Software system safety

In software engineering, software system safety optimizes system safety in the design, development, use, and maintenance of software systems and their integration with safety-critical hardware systems in an operational environment.
Overview.
Software system safety is a subset of system safety and system engineering and is synonymous with the software engineering aspects of Functional Safety. As part of the total safety and software development program, software cannot be allowed to function independently of the total effort. Both simple and highly integrated multiple systems are experiencing an extraordinary growth in the use of computers and software to monitor and/or control safety-critical subsystems or functions. A software specification error, design flaw, or the lack of generic safety-critical requirements can contribute to or cause a system failure or erroneous human decision. To achieve an acceptable level of safety for software used in critical applications, software system safety engineering must be given primary emphasis early in the requirements definition and system conceptual design process. Safety-critical software must then receive continuous management emphasis and engineering analysis throughout the development and operational lifecycles of the system. 
Functional Hazard Analyses (FHA) are often conducted early on - in parallel with or as part of system engineering Functional Analyses - to determine the safety-critical functions (SCF) of the systems for further analyses and verification. Software system safety is directly related to the more critical design aspects and safety attributes in software and system functionality, whereas software quality attributes are inherently different and require standard scrutiny and development rigor. Development Assurance levels (DAL) and associated Level of Rigor (LOR) is a graded approach to software quality and software design assurance as a pre-requisite that a suitable software process is followed for confidence. LOR concepts and standards such as DO-178C are NOT a substitute for software safety. Software safety per IEEE STD-1228 and MIL-STD-882E focuses on ensuring explicit safety requirements are met and verified using functional approaches from a safety requirements analysis and test perspective. Software safety hazard analysis required for more complex systems where software is controlling critical functions generally are in the following sequential categories and are conducted in phases as part of the system safety or safety engineering process: software safety requirements analysis; software safety design analyses (top level, detailed design and code level); software safety test analysis, and software safety change analysis. Once these "functional" software safety analyses are completed the software engineering team will know where to place safety emphasis and what functional threads, functional paths, domains and boundaries to focus on when designing in software safety attributes to ensure correct functionality and to detect malfunctions, failures, faults and to implement a host of mitigation strategies to control hazards. Software security and various software protection technologies are similar to software safety attributes in the design to mitigate various types of threats vulnerability and risks. Deterministic software is sought in the design by verifying correct and predictable behavior at the system level.
Goals.
This article incorporates public domain material from the United States Government document "Joint Software System Safety Committee"
SOFTWARE SYSTEM SAFETY HANDBOOK "A Technical & Managerial Team Approach" This document was originally obtained from the web site "https://www.dsmartsolutions.com/Mobile-Applications-Development. which is now a dead link since this base closed in 2011. A PDF of the document is available at http://www.system-safety.org/Documents/Software_System_Safety_Handbook.pdf 2.15MB. In addition, an updated version can be obtained from: http://www.acqnotes.com/Attachments/Joint-SW-Systems-Safety-Engineering-Handbook.pdf 4.6MB.