Page 102 - Serious Incident Prevention How to Achieve and Sustain Accident-Free Operations in Your Plant or Company

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80 Serious Incident Prevention

TABLE 7-2 continued
Suggested Mishap Probability Levels (Based on MIL-STD-882D) 7
Description* Level Specific Individual Item Fleet or Inventory**
Occasional C Likely to occur some time in Will occur several times
the life of an item, with a
probability of occurrence less
than 10 but greater than 10 -23
-2
in that life
Remote D Unlikely but possible to occur in Unlikely, but can reasonably
the life of an item, with a be expected to occur
probability of occurrence less
-3
-6
than 10 but greater than 10 in
that life
Improbable E So unlikely it can be assumed Unlikely to occur, but
occurrence may not be experi- possible
enced, with a probability of
occurrence less than 10 in that life
-6
* Definitions of descriptive words may have to be modified based on quantity of items involved.
** The expected size of the fleet or inventory should be defined prior to accomplishing an assessment
of the system.

Mishap Risk Assessment

Mishap classification by severity and probability can be performed by
using a mishap risk assessment matrix. This assessment allows one to as-
sign a mishap risk assessment value to a hazard based on its mishap sever-
ity and its mishap probability. This value is then often used to rank different
hazards as to their associated mishap risks. An example of a mishap risk as-
sessment matrix is shown in Table 7-3.

TABLE 7-3
Example Mishap Risk Assessment Values (Based on MIL-STD-882D) 8

Severity Probability: Catastrophic Critical Marginal Negligible
Frequent 1 3 7 13
Probable 2 5 9 16
Occasional 4 6 11 18
Remote 8 10 14 19
Improbable 12 15 17 20