SIL (Safety Integrity Level) analysis, SIL verification, and SRS (Safety Requirement Specifications)
The handling and movement of hazardous substances at facilities require safety measures with demanding criteria for the infringement of pre-set conditions, in order that the process is run in conditions of safety for people, the environment, and infrastructure. This translates to a need to implement special systems that are independent of any other system, in order that they may act in the event of other prevention systems failing and make the process safe.
These systems are called safety instrumented systems (SIS). The nature of these systems means they must have sufficient conditions of safety and reliability to ensure they function properly when they are required. This is the reason for the SIL analysis, which calculates the SIL (safety integrity level) index in order to assess the safety level required of those systems and verifies that they meet the required level.
Quantitative Risk Analysis (QRA)
Quantitative risk assessment (QRA) is a formal and systematic risk analysis approach to quantifying the risks associated with the operation of an engineering process. The results quantitatively address the risk to people, the environment, or the business.
QRA studies are typically required for production and processing facilities, high-pressure pipelines, and storage and importation sites, including liquefied natural gas (LNG). They contribute to improved decision-making by highlighting the accident scenarios that contribute most to overall risk. This is carried out in order to demonstrate if the acceptability criteria have been met and that the residual risks are as low as reasonably practicable (ALARP).
A QRA study normally comprises the following:
• Identification of hazards by using a technique such as the hazard and operability (HAZOP) study method.
• Safety integrity level (SIL) study using layers of protection analysis (LOPA) methods for the safety instrumented functions (SIFs) associated with the prevention of loss of containment from the facilities under consideration (e.g., loss of containment due to overpressure causes).
• Frequency estimation of the identified scenarios that can cause loss of containment from the facilities under consideration.
• Consequence analysis to determine the severities associated with each hazardous effect for the identified scenarios.
• Quantitative risk assessment to calculate and determine the safety risks to persons in the proximity of or affected by the facilities under consideration.
By Antonia Beri
Technical & Process Safety Expert
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