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to identify to program management the hazards associated with the design. Hazard identification
approaches often include using system users in the effort. Commonly used approaches for
identifying hazards can be found in the Defense Acquisition Deskbook and System Safety
Society’s System Safety Analysis Handbook (see A.6.1)
A.4.4.3 Assessment of mishap risk. Assess the severity and probability of the mishap
risk associated with each identified hazard, i.e., determine the potential impact of the hazard on
personnel, facilities, equipment, operations, the public, or environment, as well as on the system
itself. Other factors, such as numbers of persons exposed, may also be used to assess risk.
A.4.4.3.1 Mishap risk assessment tools. To determine what actions to take to eliminate
or control identified hazards, a system of determining the level of mishap risk involved must be
developed. A good mishap risk assessment tool will enable decision makers to properly
understand the level of mishap risk involved, relative to what it will cost in schedule and dollars
to reduce that mishap risk to an acceptable level.
A.4.4.3.2 Tool development. The key to developing most mishap risk assessment tools
is the characterization of mishap risks by mishap severity and mishap probability. Since the
highest system safety design order of precedence is to eliminate hazards by design, a mishap risk
assessment procedure considering only mishap severity will generally suffice during the early
design phase to minimize the system’s mishap risks (for example, just don’t use hazardous or
toxic material in the design). When all hazards cannot be eliminated during the early design
phase, a mishap risk assessment procedure based upon the mishap probability as well as the
mishap severity provides a resultant mishap risk assessment. The assessment is used to establish
priorities for corrective action, resolution of identified hazards, and notification to management
of the mishap risks. The information provided here is a suggested tool and set of definitions that
can be used. Program managers can develop tools and definitions appropriate to their individual
programs.
MIL-STD-882D
APPENDIX A
18
A.4.4.3.2.1 Mishap severity. Mishap severity categories are defined to provide a
qualitative measure of the most reasonable credible mishap resulting from personnel error,
environmental conditions, design inadequacies, procedural deficiencies, or system, subsystem, or
component failure or malfunction. Suggested mishap severity categories are shown in Table A-I.
The dollar values shown in this table should be established on a system by system basis
depending on the size of the system being considered to reflect the level of concern.
TABLE A-I. Suggested mishap severity categories.
Description Category Environmental, Safety, and Health Result Criteria
Catastrophic I Could result in death, permanent total disability, loss
exceeding $1M, or irreversible severe environmental
damage that violates law or regulation.
Critical II Could result in permanent partial disability, injuries
or occupational illness that may result in
hospitalization of at least three personnel, loss
exceeding $200K but less than $1M, or reversible
environmental damage causing a violation of law or
regulation.
Marginal III Could result in injury or occupational illness
resulting in one or more lost work days(s), loss
exceeding $10K but less than $200K, or mitigatible
environmental damage without violation of law or
regulation where restoration activities can be
accomplished.
Negligible IV Could result in injury or illness not resulting in a lost
work day, loss exceeding $2K but less than $10K, or
minimal environmental damage not violating law or
regulation.
NOTE: These mishap severity categories provide guidance to a wide variety of programs.
However, adaptation to a particular program is generally required to provide a mutual
understanding between the program manager and the developer as to the meaning of the terms
used in the category definitions. Other risk assessment techniques may be used provided that
the user approves them.
A.4.4.3.2.2 Mishap probability. Mishap probability is the probability that a mishap
will occur during the planned life expectancy of the system. It can be described in terms of
potential occurrences per unit of time, events, population, items, or activity. Assigning a
quantitative mishap probability to a potential design or procedural hazard is generally not
possible early in the design process. At that stage, a qualitative mishap probability may be
MIL-STD-882D
APPENDIX A
19
derived from research, analysis, and evaluation of historical safety data from similar systems.
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