Dimensioning safety system

The other global dimension of the systems approach is the need for the existence of policies which address human factors issues at senior levels in the company. This implies that senior management realizes that resources spent on programs to reduce error will be as cost-effective as investments in engineered safety systems. 

Brookes, Malcolm J. 1982. Human factors in the design and operation of reactor safety systems. In Accident at Three Mile Island The Human Dimensions, ed. David L. Sills, C. P. Wolf, and Vivien B. Shelanski, 155-160. Boulder, Colo. Westview Press. 

This is, however, not the case and cannot be achieved. Apart from the— although remote—possibility of wrong dimensioning (e.g. walls too weak) components of technical systems can fail, humans can commit errors in operating the technical system or external threats such as flood, storm or lightening may lead to failures within the plant. Thus, temperature and pressure increases or other damaging events may be triggered. In addition, it is conceivable that safety systems are not available due to component failures. Probabilities for such events may be assessed. However, the instant in time of a component failure, human error or destructive external event cannot be predicted. 

The safety design of a plant results from extensive analyses (cf. [2]) to be discussed later. The dimensioning of safety systems is also carried out deterministically. It is based on the concept of disturbances which have to be avoided, for example a cooling failure in a reactor for an exothermal reaction. This is the basis for determining the type and capacity of the safety system coping with it. Its quality and degree of redundancy may then be determined... 

In nuclear installations the so-called design basis accidents are used for this purpose [19]. For example, the complete failure of the main coolant pipe of a reactor ( 2-F — rupture because the entire cross section is open on both sides) or the failure of the electric supply [19]. The design basis accidents serve to determine the type and dimensions (e.g. capacity, temperatures, cooling power...) of the corresponding safety systems, for example the emergency cooling system for counteracting the breach of the main coolant pipe. 

Equipment should first be inspected for compliance with specifications. This action includes checks of dimensions, internals, materials of construction, the quality of welds, and the installation of instruments and process connections. Before commissioning the liquid chlorine system, it is also necessary to have all relevant safety systems in operating order, operators trained, and operating manuals and instructions ready. 

V-1 American National, Canadian, and Compressed Gas Association Standard for Compressed Gas Cylinder Valve Outlet and Inlet Connections, Detailed dimensioned drawings of 65 valve outlet connections for almost 200 different products. The standard covers threaded connections, yoke outlets, and the Pin Index Safety System for flush outlet valves of the yoke type used for medical gases. (92 pages)... 

V-5 Diameter Index Safety System. Describes a standard to provide noninterchangeable connections where removable exposed threaded connections are employed in conjunction with individual gas lines of medical gas administering equipment at pressures of 200 psig or less, such as outlets from medical gas regulators and connectors for anesthesia, resuscitation, and therapy apparatus. Detailed dimensioned drawings are included. In addition to the medical gases covered by the Pin Index Safety System, this standard includes air and suction. (20 pages)... 

In the electrical characterization the electrical parameters and the function of a component under extreme conditions are measured on a sufficient number of components. In this way the behaviour of the component under extreme conditions becomes known. Parameters for the proper dimensioning of systems can be obtained, if nonspecified parameters are important. Also it can be checked, whether all specified parameters remain within their limits.The behaviour of components and system under extreme conditions is particularly important for safety systems, since frequently these systems are only needed to control accidents i.e. just when the environmental conditions are extreme. 

The group selected questions 36, 37, and 47 as most important. Participants told us they chose these questions for two reasons the question represented an important dimension of the safety system, and it identified a dimension in the company that was in need of improvement. Our statistical analysis of the survey demonstrated the greatest weakness on virtually the same questions. 

Fig. 2. The multiple component engineered barrier safety system for vitrified HLW which constitutes the repository near-field (dimensions in metres).

Scope, 52 Basis, 52 Compressible Flow Vapors and Gases, 54 Factors of Safety for Design Basis, 56 Pipe, Fittings, and Valves, 56 Pipe, 56 Usual Industry Pipe Sizes and Classes Practice, 59 Total Line Pressure Drop, 64 Background Information, 64 Reynolds Number, R,. (Sometimes used Nr ), 67 Friction Factor, f, 68 Pipe—Relative Roughness, 68 Pressure Drop in Fittings, Valves, Connections Incompressible Fluid, 71 Common Denominator for Use of K Factors in a System of Varying Sizes of Internal Dimensions, 72 Validity of K Values,... 

All equipment should comply with the relevant British and other Standards regarding dimensions, methods of determining ratings, compliance with safety regulations, robustness and general quality of manufacture [70]. BS.5750, Quality Systems, concentrates on the subject of product quality as it affects design, manufacture and installation. In addition to Standards, there are various Codes of Practice [71, 72]. 

There are inherent scale limitations in the time and space dimensions covered by laboratory studies. The applicability of the near field geochemical models derived from laboratory observations have to be applied to long-term, large-scale situations like the ones involved in the safety assessment of nuclear waste repositories. Hence, there is a need to test the models developed from laboratory investigations in field situations that are related to the ones to be encountered in repository systems. 

In the fine chemicals and pharmaceutical industries, reactors are often used for diverse processes. In such a case, it is difficult to define a scenario for the design of the pressure relief system. Nevertheless, this is required by law in many countries. Thus, a specific approach must be found to solve the problem. One possibility, that is applicable for tempered systems, consists of reversing the approach. Instead of dimensioning the safety valve or bursting disk, one can choose a practicable size and calculate its relief capacity for two-phase flow with commonly-used solvents. This relief capacity will impose a maximum heat release rate for the reaction at the temperature corresponding to the relief pressure. 

Process safety metrics are critical indicators for evaluating a process safety management system s performance. Tracking the number of process safety incidents is one common measure of performance, but merely tracking the number of incidents after the fact is insufficient to understand the system failure that allowed the incident to occur and what can be done to prevent a recurrence. More than one metric and more than one type of metric are needed to monitor performance of a process safety management system. A comprehensive process safety management system should contain a variety of different metrics that monitor different dimensions of the system and the performance of all critical elements. 

---