In the sense of reliability

Fig. 9.14 Flow sheet and fault tree for a series configuration in the sense of reliability...

Figure 9.14 shows two valves which are arranged in series in the sense of reliability ( OR gate logical union). The valves are normally open. The undesired event in this case is the interruption of flow. This can occur if any one of the valves, V-1 or V-2, or both fail adopting the closed position ( fail closed ). 

In Eq. (9.66) there figure products of binary variables, since we are dealing with components arranged in parallel in the sense of reliability [cf. Eq. (9.63)]. Each of the sets Kj to K4 is called cut set. ... 

Since the visible configuration does not necessarily correspond to the logical one, which depends on the criterion for system failure, the addition in the sense of reliability made previously is always required for unambiguity. ... 

We are dealing with a series system in the sense of reliability. Hence we obtain... 

A review of the current state of scientific and technical knowledge on evaluation of the pre-crash phase set the starting point for this thesis (Chap. 2). Safety evaluation can be conducted at different levels (e.g., component-, system-, vehicle-based or with focus on the overall benefits in traffic). The method of choice depends on the level of evaluation and the underlying research question. Functions of active safety rely on sensors which perceive information from their environment and are thus subjeet to uneertainty. Besides possible technical limitations, the prediction of future movements of all involved participants contributes to this inherent uncertainty. As a eonsequenee, systems subject to uncertainties will not work perfectly in the sense of reliability. False-positive activations, e.g., due to misinterpretation of information or technical limitations, will occur with consequences on acceptance and controllability of the system. With an increasing number of false-positive activations, acceptance by the driver will decrease. In case of severe interventions in traffic, such as high velocity reductions and sharp decelerations, false-positive activations become a matter of controllability for the driver and the surrounding traffic and can ultimately have a negative impact on safety. 

Where the prime requirement is to obtain absolute values of microhardness in the sense of resistance to plastic deformation, a logical approach is to replace the optical microscope of a microindenter by an electron microscope. A nanoindentation attachment that can be used inside a SEM has been the basis of patents and is commercially available (Bangert Wagendistrel, 1985). In principle, this approach makes it possible to establish a reliable comparison between nanoindentation microhardness values and established scales of microhardness numbers, such as those defined in national standards specifications. It is necessary to overcome the difficulties of imaging small indentations with sufficient contrast, and, at the smallest depths, to correct for the deformation of the required conductive layer of soft metal (Wagendristel et al., 1987). 

Reliability problems in the sense of avoiding fracture of components resulting in breakdown of installations is especially important in large units such as, for example, membrane reactors. The problems caimot be solved in a satisfactory way by improving the material properties only. By appropriately designing modules and processes, satisfactory solutions might be obtained as has been shown for industrial processes with related problems, e.g., ethylene oxide production. 

In the absence of reliable data indicating a history of control for an aseptic manufacturing facility, it is good sense to list all those events that might have a deleterious effect on the provision of an aseptic environment (batch changes, shift changes, process interruptions, etc.). The environment should at first be... 

McIntyre and Popper (1983) argue that being an authority, in the sense of a wise and reliable fount of knowledge, is often seen as a professional ideal in both science and medicine. However, this idealized view of authority is both mistaken and dangerous. Authority tends to become important in its own right an authority is not expected to err and, if he does, his errors tend to be covered up to uphold the idea of authority. So mistakes are hidden, and the consequence of this tendency may be worse than those of the mistake being hidden. 

Both measures of harm and assessments of failures in the process of care may reflect overall levels of safety. Failure to give appropriate care may or may not lead to harm, but it certainly seems reasonable to class these failures under the general heading of safety. These process measures however, seem similar if not identical to broader quality measures of effectiveness, reliability and efficiency captured in numerous studies of the quality of care. Does this mean that safety measures are nothing more than quality measures under another name Not exactly, though when we examine the level of process rather than outcomes, the same measures may reflect both safety (in the sense of potential for harm)... 

The reliability and validity of the accident data proves to be a difficult issue as the data collection is always a sample and not a census in the sense of an absolute true number [33, 35] (see also abstract description of different accident bases and sampling schemes above). Furthermore, even the data available most of the time include inconsistencies and uncertainties due often to the process of reconstruction and the assumptions necessary therein [35]. 

ReHabUity is the ability of a product to perform as intended (i.e., without failure and within specified performance limits) for a specified life cycle. Reliability is a characteristic of a product, in the sense that reliability can be designed into a product, controlled in manufacture, measured during test, and sustained in the field. 

Reliability is dynamic in the sense that it is an ongoing condition in which problems are momentarily under control due to compensating changes in components. Reliability is invisible in at least two ways. First, people often don t know how many mistakes they could have made but didn t, which means they have at best only a crude idea of what produces reliability and how reliable they are. [...] Reliability is also invisible in the sense that reliable outcomes are constant, which means there is nothing to pay attention to. 

Probabilistic methods, introduced in international standards, are based on the assumption that the reliability of a structure can be measured through the probability of failure. Failure means failure to satisfy a limit state criterion rather than a failure in the sense of a dramatic physical event, Ditlevsen (1997). As a consequence of this, the probability of failure P( can be expressed in the following way ... 

Many of the readers of the first edition have commented that the book was easy to read. I have attempted to maintain that tone in this new edition. The major change to the book is the addition of a chapter on reliability. As in the other chapters, this one also leaves the high power statistics for someone else and instead uses a common sense approach. It probably has a do and don t flavor, which just seemed appropriate as I was writing it. Because the subject of reliability is so important and so much can be written about it, the chapter had to be limited to what I felt was the more pertinent information. I had to remind myself that the subject of the book was compressors, not just their reliability. It is hoped that a proper balance was obtained. 

After the inherent hazards are reduced, layers of protection are frequently used to protect the receptors of the hazard—the public, the environment, workers, other processes, or the process itself (Figure 1.1). In the strictest sense, one could argue that the definition of inherently safer applies only to elimination or reduction of the hazard. In the broad sense, the strength of a layer of protection can be improved by features that are permanent and inseparable from that layer. Thus, layers of protection can be classified into three categories, listed in decreasing order of reliability passive, active, and procedural. A passive layer of protection can be described as inherently safer than an active... 

Standard operating procedures (SOPs) are step-by-step job instructions which can help workers perform their jobs safely and efficiently. When the end users are involved in their design, SOPs can provide a basis for arriving at a method of work agreed-to by different shifts. In this sense, SOPs can be used to develop training programs and specify measures of competence. Because of the importance of SOPs in the work situation, a systematic framework is needed to enable the design of reliable procedures which are acceptable by the workforce. 

---