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AN ENGINEER’S VIEW OF HUMAN ERROR
Trevor Kletz
Loughborough University
ALL ERROR IS HUMAN ERRORAS:
People have to decide what to do.People have to decide how to do it.
People have to do it.
The concept of human error
is unhelpful as it lumps
together different types
which need different
actions.
TYPES OF HUMAN ERROR
1 MISTAKES
Does not know what to do -
Poor training or instructions.
Intention wrong.
,
TYPES OF HUMAN ERROR
2 VIOLATIONS
Does not want to do it -
Poor motivation
TYPES OF HUMAN ERROR
3 MISMATCHES
Is not able to do it -
Beyond ability
TYPES OF HUMAN ERROR:
4 SLIPS OR LAPSES OF ATTENTION.
Inevitable from time to time.
THIS CLASSIFICATION HELPS US SEE THE BEST METHODS OF PREVENTION FOR EACH TYPE OF ERROR.
PREVENTING MISTAKESTeach flexibility
Provide training and instructions
Make task easier
Avoid contradictory instructions
(What you don’t say is as
important as what you do say.)
Human Error
Are your instructions written to help the readers or protect
the writer?
PREVENTING VIOLATIONS
• Explain need
• Make task easier
• Checks and audits
• Don’t turn a blind eye
BEFORE BLAMING SOMEONE ASK:
Were the rules known & understood?
Was it possible to follow them?
Were the reasons for them known?
Were previous violations overlooked?
Did the rules cover the problem?
Was he/she trying to help?
Human Error
AN IRREGULAR VERB
• I SHOW INITIATIVE
• YOU BREAK THE RULES
• HE IS TRYING TO WRECK THE JOB
If instructions are wrong (due to ignorance or slips) violations can prevent accidents
Human Error
A good method of
persuasion is to discuss
accidents and let those
present say what they think
should be done.
Impossible tasksOverloadUnderloadHabit breakingMind-sets
REASONS FOR MISMATCHES
PREVENTING MISMATCHES
• Change Work Situationie, design or methods of
working
PREVENTING SLIPS AND LAPSES OF ATTENTION
(Intention correct but not fulfilled)
• Change work situation
SLIPS & LAPSES OF
ATTENTION OCCUR ONLY
WHEN PEOPLE ARE WELL-
TRAINED.
MANAGERS’ & DESIGNERS’
ERRORS:
are rarely slips as there is
usually time to check.
Sometimes violations.
Usually mistakes.
CHAOSSLIPS & LAPSES OF ATTENTION
CHAOSMISMATCHES –Unable to do it
Persuasion/CHAOSVIOLATIONS –Decides not to do it
Better training & instructions/CHAOS
MISTAKES – Does not know what to do
ACTIONERROR TYPE
CHAOS = Change Hardware And/Or Software
Early chloroform dispenser
From air bulb
To face mask
Typical Piping Settling Leg arrangement
Phillips 66 IncidentOctober 23, 1989
•23 lives lost
• More than 130 people injured
• $750 million in property damages
• Explosive Force = 2.4 tons of TNT
DURING ROUGH WEATHER
WATER ENTERED SHIP’S
ENGINE ROOM THROUGH
VENTILATION INTAKE AS
LOUVRES WERE
INSTALLED INCORRECTLY.
Wrong Right
WATER FELL ON
SWITCHBOARD.
ALL POWER LOST.
SHIP TOWED TO PORT.
RECOMMENDATION:
INSPECT LOUVRES.
NO MENTION OF DESIGN
PROBABILITY OF SUCCESS -TOTAL
0.9999 x 0.9995 x 0.9998 x 0.9985 x 0.9998 x 0.9996
= 0.9971
ie, three or four errors can be expected in every 1000 operations.
Figure 5
Temperature recordercontroller
& high temperature trip
Temperature recordercontroller
& high temperature trip
Furnace A Furnace B
Auto Hand control Auto Hand control
ACTIONS IN ORDER OF
CHOICE
1 Avoid hazards by IS design
2 Passive protection
3 Active protection
4 Procedures
5 Behavioural science
OPERATORS ARE THE LAST LINE OF DEFENCE.
STRONG OUTER DEFENCES REDUCE THE DEMANDS ON THEM.
CAN THE TECHNIQUES OF
BEHAVIOURALSCIENCE BE
EXTENDED TO INCLUDEE
DESIGNERS AND
MANAGERS?
DON’T ASK FOR CAUSES.ASK WHAT WE SHOULD DO DIFFERENTLY.
DON’T SAY AN ACCIDENT WAS DUE TO POOR DESIGN, MAINTENANCE, OPERATION etc.
SAY IT COULD BE PREVENTED BY BETTER DESIGN, MAINTENANCE, OPERATION etc.
Blaming human error
diverts attention from
what can be done by
better engineering.
ERRORS BY DESIGNERS
TURN OPERATORS’
SLIPS INTO ACCIDENTS.
We cannot change the human
condition but we can change the
conditions in which humans work.
- James Reason
Man was a creature made at the
end of a week’s work…. when
God was tired. - Mark Twain
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