Seeking help with SIL verification issues
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The SIL certificate only provides the total failure rate and the undetected hazardous failure rate. How can one carry out SIL calculations then? Four failure rates are required to conduct such calculations. Everyone must have encountered this situation; what is the usual way to handle it?
When only the total failure rate and the undetected hazardous failure rate are provided, the SIL can be calculated using the following method: 1. Assume that there are only two failure modes in the system: one is a hazardous failure mode and the other is a non-hazardous failure mode. 2. Assuming all the undetected hazardous failure modes occur, the system reaches its most severe state. 3. Determine the overall failure rate of the system based on the provided overall failure rates. 4. Use the determined total failure rate and the undetected hazardous failure rate to calculate the system’s non-hazardous failure rate. 5. The SIL verification can be performed using the calculated non-hazardous failure rates of the system and the provided hazardous failure rates. It should be noted that the SIL calculated in this way is only an estimate, and there may be certain errors in practice. Therefore, where feasible, strive to obtain more detailed failure rate data to conduct accurate SIL calculations. .
Do you also recognize the certification certificates for ECM?
If you only have the total failure rate and the undetected hazardous failure rate, without the other two failure rate values, you can use qualitative analysis methods to evaluate the System Safety Integrity Level (SIL). The basic principle of qualitative analysis methods is to determine the SIL level of a system by analyzing its functional safety requirements, the safety performance of its components, and potential hazard factors. In your case, you first need to determine the minimum SIL level required based on the security requirements of the system’s functions. Then, you need to re-analyze the system’s design, composition, and operation in order to identify potential hazardous failure modes, and assess and rank them. Based on the system design and equipment usage, you can assess the probability and frequency of various failure modes, determine the undetected dangerous failure rates, and thus establish the range of system failure rates. Finally, you can calculate the system’s safety integrity level based on the SIL level and the range of system failure rates, and take necessary measures to reduce failure rates and improve the system’s safety performance. It should be noted that although qualitative analysis methods can provide a preliminary assessment of a system’s SIL, the results of such assessments often carry a high degree of uncertainty. If you need more accurate SIL assessment results, it is recommended that you use quantitative analysis methods to obtain more failure rate data for calculation and simulation.