Definition
Killer items is Daniel Boorman's name, at Boeing's checklist factory, for the steps a checklist must focus on — the steps that are most dangerous to skip and yet sometimes overlooked nonetheless. Identifying killer items is the engineering discipline that lets a checklist stay short. A list that tries to be comprehensive becomes too long to use; a list that ignores killer items is too thin to matter. The discipline is to find the small set that meets both tests: high consequence and historically missed.
Why it matters
How it works
The discipline is a triage. For each candidate step on a proposed checklist, ask two questions: if this step were missed, how often does that miss lead to serious harm? And historically, how often is it missed? A step goes on the list only if both answers are high.
This produces uncomfortable trade-offs. During the WHO checklist's design, deep-vein-thrombosis prophylaxis (heparin or compression stockings before long operations) was dropped — the literature was inconsistent across populations and the omission risk varied by site. Surgical fires were dropped — terrifying, but vanishingly rare compared with the routine killers (infection, bleeding, anaesthesia). Checks to prevent wrong-site surgery stayed in — also rare, but quick to verify and culturally salient.
The bigger lesson is that killer-items lists are not the same everywhere. Boeing's polar-icing checklist and a community hospital's antibiotic checklist have completely different killer items. The discipline is local; the design move is universal.