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review.
HAZARD CATEGORIES
FREQUENCY OF
OCCURENCE
I
CATASTROPHIC
II
CRITICAL
III
MARGINAL
IV
NEGLIGIBLE
(A) Frequent IA IIIA IVA
(B) Probable R1 IB
IIA
IIB IIIB IVB
(C) Occasional IC IIC IIIC IVC R4
(D) Remote R2 ID IID IIID IVD
(E) Improbable R3 IE IIE IIIEP IVE
Hazard Risk Index (HRI) Suggested Criteria
R1 Unacceptable
R2 Must control or mitigate (MA review)
R3 Acceptable with MA review
R4 Acceptable without review
Figure 3-5: Example of a Comparative Safety Assessment Matrix
FAA System Safety Handbook, Chapter 3: Principles of System Safety
December 30, 2000
3-
11
Early in a development phase, performance objectives may tend to overshadow efforts to reduce safety
risk. This is because sometimes safety represents a constraint on a design. For this reason, safety risk
reduction is often ignored or overlooked. In other cases, safety risk may be appraised, but not fully
enough to serve as a significant input to the decision making process. As a result, the sudden
identification of a significant safety risk, or the occurrence of an actual incident, late in the program can
provide an overpowering impact on schedule, cost, and sometimes performance. To avoid this situation,
methods to reduce safety risk must be applied commensurate with the task being performed in each
program phase.
In the early development phase (investment analysis and the early part of solution implementation), the
system safety activities are usually directed toward: 1) establishing risk acceptability parameters; 2)
practical tradeoffs between engineering design and defined safety risk parameters; 3) avoidance of
alternative approaches with high safety risk potential; 4) defining system test requirements to demonstrate
safety characteristics; and, 5) safety planning for follow-on phases. The culmination of this effort is the
safety Comparative Safety Assessment that is a summary of the work done toward minimization of
unresolved safety concerns and a calculated appraisal of the risk. Properly done, it allows intelligent
management decisions concerning acceptability of the risk.
The general principles of safety risk management are:
All system operations represent some degree of risk.
Recognize that human interaction with elements of the system entails some element of risk.
Keep hazards in proper perspective.
Do not overreact to each identified risk, but make a conscious decision on how to deal with it.
Weigh the risks and make judgments according to your own knowledge, inputs from subject matter
experts, experience, and program need.
It is more important to establish clear objectives and parameters for Comparative Safety Assessment
related to a specific program than to use generic approaches and procedures.
There may be no "single solution" to a safety problem. There are usually a variety of directions to pursue.
Each of these directions may produce varying degrees of risk reduction. A combination of approaches
may provide the best solution.
Point out to designers the safety goals and how they can be achieved rather than tell him his approach will
not work.
There are no "safety problems" in system planning or design. There are only engineering or management
problems that, if left unresolved, may lead to accidents.
The determination of severity is made on a “worst credible case/condition” in accordance with MIL-STD-
882, and AMJ 25.1309.
· Many hazards may be associated with a single risk. In predictive analysis, risks are
hypothesized accidents, and are therefore potential in nature. Severity assessment is made
regarding the potential of the hazards to do harm.
FAA System Safety Handbook, Chapter 3: Principles of System Safety
December 30, 2000
3-
12
3.5 Risk Management Decision Making
For any system safety effort to succeed there must be a commitment on the part of management. There
must be mutual confidence between program managers and system safety management. Program
managers need to have confidence that safety decisions are made with professional competence. System
safety management and engineering must know that their actions will receive full program management
attention and support. Safety personnel need to have a clear understanding of the system safety task along
with the authority and resources to accomplish the task. Decision-makers need to be fully aware of the
risk they are taking when they make their decisions. They have to manage program safety risk. For
effective safety risk management, program managers should:
Ensure that competent, responsible, and qualified engineers be assigned in program offices and contractor
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