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What is Safety Integrity Level (SIL)?

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Safety integrity level (SIL) is a measure of the likelihood that a safety system or safety function will fail to perform its intended safety function. The higher the SIL level, the less likely it is that the safety system or safety function will fail.

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The SIL level is typically expressed on a scale of 1 to 4; SIL 1 is the lowest level and SIL 4 is the highest level. Each SIL level is associated with a specific target safety level, expressed as the probability of a hazardous malfunction occurring.

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The target safety level is expressed in terms of the probability of failure on demand (PFD), which is the probability that the safety function will fail when needed. The lower the PFD, the higher the level of security provided by the security system or security function.

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SIL Security Standards
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SIL classification follows two international standards IEC 61508 and IEC 61511:

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IEC 61508 ("Functional safety of electrical/electronic/programmable electronic systems") is the core standard. Describes risk assessment and measures to design relevant security functions.

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IEC 61511 ("Functional Safety - Safety Systems for the Process Industry") applies specifically to process automation. Essentially, the rule in applications is that lower demands relate to applications with lower requirements.

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SIL Level Determination

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What potential danger does my system pose? Every engineer of a process plant in the chemical industry must ask himself this question. A risk chart that combines four defined parameters according to IEC 61508 and 61511 into a decision tree helps answer these:

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1. Damage coverage (S): How serious are the foreseeable consequences?

2. Probability of exposure (F): How often and for how long do people stay in the danger zone?

3. Hazard prevention / avoidance (P): Can I prevent or limit the event?

4. Probability of occurrence (W): How often should I expect an event?

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Major Accident Scenario Document Communiqué According to the Regulation on Preventing Major Industrial Accidents and Reducing Their Effects
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Obligations:

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The operator of a lower or higher level organization prepares or has a major accident scenario document prepared by complying with the specified format and general rules and fulfilling the minimum requirements. The major accident scenario document is not sent to the Ministry of Family, Labor and Social Services, but is kept in the organization.

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NOTIFICATION OF MAJOR ACCIDENT SCENARIO DOCUMENT TO BE PREPARED REGARDING MAJOR INDUSTRIAL ACCIDENTS

Annex-1 FORMAT AND GENERAL RULES OF MAJOR ACCIDENT SCENARIO DOCUMENT

8.4. Principle of independence and effectiveness
In calculating the frequency of occurrence of scenarios, the principle of independence, the effect of common cause errors and the principle of effectiveness are also taken into account.

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MINIMUM REQUIREMENTS FOR MAJOR ACCIDENT SCENARIO DOCUMENT:

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• Major accident scenario document team: A team should be formed to prepare the scenario document.

• Steps for preparing scenarios: Steps such as identification and classification of hazardous substances, identification of hazardous equipment, identification of internal hazards, identification of external hazards, creation, analysis and evaluation of major accident scenarios are followed.

• Identification and classification of hazardous substances: Hazardous substances are identified and classified. The SEA Regulation is taken as basis.

• Identification of hazardous equipment: Hazardous equipment is identified and listed.

• Identification of internal hazards: Internal hazards related to hazardous equipment are identified.

• Identification of external hazards: External hazards in the organization's environment are identified.

• Creation, analysis and evaluation of major accident scenarios: Scenarios are created, frequencies are calculated, compared with limit values and necessary measures are decided.

• Other issues: Other important issues such as critical equipment, frequency calculation methods, operator errors, independence and efficiency principles are stated.

The steps to be followed to prepare the major accident scenario document are explained in detail below:

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Step 1: Identification and Classification of Hazardous Substances

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Step 2: Identifying Hazardous Equipment

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Step 3: Identifying Internal Hazards

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Step 4: Identifying External Hazards

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Step 5: Creation, Analysis and Evaluation of Major Accident Scenarios

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This document specifies how the major accident scenario document should be prepared in accordance with the requirements of the "Regulation on the Prevention of Major Industrial Accidents and Reducing Their Effects" and the limit value of the major industrial accident frequency.

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Limit Value of Major Industrial Accident Frequency:

For hazardous equipment that may cause major accidents, the operator reduces the frequency of occurrence of each major industrial accident scenario to 1x10-4/year or less.

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This document explains how an enterprise should prepare its major accident scenario document in accordance with these regulations and what kind of values are targeted in order to prevent major industrial accidents and reduce their effects.

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To get a detailed idea about Quantitative Risk Assessment and GMS, please review the Article and Blog section.