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Hazard analysis

A hazard analysis is a process used to characterize the elements of risk. The results of a hazard analysis is the identification of unacceptable risks and the selection of means of controlling or eliminating them. The term is used in several engineering specialties, including avionics, chemical process safety, safety engineering and food safety. Alternative definitions include:

Identification, studies and monitoring of any hazard to determine its potential, origin, characteristics and behaviour. [1]

The process of collecting and evaluating information on hazards associated with the food under consideration to decide which are significant and must be addressed in the HACCP plan. [2]

An analysis or identification of the hazards which could occur at each step in the process, and a description and implementation of the measures to be taken for their control. [3]

Hazards and risk

A hazard is defined in FAA Order 8040.4 as a "Condition, event, or circumstance that could lead to or contribute to an unplanned or undesirable event." Seldom does a single hazard cause an accident. More often, an accident occurs as the result of a sequence of causes. A hazard analysis will consider system state, for example operating environment, as well as failures or malfunctions.

While in some cases safety risk can be eliminated, in most cases a certain degree of safety risk must be accepted. In order to quantify expected accident costs before the fact, the potential consequences of an accident, and the probability of occurrence must be considered. Assessment of risk is made by combining the severity of consequence with the likelihood of occurrence in a matrix. Risks that fall into the "unacceptable" category (e.g., high severity and high probability) must be mitigated by some means to reduce the level of safety risk.

When software is involved in a system, the development of that software is often governed by DO-178B. The severity of consequence identified by the hazard analysis establishes the criticality level of the software. Software criticality levels range from A to E, corresponding to severities of Catastrophic to No Safety Effect.

Severity definitions

Severity Definition
Catastrophic Results in multiple fatalities and/or loss of the system
Hazardous Reduces the capability of the system or the operator ability to cope with adverse conditions to the extent that there would be:
• Large reduction in safety margin or functional capability
• Crew physical distress/excessive workload such that operators cannot be relied upon to perform required tasks accurately or completely
• Serious or fatal injury to small number of occupants of aircraft (except operators)
• Fatal injury to ground personnel and/or general public
Major Reduces the capability of the system or the operators to cope with adverse operating conditions to the extent that there would be:
• Significant reduction in safety margin or functional capability
• Significant increase in operator workload
• Conditions impairing operator efficiency or creating significant discomfort
• Physical distress to occupants of aircraft (except operator)

including injuries

• Major occupational illness and/or major environmental damage, and/or major property damage
Minor Does not significantly reduce system safety. Actions required by operators are well within their capabilities. Include:
• Slight reduction in safety margin or functional capabilities
• Slight increase in workload such as routine flight plan changes
• Some physical discomfort to occupants or aircraft (except operators)
• Minor occupational illness and/or minor environmental damage, and/or minor property damage
No Safety Effect Has no effect on safety

Likelihood of occurrence

Likelihood Definition
Probable
• Qualitative: Anticipated to occur one or more times during the entire system/operational life of an item.
• Quantitative: Probability of occurrence per operational hour is greater than $1 \times 10^{-5}$
Remote
• Qualitative: Unlikely to occur to each item during its total life. May occur several times in the life of an entire system or fleet.
• Quantitative: Probability of occurrence per operational hour is less than $1 \times 10^{-5}$, but greater than $1 \times 10^{-7}$
Extremely Remote
• Qualitative: Not anticipated to occur to each item during its total life. May occur a few times in the life of an entire system or fleet.
• Quantitative: Probability of occurrence per operational hour is less than $1 \times 10^{-7}$ but greater than $1 \times 10^{-9}$
Extremely Improbable
• Qualitative: So unlikely that it is not anticipated to occur during the entire operational life of an entire system or fleet.
• Quantitative: Probability of occurrence per operational hour is less than $1 \times 10^{-9}$

• Hazop
• Safety engineering
• Occupational safety and health
• RTCA DO-178B (Software Considerations in Airborne Systems and Equipment Certification)
• RTCA DO-254 (similar to DO-178B, but for hardware)
• SAE ARP4761 (System safety assessment process)
• SAE ARP4754 (System development process)
• MIL-STD-882 (Standard practice for system safety)