How many levels are there in the hierarchical management of process interlocks? What are the criteria for its grading?
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Those working in the chemical industry are aware that interlocks within a facility are classified into several levels. After reviewing numerous sources, there are two approaches to this classification: one is based on the importance of the interlock, such as for core equipment or critical points that could lead to accidents; the other is based on the continuity of the system, namely whether it could cause the entire system to stop operating. I’m not sure which one is the correct answer; is the grading done as A/B or as levels 1, 2, and 3? Are there any relevant standards that specify this? The \"HGT20511-2000 Specifications for the Design of Signal Alarm and Safety Interlock Systems\" only stipulates that, when designing safety interlocks, these systems should be classified into levels 1, 2, and 3 based on their level of hazard, in order to determine which instrumentation devices should be used; this is not what I am looking for.
Are process interlocks also classified by level? We only distinguish between safety interlocks and process interlocks.
You may refer to the following SYT 6966-2013 Code for Design of Safety Instrumented Systems in Oil and Gas Pipeline Projects
If it refers to the safety level of SIL circuits, there are five levels: SIL 0, 1, 2, 3, and 4. SIL 0, as the name implies, does not require a safety interlock system; it can be implemented using DCS or PLC systems that do not have any SIL level requirements. For SIL1 and above, there are SIL level requirements for all the instruments and cards involved in the entire safety interlock circuit. As for which specific SIL level to use? This issue cannot be determined by the instrument itself; rather, it is the safety engineer who determines the level after conducting various assessments regarding potential risks to human safety and equipment damage in case of an anomaly at that location. For example, factors such as whether it can cause injury, whether it can start a fire, and the level of economic loss are classified into different categories. The process engineer then describes the safety measures that have been designed for that location, such as safety valves, on-site manual valves, or other safety devices; for each measure provided, the required safety level for the instrumentation can be reduced by one tier. The 2oo3 interlock is just one part of it. Therefore, the safety level that the instrument SIL loop needs to achieve should be determined by considering the completeness of the existing safety measures at that location. So there is no fixed standard.
Thank you for the answer above, but what I want to ask is about the management hierarchy for process interlocks, not the design aspect. It is mentioned in the encyclopedia on process interlocks, but I’m not aware of the origin of these standards.
Our company classifies things into levels one, two, and three, based on the impact of the interlock system; those that cause the shutdown of all equipment are classified as level one. Examples include important compressors and valves in the steam system. Secondary interlocking will shut down important equipment units, but it will not cause a complete shutdown of production; however, the production load will be reduced. Three-level interlock usually means shutting down individual small devices, which has little impact on production, such as those related to utility systems and hydrogen recovery.
Oh, I’m sorry, I didn’t understand before. The classification into Grade A and Grade B is generally carried out for the purpose of project or enterprise management, and it is usually in accordance with industry regulations. For example, the Regulations on Interlock Protection Systems of Sinopec, as well as the Regulations on Instrumentation Equipment of Sinopec (2011) No. 62, both classify safety instrumented equipment into Grade A and Grade B, providing clear definitions for these two grades. Many other companies also use this as a basis to establish their own corporate standards. As for whether Sinopec’s regulatory requirements have an even deeper origin, and whether they draw on foreign standards such as those from API or Shell, UOP, and similar organizations, I’m not sure. I guess there must be an original version of these regulations.
This post was last edited by Linggucheng on 16:06 on January 9, 2019. Thank you; however, the above two documents only specify the need for hierarchical management, but there are various types of hierarchies – some with two levels and others with three levels. Moreover, the ways in which these two or three levels are structured differ as well: some classifications are based on the consequences resulting from certain actions, while others are based on companies or workshops. It’s not clear which standard provides detailed requirements for such hierarchical structures.
Refer to the following standards: GB T 20438-2017 Functional Safety for Electrical/Electronic/Programmable Electronic Safety-Related Systems; GB T 21109-2007 Functional Safety for Safety Instrumented Systems in the Process Industry; GB T 36324-2018 Specifications for Classifying Information Security in Industrial Control Systems. **Guidelines issued by the State Administration for Work Safety on Strengthening the Management of Safety Instrumented Systems in the Chemical Industry (An Jian Zong Guan San [2014] No. 116)**
Which standards do these screenshots correspond to respectively?
I thought it was standard, but I couldn’t find it; searching didn’t help either. It’s not clear where this management system originated; there are countless results when searching online, but no standard reference can be found