Human factors in high consequence manufacturing systems Page: 4 of 10
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modes of failure. Second, high consequence events tend to result from unique
permutations of events that defy prediction of their exact make-up. However, certain
attributes of a high consequence event may be highly predictable from an understanding of
system vulnerabilities.
Understanding the risks within a complex system may begin with identification of
hazards that are present. A good point to start is with a general consideration of what
energetic substances are present? With this knowledge, process steps may be reviewed
to identify where actions have the potential for initiating energetic release. Similar
questions might address what energy sources are available, or what materials are present
and what risks might they pose? The point of these analyses is to conduct a systematic
review that identifies vulnerabilities within a system.
Once cognizant of the hazards, the specific methodology applied may vary. For
instance, fault trees may be used to derive combinations of basic events that lead to
specific accidents (see Figure 1). Here, one works backwards from the accident to
determine the chain of events or combinations of events sufficient to produce the
accident. In contrast, event trees may be used to extrapolate possible accident scenarios
from basic events (See Figure 1). Following this approach, one first asks what might go
wrong at a given point and then, speculates on what might happen if it were accompanied
by other failures.
There are many analytic possibilities and whichever is employed, the result
should be a collection of events that contribute to accident scenarios. An important point
to remember is that no event, in itself, may be particularly worrisome. The history of
disasters suggests that they are rarely attributable to a specific cause, but instead, result
from the combination of many small events. The goal is to assure prevention of highly
salient modes of failure, as well as less consequential events that, under the right
circumstances, may contribute to a high consequence event.
Positive Controls
The prevention of accidents occurs through control of events that could contribute
to an accident. To discuss controls, three terms should be defined:
Risk State - condition in which potential exists for the occurrence of an event that may
lead to undesired consequences
Event - occurrence of the potential for undesired consequences
Consequence - results, such as injury, death or loss, whose potential defines the presence
of a risk
For the example shown in Figure 2, an open electrical circuit (the risk) would create a
condition in which there existed a potential for contact (the event) and given contact, a
potential would exist for electric shock (the consequence).
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Forsythe, C. & Grose, E. Human factors in high consequence manufacturing systems, article, November 1, 1997; Albuquerque, New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc698800/m1/4/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.