1. Engineering a Safer World

2. Traditional Approach to Safety Traditionally view safety as a failure problem –Chain of random, directly related failure events leads to loss –Establish barriers between events or try to prevent individual component failures e.g., redundancy, overdesign, safety margins, punishment and training for operators, defense in depth Analysis techniques –Focus on probability of component failures and combinations of component failures –Where do they get the probabilities? Historical failure rates Make up numbers for human error and software error or ignore these in the analysis

3. Chain-of-events example

4. Confusing Safety and Reliability

5. It’s only a random failure, sir! It will never happen again.

6. Limitations of Traditional Approach Systems are becoming more complex –Accidents often result from interactions among components, not just component failures –Too complex to anticipate all potential interactions By designers By operators –Indirect and non-linear interactions –Can no longer exhaustively test and get out design errors Omits or oversimplifies important factors –Human error –New technology, particularly software –Culture and management –Evolution and adaptation

7. Accident with No Component Failures

8. Types of Accidents Component Failure Accidents –Single or multiple component failures –Usually assume random failure Component Interaction Accidents –Arise in interactions among components –Complexity getting to point where cannot anticipate or guard against all potential interactions –Exacerbated by introduction of computers and software

9. Interactive Complexity Arises in interactions among system components –Software allows us to build highly coupled and interactively complex systems –Coupling causes interdependence –Increases number of interfaces and potential interactions Too complex to anticipate all potential interactions –By designers –By operators May lead to accidents even when no individual component failures

10. Non-Linear Complexity Cause and effect not related in an obvious way Systemic factors in accidents, e.g., safety culture, work environment, production pressures, etc. –Our safety engineering techniques assume linearity –Systemic factors affect events in non-linear and indirect ways

11. Dynamic Complexity Related to changes over time –Systems are not static, but we often assume they are –Systems migrate toward states of high risk under competitive and financial pressures [Rasmussen] –Need to control and identify unsafe changes

12. Software-Related Accidents Are usually caused by flawed requirements –Incomplete or wrong assumptions about operation of controlled system or required operation of computer –Unhandled controlled-system states and environmental conditions Merely trying to get the software “correct” or to make it reliable will not make it safer under these conditions.

13. Software-Related Accidents (2) Software may be highly reliable and “correct” and still be unsafe: –Correctly implements requirements but specified behavior unsafe from a system perspective. –Requirements do not specify some particular behavior required for system safety (incomplete) –Software has unintended (and unsafe) behavior beyond what is specified in requirements.

14. Systems Thinking Event-based Thinking

15. STAMP: System-Theoretic Accident Model and Processes Based on Systems Theory (vs. Reliability Theory)

16. Applying Systems Thinking to Safety Accidents involve a complex, dynamic “process” –Not simply chains of failure events –Arise in interactions among humans, machines and the environment Treat safety as a dynamic control problem –Safety requires enforcing a set of constraints on system behavior –Accidents occur when interactions among system components violate those constraints –Safety becomes a control problem rather than just a reliability problem

17. Safety as a Dynamic Control Problem Examples –O-ring did not control propellant gas release by sealing gap in field joint of Challenger Space Shuttle –Software did not adequately control descent speed of Mars Polar Lander –At Texas City, did not control the level of liquids in the ISOM tower; –In DWH, did not control the pressure in the well; –Financial system did not adequately control the use of financial instruments

18. Safety as a Dynamic Control Problem Safety as a Dynamic Control Problem (2) Most major accidents arise from a slow migration of the entire system toward a state of high-risk Need to control and detect this migration A change in emphasis: “prevent failures” ↓ “enforce safety constraints on system behavior”

19. Example Safety Control Structure

20. Qi Hommes, 2012

21. Safety as a Control Problem (3) Goal: Design an effective control structure that eliminates or reduces adverse events. –Need clear definition of expectations, responsibilities, authority, and accountability at all levels of safety control structure –Entire control structure must together enforce the system safety property (constraints) Physical design (inherent safety) Operations Management Social interactions and culture

22. Controlled Process Process Model Control Actions Feedback Role of Process Models in Control Controllers use a process model to determine control actions Accidents often occur when the process model is incorrect Four types of hazardous control actions: Control commands required for safety are not given Unsafe ones are given Potentially safe commands given too early, too late Control stops too soon or applied too long Controller 22 (Leveson, 2003); (Leveson, 2011) Control Algorithm

23. STAMP: Theoretical Causality Model Accident/Event Analysis CAST Hazard Analysis STPA System Engineering (e.g., Specification, Safety-Guided Design, Design Principles) Specification Tools SpecTRM Risk Management Operations Management Principles/ Organizational Design Identifying Leading Indicators Organizational/Cultural Risk Analysis Tools Processes Regulation

24. Learning from Events CAST: Causal Analysis based on System Theory Goal: more complete causal analysis of accidents, incidents, and adverse events

25. Facts about Accidents Almost never have single causes –“Root cause seduction” –Accidents are complex processes Usually involve flaws in –Engineered equipment –Operator behavior –Management decision making –Safety culture –Regulatory oversight

26. Root Cause Seduction Assuming there is a root cause gives us an illusion of control. –Usually focus on operator error or technical failures –Ignore systemic and management factors –Leads to a sophisticated “whack a mole” game Fix symptoms but not process that led to those symptoms In continual fire-fighting mode Having the same accident over and over

27. Three Levels of Analysis What (events) –e.g., explosion Who and how (conditions) –e.g., bad valve design, operator did not notice something Why (systemic factors) –e.g., production pressures, cost concerns, flaws in design process, flaws in reporting process, etc. –Why was safety control structure ineffective in preventing the loss?

28. Goals for an Accident Analysis Technique Minimize hindsight bias Provide a framework or process to assist in understanding entire accident process and identifying systemic factors Get away from blame (“who”) and shift focus to “why” and how to prevent in the future Goal is to determine –Why people behaved the way they did –Weaknesses in the safety control structure that allowed the loss to occur

29. Hazard Analysis “Investigating an accident before it occurs” Identify potential causal scenarios and try to eliminate them Must be based on some model of how and why accidents occur STPA (System-Theoretic Process Analysis) –Based on STAMP –Assumes accidents are more complex processes than just chains of component failure events

30. STPA (System-Theoretic Process Analysis) A top-down, system engineering technique Identifies safety constraints (system and component safety requirements) Identifies scenarios leading to violation of safety constraints; use results to design or redesign system to be safer Can be used on technical design and organizational design Supports a safety-driven design process where –Hazard analysis influences and shapes early design decisions –Hazard analysis iterated and refined as design evolves

31. Steps in STPA Establish fundamentals –Define “accident” for your system –Define hazards –Rewrite hazards as constraints on system design –Draw preliminary (high-level) safety control structure Identify potentially unsafe control actions (high-level safety requirements and constraints) Determine how each potentially hazardous control action could occur

32. Steps in STPA Establish foundation for analysis –Define “accident” for your system –Define hazards –Rewrite hazards as constraints on system design –Draw preliminary (high-level) safety control structure Step 1: Identify potentially unsafe control actions (high-level safety requirements and constraints) [Step 1 STPA] Step 2: Determine how each potentially hazardous control action could occur [Step 2 STPA] x

33. Identifying Accidents and Hazards Accident (Loss): An undesired or unplanned event that results in a loss, including a loss of human life or human injury, property damage, environmental pollution, mission loss, financial loss, etc. Hazard: A system state or set of conditions that together with a worst-case set of environmental conditions, will lead to an accident (loss)

34. Accident (Loss): An undesired or unplanned event that results in a loss, including a loss of human life or human injury, property damage, environmental pollution, mission loss, financial loss, etc. Hazard: A system state or set of conditions that together with a worst-case set of environmental conditions, will lead to an accident (loss) SystemAccidentHazard ACCTwo vehicles collideInadequate distance between vehicle and one in front or in back Chemical Plant People die or are injured due to exposure to chemicals Chemicals in air after release from plant Train door controller Passenger falls out of trainDoor is open when train starts Door is open while train moving

35. Identify High-Level Safety Constraints (Requirements) HazardSafety Constraint (Requirement) Inadequate distance between vehicle and one in front or in back Vehicles must never violate minimum separation requirements Chemicals in air after release from plant Chemicals must never be released inadvertently from plant Door is open when train startsTrain must never start while door is open Door is open while train movingTrain must never open while train is moving

36. Safety Constraints vs. Safety Requirements Design constraints: –ACC must not violate separation requirements with object ahead –ACC must not brake too abruptly Design requirements –ACC shall maintain a TBD amount of distance between the vehicle and the object in front when engaged –ACC shall limit vehicle deceleration to no more than TBC m/s 2

37. In-Class Example In-Trail Procedure (ITP) A new passing procedure for oceanic flights

38. In-Trail Procedure (ITP) Enables aircraft to achieve FL changes on a more frequent basis. Designed for oceanic and remote airspaces not covered by radar. Permits climb and descent using new reduced longitudinal separation standards. Potential Benefits –Reduced fuel burn and CO2 emissions via more opportunities to reach the optimum FL or FL with more favorable winds. –Increased safety via more opportunities to leave turbulent FL. But standard separation requirements not met during maneuver

39. ITP Procedure – Step by Step 1.Check that ITP criteria are met.ITP criteria 2.If ITP is possible, request ATC clearance 3.Check that there are no blocking aircraft other than Reference Aircraft in the ITP request. 4.Check that ITP request is applicable (i.e. standard request not sufficient) and compliant with ITP phraseology. 5.Check that ITP criteria are met.ITP criteria 6.If all checks are positive, issue ITP clearance. Flight Crew Air Traffic Controller 8. When ITP clearance is received, check that ITP criteria are still met. 9. If ITP criteria are still met, accept ITP clearance via CPDLC. 10. Execute ITP clearance without delay. 11. Report when established at the cleared FL. Involves multiple aircraft, crew, communications (ADS-B, GPS), ATC

40. Accident and Hazard Definition for ITP Accident: Two aircraft collide Hazard?:

41. Accident and Hazard Definition for ITP Accident: Two aircraft collide Hazard: Two aircraft violate minimum separation requirement

42. Accident with No Component Failures

43. Batch Reactor In-Class Exercise What is the accident? What is the system-level hazard (associated with that accident)? What is the high-level system safety requirement (safety constraint)?

44. Steps in STPA Establish foundation for analysis –Define “accident” for your system –Define hazards –Rewrite hazards as constraints on system design –Draw preliminary (high-level) functional control structure Step 1: Identify potentially unsafe control actions (high-level safety requirements and constraints) Step 2: Determine how each potentially hazardous control action could occur

45. Draw the Functional Control Structure Identify major components and controllers (HINT: Start at very high level) Label control and feedback arrows Create the preliminary process models

46. ITP High-Level Control Structure What are the major components and controllers of the system?

47. ITP High-Level Control Structure What are the major components and controllers of the system? ATC, pilot, aircraft Who controls who or what?

48. ITP High-Level Control Structure What are the major components and controllers of the system? ATC, pilot, aircraft Who controls who or what? ATC Pilot Aircraft

49. ITP High-Level Control Structure (2) What commands are sent and feedback provided? ATC Pilot Aircraft

50. ITP High-Level Control Structure (2) What commands are sent and feedback provided? ATC Clearance to pass (to execute ITP) Requests Acknowledgements Pilot Aircraft Execute ITP maneuver A/C status, position, etc.

51. High-Level Control Structure for ITP

52. Pilot Responsibilities and Process Model Responsibilities: –Assess whether ITP appropriate –Check if ITP criteria are met –Request ITP –Receive ITP approval –Recheck criteria –Execute flight level change –Confirm new flight level to ATC Process Model –Own ship climb/descend capability – ADS-B data for nearby aircraft (velocity, position, orientation) –ITP criteria (speed, distance, relative attitude, similar track, data quality) –State of ITP request/approval –etc.

53. For the Batch Reactor Draw the functional control structure

54. VALVES Open water Open catalyst Close water Close catalyst PROCESS MODEL: Water valve: Open, closed, unknown Catalyst valve: Open, closed, unknown Plant state: OK, not OK, unknown Start process Stop process Status information Plant state alarm Plant PROCESS MODEL Plant state: OK, Not OK, unknown Reactor state: Operating, not operating, unknown COMPUTER OPERATOR ??? Status info

55. What are the Responsibilities of the Software Controller? Not the requirements, simply the basic functions to be implemented

56. What are the Responsibilities of the Software Controller? Open water valve Open catalyst valve Tell operators when get message about problem in plant state

57. Steps in STPA Establish foundation for analysis –Define “accident” for your system –Define hazards –Rewrite hazards as constraints on system design –Draw preliminary (high-level) safety control structure Step 1: Identify potentially unsafe control actions (high-level safety requirements and constraints) Step 2: Determine how each potentially hazardous control action could occur

58. Four Ways Unsafe Control Can Occur A control action required for safety is not provided or is not followed An unsafe control action is provided that leads to a hazard A potentially safe control action provided too late, too early, or out of sequence A safe control action is stopped too soon or applied too long (for a continuous or non-discrete control action) Control Action Not providing causes hazard Providing causes hazard Too early/too late, wrong order Stopped too soon/ applied too long

59. Step 1 for Pilot Control Action Not providing causes hazard Providing causes hazard Too early/too late, wrong order Stopped too soon/ applied too long Execute ITP Maneuver Pilot Aircraft Execute ITP maneuver A/C status, position, etc.

60. Potentially Hazardous Control Actions by the Flight Crew Control Action Not Providing Causes Hazard Providing Causes Hazard Wrong Timing/Order Causes Hazard Stopped Too Soon/Applied Too Long Execute ITP ITP executed when not approved ITP executed when ITP criteria are not satisfied ITP executed with incorrect climb rate, final altitude, etc ITP executed too soon before approval ITP executed too late after reassessment ITP aircraft levels off above requested FL ITP aircraft levels off below requested FL Abnormal Termination of ITP FC continues with maneuver in dangerous situation FC aborts unnecessarily FC does not follow regional contingency procedures while aborting

61. High Level Constraints on Flight Crew The flight crew must not execute the ITP when it has not been approved by ATC. The flight crew must not execute an ITP when the ITP criteria are not satisfied. The flight crew must execute the ITP with correct climb rate, flight levels, Mach number, and other associated performance criteria. The flight crew must not continue the ITP maneuver when it would be dangerous to do so. The flight crew must not abort the ITP unnecessarily. (Rationale: An abort may violate separation minimums) When performing an abort, the flight crew must follow regional contingency procedures. The flight crew must not execute the ITP before approval by ATC. The flight crew must execute the ITP immediately when approved unless it would be dangerous to do so. The crew shall be given positive notification of arrival at the requested FL

62. Potentially Hazardous Control Actions for ATC Control Action Not Providing Causes Hazard Providing Causes Hazard Wrong Timing/Order Causes Hazard Stopped Too Soon or Applied Too Long Causes Hazard Approve ITP request Approval given when criteria are not met Approval given to incorrect aircraft Approval given too early Approval given too late Deny ITP request Abnormal Termination Instruction Aircraft should abort but instruction not given Abort instruction given when abort is not necessary Abort instruction given too late

63. High-Level Constraints on ATC Approval of an ITP request must be given only when the ITP criteria are met. Approval must be given to the requesting aircraft only. Approval must not be given too early or too late [needs to be clarified as to the actual time limits] An abnormal termination instruction must be given when continuing the ITP would be unsafe. An abnormal termination instruction must not be given when it is not required to maintain safety and would result in a loss of separation. An abnormal termination instruction must be given immediately if an abort is required.

64. Hazard: Catalyst in reactor without reflux condenser operating (water flowing through it) Control Action Not providing causes hazard Providing causes hazard Too early/too late, wrong order Stopped too soon/ applied too long Create this table for the computer controlling the valves loop in your control diagram For the Batch Reactor:

65. Hazard: Catalyst in reactor without reflux condenser operating (water flowing through it) Control Action Not providing causes hazard Providing causes hazard Too early/too late, wrong order Stopped too soon/ applied too long Open water Not opened when catalyst open Open water more than X seconds after open catalyst Stop before fully opened Close water Close while catalyst open Close water before catalyst closes Open catalyst Open when water valve not open Open catalyst more than X seconds before open water Close catalyst Do not close when water closed Close catalyst more than X seconds after close water Stop before fully closed

66. What are the safety requirements (constraints) on the software controller given this table?

67. Water valve must always be fully open before catalyst valve is opened. –Water valve must never be opened (complete opening) more than X seconds after catalyst valve opens Catalyst valve must always be fully closed before water valve is closed. –Catalyst valve must never be closed more than X seconds after water valve has fully closed.

68. Steps in STPA Establish foundation for analysis –Define “accident” for your system –Define hazards –Rewrite hazards as constraints on system design –Draw preliminary (high-level) safety control structure Step 1: Identify potentially unsafe control actions (high-level safety requirements and constraints) Step 2: Determine how each potentially hazardous control action could occur

69. STPA Step 2 69 Inadequate Control Algorithm (Flaws in creation, process changes, incorrect modification or adaptation) Controller Process Model (inconsistent, incomplete, or incorrect) Control input or external information wrong or missing Actuator Inadequate operation Inappropriate, ineffective, or missing control action Sensor Inadequate operation Inadequate or missing feedback Feedback Delays Component failures Changes over time Controlled Process Unidentified or out-of-range disturbance Controller Process input missing or wrong Process output contributes to system hazard Incorrect or no information provided Measurement inaccuracies Feedback delays Delayed operation Conflicting control actions Missing or wrong communication with another controller Controller

70. Example STPA Results

71. Example Causal Analysis Unsafe control action: Pilot executes maneuver when criteria not met Possible Causes?

72. Four Ways Unsafe Control Can Occur A control action required for safety is not provided or is not followed An unsafe control action is provided that leads to a hazard A potentially safe control action provided too late, too early, or out of sequence A safe control action is stopped too soon or applied too long (for a continuous or non-discrete control action)

73. Inadequate Control Algorithm (Flaws in creation, process changes, incorrect modification or adaptation) Controller Process Model ( inconsistent, incomplete, or incorrect) Control input or external information wrong or missing Actuator Inadequate operation Sensor Inadequate operation Inadequate or missing feedback Feedback Delays Component failures Changes over time Controlled Process Unidentified or out-of-range disturbance Controller Process input missing or wrong Process output contributes to system hazard Incorrect or no information provided Measurement inaccuracies Feedback delays Delayed operation Conflicting control actions Missing or wrong communication with another controller Controller Safe control action provided but not followed

74. Exercise Continued (Batch Reactor) STEP 2: Identify some causes of the hazardous control action: Open catalyst valve when water valve not open –HINT: Consider how controller’s process model could identify that water valve is open when it is not. What are some causes for a required control action (e.g., open water valve) being given by the software but not executed. What design features (controls) might you use to protect the system from the scenarios you found?

75. Results What did you find? What “controls” did you add? What about the actual scenario that occurred in the accident?

76. Next Steps Use causal analysis to identify detailed safety design requirements and design options If desired, iterate top-down –Refine into more detailed control structures –Refine safety constraints (requirements) into more detailed requirements for each component Use STPA results to assure safety when use in different environment(s) than assumed for original certification Use STPA results to evaluate other types of changes to system and environment

77. Example Controls for Causal Scenarios Scenario 1 - Operator was expecting patient to have been positioned, but table positioning was delayed compared to plan (e.g. because of delays in patient preparation or patient transfer to treatment area; because of unexpected delays in beam availability or technical issues being processed by other personnel without proper communication with the operator). Controls: –Provide operator with direct visual feedback to the gantry coupling point, and require check that patient has been positioned before starting treatment (M1). –Provide a physical interlock that prevents beam-on unless table positioned according to plan

78. Example Controls for Causal Scenarios (2) Scenario 2 - Operator is asked to turn the beam on outside of a treatment sequence (e.g. because the design team wants to troubleshoot a problem) but inadvertently starts treatment and does not realize that the facility proceeds with reading the treatment plan. Controls : –Reduce the likelihood that non-treatment activities have access to treatment-related input by creating a non- treatment mode to be used for QA and experiments, during which facility does not read treatment plans that may have been previously been loaded (M2); –Make procedures (including button design if pushing a button is what starts treatment) to start treatment sufficiently different from non-treatment beam on procedures that the confusion is unlikely.

79. Additional Things Not Covered Today Rigorous method for performing Step 1 –Much of it can be automated or assistance provided –Generate executable and analyzable model-based safety requirements Multiple controller analysis

80. Organizational Aspects of Risk Examples so far focus on physical level Also requirements and control responsibilities at management level to satisfy system safety requirements Can identify unsafe control actions and causal scenarios at higher levels of the control structure (perform a risk analysis) and build in controls to prevent them Behavior and control structures change over time –Prevent migration to higher levels of risk –Detect when occurs

81. Organizational Aspects of Risk (2) Can look at non-safety risks, including project risks, budget risks, schedule risks and tradeoffs Goal may be to evaluate an existing control structure or to create a new one Creating leading indicators Current or past examples: –NASA safety management after Columbia –Radiation therapy at UCSD and UCLA hospitals (and maybe Boston Mass General) –CO 2 capture, transport, and storage (Samadi, Ecole des Mines) –Product Development Process (Goerges, Cummins Engine)

82. Current Research Projects Human factors engineering –Design to reduce human error –Integrating sophisticated human factors into hazard analysis Leading Indicators Cyber Warfare and Nuclear Security Organizational, Managerial, and Project Risk Analysis More applications: high-speed rail, autos, medicine, aircraft, NextGen (TBO) Application to Financial Systems Other Emergent System Properties Tools and formal assistance with analysis