A presentation by:
Dr. Alexander Cohen
Hazmat, risk analysis division
In this presentation:
Task analysis goals
Failure modes of humans
HAZOP of tasks
Basic task analysis
Quantitative analysis
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Task analysis goals
The term ‘task analysis’ refers to the analysis of the
human interface with the process.
Protecting the (human) operator.
Human errors reduction.
Inherently safe processes.
Human engineering aspects.
Standing operating procedures (SOP) and safety SOP
(SSOP).
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In many cases task analysis is only a by-product of
the risk analysis due to the complexity of the analysis
of human behavior.
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Failure modes of humans
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An operator in a plant
Plant (perception)
Detection
Information
processing
Plant (real)
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Operation
Human errors – Human mistakes
Errors
Operator is skilled.
Incorrect/absent information.
Incorrect/absent interface.
Environmental conditions.
Mistakes
?
And sometimes, the operator just slip, hang on the first thing he can grab and Unfortunately it is an emergency releasing valve, and the rest is history…
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Basic modes of human errors
Omission of a task (the oops syndrome).
Commission of an extra action.
Changes in operator’s physical conditions.
Changes in operator’s mental conditions.
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Psychological failure modes
Failure to consider special circumstances.
Shortcut invoked.
Stereotype takeover.
Need for information not prompted.
Misinterpretation.
Assumption.
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Psychological failure modes (cont.)
Forget isolated acts.
Mistake among alternatives.
Place-losing error.
Other slip of memory.
Motor variability.
Topographic or spatial orientation inadequate.
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Environmental aspects
Work at heights
Dust.
Slippery floor.
Noise.
Limited approach.
Radiation.
Hot/cold surfaces.
Ventilation.
Rails.
Visibility.
Vibrations.
Heat/cold stress
Repulsive odor.
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Ineffectiveness
Response to gauge in auto-mode (100%).
Response to gauge in manual mode (10%).
Failure to confirm shutdown (15%).
Response to multiple alarms (15%).
Response to single alarms (2%).
Critical action under high stress (30%).
Critical action – SOP available (10%).
Procedure on a checklist (2%).
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Task analysis methodology
This analysis could be carried out in many methods such as:
HAZOP of operating procedures.
Task analysis
Workplace study (occupational health & hygiene).
Ergonomic (human engineering) surveys.
Performance analysis.
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Hazard & operability study
Carried out as a standard HAZOP with the application
of the guidewords on tasks rather than process nodes.
(In many batch processes a HAZOP of the tasks gives better
results than a HAZOP of the process diagrams)
.
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Task HAZOP
Changing a flat tyre
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Changing tyre
SOP - summary
1.
2.
3.
4.
Park the car in a safe place.
Jack up car.
Remove flat tyre and replace with spare.
Un-jack car.
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Changing tyre
SOP breakdown
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Park in a safe place.
Identify flat tyre. Get wheel spanner and jack.
loose nuts.
Jack up car.
Unscrew nuts and remove flat tyre.
Fetch spare and fit in place.
Screw nuts.
Un-jack car.
Tight nuts.
Get your staff and …
drive safely …
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JACK UP CAR
GUIDE WORDS
NO or Not
MORE
LESS
AS WELL AS
PART OF
REVERSE
OTHER THAN
FASTER/SLOWER
(THAN)
MEANINGS
The complete negation of these
intentions.
Quantitative increases or decreases
A qualitative increase
A qualitative decrease
The logical opposite of the intention
Complete substitution
Timing and synchronization issues.
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HAZOP example
Jack up car
Guideword
No
No
More
Less
Less
Deviation
Car not lifted
Car not lifted
Car lifted too high
Cause
Incorrect jack placement
Jack malfunctioning
Driver unaware of risks
Car hardly being
lifted
Car hardly being
lifted
1) Incorrect jack
placement
2) Driver hasn't enough
power to operate jack.
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Suggestions
Mark the jack socket.
Hitchhike!
Limit jack max height.
Use a car-specific jack.
1) See above
2) Use a hydraulic jack
as a standard
HAZOP example
Jack up car
Guideword
As well as
Part of
Deviation
Jack may catch
sleeves, dresses etc.
Car de-jacked.
Reverse
Car de-jacked.
Other than
Before
After
Malfunctioning at
nighttime.
Car slides forward
Cause
Jack slides on a greasy
surface.
Mechanism has broken
while car is up.
Darkness
Driver has forgotten to
pull hand break.
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Suggestions
Isolate the jack's
mechanism.
Use rubber to increase
friction.
1) Revise test criteria.
2) Determine an
expiration date.
Add a flashlight to the
standard tool kit.
Add instruction to the
manual.
HAZOP: pros
Structural.
Thorough.
Technical solutions to human engineering
problems.
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HAZOP: cons
Time consuming.
Requires a specific HAZOP team*.
Many uncertainties in the design phase.
Many subjects fall into ‘other than’.
*In many cases, the technical team doesn’t know how to assess human
engineering aspects.
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Basic tasks analysis
(the WH-questions approach)
Task analysis keywords
•
WHAT
•
WHEN
•
WHERE
•
HOW
•
WHO
&
•
WHY
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Questions
WH
question
What
When
Proposal
What has to be
done
Why
question
Why, for what
purpose?
When is it done?
Why then?
Alternative
What if omitted?
What else might be done as well
as?
What else might be done instead?
What else can go wrong?
What if done earlier, later, before,
after or out of sequence?
What, When, How, Who, Where
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Questions (cont.)
WH
question
How
Who
Where
Proposal
How is it done?
How much is it
done?
How fast is it done?
How often is it
done?
Who does it?
Where is it done?
Why
question
Why that
way?
Why them?
Why there?
Alternative
What
What
What
What
if done some other way?
if more or less done.
if quicker or slower?
if done more or less often?
Who else can do it?
What if it done elsewhere?
What, When, How, Who, Where
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n-Pentane filling
TGC system, simplified
1.
2.
3.
4.
…
Verify a low level in the tank.
Open V1, and the two connected valves V2,3.
Activate the pump.
Monitor filling and close pump when level reaches high level indication.
…
vent
LI
HL
V1
filter
Manual pump
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V2,3
n-pentane
n-Pentane filling
Asking questions
What
Question
What has
to be done
What if
omitted?
What else
can go
wrong?
When
When is it
done?
Answer
Operator monitors tank filling and
stops the pump when level reaches
high-level indication.
If reaches overflow level the liquid
should run to the suction line and
therefore flooding is prevented.
If overflow line fails to discharge
excess of fluid pentane might be spilled
out through the vent causing a series
danger of gas explosion.
It should be done immediately after
low-level signal indicate low-level.
If done later, might affect the TGC
performance.
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n-pentane
Suggestions
Consider on site
gas detector +
alarm
Consider installing
a LALL.
n-Pentane filling
Asking questions (cont.)
Who
Question
Who does
it?
How
What if
done some
other way?
Where
What if
done
elsewhere?
Answer
Normally by the TGC operators.
However, during nights and weekends,
any other operator can carry it out.
It is strictly prohibited to use any
alternative way for filling the tank (due
to static electricity hazards).
Impossible.
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n-pentane
Suggestions
Make sure that all
operators are well
trained.
Make sure that
manhole is sealed
and cannot be
opened easily.
n-Pentane filling
Cleaning the filter
1.
2.
3.
4.
5.
6.
7.
n-pentane
…
NEVER open filter cop when pump is operating.
Insert a large metal bowl below the filter to collect possible spillage.
Unscrew the cap cautiously by hand.
If stuck DO NOT attempt to use any tools.
Wash the cop with small portions of pentane until well cleaned.
Re-screw the cop by hand.
Activate the pump for 5 seconds (V2,3 closed!) and see if cop leaks.
…
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n-Pentane filling
Cleaning the filter (cont)
•
•
n-pentane
Unscrew the cop cautiously by hand.
If stuck DO NOT attempt to use any tools.
What, When, How, Who, Where
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Quantitative analysis of human activities
In fault trees.
In event trees.
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Failure densities
Generic task
Range
Average
a) Totally unfamiliar, performed at speed, with no real idea of consequences.
0.35-0.97
0.55
b) Shift or restore system to a new or original state on a single attempt without 0.14-0.42
supervision or procedure
0.26
c) Complex task requiring a high level of comprehension or skill.
0.12-0.28
0.16
d) Fairly simple task performed rapidly or given scant attention.
0.06-0.13
0.09
e) Routine, highly practiced, rapid task involving relatively low level of skill.
0.007-0.045
0.02
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Failure densities (cont.)
Generic task
Range
Average
f) Restore or shift a system to original or new state following procedures, with some 0.0008-0.007
checking.
0.003
g) Completely familiar highly practiced routine task performed by well-trained 0.00008-0.009
individual with time to effect recovery.
0.0004
h) Miscellaneous task for which no description can be found
0.11-0.008
0.03
0.04-0.27
0.088
i) 2
nd
order error
*
*2nd order errors are errors composed by a sequence of ‘simple’ human errors.
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n-Pentane filling
Event tree
n-pentane
0.95
Operator fills OK 0.95
Operator stops 0.9
0.00041
Alarm sounds 0.9
Overflow failure 0.01
Operator fails 0.1
0.0000045
Alarm fails 0.1
0.00005
Failure to detect HL 0.05
Overflow functions 0.99
0.0495
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Task Analysis
WORKSHOP
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Tasks
Task analysis or HAZOP of SOPs.
•
Uranium oxide / graphite – mixing.
•
Uranium oxide / graphite – pill making
•
Methylal filling
•
Isobutane inspection
Action items
1. Task analysis or HAZOP of SOPs.
2. Event tree for the task.
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Tasks (alternative)
Do it yourself…
•
Choose a task that you are familiar with.
•
Write your own SOP (name it draft and keep it).
•
Analyze your task (choose a method as convenient).
•
Rewrite the SOP (if required, and name it final).
•
Compare the draft SOP with the final SOP.
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