Improving Human Reliability on Checking

Toru Nakata (AIST, Japan)

IDHF 2014 (Nov. 26, 2014) 1

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About me

• An expert of IEC TC/SC65A– Administrating IEC 61508 “Functional Safety”

• TC is now discussing expansion of 61508 to cover human factors.– How can humans undertake safety critical

tasks?

• Research Question: How to evaluate/design the reliability of safety-critical systems including human?

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Three points to make check more reliable

1. ‘Staticization’ of workflow

2. Independent triggering of checks

3. Objective questioning

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1)‘Staticization’• Changing dynamic process to static process

• Operation becomes safe and easy if you can halt it at any timing.

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‘Dynamic’ Process: The operators have to continue the work unless the beam falls.

‘Static’ Process: The operator can take a break. The supporting pillars make the process static.

Check under standstill is reliable

• Counting moving targets is difficult.

• Static work process allows easy checking under standstill condition.

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Standstill at end of work

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2) Independent triggering of checks

• Ordinary “Check after action” scheme is not safe.

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“Check after action” scheme

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2) Independent triggering of checks

• Ordinary “Check after action” scheme is not safe.1. The same person undertakes both of action and

check for it. – When other workers are busy, the same person have

to do both. – Check will be less objective.

2. The worker may omit both of “action” and “check”.– If he forget the action, he also omit the check.– Dependency is the problem.

• The trigger of the check is the end of the action.

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Independent triggering

• Check gates should be set.– All of workflows should be stopped and checked.

• Operators can check other people’s results.• Resistance against omission.

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3) Objective QuestioningYes/No Interrogation

“Is Toronto the capital of Canada?”

Less objective(Bad checklists contain many of those questions.)

Question without hints

“What is the capital of Canada?”

Question requiring rebut

“Is New York the capital of Canada, isn’t it?”

More objective

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Examples for industryYes/No Interrogation

“Have you turned on the light?”

Less objectivity

Question without hints

“When did you turn on the light?”

Question requiringrebut

“Why did you turn on the light?”

More objectivity.

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Conclusion

1. ‘Staticization’ of workflow

2. Independent triggering of checks

3. Objective questioning

• Those techniques will improve reliability of humans undertaking critical checking.

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