15 Mar 2017

The Great Molasses Flood of 1919

From Nights, 7:13 pm on 15 March 2017

In 1919 a tank containing 13,000 metric tonnes of molasses collapsed in Boston, killing 19 people.

Science communicator and specialist in fluid dynamics Nicole Sharp has been investigating the tragedy to see how something as sticky, and normally, as slow moving as molasses, did so much damage.

Sharp told RNZ’s Bryan Crump the volume of molasses that flooded could have filled three and a half Olympic swimming pools.

Molasses is a by-product of sugar production, and is similar to treacle or malt.

“Molasses itself is very dense, it’s about one and half times heavier than water and the tank that it was being held in was very tall, it was over 15m tall.

“That’s a lot of weight and a lot of potential energy.

The tank holding the molasses was not structurally sound as its construction had not been overseen by somebody who had technical experience and could not read blueprints.

It leaked from its initial construction and eventually collapsed, releasing a giant sticky wave.

Unfortunately 21 people were unable to outrun the wave, nor could a number of horses which were in carts nearby.

“Historical estimates say that they think the molasses moved at about 56 kilometres per hour.”

The fact that the molasses was so heavy and piled up so high caused it to move so quickly at first.

“It takes about 30 to 60 seconds before the fact that molasses is extremely viscose actually makes a significant difference and… sort of takes over as dominating the sort of flow that you get.

“For that first half a minute to a minute it’s like you have a tsunami, only this wave is one and a half times denser than water.”

She says there are reports that people managed to ‘surf’ the wave.

“For some of them that pushed them to safety, for some of them that pushed them into heavy metal objects.

“There were also some people who were swept up by the molasses and thrown into the harbour.”

The temperature in Boston at the time of the incident was around 4°C. As rescuers worked to help survivors and recover bodies, they had to battle with the molasses becoming increasingly viscose.

“[It] would’ve started like honey but become like tar.”

While most things don’t tend to small quite as strongly when it’s cold, Sharp says her experiments have revealed molasses is still extremely pungent at 4°.

“There’s a wives tale that says that on a hot summer’s day, that that neighbourhood of Boston still smells like molasses, which I find hard to believe but it was certainly true for some amount of time.

“It has been almost 100 years, which is a long time for the smell of molasses to stick around.”

In the aftermath of the molasses flood, Sharp says there was a protracted legal argument about who was to blame.

“It was one of the early prototype for a class action law suit because so many people sued the company over this accident

“It caused a lot changes in how a companies were required to file with the city for the building of different structures and containers that were going to be holding different materials

Today there’s a small plaque marking the tragedy, but Sharp says most of the area is a park.

“There’s very little indication, other than this one very small plaque tucked away in a corner that this is where this massive disaster occurred.”

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