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Safety and SIS · Glossary

What is a Spurious Trip?

trip without a real demandSafety and SIS

A spurious trip is an unwanted shutdown caused by a safety system fault rather than a real process hazard.

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Spurious Trip Explained

Spurious trips cost production and can create hazards during restart. Frequent ones tempt people to bypass the SIS.

Voting such as 2oo3 or 2oo2 and good maintenance reduce spurious trips; safe failures of 1oo1 and 1oo2 designs cause them.

Spurious Trip Formula

STR ≈ λS   (1oo1)   and   MTTFspurious = 1 ÷ STR
λSsafe failure rate (per year)
Example: λS = 0.05 per year: about one spurious trip every 20 years.
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Calculators for Spurious Trip

CalculatorSpurious Trip Rate CalculatorFree online calculator with formula and worked example.CalculatorAvailability CalculatorFree online calculator with formula and worked example.

Frequently Asked Questions

What is a Spurious Trip?

A spurious trip is an unwanted shutdown caused by a safety system fault rather than a real process hazard.

Is a spurious trip safe?

The plant reaches its safe state, but start up and shutdown are the riskiest phases, so trips are not free.

How do I reduce spurious trips?

Better voting, delay timers where the process safety time allows, and fixing recurring causes.

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What is SIL (safety integrity level)

A practical guide on instrumentationblog.in with more detail on spurious trip and how it is applied on real plants.

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