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