court-appointed inspector, Hugh W. Ogden, documented these findings during a lengthy investigation. 

In 1925, the court found USIA liable for the disaster and ordered it to pay over $600,000 in damages, a figure which was later estimated to be worth more than $9 million today.

The outcome led to stricter rules for industrial safety and building construction.

Engineers were required to approve major projects, and cities like Boston began enforcing stricter inspections and permit requirements for dangerous structures.

The disaster also contributed to nationwide calls for more rigorous building codes and closer checks of industrial sites. 

Although the idea of a molasses flood may seem absurd, the disaster showed how industrial carelessness and ignoring safety measures could lead to disastrous consequences.

The event forced changes that made similar failures far less likely and became a clear warning from the industrial age.