Process Safety Time - SIL


Thread Starter


Does the process safety time need to be considered as part of the SIL Verification exercise?

I understand, the process safety time needs to be evaluated and specified during the SRS.

Shall the process response time be calculated during SIL Verification and compared with the process safety time?

Mike Boudreaux


I'm going to answer your question according to IEC 61511, which is the functional safety standard that applies to the process industry sector.

IEC 61511 doesn't use the term "SIL Verification," but this term is commonly used to describe the concept design phase of a safety instrumented function. IEC 61511 calls this phase "SIS design and engineering." It is covered by clauses 11 and 12 in the standard. In this phase, you design the SIS to meet the requirements for safety instrumented functions and safety integrity. The SRS is an input for this activity.

Taken literally, "SIL Verification" would mean that you're only verifying that the SIF design meets the specified SIL target. However, it is common that you also verify the response time during this activity (as well as other functional specifications from the SRS). Your selection of components and subsystems effects response time, and if your design doesn't meet the requirements then you'll have to select different components and reverify your SIL performance, response time, and other performance criteria.

Best regards,

Mike Boudreaux
DeltaV SIS Product Manager
Emerson Process Management
Mr. Mike Boudreaux,

My question concerns Safety system and SIL certification. If we want to install a device in an ESD system, is it necessary that the device to have SIL 3 certification? Or the entire system shall meet the SIL 3 requirements? Is it correct if we say that each device/component that is installed/used in an ESD system should be SIL 3?

For example an ESD valve includes a valve and an actuator, is it necessary that the actuator meet the SIL 3 certification?

I do appreciate your concern and advice.

Best regards.
Dear Mr. Valid, we have a SIL MANUAL, that is free of charge. I'm sure it will help you in answering your questions.

if you email me at giorgio.landrini (at)

I will send you the pdf version.

John Wetherall

Can you please send me a copy of the SIL Manual


John Wetherall (John.Wetherall [at]