Case Studies

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Case Studies
On this page you can find 2 engineering case studies: The Boston Molasses Disaster and
Three Mile Island.

CASE STUDY 1
The Molasses Disaster of January 15, 1919

Disaster location

Can molasses kill people?
Yes, a molasses tank in Boston exploded with great force and flooded the streets with a
huge wave of molasses. It killed 21 people, crumpled the steel support of an elevated train,
and knocked over a fire station.

The Violence of the Explosion
Fermentation, a sudden rise in temperature, and an inadequate tank caused the tank
containing two million gallons of molasses to explode. The force of the explosion was so
great that:


Half-inch steel plates of the huge molasses tank were torn apart. (“Seeking Cause of
Explosion,” The Salem Evening News, January 16, 1919: 7.)



The plates were propelled in all directions, hard enough to cut the girders of the
elevated railway. (Ibid.)



After the explosion, a tremendous vacuum sucked into ruin buildings which had
withstood the primary blast. (Ibid.)



The vacuum also picked up a truck and dragged it across the street toward the
molasses tank. (“Big Molasses Tank Blast Kills Eleven,” The Boston Globe,
January 16, 1919: 8.)



An elevated train was lifted off the rails and fell onto the ties. (Ibid.)



Some buildings collapsed.



Some buildings were knocked off their foundations.



Some buildings were buried under the flood of molasses.

The disaster occurred at the Purity Distilling Company facility on January 15, 1919, an
unusually warm day. At the time, molasses was the standard sweetener in the United States.
Molasses can also be fermented to produce rum and ethyl alcohol, the active ingredient in
other alcoholic beverages and a key component in the manufacturing of munitions at the
time.
The stored molasses was awaiting transfer to the Purity plant situated between Willow
Street and what is now named Evereteze Way in Cambridge, Massachusetts. Near Keany
Square,[3] at 529 Commercial Street, a huge molasses tank 50 ft (15 m) tall, 90 ft (27 m) in
diameter and containing as much as 2,300,000 US gal (8,700,000 L) collapsed.
Witnesses stated that as it collapsed there was a loud rumbling sound like a machine gun as
the rivets shot out of the tank, and that the ground shook as if a train were passing by. The
collapse unleashed an immense wave of molasses between 8 and 15 ft (2.5 to 4.5 m) high,
moving at 35 mph (56 km/h) and exerting a pressure of 2 ton/ft² (200 kPa).

Causes

The cause of the accident is not known with certainty, but the company was found liable
and paid damages.
Several factors that occurred on that day and the previous days may have contributed to the
disaster. The tank was poorly constructed and insufficiently tested. Due to fermentation
occurring within the tank, carbon dioxide production may have raised the internal pressure.
The rise in the local temperatures that occurred over the previous day also would have
assisted in the building of this pressure. Records show that the air temperature rose from
2°F to 41°F (from −17°C to 5°C) over that period.
The failure occurred from a manhole cover near the base of the tank, and it is possible that
a fatigue crack grew here to criticality. The hoop stress is greatest near the base of a filled,
cylindrical tank. The tank had only been filled to capacity eight times since it was built a
few years previously, putting the walls under an intermittent cyclical load.
An inquiry after the disaster revealed that Arthur Jell, who oversaw the construction,
neglected basic safety tests, such as filling the tank with water to check for leaks. When
filled with molasses, the tank leaked so badly that it was painted brown to hide the leaks.
Local residents collected leaked molasses for their homes.
Based on the date of the accident, some have claimed that the tank may have been
overfilled so that the owners could produce as much ethanol for liquor as possible before
Prohibition came into effect. But the 18th Amendment, enacting Prohibition, did not
become law until more than a year later, and the Volstead Act did not ban the production of
industrial alcohol, so these claims are groundless.

Activities
1. Problem Solving


You are a team of engineers assessing the damage.



Discuss why the explosion was so violent.



What materials should have been used?



Discuss the ethical and technical issues you are faced with when building
production sites.



Present your problem to the class and how you solved it.

2. Negotiating
Negotiate the implementation of safety measures between:
1. Arthur Jell, the engineer who oversaw the construction.
2. A worker who tries to convince him that safety measures are necessary.

3. Emailing
1. Try to warn your superiors of the dangers.
2. Find the most appropriate (convincing) argumentative strategies.

CASE STUDY 2
Three Mile Island

Intro
At 4:00 AM on March 28, 1979, a reactor at the Three Mile Island nuclear power facility
near Harrisburg, Pennsylvania suddenly overheated, releasing radioactive gases. During the
ensuing tension-packed week, scientists scrambled to prevent the nightmare of a meltdown,
officials rushed in to calm public fears, and thousands of residents fled to emergency
shelters. Equipment failure, human error, and bad luck would conspire to create
America’s worst nuclear accident.

The nuclear power plant had two pressurized water reactors. One PWR was of 800 MWe
and entered service in 1974. It remains one of the best-performing units in USA. Unit 2 was
of 900 MWe and almost brand new.
The accident to unit 2 happened when the reactor was operating at 97% power. Iinvolved a
relatively minor malfunction in the secondary cooling circuit which caused the temperature
in the primary coolant to rise. This in turn caused the reactor to shut down automatically.
Shut down took about one second.
At this point a relief valve failed to close, but instrumentation did not reveal the fact, and so
much of the primary coolant drained away that the residual decay heat in the reactor core
was not removed. The core suffered severe damage as a result.
The scope and complexity of this reactor accident became clear over the course of five
days, as a number of agencies at the local, state and federal levels tried to solve the problem
and decide whether the on-going accident required a full emergency evacuation of the local
community, if not the entire area to the west/southwest. In the end, the reactor was brought
under control, although full details of the accident were not discovered until much later.

The Public
A series of misunderstandings caused, in part, by problems of communication within
various state and federal agencies. Public reaction to the event was probably influenced by
at least three factors:


Firstly, the release (12 days before the accident) of a popular movie called The
China Syndrome, concerning an accident at a nuclear reactor.



Secondly, there was a general feeling of a lack of official information in the initial
phases of the accident.



Lastly, many of the statements made by political and social activists long opposed to
nuclear power. A political storm was raging based on confusion and misinformation.

The accident was followed by essentially a complete cessation of nuclear construction in
the US. The impact of news stories about the accident was no doubt a factor, but other
factors were the availability of cheap natural gas, a transition away from manufacturing and
toward importation of consumer products, and federal policies that tolerated air pollution in
the interest of keeping coal-fired electricity cheap.

Lessons Learned
Three Mile Island has been of interest to human factors engineers as an example of how
groups of people react and make decisions under stress. There is consensus that the
accident was exacerbated by wrong decisions made because the operators were
overwhelmed with information, much of it irrelevant, misleading or incorrect.

As a result of the TMI-2 incident, nuclear reactor operator training has been improved.
Before the incident it focused on diagnosing the underlying problem; afterwards, it focused
on reacting to the emergency by going through a standardized checklist to ensure that the
core is receiving enough coolant under sufficient pressure.
In addition to the improved operating training, improvements in quality assurance,
engineering, operational surveillance and emergency planning have been instituted.
Improvements in control room habitability, “sight lines” to instruments, ambiguous
indications and even the placement of “trouble” tags were made; some trouble tags were
covering important instrument indications during the accident.
Improved surveillance of critical systems, structures and components required for cooling
the plant and mitigating the escape of radio nuclides during an emergency were also
implemented.
In addition, each nuclear site must now have an approved emergency plan to direct the
evacuation of the public within a ten mile Emergency Planning Zone (EPZ) and to facilitate
rapid notification and evacuation.
This plan is periodically rehearsed with federal and local authorities to ensure that all
groups work together quickly and efficiently.

What Happened
1. The reactor’s fuel core became uncovered and more than one third of the fuel
melted.
2. Inadequate instrumentation and training programs at the time hampered operators’
ability to respond to the accident.
3. The accident was accompanied by communications problems that led to conflicting
information available to the public, contributing to the public’s fears.
4. Radiation was released from the plant. The releases were not serious and were not
health hazards. This was confirmed by thousands of environmental and other
samples and measurements taken during the accident.
5. The containment building worked as designed. Despite melting of about one-third
of the fuel core, the reactor vessel itself maintained its integrity and contained the
damaged fuel.

What did NOT happen
There was no “China Syndrome”.
There were no injuries or detectable health impacts from the accident, beyond the initial
stress.

Longer-Term Impacts
Applying the accident’s lessons produced important, continuing improvement in the
performance of all nuclear power plants.
The accident fostered better understanding of fuel melting, including improbability of a
“China Syndrome” meltdown breaching the reactor vessel or the containment building.
Public confidence in nuclear energy, particularly in USA, declined sharply following the
TMI accident. It was a major cause of the decline in nuclear construction in the 80s & 90s.

The TMI-2 Cleanup
The cleanup of the damaged nuclear reactor system at TMI-2 took nearly 12 years and cost
approximately US$973 million. The cleanup was uniquely challenging technically and
radiologically. Plant surfaces had to be decontaminated. Water used and stored during the
cleanup had to be processed. And about 100 tonnes of damaged uranium fuel had to be
removed from the reactor vessel — all without hazard to cleanup workers or the public.
A cleanup plan was developed and carried out safely and successfully by a team of more
than 1000 skilled workers. It began in August 1979, with the first shipments of accidentgenerated low-level radiological waste to Richland, Washington. In the cleanup’s closing
phases, in 1991, final measurements were taken of the fuel remaining in inaccessible parts
of the reactor vessel. Approximately one percent of the fuel and debris remains in the
vessel.
In February 1991, the TMI-2 Cleanup Program was named by the National Society of
Professional Engineers as one of the top engineering achievements in the U.S. completed
during 1990.

Activities
1. Problem Solving


First read about the nuclear accident at Three Mile Island and discuss what went
wrong.



Why was it that even though no one was killed America is still doubtful about
nuclear energy?



Could this happen in France?



Present your problem to the class and how you solved it.

2. Negotiating

Team 1: You are the French government and a group of French engineers. (choose your
company)


Negotiate the sale of French nuclear power plants to the US.



Explain why your technology won’t create a new Three Mile Island.



Think about the arguments you might use to sell your product. What is the current
energy environment like?



Think about the American psyche when it comes to nuclear power.

Team 2: You are the US government and a group of American engineers. (choose your
company)


Negotiate the sale and set up of French nuclear power plants in the US.



Think about from where America gets its energy?



Can it continue producing energy according to current methods?

3. Emailing
Write an email to the clean-up team. Use accurate and operational directions.

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