The DCS interlock result is sent to the SIS to drive the relevant solenoids
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I would like to ask everyone whether it complies with relevant specification requirements to use the DCS interlock output to drive the relevant solenoids in SIL1 circuits What are the specific specifications?
From a regulatory perspective, when using DCS interlocks to drive SIS solenoids in SIL1 circuits, special attention should be paid to the following points: The IEC 61511 standard requires that the SIS be independent of the BPCS system; if DCS interlock signals are used to drive SIS actuators, signal isolation through safety relays or isolators is necessary to prevent common-cause failures. It is recommended to use SIL-certified solenoid valves, with their hardware fault margin being verified in accordance with IEC 61508. For SIL1 circuits, a hardware fault margin of ≥1 is typically required. In actual projects, the failure modes of solenoid valves (such as safe in case of power loss/dangerous in case of power loss) also need to be considered; it is recommended to consult the specific safety requirements outlined in the HAZOP analysis report. Before implementation, it is recommended to have a professional functional safety engineer conduct SIL calculations and keep complete verification records.
Regarding the specifications for sending DCS interlock signals to the solenoids driven by the SIS, the IEC 61511 mentioned above is indeed the most fundamental standard reference. Here are two additional practical insights for reference: 1) In actual projects, we have encountered situations where insufficient capacity of the DCS relay contacts caused signal fluctuations on the SIS side; it is recommended to pay close attention to the selection of intermediate relays ； 2) If a hardwired connection is used, be sure to implement signal status monitoring on the SIS side (such as heartbeat detection) to prevent failures due to broken connections. For the specific design, it is recommended to engage a unit with qualifications for functional safety assessment to carry out comprehensive verification.
You’re using the valves together; the standard specifies that they should be separated, according to HG22820-2024, 7.2.2.
Clause 6.2.2 of HGT22020-2024 Design Specifications for Chemical Process Safety Instrumentation Systems: The measuring instruments for SIL1-level safety instrument functions should be separated from the basic process control system; it is recommended to install detection instruments, interlock output instruments, etc. separately