Safety and SIS · Glossary

What is an Independent Protection Layer?

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An independent protection layer is a safeguard that can prevent a hazardous scenario on its own and is independent of the initiating cause and other layers.

Independent Protection Layer Explained

Examples are a BPCS control loop, an operator response to an alarm, a relief valve and a SIF. To be credited, each must be effective, independent and auditable.

Safeguards that share sensors or logic with the initiating cause are not independent.

Independent Protection Layer: Typical Values

BPCS loop	PFD 0.1 at best
Operator response to alarm	often 0.1, with enough time
Relief valve	often 0.01

Calculators for Independent Protection Layer

CalculatorLOPA SIL CalculatorFree online calculator with formula and worked example.

Frequently Asked Questions

What is an Independent Protection Layer?

An independent protection layer is a safeguard that can prevent a hazardous scenario on its own and is independent of the initiating cause and other layers.

Can an alarm and a trip use the same transmitter?

Then they are not independent; only one can be credited.

Is a procedure an IPL?

Generally no, unless it meets the IPL criteria with a defined response and time.

Learn more on the blog

What is SIL (safety integrity level)

A practical guide on instrumentationblog.in with more detail on independent protection layer and how it is applied on real plants.

Read Full Article

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