Risk, Reliability & Functional Safety Knowledge Base

Most engineers know that testing is part of functional safety — but the same physical test can be a proof test in one context and a diagnostic test in another, and that distinction directly affects your PFD calculation and SIL claim. The difference comes down to four specific conditions: whether the test runs automatically, how frequently it runs, whether it triggers a defined automated response, and whether it targets failures relevant to the safety function. Get the classification wrong and your numbers are wrong — even if the test itself is sound.

Most engineers know HFT — hardware fault tolerance for safety. Fewer know that the same architecture can have a completely different fault tolerance for process availability. This article breaks down the difference between HFT and HFTs, and why picking 1oo2 over 2oo3 based on safety alone can be the right safety call and the wrong process call at the same time.

IEC 61511 does not require SIL-certified devices — it requires evidence. Learn the three compliance routes and what really matters in functional safety.

Safety functions can be designed to de-energize to trip or energize to trip. The required action is defined during hazard and risk analysis, and the system must then be engineered to achieve the necessary safety performance.

When a redundant safety system loses one channel, safety must not disappear. Learn how graceful degradation works, how to quantify it, and how to avoid systematic weaknesses.

SIL verification and PFD calculation are not the same thing. A precise, standards-based explanation of what verification really means in IEC 61511 and IEC 61508.

Defensive programming detects anomalous control flow and invalid values during execution. Learn how IEC 61508-3 recommends it and how it prevents systematic failures in safety software.

Static resource allocation reserves all memory at compile-time. Learn why IEC 61508 recommends it for safety-critical systems and how it controls systematic failures.

Event-driven systems with bounded response times ensure safety-relevant events are processed within a proven time limit. Learn how they support IEC 61508 and prevent unsafe delays.

Time-Triggered Architecture runs tasks and messages on a globally synchronised clock. Learn how TTA supports functional safety, eliminates systematic failures, and simplifies certification.