DOCSLIB.ORG

Standardizing Functional Safety Assessments for Off-The-Shelf Instrumentation and Controls

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Standardizing Functional Safety Assessments for Off-The-Shelf Instrumentation and Controls University of Tennessee, Knoxville TRACE: Tennessee Research and Creative Exchange Masters Theses Graduate School 5-2016 STANDARDIZING FUNCTIONAL SAFETY ASSESSMENTS FOR OFF-THE-SHELF INSTRUMENTATION AND CONTROLS Andrew Michael Nack University of Tennessee - Knoxville, [email protected] Follow this and additional works at: https://trace.tennessee.edu/utk_gradthes Part of the Other Computer Engineering Commons, and the Systems Engineering Commons Recommended Citation Nack, Andrew Michael, "STANDARDIZING FUNCTIONAL SAFETY ASSESSMENTS FOR OFF-THE-SHELF INSTRUMENTATION AND CONTROLS. " Master's Thesis, University of Tennessee, 2016. https://trace.tennessee.edu/utk_gradthes/3793 This Thesis is brought to you for free and open access by the Graduate School at TRACE: Tennessee Research and Creative Exchange. It has been accepted for inclusion in Masters Theses by an authorized administrator of TRACE: Tennessee Research and Creative Exchange. For more information, please contact [email protected]. To the Graduate Council: I am submitting herewith a thesis written by Andrew Michael Nack entitled "STANDARDIZING FUNCTIONAL SAFETY ASSESSMENTS FOR OFF-THE-SHELF INSTRUMENTATION AND CONTROLS." I have examined the final electronic copy of this thesis for form and content and recommend that it be accepted in partial fulfillment of the equirr ements for the degree of Master of Science, with a major in Computer Engineering. Gregory D. Peterson, Major Professor We have read this thesis and recommend its acceptance: Qing C. Cao, Mingzhou Jin Accepted for the Council: Carolyn R. Hodges Vice Provost and Dean of the Graduate School (Original signatures are on file with official studentecor r ds.) STANDARDIZING FUNCTIONAL SAFETY ASSESSMENTS FOR OFF-THE-SHELF INSTRUMENTATION AND CONTROLS A Thesis Presented for the Master of Science Degree The University of Tennessee, Knoxville Andrew Michael Nack May 2016 Copyright © 2016 by Andrew Michael Nack All rights reserved. ii ACKNOWLEDGEMENTS Thank you to my wife Leslie, my kids Jerrett, Mikie, Elijah, and Anna Bowden, my advisor Dr. Gregory Peterson, my committee members Dr. Charles Cao, and Dr. Mingzhou Jin, my unofficial committee member Dr. Richard Wood, my friend Dr. M. Nance Ericson, my new friend Gary Johnson, my previous and current bosses Matthew Bowman, and Milton Concepcion, and my employer ATC Nuclear. I received critical support from all these people and entities, and I would not have been able to be successful without them. iii ABSTRACT It is typical for digital instrumentation and controls, used to manage significant risk, to undergo substantial amounts of scrutiny. The equipment must be proven to have the necessary level of design integrity. The details of the scrutiny vary based on the particular industry, but the ultimate goal is to provide sufficient evidence that the equipment will operate successfully when performing their required functions. To be able to stand up to the scrutiny and more importantly, successfully perform the required safety functions, the equipment must be designed to defend against random hardware failures and also to prevent systematic faults. These design activities must also have been documented in a manner that sufficiently proves their adequacy. The variability in the requirements of the different industries makes this task difficult for instrumentation and controls equipment manufacturers. To assist the manufacturers in dealing with these differences, a standardization of requirements is needed to facilitate clear communication of expectations. The IEC 61508 set of standards exists to fulfill this role, but it is not yet universally embraced. After that occurs, various industries, from nuclear power generation to oil & gas production, will benefit from the existence of a wider range of equipment that has been designed to perform in these critical roles and that also includes the evidence necessary to prove its integrity. The manufacturers will then be able to enjoy the benefit of having a larger customer base interested in their products. The use of IEC 61508 will also help industries avoid significant amounts of uncertainty when selecting commercial off-the-shelf equipment. It is currently understood that it cannot be assumed that a typical commercial manufacturer’s equipment designs and associated design activities will be adequate to allow for success in these high risk applications. In contrast, a manufacturer that seeks to comply with IEC 61508 and seeks to achieve certification by an independent third party can be assumed to be better suited for meeting the needs of these demanding situations. Use of these manufacturers help to avoid substantial uncertainty and risk. iv TABLE OF CONTENTS Chapter One Introduction and General Information ................................... 1 Chapter Two Literature Review .................................................................. 5 Chapter Three Multi-Industry Survey ......................................................... 9 Process Industries .................................................................................. 9 IEC 61508 ......................................................................................... 10 ISA 84.00.01(IEC 61511 Mod) .......................................................... 12 Commercial Nuclear Power Generation ............................................... 15 General ............................................................................................. 15 International Standards Structure ..................................................... 16 United States of America .................................................................. 20 France ............................................................................................... 24 United Kingdom ................................................................................ 25 United States Department of Defense .................................................. 27 MIL-STD-882E Standard Practice of System Safety ......................... 28 Joint Software Systems Safety Engineering Handbook .................... 29 General Observations ....................................................................... 32 Chapter Four Compare and Contrast Methodologies ............................... 33 Classification of Systems and Components .......................................... 33 Probabilistic vs Deterministic ............................................................ 33 Level of Rigor .................................................................................... 35 Defending Against Random Failures .................................................... 37 Hardware .......................................................................................... 37 Software ............................................................................................ 40 Preventing Systematic Faults ............................................................... 40 Lifecycle Processes and Designing Techniques ............................... 41 Built-in Safety Features ..................................................................... 41 Design Analysis and Verification & Validation ................................... 46 Hazard Analysis ................................................................................ 46 Common Cause Failure Prevention .................................................. 48 Environmental Qualification .............................................................. 50 Suitability Evaluation of “Off-the-Shelf” Equipment ............................... 51 Synthesis of Observations .................................................................... 52 Chapter Five Standardization of Component Functional Safety ............... 55 Moore Industries STZ Transmitter ........................................................ 55 Fisher Controls DVC6200 SIS Digital Valve Controller ......................... 62 Additional Notes in Support of Standardization .................................... 63 Chapter Six Conclusion ............................................................................ 65 Comparison of Industries ...................................................................... 65 Suitability Evaluations of Off-the-Shelf Equipment. .............................. 66 Future Work .......................................................................................... 66 List of References .................................................................................... 67 Vita ........................................................................................................... 73 v LIST OF TABLES Table 2.1. Most Similar Works 6 Table 2.2. Documents Regarding Classification 7 Table 2.3. Documents Regarding Random Failures 7 Table 2.4. Documents Regarding Systematic Faults 8 Table 2.5. Documents Regarding Suitability Evaluations of COTS 8 Table 4.1. Comparison of System and Component Levels 54 Table 5.1. Evaluation of MII STZ Transmitter 56 Table 5.2. Evaluation of Fisher Controls DVC6200 Valve Controller 58 vi LIST OF FIGURES Figure 3.1. SIL Standardization .......................................................................... 14 Figure 3.2. IEC Standards Hierarchy .................................................................. 17 Figure 3.3. IEEE NPEC Standards [56] .............................................................. 22 Figure 4.1. A Comparison of Different Classification Systems ............................ 34 Figure 4.2. Software Criticality Matrix ................................................................
Load more

Recommended publications
  • A Software Safety Process for Safety-Critical Advanced Automotive Systems
    PROCEEDINGS of the 21st INTERNATIONAL SYSTEM SAFETY CONFERENCE - 2003 A Software Safety Process for Safety-Critical Advanced Automotive Systems Barbara J. Czerny, Ph.D.; Joseph G. D’Ambrosio, Ph.D., PE; Paravila O. Jacob, Ph.D.; Brian T. Murray, Ph.D.; Padma Sundaram; Delphi, Corp.; Brighton, Michigan Keywords: SW Safety, Safety-Critical Advanced Automotive Systems, By-Wire Systems Abstract A new generation of advanced automotive systems are being implemented to enhance vehicle safety, performance, and comfort. As these new, often complex systems are added, system safety programs are employed to help eliminate potential hazards. A key component of these advanced automotive systems is software. Software itself cannot fail or wear out, but its complexity coupled with its interactions with the system and the environment can directly and indirectly lead to potential system hazards. As such, software safety cannot be considered apart from system safety, but the unique aspects of software warrant unique development and analysis methods. In this paper we describe the main elements of a software safety process for safety-critical advanced automotive systems. We describe how this proposed process may be integrated with an established system safety process for by-wire automotive systems, and how it may be integrated with an established software development process. Introduction Expanding demand for further improvements in vehicle safety, performance, fuel economy and low emissions has led to a rapid and accelerating increase in the amount and sophistication of vehicle electronics. Emerging vehicle electronics systems are programmable, with a substantial software component, and are highly complex distributed systems. Increasingly, they are receiving driver inputs and directly controlling essential vehicle functions like braking and steering.
    [Show full text]
  • Appendix J Software Safety
    FAA System Safety Handbook, Appendix J: Software Safety December 30, 2000 Appendix J Software Safety SOFTWARE SAFETY...............................................................................................................................1 J.0 SOFTWARE SAFETY DURING LIFE CYCLE PHASES................................................................2 J-1 FAA System Safety Handbook, Appendix J: Software Safety December 30, 2000 J.0 Software Safety During Life Cycle Phases The safety process should support a structured program life cycle model that incorporates both the system design and engineering process and the software acquisition process. Prominent software life cycle models include the waterfall and spiral methodologies. Although different models may carry different lifecycle emphasis, the adopted model should not affect the safety process itself. For discussion purposes only, this enclosure adopts a waterfall model (subject to IEEE/IEA Standard for Information Technology-software life cycle processes No. 12207.) For brevity, only the development phase of the Standard is addressed in terms of the relationship to software safety activities. J.1 Safety Critical Software Development A structured development environment and an organization using state-of-the-art methods are prerequisites to developing dependable safety critical software. The following requirements and guidelines are intended to carry out the cardinal safety rule and its corollary that no single event or action shall be allowed to initiate a potentially hazardous event. The system, upon detection of an unsafe condition or command, shall inhibit the potentially hazardous event sequence and originate procedures/functions to bring the system to a predetermined “safe” state. The purpose of this section is to describe the software safety activities that should be incorporated into the software development phases of project development. The software safety information that should be included in the documents produced during these phases is also discussed.
    [Show full text]
  • A Study on Hazard Analysis in High Integrity Software Standards and Guideiines
    A Study on Hazard Analysis in High Integrity Software Standards and Guideiines Laura M. Ippolito Dolores R. Wallace U.S. DEPARTMENT OF COMMERCE Technology Administration National Institute of Standards and Technology Computer Systems Laboratory Gaithersburg, MD 20899 QC 100 isiisr .056 NO. 5589 1995 A Study on Hazard Analysis in High integrity Software Standards and Guideiines Laura M. Ippolito Dolores R. Wallace U.S. DEPARTMENT OF COMMERCE Technology Administration National Institute of Standards and Technology Computer Systems Laboratory Gaithersburg, MD 20899 January 1995 U.S. DEPARTMENT OF COMMERCE Ronald H. Brown, Secretary TECHNOLOGY ADMINISTRATION Mary L. Good, Under Secretary for Technology NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY Arati Prabhakar, Director ABSTRACT This report presents the results of a study on hazard analysis, especially software hazard analysis, in high integrity software standards and guidelines. It describes types of system hazard analysis (that influence software), types of software hazard analysis, techniques for conducting hazard analysis (along with some of their advantages and disadvantages), and other practices and processes that should be employed in order to ensure the safety of software. KEYWORDS High integrity software, software assurance, software development, software engineering, software hazard analysis, software quality, software reliability, software safety, system hazard analysis. Ill TABLE OF CONTENTS Page EXECUTIVE SUMMARY vii ABBREVIATIONS ix 1. INTRODUCTION 1 1.1. Review Process 2 2. CONTEXT FOR SOFTWARE HAZARD ANALYSIS 5 2.1. Criticality Assessment 5 2.2. Types of Software Related System Hazard Analyses 7 2.3. Types of Software Hazard Analysis 7 3. HAZARD ANALYSIS TECHNIQUES 11 3.1. Code Walk-Throughs 13 3.2.
    [Show full text]
  • Guide to Reusable Launch and Reentry Vehicle Software and Computing System Safety
    FAA Commercial Space Transportation Guide to Reusable Launch and Reentry Vehicle Software and Computing System Safety Version 1.0 July 2006 Guide to Reusable Launch and Reentry Vehicle Software and Computing System Safety Version 1.0 July 2006 Federal Aviation Administration Office of Commercial Space Transportation 800 Independence Avenue, Room 331 Washington, DC 20591 NOTICE Use of trade names or names of manufacturers in this document does not constitute an official endorsement of such products or manufacturers, either expressed or implied, by the Federal Aviation Administration. TABLE OF CONTENTS 1.1 INTRODUCTION ........................................................................................................ 1 1.2 Purpose .................................................................................................................. 1 1.3 Background ........................................................................................................... 1 1.4 Scope ..................................................................................................................... 1 1.5 Authority ............................................................................................................... 1 2.1 DEFINITIONS AND ACRONYMS ............................................................................ 2 2.2 Definitions ............................................................................................................. 2 2.3 Acronyms .............................................................................................................
    [Show full text]
  • Software Quality Assurance Applied Towards the Development of VHDL‐Based Safety Critical Hardware
    Software Quality Assurance Applied towards the Development of VHDL‐Based Safety Critical Hardware David A. Geremia Principal Electrical Design Engineer [email protected] 61st NDIA Annual Fuze Conference San Diego CA May 16, 2018 NOTICE ‐ This document does not contain export controlled technical data. Introduction The software used in today’s safety critical systems requires a significant amount of analysis and testing as well as traceability to the requirements “Software‐like” languages are treated similarly by today’s munition‐related safety technical review panels 2 Introduction Very High Speed Integrated Circuit (VHSIC) Hardware Description Language (VHDL) is one of these “software‐like” languages Requires the generation of the appropriate Level of Rigor (LOR) and the resultant analyses As part of the academic pursuit on which this presentation is based, software was created in order to automate the generation of the appropriate LOR tasks, establish traceability, & provide transparency 3 Background The implementation of safety features in safety critical systems has evolved in the last few decades Initially, safety features were implemented using a mechanical means such as springs, setback weights, rotors and shear pins Recently, electronics have been used in order to implement safety features i.e. analog and/or simple digital circuits 4 Background Most recently, software and “software‐like” devices are being used to implement safety features Field Programmable Gate Arrays (FPGAs) are hardware devices that are being used more often in today’s munition‐related safety‐critical applications in order to implement safety features A high‐level language (such as VHDL) is used to design the safety features which are implemented using an FPGA.
    [Show full text]
  • Joint Software Systems Safety Engineering Handbook ------Developed by the Joint Software Systems Safety Engineering Workgroup
    DEPARTMENT OF DEFENSE JOINT SOFTWARE SYSTEMS SAFETY ENGINEERING HANDBOOK ----------------------------------------- DEVELOPED BY THE JOINT SOFTWARE SYSTEMS SAFETY ENGINEERING WORKGROUP Original published December 1999 Version 1.0 Published August 27, 2010 Naval Ordnance Safety and Security Activity 3817 Strauss Avenue, Building D-323 Indian Head, MD 20640-5555 Prepared for: Director of Defense Research and Engineering Distribution Statement A Approved for public release; distribution is unlimited. Software Systems Safety Engineering Handbook Table of Contents Table of Contents 1 Overview ........................................................................................................... 1 2 Introduction to the Handbook ........................................................................... 3 2.1 Introduction ....................................................................................................... 3 2.2 Purpose .............................................................................................................. 4 2.3 Scope ................................................................................................................. 4 2.4 Authority and Standards ................................................................................... 5 2.5 Handbook Overview ......................................................................................... 6 2.5.1 Historical Background ...................................................................................... 6 2.5.2 Management Responsibilities
    [Show full text]
  • A Validation Metrics Framework for Safety-Critical Software-Intensive Systems
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Calhoun, Institutional Archive of the Naval Postgraduate School Calhoun: The NPS Institutional Archive Theses and Dissertations Thesis Collection 2009-03 A validation metrics framework for safety-critical software-intensive systems Cruickshank, Kristian John. Monterey, California. Naval Postgraduate School http://hdl.handle.net/10945/4891 NAVAL POSTGRADUATE SCHOOL MONTEREY, CALIFORNIA THESIS A VALIDATION METRICS FRAMEWORK FOR SAFETY- CRITICAL SOFTWARE-INTENSIVE SYSTEMS by Kristian John Cruickshank March 2009 Thesis Advisor: James B. Michael Thesis Co-Advisor: Man-Tak Shing Approved for public release; distribution is unlimited THIS PAGE INTENTIONALLY LEFT BLANK REPORT DOCUMENTATION PAGE Form Approved OMB No. 0704-0188 Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instruction, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-0188) Washington DC 20503. 1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED March 2009 Master’s Thesis 4. TITLE AND SUBTITLE A Validation Metrics Framework for Safety-Critical 5. FUNDING NUMBERS Software-Intensive Systems 6. AUTHOR(S) Kristian John Cruickshank 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8.
    [Show full text]
  • NASA Software Safety Guidebook
    NOT MEASUREMENT SENSITIVE National Aeronautics and NASA-GB-8719.13 Space Administration March 31, 2004 NASA Software Safety Guidebook NASA TECHNICAL STANDARD PREFACE Effective Date: 31 March 2004 This document has been issued to make available to software safety practitioners a guidebook for assessing software systems for software’s contribution to safety and techniques for analyzing and applying appropriate safety techniques and methods to software. Software developers and software safety engineers are the primary focus; however, software assurance (SA) engineers, project managers, system engineers, and system safety engineers will also find this guidebook useful. The document: Provides an overview of general software safety and good software engineering practices which contribute to software system safety. Provides the means to scope and tailor the software safety and software engineering activities to obtain the most cost effective, best quality, and safest products. Provides analyses, methods and guidance which can be applied during each phase of the software life cycle. Multiple checklists and examples are provided as well as specific instructions for applying FMEA/CIL and FTA to software. Includes development approaches, safety analyses, and testing methodologies that lead to improved safety in the software product. Procuring NASA Enterprise Programs or Centers shall review this document for applicability to NASA contracts as well as for applicability to its internal activities. Questions concerning the application of this publication to specific procurements or requests should be referred to the NASA Enterprise Program or Center. This guidebook cancels NASA-GB-1740.13-96, NASA Guidebook for Safety Critical Software Analysis and Development. /s/ Bryan O’Connor Associate Administrator for Safety and Mission Assurance NASA-GB-8719.13 1 Foreword This guidebook was created to provide specific information and guidance on the process of creating and assuring safe software.
    [Show full text]
  • Software Engineering for Safety: a Roadmap Robyn Lutz
    Software Engineering for Safety: A Roadmap Robyn Lutz Key Research Pointers Provide readier access to formal methods for developers of safety-critical systems by further integration of informal and formal methods. Develop better methods for safety analysis of product families and safe reuse of Commercial- Off-The-Shelf software. Improve the testing and evaluation of safety-critical systems through the use of requirements- based testing, evaluation from multiple sources, model consistency, and virtual environments. Advance the use of runtime monitoring to detect faults and recover to a safe state, as well as to profile system usage to enhance safety analyses. Promote collaboration with related fields in order to exploit advances in areas such as security and survivability, software architecture, theoretical computer science, human factors engineering, and software engineering education. The Author Robyn R. Lu~z is a senior engineer at Jet Propulsion Laboratory, California Institute of Technology. She is also an Affiliate Assistant Professor in the Department of Computer Science at Iowa State University, Ames, Iowa, where she teaches software engineering. Dr. Lutz has worked on spacecraft projects in fault protection, real-time commanding, and software requirements and design verification. Her research interests include software safety, software certification, safe reuse of product families, formal methods for requirements analysis, and fault monitoring and recovery strategies for spacecraft: http://www.cs.iastate.edu/-rlutz/; email: [email protected].
    [Show full text]
  • AC 450.141-1 Computing Systems and Software
    U.S. Department Advisory of Transportation Federal Aviation Administration Circular Subject: Computing System Safety Date: 10/15/2020 AC No: 450.141-1 Initiated By: AST-1 This Advisory Circular (AC) provides guidance for an applicant to identify computing system safety items, develop safety requirements for each computing system safety item, and mitigate the risks presented by computing system safety items in accordance with title 14 of the Code of Federal Regulations (14 CFR) § 450.141. An applicant must identify all computing system safety items and implement safety requirements for each computing system safety item based on level of criticality, in accordance with § 450.141(a) and (b). An applicant must then implement a development process appropriate for each computing system safety item’s level of criticality, in accordance with § 450.141(c). The FAA considers this AC an accepted means of compliance with the regulatory requirements of § 450.141. It presents one, but not the only, acceptable means of compliance with the associated regulatory requirements. The FAA will consider other means of compliance that an applicant may elect to present. The contents of this document do not have the force and effect of law and are not meant to bind the public in any way. The document is intended only to provide clarity to the public regarding existing requirements under the law or agency policies. If you have suggestions for improving this AC, you may use the Advisory Circular Feedback form at the end of this AC. Wayne R. Monteith Associate Administrator
    [Show full text]
  • Software System Safety
    Software System Safety Nancy G. Leveson MIT Aero/Astro Dept. ([email protected]) http://sunnyday.mit.edu MIT, Room 33−334 77 Massachusetts Ave., Cambridge MA 02139 Tel: 617−258−0505 c Copyright by the author,, February 2004.All rights reserved. Copying without fee is permitted provided that the copies are not made or distributed for direct commercial advantage and provided that credit to the source is given. Abstractingwith credit is permitted. Overview of the Class c ¢¡¢£¤¡¢¥¤¦¢§©¨ Week 1: Understanding the Problem Week 2: The Overall Process and Tasks Week 3: Hazard Causal Analysis (Root Cause Analysis) Week 4: A New Approach to Hazard, Root Cause, and Accident Analysis Week 5: Requirements Analysis Week 6: Design for Safety Week 7: Human−Machine Interaction and Safety Week 8: Testing and Assurance, Operations, Maintenance Week 9: Management and Organizational Issues (including safety culture) Week 10: Summary and Conclusions c ¢¡¢£¤¡¢¥¤¦¢§©¨ The Problem The first step in solving any problem is to understand it. We often propose solutions to problems that we do not understand and then are surprised when the solutions fail to have the anticipated effect. Accident with No Component Failures c ¢¡¢£¤¡¢¥¤¦¢§©¨ ¢¡© ¦¢¢ ¡¢ VENT LA GEARBOX LC CONDENSER CATALYST VAPOR COOLING WATER REFLUX REACTOR COMPUTER c ¢¡¢£¤¡¢¥¤¦¢§©¨ ¢¡© ¦¢¢ ¡¢ Types of Accidents Component Failure Accidents Single or multiple component failures Usually assume random failure System Accidents Arise in interactions among components No components may have "failed" Caused by interactive complexity and tight coupling Exacerbated by the introduction of computers. c ¢¡¢£¤¡¢¥¤¦¢§©¨ $ ¦¢¢ ¡¢ Interactive Complexity ¢¡© Complexity is a moving target The underlying factor is intellectual manageability 1. A "simple" system has a small number of unknowns in its interactions within the system and with its environment.
    [Show full text]
  • Engineering Safety Requirements, Safety Constraints, and Safety-Critical Requirements
    JOURNAL OF OBJECT TECHNOLOGY Online at http://www.jot.fm. Published by ETH Zurich, Chair of Software Engineering ©JOT, 2004 Vol. 3, No. 3, March-April 2004 Engineering Safety Requirements, Safety Constraints, and Safety-Critical Requirements Donald Firesmith, Software Engineering Institute, U.S.A. Abstract As software-intensive systems become more pervasive, more and more safety-critical systems are being developed. In this column, I will use the concept of a quality model to define safety as a quality factor. Thus, safety (like security and survivability) is a kind of defensibility, which is a kind of dependability, which is a kind of quality. Next, I discuss the structure of quality requirements and show how safety requirements can be engineered based on safety’s numerous quality subfactors. Then, I define and discuss safety constraints (i.e., mandated safeguards) and safety-critical requirements (i.e., functional, data, and interface requirements that can cause accidents if not implemented correctly). Finally, I pose a set of questions regarding the engineering of these three kinds of safety-related requirements for future research and experience to answer. 1 INTRODUCTION As software-intensive systems become more pervasive, a large number of safety-critical systems are being developed and fielded. To improve productivity, performance, and cost-effectiveness, we are developing more and more safety-critical systems that are under computer control. And centralized computer control is enabling many safety- critical systems (e.g., chemical and pesticide factories) to grow in size, complexity, and potential for catastrophic failure. We use software to control our factories and refineries as well as power generation and distribution.
    [Show full text]