According to the requirements of independence,functionality,integrity,reliability,auditability,access security and management of change for an independent protection layer (IPL),an IPL identificatio on typical protection layer in chemical enterprise was conducted.The results showed that the inherently safer design and the emergency response of factory and community were not treated as IPL generally.As IPL,the elements of basic process control systems (BPCS)should be isolated from similar devices in the safety instrumented function (SIF).The requirements of probability of failure on demand (PFD) should be met and the required action must be taken in the time available for BPCS.For the critical alarms and human response,besides the indication for action required by the operator must be detectable,the time available to take the action must be adequate.Moreover,the action should be unique and operable.SIF must be functionally independent from BPCS and meet requirements of SIL.The required action must be taken in the time available for SIF.The physical and postrelease protection devices should be independent from the other IPLs.The appropriate PFD value should be evaluated according to their practical running environment.The results of this paper can instruct the enterprise to identify IPL correctly in layer of protection analysis (LOPA).%按照独立保护层(IPL)独立性、功能性、完整性、可靠性、可审查性、安全许可保护性和变更管理的要求,对化工企业典型保护层进行了IPL识别.结果表明:本质安全设计、工厂和社区应急响应一般不作为IPL;作为IPL,基本过程控制系统(BPCS)应在物理上与安全仪表功能(SIF)分离,并满足要求时失效概率(PFD)的要求,在规定时间内完成所要求的动作；关键报警和人员响应应满足操作人员能得到采取行动的指示或报警,有足够的响应时间,任务应具有单一性和可操作性；SIF应在功能上独立于BPCS,SIF各元件应能及时提供响应,并满足相应SIL要求；物理保护和释放后保护设施应独立于其他IPL,并根据实际运行环境对其PFD进行修正.通过IPL的识别研究,可指导企业在进行保护层分析(LOPA)时正确的进行IPL识别,确保LOPA结果的准确有效.
展开▼
