Kn Knowl wledge dge Shar aring ing Ses essio sion Serie eries, s, GAIL Jhab abua WELCOME TO THE PRESENTATION ON FUNCTIONAL SAFETY 10 FEB 2017 (MANAGER-NG P/L O&M-INST.), GAIL JHABUA BY- CHANDRESH PARSEDIA 1
Kn Knowl wledge dge Shar aring ing Ses essio sion Serie eries, s, GAIL Jhab abua What is Functional Safety? • The exact definition according to IEC 61508: “part of the overall safety relating to the EUC and the EUC control system that depends on the correct functioning of the E/E/PE safety-related systems and other risk reduction measures” 2
Kn Knowl wledge dge Shar aring ing Ses essio sion Serie eries, s, GAIL Jhab abua Functional safety as per IEC 61508 IEC 61508 mandates an ”overall” safety approach could also be referred to as a: – System safety approach or – Holistic approach (accounts also for the whole life cycle of a system) 3
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Kn Knowl wledge dge Shar aring ing Ses essio sion Serie eries, s, GAIL Jhab abua The risk reduction required from a function is characterised by the ‘Safety Integrity Level’ or SIL. To put it simply, each safety function is designed to deliver either 1, 2 or 3 orders of magnitude in risk reduction. SIL 1, SIL 2 and SIL 3 correspond to Risk 7 Reduction Factors of at least 10, 100 and 1,000.
Kn Knowl wledge dge Shar aring ing Ses essio sion Serie eries, s, GAIL Jhab abua Safety Measurements MTBF = 1/(failure rate) failure rate = RHF + SHF + SSF SIL 1/(failure rate) SIL 1/(RHF + SHF + SSF) RHF - Random Hardware Failure SHF - Systematic Hardware Failure SSF – Systematic Software Failure SIL - Safety Integrity Level 8
Kn Knowl wledge dge Shar aring ing Ses essio sion Serie eries, s, GAIL Jhab abua The Probability of Failure on Demand (PFD) is a likelihood that a loop will fail when a demand is placed on it. The PFD of a SIF is calculated using the number of potential dangerous undetected failures and the test interval of the loop. SIL is one of the most misused terms in the field of reliability. ‘SIL’ is often used to imply that a product has better quality, higher reliability, or some other desirable feature. It does not. SIL means safety integrity level, a number between 1 and 4. It is used to describe the degree of safety protection needed by a process and consequently the safety reliability of the safety system necessary to achieve 9 that protection. SIL1 is the lowest level of safety protection and SIL4 the highest.
Kn Knowl wledge dge Shar aring ing Ses essio sion Serie eries, s, GAIL Jhab abua CONTROL SYSTEM: system which responds to input signals from the process and/or from an operator and generates output signals causing the process to operate in the desired manner. BASIC PROCESS CONTROL SYSTEM (BPCS): system which responds to input signals from the process, its associated equipment, other programmable systems and/or an operator and generates output signals causing the process and its associated equipment to operate in the desired manner but which does not perform any safety instrumented functions with a claimed SIL > 1. FUNCTIONAL SAFETY: part of the overall safety relating to the process and the BPCS which depends on the correct functioning of the SIS and other protection layers FUNCTIONAL SAFETY ASSESSMENT: investigation, based on evidence, to judge the functional safety achieved by one or more protection layers. 10
Kn Knowl wledge dge Shar aring ing Ses essio sion Serie eries, s, GAIL Jhab abua SAFE FAILURE : failure which does not have the potential to put the safety instrumented system in a hazardous or fail-to-function state. SAFE FAILURE FRACTION : fraction of the overall random hardware failure rate of a device that results in either a safe failure or a detected dangerous failure. SAFE STATE : state of the process when safety is achieved. NOTE 1: In going from a potentially hazardous condition to the final safe state, the process may have to go through a number of intermediate safe-states. For some situations, a safe state exists only so long as the process is continuously controlled. Such continuous control may be for a short or an indefinite period of time. SAFETY : freedom from unacceptable risk. SAFETY FUNCTION : function to be implemented by an S1S, other technology safety related system or external risk, reduction facilities, which is intended to achieve or maintain a safe state for the process, with respect to a specific hazardous event. 11
Kn Knowl wledge dge Shar aring ing Ses essio sion Serie eries, s, GAIL Jhab abua SAFETY INSTRUMENTED CONTROL FUNCTION : safety instrumented function with a specified SIL operating in continuous mode which is necessary to prevent a hazardous condition from arising and/or to mitigate its consequences. SAFETY INSTRUMENTED CONTROL SYSTEM : instrumented system used to implement one or more safety instrumented control functions. NOTE Safety instrumented control systems are rare within the process industries. Where such systems are identified, they will need to be treated as a special case and designed on an individual basis within this standard should apply but further detailed analysis may be required to demonstrate capable of achieving the safety requirements. SAFETY INSTRUMENTED FUNCTION (SIF) : Safety function with a specified safety integrity level which is necessary to achieve functional safety and which can be either a safety instrumented protection function or a safety instrumented control function. DEMAND MODE SAFETY INSTRUMENTED FUNCTION: where a specified action (for example, closing of a valve) is taken in response to process conditions or other demands. In the event of a dangerous failure of the safety instrumented function a potential hazard only occurs in the event of a failure in the process or the BPCS. 12
Kn Knowl wledge dge Shar aring ing Ses essio sion Serie eries, s, GAIL Jhab abua CONTINUOUS MODE SAFETY INSTRUMENTED FUNCTION : where in the event of a dangerous failure of the safety instrumented function a potential hazard will occur without further failure unless action is taken to prevent it. Continuous mode covers those safety Instrumented functions which implement continuous control to maintain functional safety. NECESSARY RISK REDUCTION: risk reduction required to ensure that the risk is reduced to a tolerable level. M OO N: safety instrumented system, or part thereof, made up of “N” independent channels, which so connected, that “M” channels are sufficient to perform, the safety instrumented function. PROTECTION LAYER : any independent mechanism that reduces risk by control, prevention or mitigation SAFETY INSTRUMENTED SYSTEM (SIS) : instrumented system used to implement one or more safety instrumented functions. An SIS is composed of any combination of sensor (s), logic solver (s), and final elements(s). Safety instrumented systems are used to implement SIFs as layers of protection to reduce process hazards. Its an automated way to take an action against a potentially unsafe condition and return a process to a safe or stable state. 13
Kn Knowl wledge dge Shar aring ing Ses essio sion Serie eries, s, GAIL Jhab abua SAFETY INTEGRITY : average probability of a safety instrumented system satisfactorily performing the required safety instrumented functions under all the stated conditions within a stated period of time. NOTE 1 The higher the safety integrity level, the higher the probability that the required safety instrumented function (S IF) will be carried out. SAFETY INTEGRITY LEVEL (SIL): discrete level (one out of four) for specifying the safety integrity requirements of the safety instrumented functions to be allocated to the safety instrumented systems. Safety integrity level 4 has the highest level of safety integrity; safety integrity level 1 has the lowest. FAILURE Termination of the ability of a functional unit to perform a required function. Failures are either random or systematic 14
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Kn Knowl wledge dge Shar aring ing Ses essio sion Serie eries, s, GAIL Jhab abua REQUIREMENTS ON THE BASIC PROCESS CONTROL SYSTEM AS PROTECTION LAYER » 18 Typical risk reduction methods found in process plants
Kn Knowl wledge dge Shar aring ing Ses essio sion Serie eries, s, GAIL Jhab abua Relationship between the hardware and software architectures of SIS 19
Kn Knowl wledge dge Shar aring ing Ses essio sion Serie eries, s, GAIL Jhab abua THANK YOU Motivation and Guidance from DGM(O&M) and OIC Jhabua has been provided for this Knowledge Sharing 20
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