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:
Hazard analysis is usually performed during the early stages of design, but it can also take place during different stages in the life cycle of processes and facilities.
The major goal of a PHA is the ability to identify and characterize possible known hazards in the beginning of a design phase. Partial lists of those hazards are listed below:
PHA identifies known hazards such as explosions, radioactive sources, pressure vessels or lines, toxic materials, high voltage, machinery, and so on. PHA specifies where each hazard will occur, their significance, and the method that will be used to eliminate the hazards or how the associated risk will be controlled.
The probability of occurrence of an unexpected release of hazardous energy or material (an accident) determines its credibility for the purpose of PHA as follows:
For most nonnuclear facilities, qualitative determinations of credibility are all that is necessary, while nuclear facilities require quantitative determinations of credibility.
Quantitative measures are
A PHA seeks to rank hazards in a qualitative measurement of the worst potential consequence resulting from personnel error, environmental conditions, design inadequacies, procedural deficiencies, and system, subsystem and component failure, or malfunction. The categories are defined as follows:
The most reliable solution when identifying PHAs is to eliminate the source or cause of the hazards. If the source or cause cannot be eliminated, the hazard should be reduced or redesigned as much as possible, such as by
Once a PHA has been established a preliminary hazards list needs to list details of the hazards and serve as the central reference that documents the safety characteristics of the system being analyzed. A hazards list should be kept for the entire life cycle of the system. The structure of a hazards list should be as follows:
There are numerous software programs specifically designed for conducting PHAs. Standard word processing and spreadsheets can assist with documenting the PHA results. Uses of flowchart diagrams and process modeling as discussed in Chapter 5, Task Analysis, are also beneficial when developing PHAs. Table 6.1 shows a hazard list, and Table 6.2 presents a template for a PHA.
Qualitative measure of significance for the potential effect has already been described in Section 6.1.1.
Table 6.3 lists some of the examples of hazardous energy sources.
Chemical energy | Electrical energy | Thermal energy |
Corrosive materials | Capacitors | Steam |
Flammable materials | Transformers | Fire |
Toxic materials | Batteries | Friction |
Reactive material | Exposed conductors | Chemical reaction |
Oxygen deficiency | Static electricity | Spontaneous combustion |
Carcinogens | Cryogenic materials | |
Ice, snow, wind, rain | ||
Radiant energy | Kinetic energy | Pressure energy |
Intense light | Pulley, belts, gears | Confined gases |
Lasers | Shears, sharp edges | Explosives |
Ultraviolet | Pinch points | Noise |
X-rays | Vehicles | |
Infrared sources | Mass in motion | |
Electron beam | ||
Magnetic fields | Potential energy | Biological energy |
RF fields | Falling | Pathogens (virus, bacteria, etc.) |
Nuclear criticality | Falling objects | Allergens |
High energy particles | Lifting | |
Tripping, slipping | ||
Earthquakes |
3.145.12.156