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event.
RESOURCES: The key resource for the Scenario Process tool is the Operations Analysis. It provides
the script for the flow of events that will be visualized. Using the tool does not require a specialist.
Operational personnel leading or actually performing the task being assessed are key resources for the
OA. Using this tool is often entertaining, dynamic and often motivates even the most junior personnel in
the organization.
COMMENTS: A special value of the Scenario Process tool is its ability to link two or more individual
hazards developed using other tools into an operation relevant scenario.
EXAMPLES. Following is an example (Figure 1.1.4A) of how the Scenario Process tool might be used in
an operational situation.
Figure 1.1.4A Example Machine Movement Scenario
1.1.5 THE LOGIC DIAGRAM
FORMAL NAME: The Logic Diagram
ALTERNATIVE NAMES: The Logic Tree
PURPOSE: The Logic Diagram is intended to provide considerable structure and detail as a primary
hazard identification procedure. Its graphic structure is an excellent means of capturing and correlating
FROM MACHINE MOVEMENT EXAMPLE: As the machine was being jacked-up to
permit placement of the forklift, the fitting that was the lift point on the machine broke. The
machine tilted in that direction and fell over striking the nearby wall. This in turn broke a
fuel gas line in the wall. The gas was turned off as a precaution, but the blow to the metal
line caused the valve to which it was attached to break, releasing gas into the atmosphere.
The gas quickly reached the motor of a nearby fan (not explosion proof) and a small
explosion followed. Several personnel were badly burned and that entire section of the shop
was badly damaged. The shop was out of action for 3 weeks.
FAA System Safety Handbook, Appendix F
December 30, 2000
F-11
the hazard data produced by the other primary tools. Because of its graphic display, it can also be an
effective hazard-briefing tool. The more structured and logical nature of the Logic Diagram adds
substantial depth to the hazard identification process to complement the other more intuitive and
experiential tools. Finally, an important purpose of the Logic Diagram is to establish the connectivity and
linkages that often exist between hazards. It does this very effectively through its tree-like structure.
APPLICATION: Because it is more structured, the Logic Diagram requires considerable time and effort
to accomplish. Following the principles of ORM, its use will be more limited than the other primary tools.
This means limiting its use to higher risk issues. By its nature it is also most effective with more
complicated operations in which several hazards may be interlinked in various ways. Because it is more
complicated than the other primary tools, it requires more practice, and may not appeal to all operational
personnel. However, in an organizational climate committed to ORM excellence, the Logic Diagram will
be a welcomed and often used addition to the hazard identification toolbox.
METHOD: There are three types of Logic Diagrams. These are the:
Positive diagram. This variation is designed to highlight the factors that must be in place if risk is to be
effectively controlled in the operation. It works from a safe outcome back to the factors that must be in
place to produce it.
Event diagram. This variation focuses on an individual operational event (often a failure or hazard
identified using the "What If" tool) and examines the possible consequences of the event. It works from an
event that may produce risk and shows what the loss outcomes of the event may be.
Negative diagram. This variation selects a loss event and then analyzes the various hazards that could
combine to produce that loss. It works from an actual or possible loss and identifies what factors could
produce it.
All of the various Logic Diagram options can be applied either to an actual operating system or one being
planned. Of course, the best time for application is in the planning stages of the operational lifecycle. All
of the Logic Diagram options begin with a top block. In the case of the positive diagram, this is a desired
outcome; in the case of the event diagram, this is an operations event or contingency possibility; in the
case of the negative diagram, it is a loss event. When working with positive diagram or negative diagram,
the user then, reasons out the factors that could produce the top event. These are
entered on the next line of blocks. With the event diagram, the user lists the possible results of the event
being analyzed. The conditions that could produce the factors on the second line are then considered and
they are entered on the third line. The goal is to be as logical as possible when constructing Logic
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