System Safety Assessment process hazards

This publication establishes design requirements for stractures, systems and components important to safety that must be met for safe operation of a nnclear power plant, and for preventing or mitigating the consequences of events that could jeopardize safety. It also establishes requirements for a comprehensive safety assessment, which is carried out in order to identify the potential hazards that may arise from the operation of the plant, under the various plant states (operational states and accident conditions). The safety assessment process includes the complementary techniqnes of deterministic safety analysis and probabilistic safety analysis. These analyses necessitate consideration of postulated initiating events (PIEs), which include mat r factors that, singly or in combination, may affect safety and which may ... 

The DAL is an index number ranking the safety-criticality of the system functions. This ranking implies that in order to make the system safe, greater development rigor must be applied to each successively critical level. Table 2.3 correlates the hardware DALs to the five classes of failure conditions and provides definitions of hardware failure conditions and their respective DALs. Initially, the hardware DAL for each hardware function is determined by the SSA process using a functional hazard analysis (FHA) to identify potential hazards and then the preliminary system safety assessment (PSSA) process allocates the safety requirements and associated failure conditions to the function implemented in the hardware. 

ZSA is an HA technique that identifies hazards that are created by failures that cross system zones and violate design safety independence requirements. ZSA is part of a comprehensive CCF analysis. It was developed for analysis of aircraft systems and is described in SAE/ARP-4761, Guidelines and Methods for Conducting the Safety Assessment Process on Civil Airborne Systems and Equipment, 1996. 

This section discusses a generic safety life cycle, illustrated in Figure 4, and its relationship to the system life cycle. The first row represents a generic and simplified version of the development process. The second row shows the main phases of the safety life cycle, which consists of Preliminary Hazard Identification (PHI), Functional Hazard Assessment (FHA), Preliminary System Safety Assessment (PSSA) and System Safety Assessment (SSA). The primary question to be answered during each phase is shown at the bottom of Figure 4. 

This whole process of safety analysis is regulated by the ARP 4761. Identification of safety objectives is given by a fimctional approach, documented in a functional hazard analysis demonstrating compliance with these objectives is achieved by identifying the combinations of failiues, and this is documented in the System Safety Assessment (SSA). 

In order to guide the safety assessment process, it is necessary firstly to define the criteria used to judge the acceptability of hazards. These definitions are fundamental to understanding the data presented, as the resultant safety acceptance criteria form the baseline standards against which the system is then evaluated in the final system safety assessment (SSA) report. For more information, see Chapter 5 and Appendix B. 

Process Hazards Analysis. Analysis of processes for unrecogni2ed or inadequately controUed ha2ards (see Hazard analysis and risk assessment) is required by OSHA (36). The principal methods of analysis, in an approximate ascending order of intensity, are what-if checklist failure modes and effects ha2ard and operabiHty (HAZOP) and fault-tree analysis. Other complementary methods include human error prediction and cost/benefit analysis. The HAZOP method is the most popular as of 1995 because it can be used to identify ha2ards, pinpoint their causes and consequences, and disclose the need for protective systems. Fault-tree analysis is the method to be used if a quantitative evaluation of operational safety is needed to justify the implementation of process improvements. 

Each PSM system can then be examined to determine what system modifications (if any) are needed to address the new issues. For example, the process hazard assessment system might be modified to include participation by industrial hygienists to identify potential sources of exposure. Some process safety management systems (e.g., process documentation) may require no modification to support a wider scope. 

Facility System Safety (FSS), which is the application of system safety concepts to the facility acquisition process, has recently gained acceptance throughout the Department of Defense and most recently within the Department of Army with the conception of SAFEARMY 1990. The Army s goal is to fully integrate the total system safety, human factors, and health hazard assessments into continuous comprehensive evaluation of selected systems and facilities. The Chemical Research Development and Engineering Center (CRDEC) has mandated appropriate levels of system safety throughout the lifecycle of facility development for many reasons. These include ... 

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. 

In 1993, the Center for Chemical Process Safety (CCPS) published Guidelines for Safe Automation of Chemical Processes (referred to henceforth as Safe Automation). Safe Automation provides guidelines for the application of automation systems used to control and shut down chemical and petrochemical processes. The popularity of one of the hazard and risk analysis methods presented in Safe Automation led to the publication of the 2001 Concept Series book from CCPS, Layer of Protection Analysis A Simplified Risk Assessment Approach. This method builds upon traditional process hazards analysis techniques. It uses a semiquantitative approach to define the required performance for each identified protective system. 

Identifying the potential hazards (PHA, process hazard analysis, or HAZOP, hazard and operability analysis) during operation must be done from a wide-angle approach dangerous situations can occur due to many root-cause situations other than those specified by, for instance, ASME or PED. Based on the results of the risk assessment, the pressure equipment can be correctly designed and the most effective safety system selected. 

Topics Include methods lor calculating damage resulting from the physical effects of accidental releases, using risk assessment Information to specify safety control systems, fault tree analysis, hazards of trace substances, warehouse fires, human exposure to process systems, and solutions to human factor problems. 

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