Systems Safety Techniques

Systems safety techniques have been proven a valuable process for assessing the reliability and safety of complex systems. There are a variety of techniques that can be used to identify potential problem areas of the system. The major components of a system include the equipment, the personnel, and the environment. The systems safety techniques can be used before the fact to identify potential situations that can increase the risk for a failure, or they can be used in after-the-fact situations to determine the contributing factors that led to the accident, thus identifying prevention areas for future accidents. 

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This is because many of the factors that have been shown to be the antecedents of major process accidents (e.g., poor procedures, inadequate training) are not usually under the control of the individual worker. The other approaches can also be applied to improving quality and productivity as well as process safety and can be readily integrated with engineering system safety techniques, as will be described in Chapters 4 and 5. 

To properly apply the system safety techniques to die design and operation of potentially hazardous teclmologies, die design engineer must have a clear miderstanding of die system and be able to prepare a written response to questions such as ... 

In order to properly apply tlie system safety techniques to tlie design and operation of potentially hazardous tcclmologics, a series of questions regarding safety must be asked and answered. 

Professional credentials or experience in system safety is not required to appreciate the potential value of the systems approach and system safety techniques to general safety and health practice [p. ix]. 

Fault tree analysis (FTA) was developed by Bell Telephone Laboratories for the U.S. Air Force in 1962 and has been used as one of the primary system safety techniques since the system safety effort began. The Boeing Company was also an early pioneer in the use of fault tree analysis. 

Fault tree analysis is one of the most meaningful system safety techniques available for systematically reducing the probability of an undesired event. It can also be one of the more expensive techniques because it requires a skilled and knowledgeable analyst and a considerable amount of time, especially if the project is complex and a quantitative approach is required. 

Failure modes and effects analysis (FMEA) A systematic, methodical analysis performed to identify and document all identifiable failure modes at a prescribed level and to specify the resultant effect of the failure mode at various levels of assembly (NSTS 22254) the failure or malfunction of each system component is identified, along with the mode of failure (e.g., switch jammed in the on position). The effects of the failure are traced through the system and the ultimate effect on task performance is evaluated. Also called failure mode and effect criticality analysis (ASSE) a basic system safety technique wherein the kinds of failures that might occur and their effect on the overall product or system are considered. Example The effect on a system by the failure of a single component, such as a register or a hydraulic valve (SSDC). 

One difficulty in applying certain systems approaches and techniques to problem solving is an inability of the practitioners to merge the various approaches and techniques, to relate them to each other, and to understand the relationship of diverse system safety techniques. Joe Stephenson shows in this text not only how the approaches vary, but also how they are similar and can interact with each other. This is a valuable service to the many disciplines and practitioners of the safety and health community. 

Joe Stephenson makes practical the application of system safety techniques to safety and health problems not previously amenable to system safety solutions. Seeing the forest instead of the trees is a unique contribution of this book. The interaction of many disciplines and specialties can be seen. This book is a common ground for assessing a systems approach to safety and health disciplines and practice. 

The PHA (Figure 6.2) is perhaps the most critical analysis that will be performed because it is usually the first in-depth attempt to isolate the hazards of a new or, in some cases, modified system. The PHA will also provide rationale for hazard control and indicate the need for further, more detailed analyses, such as the subsystem hazard analysis (SSHA) and the system hazard analysis (SHA). The PHA is usually developed using the system safety techniques known as failure mode and effect analysis (FMEA) (Chapter 9) and/or the ETBA. Data required to complete... 

As technological advancements have continued to provide improvements over traditional methods of production, new types of hazard risk have also introduced that are unique to these technologies. Therefore, in order to ensure a continued emphasis on the objective of risk reduction and/or control, certain system safety techniques have also been devised to address the particular types of hazard risk associated with new or expanding technologies. 

Techniques used in systems safety frequently have specific goals and areas that they can address. For example, some techniques are used to analyze the hardware and equipment aspects of the system while other techniques are used to assess the human aspect. From a safety metrics standpoint, systems safety techniques can be used to identify areas for improvement in the organization. While there are hundreds of system safety techniques available, some of the more commonly used are Fault Tree Analysis (FTA), Procedure Analysis, Failure Modes and Effects Analysis, and Root Cause Analysis. 

Fault Tree Analysis was one of the earliest systems safety techniques developed for examining equipment failures. Fault Tree Analysis is a top down procedure that identifies undesirable events and their contributing factors. Once a tree has been developed, probabilities of failures can be determined for individual components in the tree. With the individual probabilities, overall probabilities of failures and can be calculated for event paths using Boolean algebra. 

For a safety program to be effective, the safety climate needs to be supportive of the program. The safety climate includes management, workers, the physical equipment in the workplace, and the interfaces between the people and the environment. Perception surveys can be used to assess the status of the safety climate in the workplace. Key areas that perception surveys can assess include management support for safety and employees attitudes and beliefs about safety. Environmental conditions and interfaces between equipment and workers can be assessed using various system safety techniques. Examples of system safety techniques include root cause analysis and failure modes and effects analysis. 

Failure Modes and Effects Analysis systems safety technique that analyzes systems individual components for the purpose of identifying single point hazards. 

Fault Tree Analysis systems safety technique that utilizes a top down analysis approach, failure trees and Boolean logic. 

MIL STD 882D a military standard that specifically deals with system safety techniques and program requirements. 

Much of the systems safety techniques and management program development has its roots in the military. The MIL STD 882D, Systems Safety provides a detailed framework for implementing a systems safety program. 

System safety techniques have primarily emanated from the aviation and aerospace industries, where the overriding concern is for the complete system to work as it has been designed to, so that no one becomes injured as a result of malfunction. 

Therefore, system safety techniques may be applied in order to eliminate any machinery malfunctions or mistakes in design that could have serious consequences. Thus, there is a need to analyse critically the complete system in order to anticipate risks, and estimate the maximum potential loss associated with such risks, should they not be effectively controlled. 

The contract may require a wide range or types of system safety analyses to be performed for a variety of reasons during the life of the contract. For example, any time new equipment or hardware is introduced into the work environment, a series of system safety analyses should be performed. Likewise, when existing equipment is modified to the extent that critical functions of the equipment may be affected, a series of analyses should be conducted prior to the first operational use of the modified equipment. In addition, prudent system safety protocol will dictate that certain analyses be conducted under certain circumstances. For example, an accident investigation may utilize fault tree analysis, or the system safety technique known as MORT (Management Oversight and Risk Tree) to determine the exact cause(s) that lead to an accident/incident/mishap. 

Although software hazard analysis is a separate system safety technique and is discussed later in this chapter as such, a review of compiler and/or assembly languages as well as any applicable system reference manuals and interface control specifications is advisable during the SCA. Sneak risks have been discovered due to improper or inappropriate software command initiatives. 

Soft Tree Also known as Software Fault Tree Analysis, a system safety technique used to evaluate a single loss event and/or the effect of simultaneous failures with a software system on that single loss, or top event. 

Three national standards that constitute a set should be of greater interest to safety generalists who want to become familiar with system safety techniques. The American Society of Safety Engineers is the secretariat. 

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