Barrier effectiveness
Barrier effectiveness is a judgement of how reliably a barrier performs its function in current operational reality — not as designed, but as found. Ratings like high, medium, or low must be defensible to an auditor.
An effectiveness rating answers the only question that matters about a barrier: would it actually work today? Not when it was commissioned, not as drawn — now, with the current backlog, the current crew, and the current bypass register.
Most schemes use a simple scale (high / medium / low, or effective / partially effective / ineffective). The scale matters less than the discipline behind it. A rating is defensible when it is tied to evidence: test results, inspection findings, audit observations, activation history. A rating is decoration when it was set in a workshop three years ago and never touched since.
Two failure patterns are worth naming. Optimism drift: everything is rated high because the workshop wanted to finish by four o'clock. Stale credit: the rating still reflects the barrier before the reorganisation, the SME's departure, or the deferred shutdown. Both are found by the same cure — connect each rating to the degradation factors currently active against the barrier, and to the verification evidence in its performance standard.
In Bowtie Risk Engine, effectiveness lives on the control and follows it into the register and the audit PDF, so the rating shown to a reviewer is always the one on the live model — see the control register.
Last reviewed 2026-08-09 · Back to the glossary
See the method in working software.
Six worked bowtie examples ship with the product — open one read-only, no sign-in, and read every control in full.