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.

Many investigators consider only the do-ers.

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, perhaps beyond anyone’s.

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 MISTAKESProvide training and instructions.Make task easier.Teach diagnosis and treatment of

the unforeseen.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.

ERRORS BY SENIOR PEOPLE USUALLY HAVEMORE SERIOUS RESULTS THAN ERRORS BY THEIR JUNIORS.

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

ACTIONS IN ORDER OF CHOICE:1 Avoid hazards by IS design2 Passive protection3 Active protection4 Procedures5 Better observance of them

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 design2 Passive protection3 Active protection4 Procedures5 Better observance of them

OPERATORS ARE THE LAST LINE OF DEFENCE.

STRONG OUTER DEFENCES REDUCE THE DEMANDS ON THEM.

CAN THE TECHNIQUES OF BEHAVIOURAL SCIENCE BE EXTENDED TO INCLUDE 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.

Don’t blame designers. Ask why they make errors?

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

WE CAN GET BETTER

PUMPS, VALVES,

REACTORS ETC BUT

ONLY MARK 1 PEOPLE.