The Preliminary Hazard Analysis (PHA) is the initial hazard identification effort conducted during the programming and requirements development phase of an acquisition. The PHA focuses on the details of the early system design (including their implications for human reliability) and is primarily used to perform an initial risk assessment to develop early safety-related requirements and specifications. The PHA is used to both identify new requirements and to support the verification and validation of existing requirements.
The PHA, since it is performed early in the lifecycle of a system, provides important inputs to the development of system requirements. In the case of an operational system, the PHA aids in the early determination of risk and the need for additional safety requirements to mitigate operational risks. The output of the PHA will be used to develop systems safety requirements and to assist in preparing performance and design specifications. In addition, the PHA establishes the framework for follow-on hazard analyses that may need to be performed.