Software sneak circuit analysis

Software sneak Software sneak circuit analysis (SSCA) is designed to discover... 

The recommended techniques for preliminary hazard analysis are energy trace and barrier analysis (ETBA) and failure modes and effects analysis (FMEA). Recommended techniques for system and subsystem hazard analyses are FMEA, fault tree analysis (FTA), common cause analysis, sneak circuit analysis (for electrical, electronic, and some hydraulic or pneumatic circuits) and, of course, software hazard analysis for software. 

Based on the results of the PHA, recommendations made by 30% review boards, and guidance provided in the system safety program plan, detailed hazard analyses are made of specified (critical) subsystems. The techniques for these SSHAs are as outlined in the system safety program plan or as selected by the SSWG. Failure modes and effects analysis (FMEA) and/or fault tree analysis (FTA) are generally the techniques of choice. Software hazard analysis, common cause analysis, and/or sneak circuit analysis may also be appropriate. 

Sneak circuit analysis is usually inductive and can be very difficult to perform without the software to aid in producing network trees and other graphics. Much of this software is proprietary, and a large portion of the sneak circuit analysis work done to date has been accomplished by large aerospace and weapons contractors (notably Boeing and General Dynamics). 

To illustrate this point, this chapter addresses two system safety analytical methods that have been developed as a result technological improvements the sneak circuit analysis and the software hazard analysis. Each is briefly discussed here to demonstrate its applicability and utility in the practice of industrial safety and health. 

The system safety analysis techniques known separately as sneak circuit analysis and software safety analysis have been developed in an effort to address these concerns over system safety and reliability assurance. Although various types of sneak hazards can be identified by analysis, and a variety of software hazard analysis techniques are commonly used, each method is concerned primarily with the same essential objective explained throughout this text hazard risk elimination or reduction to acceptable levels. 

Sneak circuit analysis is usually performed with complex computer codes and is very expensive. It only becomes cost-effective on subsystems that are safety critical, such as an aircraft control system. Obviously, sneak circuit analysis should be teamed with the software safety analysis tools discussed in Chapter 8. This is a very powerful combination, but not cheap, certainly, very important for the most safety-critical circuits of very high-risk systems. 

Additional safety processes are performed iteratively throughout the life cycle as other specialty engineering disciplines become involved in the effort. These include Sneak Circuit Analysis (SCA) and Software Hazard Analysis (SWHA). 

FHA is a powerful, efficient, and comprehensive system safety analysis technique for the discovery of hazards. It is especially powerful for the safety assessment of software. Since software does not have discrete failure modes as hardware does, the best way to identify software-related hazards is by evaluating the effect of potential software functions failing. Software is built upon performing functions therefore, FHA is a very natural and vital tool. After a functional hazard is identified, further analysis of that hazard may be required to determine if the causal factors of the functional failure are possible. Since the FHA focuses on functions, it might overlook other types of hazards, such as those dealing with hazardous energy sources, sneak circuit paths, and hazardous material (HAZMAT). For this reason, the FHA should not be the sole HA performed, but should be done in support of other types of HA, such as PHA and SSHA. 

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