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Bowtie — Listeria in Chilled Ready Meals

Food-safety bowtie for ready-to-eat product handled after the cook step, turning 14.5 contamination opportunities a year into 1.49 that get past the lethality step, ranking the physical high-care barrier above all environmental monitoring.

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Listeria monocytogenes in chilled ready mealsHAZARDReady-to-eat food handled after the cook stepTHREATSPREVENTIVE BARRIERSRECOVERY BARRIERSCONSEQUENCESSwab sites rotated away fromhistorical positivesVector swabbing after anyzone 1 positiveZoned environmentalmonitoring, 120 swabs aweek70% · detectionHygienic sloped stainlessdrainage55%Agency staff on nights notinducted into zoningHigh-care barrier withboot wash and change80%Colour-coded equipmentsegregated by zone60%Continuous temperaturelogging with an 8 C alarm75% · detectionShelf-life validated bychallenge testing at 8 C50%Positive release onfinished product testing60% · detectionTraceability to aone-hour productionwindow50% · recoveryMock recall exerciseachieving 99% in 4 hours45% · recoveryThird-party BRCGS auditwith unannounced visits40%Customer technicalcorrective action plan35% · recoveryHarbourage site in afloor drain or crack4/yr → 0.54/yrRaw-to-cooked crosscontamination by anoperative8/yr → 0.64/yrPost-cook chillingfailure allows growthin transit2.5/yr → 0.3125/yrListeriosis outbreakwith fatalitiessev 5 · risk 1.49Class 1 recall ofeight weeks ofproductionsev 4 · risk 3.28Retailer delistingand site suspensionsev 3 · risk 1.75Listeriacontaminatesproduct after…1.49/yrtop-event frequencyTop event1.49/yrinherent 14.5/yrResidual risk6.52inherent 174Risk reduction96.3%threat side 89.7%Barriers113 threats · 3 consequencesDominant threatRaw-to-cooked cross contamination by an…42.9% of the top eventResidual risk 6.52 against an inherent 174 — the barriers remove 96.3% of it. 2 things are probably not what was meant — every path and every escalation factor was checked.Barrier criticality — residual risk if that one barrier were removed1. High-care barrier with boot wash and change+11.19 ×2.72. Zoned environmental monitoring, 120 swabs a week+5.51 ×1.83. Colour-coded equipment segregated by zone+4.2 ×1.64. Continuous temperature logging with an 8 C alarm+4.1 ×1.65. Hygienic sloped stainless drainage+2.88 ×1.46. Mock recall exercise achieving 99% in 4 hours+2.69 ×1.4FindingsConsequence "Class 1 recall of eight weeks of production" rests on ONE barrier. Defence in depth is the claim a bowtie is drawn to make, and a single barrier is a single point of failure: the day it fails is the day the consequ…Escalation factor "Agency staff on nights not inducted into zoning" degrades barrier "Colour-coded equipment segregated by zone" and nothing is holding it off. The 60% credited to that barrier — and every figure computed from i…Each of the 3 consequences is credited the full top-event frequency of 1.49/yr — the model here is that one top event produces all of them, so the residual score of 6.52 adds 3 outcomes to one event. That is right when they hap…

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title "Listeria monocytogenes in chilled ready meals"
hazard "Ready-to-eat food handled after the cook step"
top "Listeria contaminates product after the lethality step"
unit "/yr"

threat "Harbourage site in a floor drain or crack" likelihood: 4
  barrier "Zoned environmental monitoring, 120 swabs a week" effectiveness: 0.7 type: detection
    escalation "Swab sites rotated away from historical positives"
      control "Vector swabbing after any zone 1 positive"
  barrier "Hygienic sloped stainless drainage" effectiveness: 0.55

threat "Raw-to-cooked cross contamination by an operative" likelihood: 8
  barrier "High-care barrier with boot wash and change" effectiveness: 0.8
  barrier "Colour-coded equipment segregated by zone" effectiveness: 0.6
    escalation "Agency staff on nights not inducted into zoning"

threat "Post-cook chilling failure allows growth in transit" likelihood: 2.5
  barrier "Continuous temperature logging with an 8 C alarm" effectiveness: 0.75 type: detection
  barrier "Shelf-life validated by challenge testing at 8 C" effectiveness: 0.5

consequence "Listeriosis outbreak with fatalities" severity: 5
  barrier "Positive release on finished product testing" effectiveness: 0.6 type: detection
  barrier "Traceability to a one-hour production window" effectiveness: 0.5 type: recovery

consequence "Class 1 recall of eight weeks of production" severity: 4
  barrier "Mock recall exercise achieving 99% in 4 hours" effectiveness: 0.45 type: recovery

consequence "Retailer delisting and site suspension" severity: 3
  barrier "Third-party BRCGS audit with unannounced visits" effectiveness: 0.4
  barrier "Customer technical corrective action plan" effectiveness: 0.35 type: recovery