Check is the most important task of human workers to keep safety. However, ordinary styles of check seem not enough stable. This presentation proposes 3 techniques to improve human reliability of check.

1. Task 1 hed
Time
Action
Emerg
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Finis
Improving Human Reliability on
Checking
Toru Nakata (AIST, Japan)
IDHF 2014 (Nov. 26, 2014) 1
Task 2
Task 3
Action
Emerg
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hed Action
Action
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hed
Action
Check
Check

2. 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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3. Three points to make check more reliable
1. ‘Staticization’ of workflow
2. Independent triggering of checks
3. Objective questioning
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4. 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.

5. Check under standstill is reliable
• Counting moving targets is difficult.
• Static work process allows easy checking
under standstill condition.
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6. Standstill at end of work
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7. 2) Independent triggering of checks
• Ordinary “Check after action” scheme is not
safe.
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8. “Check after action” scheme
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Emerge
nce Check
Emerge
nce Check
Emerge
nce Check
Time
Action
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hed
Task 1
Task 2
Task 3
Action
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hed
Action
Action
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hed
Action

9. 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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10. 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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Time
Action
Emerge
nce
Finis
hed
Task 1
Task 2
Task 3
Action
Emerge
nce
Finis
hed
Action
Action
Emerge
nce
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hed
Action
Check
Check

11. 3) Objective Questioning
Yes/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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12. Examples for industry
Yes/No
Interrogation
“Have you turned on the
light?”
Less
objectivity
Question
without hints
“When did you turn on
the light?”
Question
requiring
rebut
“Why did you turn on
the light?”
More
objectivity.
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13. 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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