SIS operation and maintenance

1 Operation and maintenance pianning for the safety instrumented system shall be carried 

2 Operation and maintenance procedures shall be developed in accordance with the relevant safety planning and shall provide the following  

No reproduction or networking permitted without license from IHS 

3 Operation and maintenance shaii proceed in accordance with the relevant procedures. 

4 Operators shall be trained on the function and operation of the SIS in their area. This training shall ensure the following  

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SIS operation and maintenance To ensure that the functional safety of the SIS is maintained during operation and maintenance 16 SIS requirements SIS design Plan for SIS operation and maintenance Results of the operation and maintenance activities... 

Clause 16 - SIS operation and maintenance - operate and maintain the SIS so that the functional safety and... 

SIS operation and maintenance Maintenance of functional safety during operation and maintenance. 16... 

Clause 16 SIS operation and maintenance Main aim is to ensure that required SIL of each SIF is maintained during operation and maintenance so that functional safety is maintained. 

SIS OPERATION AND MAINTENANCE (lEC 61511 CLAUSE 16) Requirements for SIS operation and maintenance... 

New items to consider regarding SIS operation and maintenance training include ... 

Operating Basis As the SIS engineering design nears completion, the resources and skills of plant operations should be considered. At some point, the SIS is turned over to operations and maintenance personnel, who must be trained on the new SIS and on their responsibilities. Consequently, thought should be given to the content and depth of the information that must be communicated to various personnel. This is especially important as the responsibility for the SIS transitions from the project team to operations and maintenance control. 

Since a device can fail at any time during its life, periodic proof tests are performed to demonstrate the functionality of the SIS. Proof tests are covered by operation and maintenance procedures that ensure that the test is done correctly, consistently, and safely and that the device is returned to a fully operational state after test. Each test serves as an opportunity for personnel to see the SIS in action and to validate the procedures associated with its operation. 

Human performance is therefore a system design element. The human machine interface (HMI) is particularly important in communicating the status of the SIS to operating and maintenance personnel. 

Remember that the BPCS operates with signals that are relatively dynamic. This makes BPCS failures generally detectable by plant personnel. Example diagnostic methods include flat line outputs, quality indicators, pre-alarms, deviation alarms, and out of range signals. While a BPCS operates under relatively dynamic conditions, safety instrumented system signals are static Boolean variables. Since the SIS only takes action when a potentially dangerous condition is detected, it can be very hard for operations and maintenance persormel to detect certain failure modes of a SIS. 

All equipment used in the SIS must be classified as a safety instrumented system. The design, installation, operation and maintenance process must follow all the rules of ANSl/lSA-84.00.01-2004 (lEC 61511 Mod), put there to prevent systematic faults. If this is not done, the standard clearly states that any safety instrumented function cannot have a risk reduction greater than 10. This is the bottom of SlLl range so, in effect, that design cannot meet SIL 1 requirements. The practical effect of this requirement is that a designer cannot combine control functions and safety functions in the same equipment imless the equipment is classified as a safety instrumented system and follows aU the design rules of the standard. 

The objective of the realisation phase is then to create the SIS conforming to the specification, especially in terms of safety functions and allocating SIL. This paper focuses on system requirements (Part 2), and does not develop software aspects (Part 3). The realisation phase consists of design requirement specification (for subsystems and elements), design and development, integration (software integration refers to Part 3), operation and maintenance, validation, modification, and verification. 

The design of the SIS shall take into account human capabilities and limitations and be suitable for the task assigned to operators and maintenance staff. The design of all human-machine interfaces shall follow good human factors practice and shall accommodate the likely level of training or awareness that operators should receive. 

ANSI/ISA-84.00.01-2004 gives requirements for the specification, design, installation, operation and maintenance of SIS, so that it can be confidently entrusted to place and/or maintain the process in a safe state. These requirements are presented in the standard, using the safety lifecycle shov /n in ANSI/ISA-84.00.01-2004-1, Figure 8, and described in ANSI/ISA-84.00.01-2004-1 Table 2. 

Validate, start-up, operate and maintain the strategy implement the SIS following the design basis and detailed design documentation and define what is required of operation and maintenance personnel to sustain the SIL. 

Operation and maintenance procedures required when SiS equipment is out of service... 

Validation demonstrates that the installed SIS operates according to the design basis and that appropriate documentation is in place to support its long-term management. An input-to-output test is used to prove that the SIS functions properly and that the SIS equipment interacts as intended with other systems, such as the BPCS and operator interface. The Site Acceptance Test (SAT) also provides an opportunity for a first-pass validation of the operating and maintenance procedures. Validation must be completed prior to the initiation of any operating mode where a hazardous event could occur that would require the operation of a new or modified SIS. Some users require that validation be repeated after any major process outage or shutdown. 

ANSI/ISA-84.00.01-2004-1, Clauses 16.2.2 and 16.3.3, identifies the data to be maintained on the SIS/SIF by Operations and Maintenance respectively. The IPRDS provides data to determine process demand frequencies and device failures, as described in ANSI/ISA-84.00.01-2004-1, Clauses 16.3.1.5. It also provides failure mode information that can be used to develop diagnostic techniques and to serve as the basis for device checklists, revealing a greater percentage of the dangerous failures. ANSI/ISA-... 

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