OEE Explained: Turning Machine Data into Productivity
OEE distils availability, performance and quality into a single number that shows how much of your true capacity you are really using — and where it leaks away.
When a process can harm people, the environment or expensive assets, hoping nothing goes wrong is not a strategy. Functional safety provides an engineered, measurable way to reduce that risk to a level society and regulators consider tolerable. This guide introduces functional safety, SIL, and the IEC 61508/61511 standards that govern it.
Functional safety is the part of a system’s overall safety that depends on it actively detecting a hazardous condition and doing something about it. A classic example: a pressure sensor detects that a vessel is over-pressurising, and a Safety Instrumented System automatically closes a valve and shuts the process down before anything ruptures.
The goal is not to eliminate risk entirely — that is impossible — but to reduce it to a defined, tolerable level using reliable protective functions.
A Safety Instrumented System (SIS) carries out these protective functions. It is made of three parts:
Each protective function the SIS performs is called a Safety Instrumented Function (SIF).
Safety Integrity Level (SIL) expresses how reliable a safety function must be, on a scale from SIL 1 (lowest) to SIL 4 (highest). A higher SIL demands a lower probability that the function fails when it is needed — and therefore more robust design, redundancy and testing.
Importantly, SIL is determined, not guessed. Techniques such as risk graphs and LOPA (Layer of Protection Analysis) establish how much risk reduction a given hazard requires, which sets the target SIL. Over-engineering wastes money; under-engineering leaves people exposed.
Two standards dominate:
Functional safety is not a one-off calculation; it is a lifecycle. It begins with hazard and risk assessment (often a HAZOP), moves through allocation of safety functions and SIL targets, into design and engineering of the SIS, and continues through installation, validation, operation, proof-testing and eventual decommissioning. Each stage must be documented and verified.
iSquare supports the full functional-safety lifecycle as part of our safety studies and engineering services — from hazard studies and SIL determination to SIS design, verification and validation. Protecting your people and assets starts with the right analysis: talk to our safety engineers.
OEE distils availability, performance and quality into a single number that shows how much of your true capacity you are really using — and where it leaks away.
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A HAZOP tells you what could go wrong. LOPA tells you whether your safeguards are enough — and bridges the gap to a required Safety Integrity Level.