Group presentation:

1
Group presentation

• Normal Accident at Three Mile Island
• by Charles Perrow

2
The accident at Three Mile Island

• The Three Mile Island (TMI) Unit 2 nuclear plant
  near Harrisburg, Pennsylvania, on March 28, 1979.
• The most serious nuclear power plant accident to
  date.
• TMI is an example of the accident potential of
  complex systems.
• Next the accident

3
The plant
Maintenance of complex systems have big room for
errors. In retrospective operators conceded that
someone didnt open the valves.
This is actually the one indicator thats
wrong. Misinterpretation of a situation or an
order. If your action results in an expected
result, you validate your action as successful.
This is not always right. In fact, if the result,
in your eyes, are correct and they do not
correspond to the result happening in the real
world, your actions may lead to disaster.
Pressure increases Pressure decreases
4
The plant

• A new shift supervisor arrives and discovers the
  open valve
• Situation improves temporarily

5
Again the operators presumed that instruments
were malfunctioning, and quickly dismissed the
sudden pressure surge in the containment
building. Only one man guessed that the surge
was caused by an explosion, but didnt warn
others that they might expect another
The plant

• The fuel rods have become so hot that they begin
  reacting with the water, producing hydrogen
• Pockets of hydrogen gas emerge inside the core,
  which then explode thirty-three hours after the
  accident began

6
Essentials (1)

• Lesson In complex systems any part of the system
  might be interacting with other parts in an
  unanticipated ways.
• In this case where several indicators gave the
  operators different information the operators
  assumed the indicators were wrong, because they
  didnt expect this complex scenario.

7
Essentials (2)

• Would better organization help, or money and
  resources for better people and equipment?
• According to Charles Perrow No.