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Diagrams, but it is more important to keep the hazard identification goal in mind than to construct a
masterpiece of logical thinking. Therefore, a Logic Diagram should be a worksheet with lots of changes
and variations marked on it. With the addition of a chalkboard or flip chart, it becomes an excellent group
tool.
Figure 1.1.5A below is a generic diagram, and it is followed by a simplified example of each of the types
of Logic Diagrams (Figures 1.1.5B, 1.1.5C, 1.1.5D).
FAA System Safety Handbook, Appendix F
December 30, 2000
F-12
Figure 1.1.5A Generic Logic Diagram
EVENT
PRIMARY
CAUSE
SUPPORTING
CAUSE
ROOT CAUSE
PRIMARY
CAUSE
PRIMARY
CAUSE
SUPPORTING
CAUSE
SUPPORTING
CAUSE
SUPPORTING
CAUSE
ROOT CAUSE
Figure 1.1.5B Positive Event Logic Diagram
TIEDOWN PROPERLY ETC. ETC.
ACCOMPLISHED
CLEAR
PROCEDURES
GOOD
MOTIVATION
GOOD
TRAINING
CONTAINER STAYS
ON VEHICLE
FAA System Safety Handbook, Appendix F
December 30, 2000
F-13
Figure 1.1.5C Risk Event Diagram
FORKLIFT PROCEDURES
VIOLATED-EXCEEDED
LIFT CAPACITY
ETC.
LIFT MECHANISM
FAILS, LIFT FAILS ETC.
LOAD BOUNCES
TO THE GROUND
CONTAINER RUPTURES,
CHEMICAL AGENT
LEAKS
FAA System Safety Handbook, Appendix F
December 30, 2000
F-14
Figure 1.1.5D Negative Event Logic Diagram
CONTAINER FALLS
OFF VEHICLE &
RUPTURES
ETC.
FAILURE OF
TIEDOWN GEAR ETC.
FAILURE TO INSPECT
& TEST TIEDOWNS
IAW PROCEDURES
VARIOUS
ROOT CAUSES
ETC.
RESOURCES: All of the other primary tools are key resources for the Logic Diagram, as it can
correlate hazards that they generate. If available, a safety professional may be an effective facilitator for
the Logic Diagram process.
COMMENTS: The Logic Diagram is the most comprehensive tool available among the primary
procedures. Compared to other approaches to hazard identification, it will substantially increase the
quantity and quality of hazards identified.
EXAMPLE: Figure 1.1.5E illustrates how a negative diagram could be constructed for moving a heavy
piece of equipment.
FAA System Safety Handbook, Appendix F
December 30, 2000
F-15
Figure 1.1.5E Example Negative Diagram
Machine fails when
raised by the forklift
Machine strikes an
overhead obstacle
and tilts
The load shifts due
to lift point or
failure to secure
Improper operator
technique (jerky,
bad technique)
Load is too heavy
for the forklift
Mechanical failure
of
the forklift
The machine
breaks at the point
of lift
Improper operator
technique (jerky,
bad technique)
Improper operator
technique (jerky,
bad technique)
Improper operator
technique (jerky,
bad technique)
Improper operator
technique (jerky,
bad technique)
Improper operator
technique (jerky,
bad technique)
Each of these items may be taken to a third level. For example:
The Logic Diagram pulls together all sources of hazards and displays them in a graphic
format that clarifies the risk issues.
1.1.6 THE CHANGE ANALYSIS
FORMAL NAME: The Change Analysis
ALTERNATIVE NAMES: None
PURPOSE: Change is an important source of risk in operational processes.
Figure 1.1.6A illustrates this causal relationship.
FAA System Safety Handbook, Appendix F
December 30, 2000
F-16
Figure 1.1.6A Change Causation
System
Impacted
Stress is
Created
Risk Controls
Overcome
Risk
Increases
Losses
Increase
Introduce
Change
Some changes are planned, but many others occur incrementally over time, without any conscious
direction. The Change Analysis is intended to analyze the hazard implications of either planned or
incremental changes. The Change Analysis helps to focus only on the changed aspects of the operation,
thus eliminating the need to reanalyze the total operation, just because a change has occurred in one area.
The Change Analysis is also used to detect the occurrence of change. By periodically comparing current
procedures with previous ones, unplanned changes are identified and clearly defined. Finally, Change
Analysis is an important accident investigation tool. Because many incidents/accidents are due to the
injection of change into systems, an important investigative objective is to identify these changes using the
Change Analysis procedure.
APPLICATION: Change analysis should be routinely used in the following situations.
　
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