Risk Assessment: Tools, Techniques, and Their Applications

6.1 Description

The PHA technique was developed by the US Army and is listed in the US Military Standard System Safety Program Requirements (2). PHAs have been proven to be cost effective in identifying hazards in the beginning of a conceptual design phase. Because of its military legacy, the PHA technique is sometimes used to review process areas where energy can be released in an uncontrolled manner.

The main purpose of a PHA is to identify the hazardous states of a system and its implications. In order to obtain maximum benefit of a PHA, it should occur as early as possible in the system's life cycle. Tasks and requirements involved in preparing a PHA should include the following:

• Establish for purpose of the analysis
  • boundaries between the system, any system with which it interacts, and the domain;
  • overall system structure and functionality.
• Identify
  • detailed list of hazards of the system based on preliminary hazards list report and the requirements;
  • update hazards list;
  • accidents to the most practicable extent;
  • events of accident sequence and those that can be discounted;
  • record in hazards list.
• Assign
  • each accident a severity categorization and each accident sequence a predicted qualitative/quantitative probability;
  • each hazard a preliminary random and systematic probability target.
• Document
  • any safety features that are to be implemented during the design and development phase.

6.1.1 Process of Preliminary Hazards Analysis

Hazard analysis is usually performed ...