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Supporting rationale for assigning a mishap probability is documented in hazard analysis
reports. Suggested qualitative mishap probability levels are shown in Table A-II.
TABLE A-II. Suggested mishap probability levels.
Description* Level Specific Individual Item Fleet or Inventory**
Frequent A Likely to occur often in the
life of an item, with a
probability of occurrence
greater than 10-1 in that life.
Continuously
experienced.
Probable B Will occur several times in the
life of an item, with a
probability of occurrence less
than 10-1 but greater than 10-2
in that life.
Will occur frequently.
Occasional C Likely to occur some time in
the life of an item, with a
probability of occurrence less
than 10-2 but greater than 10-3
in that life.
Will occur several
times.
Remote D Unlikely but possible to occur
in the life of an item, with a
probability of occurrence less
than 10-3 but greater than 10-6
in that life.
Unlikely, but can
reasonably be
expected to occur.
Improbable E So unlikely, it can be assumed
occurrence may not be
experienced, with a
probability of occurrence less
than 10-6 in that life.
Unlikely to occur, but
possible.
*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.
A.4.4.3.2.3 Mishap risk assessment. Mishap risk classification by mishap severity and
mishap probability can be performed by using a mishap risk assessment matrix. This
assessment allows one to assign a mishap risk assessment value to a hazard based on its mishap
severity 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 assessment matrix is shown at
Table A-III.
MIL-STD-882D
APPENDIX A
20
TABLE A-III. Example mishap risk assessment values.
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
A.4.4.3.2.4 Mishap risk categories. Mishap risk assessment values are often used in
grouping individual hazards into mishap risk categories. Mishap risk categories are then used
to generate specific action such as mandatory reporting of certain hazards to management for
action or formal acceptance of the associated mishap risk. Table A-IV includes an example
listing of mishap risk categories and the associated assessment values. In the example, the
system management has determined that mishap risk assessment values 1 through 5 constitute
“High” risk while values 6 through 9 constitute “Serious” risk.
TABLE A-IV. Example mishap risk categories and mishap risk acceptance levels.
Mishap Risk
Assessment Value
Mishap Risk Category
Mishap Risk Acceptance
Level
1 – 5 High Component Acquisition
Executive
6 – 9 Serious Program Executive Officer
10 – 17 Medium Program Manager
18 – 20 Low As directed
*Representative mishap risk acceptance levels are shown in the above table. Mishap risk
acceptance is discussed in paragraph A.4.4.7. The using organization must be consulted by the
corresponding levels of program management prior to mishap risk acceptance.
A.4.4.3.2.5 Mishap risk impact. The mishap risk impact is assessed, as necessary,
using other factors to discriminate between hazards having the same mishap risk value. One
might discriminate between hazards with the same mishap risk assessment value in terms of
mission capabilities, or social, economic, and political factors. Program management will
closely consult with the using organization on the decisions used to prioritize resulting actions.
A.4.4.3.3 Mishap risk assessment approaches. Commonly used approaches for assessing
mishap risk can be found in the Defense Acquisition Deskbook and System Safety Society’s
System Safety Analysis Handbook (see A.6.1)
MIL-STD-882D
APPENDIX A
21
A.4.4.4 Identification of mishap risk mitigation measures. Identify potential mishap risk
mitigation alternatives and the expected effectiveness of each alternative or method. Mishap risk
mitigation is an iterative process that culminates when the residual mishap risk has been reduced
to a level acceptable to the appropriate authority.
A.4.4.4.1 Prioritize hazards for corrective action. Hazards should be prioritized so that
corrective action efforts can be focused on the most serious hazards first. A categorization of
　
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