Process hazard and risk assessment

NOTE 1 Clause 8 of this standard is addressed to process engineers, hazard and risk specialists, safety managers as well as instrument engineers. The purpose is to recognize the multi-disciplinary approach typically required for the determination of safety instrumented functions. 

NOTE 2 Where reasonably practicable, processes should be designed to be inherently safe. When this is not practical, risk reduction methods such as mechanical protection systems and safety instrumented systems may need to be added to the design. These systems may act alone or in combination with each other. 

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1 A hazard and risk assessment shall be carried out on the process and its associated equipment (for example, BPCS). It shall result in 

The overall objective here is to establish the need for safety functions (for example, protection layers) together with associated levels of performance (risk reduction) that are needed to ensure a safe process. It is normal in the process sector to have multiple safety layers so that failure of 

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1 The requirements for hazard and risk assessment are specified only in terms of the results of the task. This means that an organization may use any technique that it considers to be effective, provided it results in a clear description of safety functions and associated levels of performance. 

A hazard and risk assessment should identify and address the hazards and hazardous events that could occur under all reasonably foreseeable circumstances (including fault conditions and reasonably foreseeable misuse). 

The approach used to identify hazards will depend on the application being considered. For certain simple processes where there is extensive operating experience of a standard design, such as simple off-shore wellhead towers, it may be sufficient to use industry developed check lists (for example, the safety analysis checklists in ISO 10418 and API RP 14C). Where the design is more complex or a new process is being considered, a more structured approach may be necessary (for example, lEC 60300-3-9 1995). 

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This International Standard addresses the application of safety instrumented systems for the Process Industries. It also deals with the interface between safety instrumented systems and other safety systems in requiring that a process hazard and risk assessment be carried out. The safety instrumented system includes sensors, logic solvers and final elements. 

This internationai standard addresses the appiication of safety instrumented systems for the Process industries, it aiso requires a process hazard and risk assessment to be carried out to enabie the specification for safety instrumented systems to be derived. Other safety systems are oniy considered so that their contribution can be taken into account when considering the performance requirements for the safety instrumented systems. The safety instrumented system inciudes aii components and subsystems necessary to carry out the safety instrumented function from sensor(s) to finai eiement(s). 

PROCESS HAZARD AND RISK ASSESSMENT (lEC 61511 CLAUSE 8) Requirements for Process Hazard and Risk Assessment... 

The safety integrity level (SIL 3 in this case) is allocated based on a process hazard and risk assessment. It forms the basis for the risk reduction target for the safety instrumented system/SIL (HIPS in this case). For on-demand systems such as a HIPS, the SIL defines the probability of... 

Jones, D., Nomenclature for Hazard and Risk Assessment in the Process Industries, Second Edition, Rugby, Wai-wickshire, UK Institution of Chemical Engineers, 1992. 

As it has been shown in this chapter knowing the concentrations of chemicals in the environment is a key aspect in order to carry out meaningful hazard and risk assessment studies. Predicting concentrations of chemicals can serve as a quick and robust way to produce an acceptable screening level assessment however if further precision is desired, the complexity of real environmental scenarios can make it a cumbersome and unaffordable task. Models improvement requires not only refining their computation algorithms but also and more important, implementing new inputs and processes in order to better describe real scenarios. 

The design-freeze phase is that interlude between the completion of the piping and instrumentation diagrams and the determination of operating procedures. For new facilities, a full hazard and risk assessment should be performed here. At this point, alterations in process design still can be made relatively inexpensively since equipment has not yet been ordered. Ozog (1985) details the steps needed in the procedure. 

Prior to starting up the process, a final check should be done to verify the status of recommended changes that emerged from the hazard and risk assessment. A site inspection should be conducted to form an impression of spatial dimensions, and the hazard and risk assessments should be brought up-to-date. Design changes at this point are expensive. 

Shortly after startup, operating procedures may be revised, and these revisions should be reviewed in the context of the hazard and risk assessments. Also, changes in the process may be made during the operational life of the plant these changes should be similarly reviewed under further hazard and risk assessments. Assessments should be carried out regularly during the operational life of the plant. 

The outcome of the hazard and risk assessment and allocation process should be a clear description of the functions to be carried out by the safety systems, including potential safety instrumented systems together with safety integrity level requirements (along with mode of operation, continuous or demand) for any safety instrumented function. This forms the basis for the SIS safety requirements specification. The description of the functions should be clear as to what needs to be done to ensure that safety is maintained. 

Hazard and risk assessment To determine the hazards and hazardous events of the process and associated equipment, the sequence of events leading to the hazardous event, the process risks associated with the hazardous event, the requirements for risk reduction and the safety functions required to achieve the necessary risk reduction 8 Process design, layout, manning arrangements, safety targets A description of the hazards, of the required safety function(s) and of the associated risk reduction... 

Changes affecting the competence or performance of other organizations providing critical services under contract (e.g., equipment design, process control software, and hazard and risk assessment)... 

Roles and Responsibilities Top management shall provide the leadership to institute and maintain effective systems for the design and redesign processes. Key points anticipate hazards and risks assess risks apply the hierarchy of controls to achieve acceptable risk levels. The following note is significant in the Roles and... 

ICheM, 1985. Nomenclature for Hazard and Risk Assessment in the Process Industry. 

System safety should be actively involved as a team member in the CM process. All ECPs must be evaluated by an experienced system safety analyst to determine if any hazards are associated with the proposed change, the associated risk, and the safety impact of the ECP on the existing system. The program should be notified when an ECP will decrease the level of safety of the existing system. It is important that only qualified safety engineers make the safety determination on proposed ECPs because they have the most experience and knowledge in regard to system hazards and risk assessments. 

Risk is the safety measure of a potential future event, stated in terms of event likelihood and event severity. Likelihood can be characterized in terms of probability, frequency, or qualitative criteria, while severity can be characterized in terms of death, injury, dollar loss, and so on. Mishap risk analysis is the process of identifying and evaluating the risk presented by a system hazard. HA is an integral part of risk analysis since safety risk can only be determined via the identification of hazards and risk assessment of those identified hazards. See Hazard Risk and Mishap Risk for additional related information. 

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