Can the SIS valve be manually intervened?
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I would like to ask everyone: Should the SIS system be completely independent, enabling an emergency stop upon the activation of interlocks? Can the SIS valve be manually closed? Which specific regulations provide support? Thank you!
SIS is static and does not require human intervention.
During normal production, manual shutdown is prohibited (the SIS is in a static state)； It can be manually turned off in the installation and debugging mode before production (relevant permissions are required).
This is no joke – any operation on the SIS system, including making changes or disabling interlocks, requires signatures at the level of the chief engineer or even the general manager. If it’s truly necessary to carry out such operations for production reasons, then the procedures for disabling interlocks must be followed, along with the required sign-offs, before proceeding.
On the system, it is possible to disable or enable interlocks; once enabled, manual operation is not allowed. To disable an interlock, approval procedures must be followed, and after it is disabled, manual operation becomes possible.
The specifications allow for software bypassing
After it is put into use, manual operation can involve pressing the emergency stop button, after which the valve will be in a safe state. If the artificial intervention in question refers to opening or closing valves, then it constitutes standard illegal operation, and moreover of a serious nature
It cannot be assumed that the SIS valve is a switch
If there is an urgent need, it is permissible to go through the necessary procedures to remove the interlock in order to resolve the issue, provided that the process and instrumentation are well understood, a risk analysis has been conducted, and preventive measures within each person’s scope of responsibility have been taken. Once the issue is resolved without any problems, the system can be put back into operation. Nowadays, if a Class A issue remains unresolved for more than a month, it is considered a serious hazard
According to IEC standards, manual intervention can be part of the SIF circuit. In actual work, everyone is just very cautious.