Schematex
bowtie·CCPS / Energy Institute 2018·engineering, construction·complexity 2/3·since v0.6.6

Working at height — fall from height

A defence-in-depth bowtie with an escalation factor — a preventative barrier is degraded by a named condition, which is itself controlled by an escalation-factor barrier dropping below the line.

For the safety officer documenting a working-at-height permit

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Working at height Bowtie: hazard "Working at height", top event "Person falls from height"; 2 threats, 2 consequences, 9 barriers, 1 escalation factor. Working at height Personfalls fromheight Working at height Guardrail removedfor access Permit-to-worksystem Temporary edgeprotection Edge protectionnot inspected Pre-useinspection regime Spotter /banksman Fragile roofsurface Crawling boards +signage Roof-access riskassessment Fatality Fall-arrestharness + lanyard Rescue plan +first aid Serious injury Safety nettingbelow On-site medic +evacuation Threat Barrier (prevent / mitigate) Top event Consequence Escalation factor
UTF-8 · LF · 18 lines · 633 chars✓ parsed·1.0 ms·10.2 KB SVG

What this shows

Two threats, two consequences, multi-barrier chains — and an escalation factor, the element that makes a bowtie an honest defence-in-depth model rather than a wish list. The "Temporary edge protection" barrier is degraded by a specific named condition ("Edge protection not inspected", amber), which drops vertically below the barrier on a muted degrades connector. That escalation factor is itself controlled by an escalation-factor barrier ("Pre-use inspection regime") one level deeper.

Reading order along each line is declaration order: the first barrier is the outermost (first line of defence, nearest the threat); the last is the innermost (nearest the knot). The escalation hangs into the whitespace below without disturbing the symmetry of the two threat lines.

Bowtie syntax