System safety preliminary hazard analysis

Assessment. An analysis of the hazards present in this laboratory show the most significant hazard to be the release of vapor CSM from engineering controls and into the workplace. The significance of this hazard mandates further efforts in system safety in the form of a Preliminary Hazard List (PHL) and a Preliminary Hazard Analysis (PHA). The user must in this instance take an active role in the design review process. 

Other possible preliminary safety analysis methods are concept safety review (CSR), critical examination of system safety (CE), concept hazard analysis (CHA), preliminary consequence analysis (PCA) and preliminary hazard analysis (PHA) (Wells et al., 1993). These methods are meant to be carried out from the time of the concept safety review until such time as reasonably firm process flow diagrams or early P I diagrams are available. 

Once the set of accidents has been agreed upon, hazards can be derived from them. This process is part of what is called Preliminary Hazard Analysis (PHA) in System Safety. The hazard log is usually started as soon as the hazards to be considered are identified. While much of the information in the hazard log will be filled in later, some information is available at this time. 

System safety is hazards-focused, as are all the subsets of the practice of safety, whatever they are called. System safety commences with hazard identification and analysis. Do that poorly, and all that follows is misdirected. Applications of the hazard analysis and risk assessment methods developed in the evolution of system safety have been successful. The generalist in safety practice ought to know more about them. As a minimum, generalist safety practitioners should be knowledgeable about these methods Preliminary Hazard Analysis What-If Analysis and Failure Modes and Effects Analysis. (See Chapter 14, Hazard Analysis and Risk Assessment. )... 

A Brief Overview of Selected System Safety Analytical Approaches Working with the Risk Assessment Matrix Preliminary Hazard Analysis Energy Flow/Barrier Analysis Failure Modes and Effects Analysis Fault Tree Analysis... 

Two types of analytical methods are used to evaluate hazards 1) preliminary hazards analysis (PHA), and 2) failure modes and effects analysis (FMEA). PHA is an accident scenario-based form of analysis. The FMEA is a complementary type of evaluation that utilizes a system failure-based form of analysis. Generally, FMEAs were only accomplished for equipment which was perceived to have a significant safety role, i.e. SSCs which were anticipated to be designated as safety significant in accordance with DOE-STD-3009. Unlike PHA, the first objective of FMEA is to subdivide the facility into several different (and, to the maximum extent possible, independent) system elements. Failure modes of each system element are then postulated and a structured esramination of the consequences of each failure mode follows. However, similar to PHA, FMEA. documents preventive and mitigative features (failure mechanisms and compensation) and anticipated accident consequences (failure effects). This appendix documents the FMEA for the HCF. 

The HazOp study differs from the FMEA and ETBA in that some suggest that the best time to conduct a HazOp is when the design is fairly firm (Goldwaite 1987). Conventional system safety wisdom dictates that the system safety effort be as far upstream as practical, with a facility preliminary hazard analysis developed as part of the initial design effort and completed by the 35% stage. Also, a HazOp study tends to include human factors and operator errors whereas a traditional FMEA or ETBA normally examines hardware failures only. 

Some of the hazard analysis (evaluation) techniques already used by the chemical industry include traditional system safety tools such as preliminary hazard analysis, failure modes and effects analysis, and fault tree analysis. 

The MORT tools and techniques can be helpful in preparing a safety analysis report (SAR), the upstream safety product most frequently required for new DOE programs, but the more common system safety products (system safety program plan, preliminary hazard analysis, system/subsystem hazard analysis, operating hazard analysis) are not a dominant part of the MORT program and are seldom even referenced in System Safety Development Center (SSDC) documents. 

The preliminary hazard list (PHL) dcKuments and provides initial assessment of hazards identified very early in the life cycle. The PHL is a feeder document for the preliminary hazard analysis (PHA) and provides the first information to aid in scaling the system safety effort. 

Fault hazard analysis is mentioned very frequently in system safety literature, sometimes as a type of analysis and occasionally as a technique. One NASA system safety document (NHB 1700.1-V3, System Safety) describes it as the analysis to be performed after the preliminary hazard analysis for further analysis of systems and subsystems and suggests that it can be either a separate analysis or an extension of the failure modes and effects analysis (NASA 1970). Most programs today (including NASA) refer to this analysis as the subsystem hazard analysis (SSHA) and the system hazard analysis (SHA). 

In some early literature gross hazard analysis described what is generally referred to as the preliminary hazard analysis. Like many system safety terms, it may have other meanings as well. 

The job safety analysis (JSA) [also referred to as the job hazard analysis (JHA)], which is a more simplified form of task analysis, has been a longstanding tool for task and function analysis. JSA has been available and utilized in general industry for many years by the industrial safety community. However, many practitioners do not understand or are simply unfamiliar with the connection between the JSA and the system safety tasks of hazard identification and analysis. It has even been suggested by some in the profession that the JSA itself is a type of oversimplified system safety analysis and, if performed earlier in the job development phase, could be used as the basis of a preliminary hazard analysis for a specific task or set of tasks. However, because JSA is often (if improperly) used to analyze a function only after it has been implemented, much of the data is not factored into the system safety process. The primary purpose of the JSA is to uncover inherent or potential hazards that may be encountered in the work environment. This basic definition is not unlike that previously discussed regarding the various system safety analyses. The primary difference between the two is subtle but important and is found in the end-use purpose of the JSA. Once the job or task is completed, the JSA is usually used as an effective tool for training and orienting the new employee into the work environment. The JSA presents a verbal picture of a specific job. 

In the analysis of system safety, the initial process begins with the development of the preliminary hazard list during the project or system concept phase. Although it is not always compiled in aU cases, an available PHL can become the working foundation for the development of the preliminary hazard analysis during the design phase of the project life cycle. 

Hazard Condition Item 2 Loss of Hydraulic Pressure. A small leak in the hydraulic cylinder system woidd result in a loss of pressure in the cylinder and a subsequent inability to maintain constant cyUnder volmne. Any damage to the cylinder jackhead would cause a leak of hydrauhc oil from the cylinder system. Such damage is possible because of an abrupt contact with the plunger mechanism and/or a failure in the neoprene seal between the jackhead and the plunger. The system safety analyst has learned from the preliminary hazard analysis report that there is no provision for oil recovery in the event of damage to the jackhead. 

Software Preliminary Hazard Analysis This type of analysis is used to identify software program routines that are considered to be safety-critical, and thus is conducted prior to software program coding. To perform the analysis, the analyst should make reference to any available system specifications, interface documentation, functional flow diagrams, software flowcharts, storage and file allocation specifications, and any other program descriptive information. 

Preliminary hazard analysis is one of the early steps in a system safety project. This step also creates assessments of risks associated with each hazard. This step defines possible corrections for the risks. The product of this step is a tabular inventory of hazards for the system under consideration. The PHA fits best during early system stages, such as concept definition, design, and development. 

Some government organizations require or apply system safety methods for construction projects. A project may require selective use of methods. Organizations apply system safety in some construction projects. Included are the Nuclear Regulatory Commission, the Department of Defense and its service agencies, the Federal Aviation Administration and others. Some projects may simply require use of preliminary hazard analysis that leads to a site safety plan for a project. Complex facilities that integrate specialized equipment into the project may require failure mode and effects analysis or even fault tree analysis. 

During the concept phase, historical data and technical forecasts are developed as a base for a system hazard analysis. A Preliminary Hazard Analysis (PHA) is conducted during this phase. At the gross level, a Risk Analysis (RA) is performed to ascertain the need for hazard control and to develop system-safety criteria. Safety management will be doing the initial work on the System Safety Program Plan (SSPP). Three basic questions must be answered by the time the concept phase is completed ... 

Concept Analysis of the Technical Plant after Planning. Preliminary hazard analysis and system structure analysis are intended to facilitate safety evaluation of the planned installation from the basic concept. Comprehensiveness of observation depends on the danger level of the installation. After concluding this work, basic changes in the technical procedure frequently become necessary and must be incorporated into the planning. 

Due to the need to check all safety measures, this part of the system analysis can become very voluminous. The method becomes difficult due to the constant change from the overall review of the plant to the review of individual components. For this reason it is important, in the case of major systems, to place preliminary hazard analysis and system structure analysis ahead of the evaluation of the planning concept. The advantages of this work plan are the following ... 

System Safety Analysis (following on from Preliminary Hazard Analysis) is conducted... 

The Preliminary Hazard Analysis (PHA) is an analysis of the generic hazard groups present in a system, their evaluation, and recommendations for control (TAI 1989). The PHA is usually the first attempt in the system safety process to identify and categorize hazards or potential hazards associated with the operation of a proposed system, process, or procedure. In many instances, however, the PHA may be preceded with the preparation of aPreliminary Hazard List (PHL). The identification of hazards on a PHL can occur through the use of a variety of methods such as but not limited to... 

Preliminary Hazard Analysis (PHA) A system safety analysis method used to formally evaluate and document the hazard risks associated with a new or modified system. 

---