Safety requirement specification requirements

Application software safety requirement specification Requirements of specification for software SIFs for each SIS function required for SIFs. Software safety integrity for each SIF allocated to that SIS. 12.2.2... 

Finally, under the heading Specific pressure equipment requirements specific requirements are set out for equipment with a risk of overheating, for piping and, last but not least, specific quantitative requirements which set out a series of safety factors for certain pressure equipment. These latter provisions apply as a general rule which means that a manufacturer or a harmonised standard may deviate from these factors if it can be demonstrated that appropriate measures have been taken to achieve an equivalent level of safety. 

One of the key elements in laminated composite structures design is the ability to tailor a laminate to suit the job at hand. Tailoring consists of the following steps. We want to design the constituents of the laminate, and those constituents include the basic building blocks of the individual laminae and as well how they are oriented within the laminate. We design those constituents to just barely meet (with an appropriate factor of safety) the specific requirements for, say, strength and stiffness. 

Safety Requirements Specification The instrumentation and electrical (I E) requirements are developed to meet the intent of any H RA findings and the process requirements. The design documentation should establish a clear connection between each process hazard and the design of its SIFs. I E personnel should meet with the process engineering representative responsible for the process requirements to ensure that the intent is understood. 

Validation—The activity of demonstrating that the safety-instrumented system under consideration, after installation, meets in all respects the safety requirements specification for that safety-instrumented system. 

Description of all important and critical specifications of the system, like process parameter, technical parameters, safety requirements, environmental requirements, and GMP-relevant specifications. 

Each phase of the SLC must be controlled to maximize the probability that a finished system meets all quality, regulatory, safety, and specification requirements. If an SLC approach is applied properly, no additional work will be required to validate a system. For each SLC period and event, computer systems validation requires that the development processes are documented work products. As explained in Chapter 2, phase gate verification activities performed during each event may be a perfect place to review and quantify the quality of all products needed to support the next phase. 

The safety requirements specification defines the safety requirements necessary for risk education... 

A review of the SIS performance should be periodically undertaken to ensure the original assumptions made during the development of the safety requirements specification (SRS) are still adhered to. For example, a periodic review of the assumed failure rate of different components In a SIS should be carried out to ensure that it remains as originally defined. If the failure rates are worse than originally anticipated, a design modification may be necessary. Likewise, the demand rate on the SIS should be reviewed. If the rate is more than that which was originally assumed, then an adjustment in the SIL may be needed. 

The development of the SIS safety requirements specification is one of the more important activities of the whole safety lifecycle. It is through this specification that the user is able to define how he wants the Safety Instrumented Functions (SIF) to be designed and integrated into a SIS. 

The SIS safety requirements specification may be a single document or a collection of several documents including procedures, drawings or corporate standard practices. These requirements may be developed by the Hazard and Risk Assessment team and/or the project team itself. 

Safety requirements specifications for individual subsystems may also be derived from this overall specification. 

Some considerations with respect to the safety requirements specifications are as follows ... 

When operator action is needed during emergency conditions, the update and refresh rates of the operator display should be carried out in accordance with the safety requirements specification. 

For each diagnostic implemented, testing interval and resulting action on fault detection should meet the safety requirements specification. 

The detailed functional safety requirements specification should include all necessary functions during all modes of operation of the process being protected. Additionally, the periodic testing of all the safety instrumented functions should be provided. This typically requires the definition of maintenance override capabilities so the sensors and final elements can be tested without shutting down the process. The same methodology described in the paragraph above can be used to document these requirements. 

Determine the proper execution order of the networks and logic, within each program and the execution sequence and desired execution rates of all the application programs. Confirm that the execution rates of the application programs are consistent with the required process response times from the software safety requirements specification. 

Components and devices used in SIF applications that comply with this standard should be provided with documentation that details all known aspects of installation, maintenance, configuration, programming and operation that should be observed if the component or device is to meet the safety requirements specification of the application. 

The application software safety requirements specification will include ... 

The objective of the SiS safety vaiidation is to vaiidate that the SIS achieves the requirements stated in the safety requirements specification. Validation activities should be completed prior to the placing of the SIS into operation. 

The proof test interval should be selected to achieve the average probability of failure on demand as required in the safety requirements specification. 

B.2.3.1 Available information from LOPA safety requirements specification and SIL for the... 

In this step, all functions of the safety requirements specification are allocated to system components, functions or software. Safety integrity requirements will determine the appropriate... 

Safety requirements specification if reactor pressure exceeds 10 bar, close off steam to the reactor jacket within 20 seconds to avoid exothermic reaction. There is no operator action necessary. The required SIL is 3. 

Step 5 - Documentation Summarize the findings of the LOPA study and, if appropriate, document that the proposed change meets the corporate risk tolerance criteria/local code targets. Safety Requirements Specification (SRS) is defined to undertake appropriate cost-effective designs for SISs in order to achieve optimal test and maintenance strategies for the lifespan of the plant... 

Each safety instrumented function is documented in the safety requirements specification. That document (or collection of documents) includes all functional information, logic, performance information, timing, b q)ass/maintenance requirements, reset requirements, the safety integrity level for each safety instrumented function, and any other requirement information that the designers may need. 

In the safety lifecycle, a safety requirements specification is done after ... 

A failure occurs when a device at some level (a system, a unit, a module, or a component) fails to perform its intended function. To many, the definition is clear. Disagreement may occur, but when this happens it is usually a matter of properly defining "intended function." For safety instrumented systems, the definition of intended function is usually clear and should be properly recorded in the safety requirements specification. 

The conceptual design process for a safety instrumented function begins with a Safety Requirements Specification (SRS). The SRS is an important document. It should contain complete specifications for designing all the safety instrumented functions. For each SIF the following information should be included ... 

Solution For each piece of equipment related to the safety instrumented function, one must ask if that equipment is needed to protect against the specified hazard. In this SIF, the hand-switch was added only to meet local regulatory requirements and is not part of the automatic protection so it is excluded. The pump is turned off to protect it from overload so it is not part of this SIF. The inlet valve for the other unit does not have to close to protect against this hazard so it is excluded. Although the need for the inlet valve closure is debatable, it does help reduce downstream pressure and was therefore included in the SIF. The SIF primary equipment is the LT-2025 level sensor, the VI-2002 Inlet Valve and the VI-2003 Outlet Valve. This is marked in the cause and effect diagram with an X. Other equipment is auxiliary. It is marked in the cause and effect diagram with an A. This information must be documented in the Safety Requirements Specification (SRS). 

Prior to carrying out SIL verification calculations for Safety Instrumented Functions (SIF) it is essential and very important that each function and its associated input and output signals be weU defined. The identification of the SIF is part of the analysis phase and the detail requirements for each function are documented in the Safety Requirements Specifications (SRS). 

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