AN ENGINEER`S VIEW OF HUMAN ERROR Trevor Kletz

AN ENGINEER’S VIEW OF
HUMAN ERROR
Trevor Kletz
Loughborough University
ALL ERROR IS HUMAN ERROR
AS:
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 MISTAKES
Teach 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
Human Error
If instructions are wrong (due
to ignorance or slips)
violations can prevent
accidents
A good method of
persuasion is to discuss
accidents and let those
present say what they think
should be done.
REASONS FOR MISMATCHES
Impossible tasks
Overload
Underload
Habit breaking
Mind-sets
PREVENTING MISMATCHES
• Change Work Situation
ie, 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 WELLTRAINED.
MANAGERS’ & DESIGNERS’
ERRORS:
are rarely slips as there is
usually time to check.
Sometimes violations.
Usually mistakes.
ERROR TYPE
ACTION
MISTAKES – Does not
know what to do
VIOLATIONS –
Decides not to do it
MISMATCHES –
Unable to do it
SLIPS & LAPSES OF
ATTENTION
Better training &
instructions/CHAOS
Persuasion/CHAOS
CHAOS
CHAOS
CHAOS = Change
Hardware And/Or Software
To face
mask
From air
bulb
Early chloroform dispenser
Typical Piping
Settling Leg arrangement
Phillips 66 Incident
October 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.
Furnace A
Furnace B
Temperature recorder
controller
& high temperature
trip
Temperature recorder
controller
& high temperature
trip
Auto
Hand control
Auto
Figure 5
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