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Contact: Cary Meier, Systems Safety Analysis Branch, AAL 240, Alaska Posted On: July 24, 2005 System Safety! What is it? . . . human performance system safety. This is more along the lines of how a human uses a component, how a process is followed. . .

 SYSTEM SAFETY – WHAT IS IT?

What is System Safety?  The textbook definition is: “The limiting of accident risk through design of a systematic, methodical, and forward-looking hazard identification and control program, beginning in the conceptual design phase and continuing through its development, fabrication, testing, production, use, and ultimate disposal.” 

Let’s expand by saying that it is about risk management, human factors, ergonomics, equipment design, reliability programs, continued analysis systems, root cause analysis, and the management of error.  We can further divide all of these things into two basic groups.

TECHNOLOGY SYSTEM SAFETY 

Let us call the first group “technology system safety”.  This group is the engineering side, the examination of present human engineering, design criteria, principles, and practices to achieve success through integration of the human into the system, subsystem, or equipment.  Further more it is the addressing of human factors input into a component’s design, development, testing, and evaluations processes.  Emphasis is put on the systems approach to human-machine interfacing.  This technology system safety is the reliability of the component, documenting the life of the component to establish life limitations, and other issues such as the size of a control knob, if it can be turned when wearing gloves, if the display of the component can be seen if the sun glares on the glass, and so on.  This also includes the analytical techniques and documentation requirements to provide proper design of equipment and systems and to protect against products liability.  Safety concepts, legal concepts, qualitative hazard evaluation, hazard classification, system life cycle safety, statistical distributions, fault tree and software safety analysis are integral processes of technology system safety.

HUMAN PERFORMANCE SYSTEM SAFETY

We also have what could be called “human performance system safety”.  This is more along the lines of how a human uses a component, how a process is followed, how an activity is conducted, or the measurement of human performance and how errors are managed.  This requires the application of the six safety attributes of System Safety (responsibility, authority, procedures, controls, process measurement, & interfaces) to identify the hazards related to all aspects of a process and the determination of their causes. This involves defining the physical and functional characteristics of a process by employing all the information available (design documents, operating procedures, standards, equipment, environment, human factors, training, etc.) and relating the interaction between this information.  Then the hazards are assessed to determine severity and probability, and to recommend a means for their elimination or control.  After that an evaluation is conducted as a follow-up analysis to determine effectiveness of preventive measures, addressing new or unexpected hazards, and issuing additional recommendations if necessary.  Human performance system safety is the assurance that a human can perform any given action correctly and safely each and every time. 

Our primary focus or objective in Flight Standards is the application of human performance system safety.  This is where we need to target our resources to enhance aviation safety and reduce accidents.  Human error is the leading primary cause of aviation accidents, while equipment failure contributes a small percentage to the probable cause.  Because of this, the improvement of human performance through the application of system safety is very important.

Cary Meier
Systems Safety Analysis Branch, AAL 240, Alaska

Reference Material and Organizations for this article:
Human Factors in Aviation Safety, University of Southern California
TapRooT® Root Cause Analysis Problem Investigation Proactive Improvement, Paradies and Unger
System Safety Society
NASA
NTSB
James Reason Publications