Safety Metrics Dependent

Communicating process safety metrics should match the needs of the intended audiences to maximize the benefit for them, and the data communicated will vary depending upon those needs. Metrics reports for upper management usually contain aggregated or normalized data, focus on trends, and are issued on a periodical basis. Personnel that use the results to carry out their day-to-day responsibilities usually need detailed data that is reported frequently. The data reporting frequency is usually dictated by the audience needs, as discussed in Section 6.2.3, and timely reporting is important for effective communications. 

CCPS defines reliability as the probability that an item is able to perform a required function under stated conditions for a stated period of time or for a stated demand. In addition to relying on QA/QC, companies use dependable data to conduct reliability analyses. Though related,- reliability is different from quality. While quality control is concerned with the performance of a product or process at one time, reliability is concerned with the performance of a product over its entire lifetime. Reliability engineering addresses all aspects of a product s life, from its conception, subsequent design, and production processes, through its practical use lifetime, with maintenance support and availability, and covers reliability, maintainability, and availability. Process safety metrics data can provide valuable input to the life data analyses used to estimate the probability and capability of parts, components, and systems to perform their required functions for desired periods without failure, in specified environments. 

As mentioned above, the appropriate metric depends on the research question as well as on the methodology used in the experiment. Considering, for example, a hardware test with dummies, the metric has to be based on the readings of the dummy. Commonly used physical measurements such as the Head Injury Criterion (HIC) can then be translated into an injury probability, which is a well-known procedure [29]. A comparable approach is feasible using simulation. In a finite-element simulation or a kinematic simulation of collisions, a human model, e.g., the Total Human Model for Safety (THUMS), can be used [30]. 

Some companies have a suite of metrics that they update weekly, monthly, or quarterly depending upon their needs. This data is usually system performance metrics that summarize the status of activities or metrics determined to be of interest. These systems can provide process safety information as soon as it is developed and entered into a network database. With the proper access, operators and craft personnel and their supervisors can view this information, and nearly any audience can view the reported data in a predetermined format. 

CCPS Guidelines for Risk Based Process Safety presents a range of metrics for each of the KBPS elements. Each element includes examples for Maintaining a Dependable Practice as well as element-specific suggestions. These metrics are presented as examples, not recommendations or expectations. Practitioners may select from this list or use the list as a point of departure for developing metrics more applicable to their situation. This is a summary listing only for the complete list, see the companion CD. 

The objective of this paper is to discuss the safety issues associated with the immobilization of excess weapons plutonium in ceramic form in the United States. The U.S. government has recommended a dual-track approach to dispose of excess weapons plutonium. According to this approach, about 33 metric tons of pure Pu will be fabricated into mixed oxide (MOX) fuels which will be burned in commercial nuclear light water reactors and up to 17 metric tons of impure Pu will be immobilized into ceramic form which will be permanently disposed of in a geologic repository. It should be noted that a portion of the 33 metric tons of pure Pu may also be immobilized into ceramic form depending on the future decision of the U.S. government. 

It can be seen that this metric is a ratio of failure rates and not dependent on the total failure rate. The result is always a number between zero and one. A high number is good. It measures the natural tendency of an instrument to fail safety or detect dangerous failures. 

As this question is often asked in this manner, two vital aspects are not explicitly named or are missing. The reference situation (i.e., the baseline of comparison) for the question as well as the validity of the expected answer (which directly depends on the method used) must be included in the question. No generally accepted definition of safety benefit , as stated in the question, exists (neither for its meaning nor for the metrics). Examples of possible interpretations are ... 

There are several metrics at different levels for the evaluation of active safety. Depending on the research question and the method used, the quality of the assessment can vary. For example, injuries coded in an in-depth data base have a different reliability than injury probabilities given by probabiUstic models or economic costs, which use injury information as basis. Stating the protection of the human as key objective, a metric based on injury severity seems to be appropriate. 

Various dependability metrics are of course safety relevant too. These include failure rate and other hardware architecture metrics. 

The hardware architectural metrics are dependent upon the whole hardware of the item. Compliance with the target figures prescribed for the hardware architectural metrics is achieved for each safety goal in which the item is involved. 

Metrics used to evaluate the safety performance of individuals, teams, and the organization as a whole have a powerful influence on context. Employee commitment, ownership, and involvement can increase or decrease depending on the evaluations employed. Injury statistics provide an overall estimate of the distance from a vision of "injury free," but they are not a diagnostic tool for proactive planning. If used as the only index of safety achievement (or failure), injury-related outcome numbers can do more harm than good, alienating people rather than empowering them to actively care for safety. 

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