Author(s): Fred Durso. Published on May 1, 2011.

The Great Boston Molasses Flood of 1919
The bizarre tale of a deadly wave of molasses that decimated a Boston neighborhood, and prompted nationwide construction safeguards.

NFPA Journal®, May/June 2011

By Fred Durso, Jr.

In 1915, construction ended on a massive tank that towered over Boston’s North End. Situated along Boston Harbor, next to the city’s most densely populated neighborhood, the steel structure stood 50 feet (15 meters) tall, was 90 feet (27 meters) in diameter, and held more than 2 million gallons (8 million liters) of molasses. When it was distilled into industrial alcohol, it became an ingredient for World War I munitions, particularly explosives. The structure was as solid as the industry it represented. Or so it seemed.

Four years later, following a substantial molasses delivery, the tank suddenly collapsed, unleashing a powerful wave that surged through the neighborhood. At its onset, the wave was 25 feet (8 meters) high and traveled at 35 miles (56 kilometers) per hour. Nothing in the path of the gooey liquid was safe: buildings were ripped from their foundations, railroad cars were knocked off their tracks, and people and animals drowned. Twenty-one people, mostly immigrants and city workers, died. About 150 were injured.

Despite its devastation, the flood remains an elusive piece of Boston history, says Stephen Puleo, historian and author of the book Dark Tide, which provides a detailed account of events leading to the flood and what followed. “The substance that caused the flood produces a little giggle at the outset,” he says. “If this were caused by fire, water, pestilence, or earthquake, it would have gotten more play.”

The flood’s aftermath was no laughing matter, however. The tank’s construction and safety tests were called into question and prompted a landmark court case and construction safeguards that took effect across the United States.

VIDEO: "Dark Tide" author Stephen Puleo tours Boston’s North End neighborhood, where he highlights areas affected by the 1919 molasses flood.

The following excerpts are from Puleo’s book, which he’ll discuss during an education session on Monday, June 13, 2011, at NFPA’s Conference & Expo in Boston.

The tank 
As [firefighter] George [Layhe] walked along the pier to the firehouse, he took in the early morning scene around him and marveled at the increase in activity since he began work five years ago. Commercial Street now was one of the main arteries in Boston … Dominating this scene … was the giant molasses tank. The tank towered over everything in the area, including the wharf itself, the tenements across Commercial Street, even the elevated tracks that ran above the busy thoroughfare. It sat just three feet from Commercial Street and 50 feet [15 meters] from the firehouse … It was painted a depressing charcoal gray color, but depending on how the sun slanted over the harbor, there were hours and moments when the huge receptacle gleamed and seemed to be almost inspiring in its size and power.

It would be hard for anything to ruin George Layhe’s day today, but he became a little queasy when he stared up at the tank and witnessed a sight that had become all too familiar in the two months that it had been standing.

Thick lines of molasses oozed down its walls and painted rust brown stains across its charcoal gray steel face. 

The leaking
[Arthur Jell was the overseer of the tank project and treasurer of the Purity Distilling Co., whose parent company, U.S. Industrial Alcohol (USIA), sold the alcohol to weapons manufacturers. Isaac Gonzales was the “general man” at the tank site, responsible for offloading the ships, monitoring the tank, and filling train cars, trucks, and wagons for transportation to a nearby distillery.]

Arthur Jell’s enthusiasm was waning and his irritation was increasing. The problem was Gonzales and his paranoia. USIA’s general man at the Commercial Street molasses tank stood to jeopardize Jell’s and the company’s success in the coming months if he could not be controlled. … Gonzales said the tank leaked from every seam every day, that workers on the dock had questioned him about it, and that the Italian neighborhood children gathered around the base of the tank each noon hour to collect molasses in their small pails. … Jell told Gonzales that there was nothing to worry about, that the tank was strong and sturdy, that some leaking was normal.

… [T]hen Gonzales had revealed that he had been sleeping at the tank for several months, bedding down in the pump-pit shack. “I’m afraid the tank is not safe, and if it should start to fall, I can sound a warning,” he said to Jell. Shocked by his employee’s admission, Jell had told him to go home at the end of his work shift. He reminded Gonzales that the tank had been caulked completely last year. “The tank still stands — the tank will stand,” Jell had said.

The delivery
[The Miliero, a 5,500-ton (4,990-metric-ton) steamer that could transport more than 1.5 million gallons (6 million liters) of molasses, made deliveries from Puerto Rico, Cuba, and the West Indies to USIA facilities in Baltimore, New York, and Boston.]

The warm molasses that had just flowed from the Miliero’s hold was mixing with the cold, thick molasses that had been congealing inside the tank for weeks, producing a bubbling churn that vibrated against the tank’s walls. The men on the Commercial Street wharf heard those walls groaning, had heard them groan many times before, usually immediately after a delivery, but it is unlikely that they knew that when warm and cold molasses mix, the reaction triggers a fermentation process that produces gas. And in a near-full tank, that gas increases the pressure against the steel walls.

There was one other thing these men could not have known. With the addition of the Miliero’s latest delivery, the tank was now filled to near capacity with 2.3 million gallons [9 million liters] of molasses that reached a height of 48 feet, nine inches [15 meters], and weighed 26 million pounds [12 million kilos].
Never in Boston’s history had an aboveground receptacle held more.

The flood
[Boston Police Patrolman Frank] McManus picked up the call box and began his report to headquarters. A few words into it, he heard a machine-gun-like rat-tat-tat sound and an unearthly grinding and scraping, a bleating that sounded like the wail of a wounded beast. McManus stopped talking, turned, and watched in utter disbelief as the giant molasses tank on the wharf seemed to disintegrate before his eyes, disgorging an enormous wall of thick, dark liquid that blackened the sky and snuffed out the daylight.

McManus froze momentarily, wanting to flee but unable to move. Then he recovered enough to bark into the phone words that sounded unbelievable to him, let alone the dispatcher at the other end:

“Send all available rescue vehicles and personnel immediately — there’s a wave of molasses coming down Commercial Street!”
Midday turned to darkness as the 2.3 million gallons [9 million liters] of molasses engulfed the Boston waterfront like a black tidal wave, 25 feet [8 meters] high and 160 feet [49 meters] wide at the outset. … Its crushing weight unleashed a terrible force that pulverized the entire waterfront and a half-mile [0.8-kilometer] swath of Commercial Street. Worse, too, unlike an ocean wave, whose momentum is concentrated in one direction, the wall of molasses pushed in all directions after it escaped the confines of the tank, so that it was more like four separate walls of viscous liquid smashing across the wharf and into the street. Add to that the speed with which the molasses traveled—35 miles [56 kilometers] per hour initially — the fact that the tank itself disintegrated into deadly steel missiles, and that thousands of fastening rivets turned into lethal steel bullets, and the result was destruction in a congested area equal to that of even the worst natural disaster.

The molasses tore the North End Paving Yard buildings into kindling, ripped the Engine 31 firehouse from its foundation and nearly swept it into the harbor … crushed freight cars, autos, and wagons, and ensnared men, women, children, horses, dogs, rats, wood, and steel. The molasses wave crashed across Commercial Street into brick tenements and storefronts, rebounded off the buildings, and retreated like the outgoing tide, leaving shattered windows and crushed walls in its wake.

… In minutes — in seconds — the landscape in the North End inner harbor area resembled a bombed-out war zone.

The cause
The cause of the disaster continued to be a source of debate carried out in the press. State chemist Walter Wedger, and U.S. inspector of explosives Daniel T. O’Connell, believed strongly in the “collapse theory”— that the tank disintegrated because of a combination of structural weakness and fermentation inside the tank. U.S. Industrial Alcohol attorney Henry F.R. Dolan continued to argue “beyond question” that outside influences, “evilly disposed persons,” were responsible for destroying the tank, insisting that the 50-foot receptacle [15-meter] was structurally sound.

The trial
[Of the company that manufactured the steel sections for the tank, the plaintiff attorney Damon Hall said:]  “… this reputable Hammond Iron Works [delivered steel] that was less than the specifications called for … they were like all other steel manufacturers in the country, hurrying to fill war orders, and in every instance, they furnished steel less than the specs called for.”

USIA lawyer Charles Choate claimed that the differences were not large enough to be a factor, and that there was a “recognized custom of tolerance” in accordance with guidelines set forth by the American Society for Testing Materials. “No inspector would be warranted in rejecting a plate if it came within the above-mentioned tolerances,” Choate argued.

Hall scoffed: “If a street car operator says, ‘I ordered axles that were sufficient to carry my car and not break, but there is a rule among car builders that they can furnish something less than I ordered and I accepted the axles under this rule. True, they are not what I ordered, and true, they are too light, but that is a rule that carbuilders follow.’ How long would the Supreme Court take to consider a defense of that kind?”

Hall had shown that the walls of the tank were up to 10 percent thinner, and thus, by definition, weaker, and less able to withstand pressure, than Hammond Iron Works had stated in the plans it had filed with the Boston Building Department.

Or put another way, the steel manufacturer had lied to the city.

[Nearly 920 witnesses spent nearly three years testifying at the trial. Eighteen months later, Col. Hugh Ogden, who presided over the trial, ruled that USIA was liable for the collapse of the tank.]

Ogden pointed out that the one area in which all experts agreed was that the tank should have been built with a greater factor of safety. “From the outset, I am faced with the defense experts saying that, while in their opinion the tank was safe as built, they would not build it the same way if they were called on today to design a tank to hold the same load … I cannot help feeling that in their position the defendant’s experts do not quite have the courage of their convictions as stated … what justification can they have for … strengthening the tank if the tank was properly designed and ‘safe’ for every purpose for which it was designed?”

Ogden recommended an estimated $300,000 in total damages, equivalent to about $30 million today, still a relatively small sum considering the harshness of his report on USIA’s negligence. … Hall was ecstatic about the victory, but dissatisfied with Ogden’s damage awards. He promptly insisted on a jury trial to determine damages. Choate and the other USIA attorneys immediately offered to negotiate, and the two sides reached a “private” agreement within hours. The company [agreed] to damage awards more than double those that Hugh Ogden had recommended. 

The aftermath
Shortly after the flood, the Boston Building Department began requiring that all calculations of engineers and architects be filed with their plans and that stamped drawings be signed, a practice that became standard across the country. The molasses case influenced the adoption of engineering certification laws in all states, as well as the requirement that all plans for major structures be sealed by a registered professional engineer before a municipality or state would issue a building permit. Interestingly, the Boston molasses flood did for building construction regulations nationwide what a subsequent Boston disaster, the great Cocoanut Grove nightclub fire, did for fire code laws.