Risk and reliability

In 1854 Elisha Otis was at the Crystal Palace exposition in New York. After being hauled up in an elevator in an open-sided shaft, haUw up he had the rope cut with an axe, calling All safe, gentlemen . The shaft conveyance safety arrest mechanism (safety dogs) then took over. 

Safety technology has a long history and is an important part of risk engineering. In the eighteenth century a competition was run for a chronometer which would operate accurately at sea so that longitude could be measured - essential for the safe operation of seagoing vessels. It was won ly a John Harrison. 

The growth in risk engineering since those far off days has been huge. One way of dividing the field is to decide whether the engineering contributes to active safety - the 

This improvement in the techniques of achieving safety is, of comse, a linchpin of the Robens-based idea of a flexible approach which encourages such initiatives. 

Random failme comes from equipment degrading due to the stresses on it The timing of such failmes is not predictable but they uniformly degrade throughout the service life. 

---

Haugen, E. B. and Wirsching, P. H. 1975 Probabilistic Design a realistic look at risk and reliability in engineering. Machine Design, 15 May. 

The confluence of sharply rising Operations and Maintenance (O M) costs. NRC requested Individual Plant Examinations (IPEs) and increased personal computer capabilities gave rise to the R R Workstation. Its uses and maintains-current PSA models and databases for individual plants to perform O M planning and scheduling, and uses the PSA in IPE models to identify plant design, procedure and operational vulnerabilities. The Risk and Reliability Workstation Alliance was organized by EPRI to support the R R Workshop in order to achieve O M cost reduction, plant productivity and safety enhancement through risk-based, user-friendly, windowed software louls (Table 3.6 8). The Alliance, initiated in 1992, includes 25 U.S. utilities and four international partners from Spain, France, Korea, and Mexico. SAIC is the prime contractor for the R R Workstation, with participation of five other PSA vendors. 

The book contains, in alphabetical order, failure rates, event rates and probabilities, and descriptive information which has been collected since 1970 in the course of doing risk and reliability assessments. Twenty appendices contain results of surveys on bursting discs, pipes, valves, relief valves, pump failures and information on human error, international fire losses, and blast effects. 

In this study detailed fault trees with probability and failure rate calculations were generated for the events (1) Fatality due to Explosion, Fire, Toxic Release or Asphyxiation at the Process Development Unit (PDU) Coal Gasification Process and (2) Loss of Availability of the PDU. The fault trees for the PDU were synthesized by Design Sciences, Inc., and then subjected to multiple reviews by Combustion Engineering. The steps involved in hazard identification and evaluation, fault tree generation, probability assessment, and design alteration are presented in the main body of this report. The fault trees, cut sets, failure rate data and unavailability calculations are included as attachments to this report. Although both safety and reliability trees have been constructed for the PDU, the verification and analysis of these trees were not completed as a result of the curtailment of the demonstration plant project. Certain items not completed for the PDU risk and reliability assessment are listed. 

Mosleh, A., M. Kazarians, and W. C. Gekler. Development of a Risk and Reliability Data Base for the Chemical Industry. Pajjer presented at the American Institute of Chemical Engineers National Meeting, Boston, MA, 1984. 

IRRAS Integrated Risk and Reliability Analysis System... 

Risk is defined as tlie product of two factors (1) tlie probability of an undesirable event and (2) tlie measured consequences of the undesirable event. Measured consequences may be stated in terms of financial loss, injuries, deatlis, or Ollier variables. Failure represents an inability to perform some required function. Reliability is the probability that a system or one of its components will perform its intended function mider certain conditions for a specified period. Tlie reliability of a system and its probability of failure are complementary in tlie sense tliat the sum of these two probabilities is unity. This cluipler considers basic concepts and llieorenis of probability tliat find application in tlie estimation of risk and reliability. 

Managing Risk and Reliability of Process Plants, Gulf Professional, Houston, Tex, 2003, p. 70) suggests that accepted risk is a better term because it makes it clear that the risk has been accepted by those responsible for the decisions on how to build, operate, and regulate the facility. 

Ang AH-S, Tang WH (1984) Probability concepts in engineering planning and design. Vol. 2. Decision, risk, and reliability. New York, NY, John Wiley and Sons. 

The principle conclusion is that the development of "expert" systems and the necessary audit tools for verification and validation of those systems is still in infancy. There are a number of interesting concepts under development which bear promise but which will probably see their first application within critical space and defense applications. Tools useful to those of us interested in more generalized risk and reliability analyses are probably at least two to three years away. 

Figure 1.1 shows that PSM is an integral component of operational integrity management. Therefore, it is useful to review the elements of PSM because they are so foundational to risk and reliability management work. Different companies and regulatory agencies have different approaches to the topic some of them are discussed below. 

Process Risk and Reliability Management. DOI http //dx.doi.Org/10.1016/B978-0-12-801653-4.00005-9... 

Risk and reliability programs are organized like any other management program using a stmcture such as the following ... 

During Phase IV, the operating and maintenance procedures will be written, and the technicians trained in their use. Guidance as to the writing of procedures and the development of training programs is provided in Process Risk and Reliability Management. 

---