Plant Safety System Architecture

Safety procedures are set of instructions to be followed in certain conditions within the plant lifecycle to keep plant safe (Van, 1999). For more details, let us analyze a sample safety procedure from OSHA (OSHA Publication No. 3132) (see Ref. OSHA Administration) as follows  

Process Safety Information Employers must complete a compilation of a written process safety information before conducting any process hazard analysis required by the standard 

The abstract of the above safety procedure could be as Safety Procedure is associated with Hazard Analysis Activity as a precondition. Employer is an actor associated with Process Safety Information . This is mapped to the object-oriented modeling approach by using Use Case and Collaboration diagrams. The completing the process safety information prior to conducting Hazard Analysis is implemented as a constraint associated with the Start Hazard Analysis  

Inspeetion/monitoring/checking. Where the unit of the operating 

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This section aims to set out the basis for good I C safety systems architecture. In particular, the I C architecture of nuclear power stations of nuclear power stations will be considered since these architectures are more complex than any other process plants. Here, architecture means the highest level of systems design. 

This method consists of characterizing the design features, especially in the safety system architecture, that are likely to pose problems in the operation, notably during the degraded situations in which the plant safety strongly depends on human reliability. The characterization of the intrinsic physical behaviour of the plant processes (safety functions), of the operating constraints of the safety systems and finally of the interrelations between these entities (most complexity theories consider these interrelations to be the main contributors to the complexity of a system), lead to the definition of an operational complexity index and to the identification of the sources of the operational constraints bearing on the operation crews. 

First, why are the architectures of safety systems different in nnclear, oil and gas, and aviation This may seem a stupid question, bnt it is worth thinking about. Some fundamental differences that affect I C architectnres in nuclear power plants, oil and gas (O G) facilities such as oil platforms and refineries, and civil aircraft, are as follows ... 

FIORINI, G.L., GAUTIER, G.-M., BERGAMASCHI, Y., Feasibility studies of a soluble boron-free 900-MWe PWR, Safety Systems Consequences of the partial or total elimination of soluble boron on plant safety and plant systems architecture. Nuclear Technology, Vol. 127 (1999), p 239-258. 

The major functions and architecture of a Nuclear Power Plant Protection System are designed to meet the safety issues. Both the analogic and the digital designs are able to satisfy the requirements. 

The safety systems built on the loo2D modules have found a strong market in the general area of process plant applications. In some of the most demanding safety areas including offshore oil and gas and in the nuclear field these systems have to compete with the alternative architecture based on the principle of 2 out of 3 voting. These are known as triple modular redundant or TMR systems. The next diagram illustrates the principle. 

Figure 7-2 shows the detailed information system architecture for implementing CAPE-SAFE within PEEE. In this figure, CAPE-SAFE is connected through the different APIs to plant lifecycle knowledgebase database, plant enterprise applications, and design and operation environments. The plant model (POOM) is the cornerstone of such implementation where safety aspects are manipulated to assist in the different functions that carried out by CAPE-SAFE. 

NOTE 1 The software architecture defines the major components and subsystems of system and application software, how they are interconnected, and how the required attributes, particularly safety integrity, are achieved. Examples of system software modules include operating systems, databases, communication subsystems. Examples of application software modules include application functions which are replicated throughout the plant. 

A computer system used in systems important to safety should be designed so that it is periodically testable during plant operation in order to verify the continued operability and lehability of the system. This may require adjustments to the computer system s architecture. 

The situation becomes more complicated when full lifecycle and maintenance activities are considered. Cyber security applies to all equipment suppliers and contractors, and also to any software maintenance and modification activities that may be done on the site to digital systems. In addition to the plant control and protection systems, there will be document management systems, work control systems and site access control systems, all of which have some relevance to safety. Hence Fig. 3.2 shows what a typical simplified information security architecture for an industrial plant site might look like. This shows a somewhat higher degree of complexity than Fig. 3.1. 

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