Root cause, design specifications

The immediate cause was failure of the ring joint seal on the solid rocket booster. Yet, a root-cause analysis revealed a much more complex scenario. According to information published after the investigation, post flight evidence from as far back as early 1984 showed that the joint seals were failing to meet design specifications. 

A common error is to limit the types of deviations reported to and evaluated by the APR system to just deviations from finished-product specifications. All deviations should be evaluated, including deviations from manufacturing procedures, in-process specifications, deviations from raw material specifications, and other expected results. Each of these occurrences could indicate changes are necessary to prevent recurrence. For example, the cause of deviations from manufacturing procedures is frequently evaluated as a lack of training. If there are several of these occurrences by different individuals, however, it is also likely that there maybe another root cause, such as unclear or insufficient batch record instructions or inadequately designed or unclear batch record data forms. 

The THIS program is specifically designed to permit the Philips Lighting Company (Danville facility see Figure A3.1) to focus all employees attention on the top three safety and health hazards that are the root cause of the vast majority of their occupational injuries and illnesses. The three identified or targeted hazards for the initial training are... 

But the selection of a stopping point and the specific operator action to label as the root cause—and operator actions are almost always selected as root causes—is not the real problem here. The problem is the oversimplification implicit in using a chain of events to understand why this accident occurred. Given the design and operating conditions of the plant, an accident was waiting to happen ... 

A software component designed and coded either manually or with the help of tools may be subject to a wide variety of faults. The root cause of these faults is to be found in the specification, in the design or in the implementation. A software fault can be seen as a deviation in the content and/or in the order of instructions or data stored in memory causing the microprocessor not to behave as expected under some event or sequences of events. Trying to consider all possible faults that could affect even a simple software component is not practicable. Nevertheless, it is possible to consider the consequences of such faults, as they will lead to a few numbers of software failure modes... 

As indicated, a poor specification was the root cause of 44% of the automation system problems, which is by far the largest single cause. In effect, needed functionality was missing or incorrect. How can a control system designer create an automatic protection fimction when that designer does not know that it is needed ... 

Once operational gaps are identified, assessment methods (Chapters 5-8 for energy operation. Chapters 12 and 13 for process operation, and Chapter 16 for utility system operation) are then applied to identify root causes— potential causes include inefficient process operation, insufficient maintenance, inadequate operating practices, procedures, and control, inefficient energy system design, and outdated technology. Assessment results are translated into specific corrective actions to achieve targets via either manual adjustments, the best practices, or by automatic control systems. Finally, the results are tracked to measure the improvements and benefits achieved. 

If the overall gap is large enough, it warrants the second phase of audit or specific audit, which is designed to identify root causes and process improvement opportunities. The audit methods are explained in the book. The methods for energy audit... 

Real-time process supervision is performed by means of a set of tools and methods, which ensure safe process operation in normal situation as well as in the presence of failures or undesired disturbances. Process supervision is conducted by integrating several tools, each specifically designed for a specific activity. These activities are fault detection, fault isolation, diagnosis (root cause analysis), fault quantification (determination of the severity of the fault), and the decision making to accommodate the fault. The presence of a fault is detected at the monitoring level, which determines whether the process is in normal operation or not. Other tools for fault isolation, diagnosis, etc., are executed when an abnormal process state is detected by the process monitoring tool. 

Cause Cause is the specific reason for the failure and can be found by asking whyl In DFMEA, design deficiency and lack of specification are the major causes of various failures. Naturally, manufacturing process/subassembly process deficiencies and lack of safety measures could be the cause of failure. One needs to explore the issue until the root cause is identified. 

In broad terms, the process for producing a specification for a safe design involves hazard identification (HAZID), which asks what sort of accidents do we need to worry about , followed by detailed analysis to identify the magnitude of potential accidents. From a safety perspective, a most important step is the clear and robust definition of the safety functional requirements, i.e., the requirements for the control and protection systems on the completed plant. The history of accidents involving design failures shows a frequent root cause to be inaccurate or inadequate definition of the safety functional requirements (see Fig. 2.3). 

Although a very powerful analysis tool, the benefits of an SCA are not as cost-effective to the system safety analyst as HA other tools. Other safety analysis techniques, such as SSHA and FTA, are more cost-effective for the identification of hazards and root causes. SCA is highly specialized, and only assists in a certain niche of potential safety concerns dealing with timing and sneak paths. The technique is not recommended for everyday safety analysis usage, and should be used when required for special design or safety-critical concerns. Specific reasons for performing an SCA include ... 

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