A very detail case studies of various disasters based on different human factors and organizational factors

1. Human Failures Involved
in Accidents
Flixborough Disaster, 1974
Three Mile Island, 1979
Space Shuttle Challenger, 1986
Chernobyl, 1986
King’s Cross Underground Fire, 1987

2. Flixborough Disaster, 1974
Staffing • The works engineer had left early in the year and had
not yet been replaced.
• At the time the bypass line was being planned and
installed, there was no engineer on site with the
qualifications to perform a proper mechanical design,
or to provide critical technical review on related
issues. There were chemical and electrical engineers
on staff, but no other mechanical engineers.

3. Flixborough Disaster, 1974
Lack of
Hazard
Identification
• In the opinion of the investigators, the urgency to resume
production distracted staff from the sort of critical consideration
of their plans that could have identified the hazards involved
(i.e., they did not intentionally establish an unsafe condition
but, rather, failed to fully assess the significance of what they
were doing).
Work Load • The fact that the works manager position was vacant also shifted
workload to remaining staff, contributing to the distractions
discussed above. The report implies that company management
was not aware of the effect of the short staffing on the
performance of the facility staff involved in the modification.

4. Flixborough Disaster, 1974
Lack of
Knowledge
• While calculations were made to confirm that the 20-inch pipe could
withstand the normal working pressure, no consideration was given to the
bending moments or hydraulic thrusts that would be imposed on the assembly
due to its dogleg configuration . There was no reference made to vendor
manuals for the expansion bellows, nor to relevant British Standards.
Lack of
Quality
Assurance
• There were no quality assurance checks made on the fabrication or
installation of the assembly other than a leak check at approximately 130 psi
(for comparison, the relief valves [RVs] on the reactor system were set to
open at approximately 155 psi). Applicable British Standards required that the
assembly be tested at a pressure of 1.3x 105 the system design pressure,
which would have been above the RV set pressure.

5. Three Mile Island, 1979
Lack of
Knowledge
• The event that occurred in 1979, caused by two workers who
made a mistake cleaning valves with air pressure hoses,
resulted in much change for nuclear safety in the world.
Lack of
Training
• Workers in the control room faced a situation that they had not
prepared for in any of their training, and were forced to make
decisions on the spot. Additionally, there were flaws in the
control panel that caused the workers to be unaware that a
valve had been left open.

6. Three Mile Island, 1979
Design
Deficiencies
• The loss of normal feed water which is an anticipated
operating occurrence leads to the opening of the pressurizer
relief valve which is an other anticipated operating
occurrence;
• A break in the steam phase of the pressurizer is not
considered. There is no procedure to identify and manage
this event and the operating staff is not trained for it;
• The actuation of the emergency core cooling system does not
actuate a complete containment building isolation.

7. Three Mile Island, 1979
Multiple latent
deficiencies
(organization, m
aintenance,
quality, ...
• The pressurizer relief valve had been known to be leaking for a
while but the repair work was postponed so increasing the
probability of a jammed open valve and depriving the
operators of a way to identify the valve situation: the
temperature of the pressurizer relief line;
• The closed connecting valves of the steam generators auxiliary
feed water system added a complete loss of feed water system
to the complete loss of emergency core cooling system and
focused the attention of the operating team;
• An effluent tank was leaking;
• The iodine filters in the auxiliary building had poor efficiency.

8. Space Shuttle Challenger,1986
Inadequate
Design
• The O-Ring was a rubber seal component in the solid rocket booster (SRB),
its purpose was to stop leaks. Due to extremely cold temperature on the
day of launch, the O-Ring lost its elastic property and became brittle
(inflexible), allowing a leak and resulting in explosion.
lack of
understanding
• During the conference call with the management team and the
engineering team, the management team did not seem to understand
that a failure in the O rings system would result into fatalities and the
engineers also did stand against the launch and refusing that the launch
would take place as the life of 7 astronauts have a very big chance of
being lost they issued a recommendation that the launch shouldn’t
happen, instead of recommending they should of used another world in
order to express the severity of the problem

9. Space Shuttle Challenger,1986
Faulty
Judgement
• managers decided to launch despite record low temperatures
and ice on launch pad
Management
Problems
• NASA managers had known since 1977 that the design of the
SRBs contained a potentially catastrophic flaw in the O-rings,
but they had failed to address this problem properly.
• NASA managers also disregarded warnings from engineers
about the dangers of launching posed by the low temperatures
of that morning, and failed to adequately report these
technical concerns to their superiors.

10. Chernobyl, 1986
Wrong
Procedure
• Correct procedure was down the reactor to 700-MW but it
was down to 200 MW. At this Power reactor became unstable.
Lack of
Knowledge
• Operator error was probably due to their lack of knowledge
of nuclear reactor physics and engineering, as well as the
lack of experience and training. Personnel had an
insufficiently detailed understanding of technical procedures
involved with the nuclear reactor, and knowingly ignored
regulations to speed test completion

11. Chernobyl, 1986
Inadequate
Design
• The reactor had a dangerously large positive void coefficient.
The void coefficient is a measurement of how a reactor
responds to increased steam formation in the water coolant.
Most other reactor designs have a negative coefficient, i.e.
the nuclear reaction rate slows when steam bubbles form in
the coolant, since as the vapor phase in the reactor
increases, fewer neutrons are slowed down. Faster neutrons
are less likely to split uranium atoms, so the reactor
produces less power (a negative feed-back)

12. King’s Cross Underground Fire, 1987
Lack of
Training
• The staff was not properly trained for emergency fire.
• Many times fire had been detected most of time due to
smokers, dropping cigarette butts and matches.
Unclean
Escalators
• Lack of cleaning of wooden escalators causes flammable
mixture of lubricating oil and dirt ( tickets, hair, Pouches)
• This flammable mixture got ignited due to smokers cigarette
butts.

13. King’s Cross Underground Fire, 1987
Design of
Escalators
• Wooden escalators ignited quickly.
• Inclination of Escalators help in Trench effect.
• No fire detection system was present.