monocytogenes, in finished productand, at the same time, control other
contaminationsources.It was recognisedthat the majorsourceof pathogens
waslikelyto be the raw materialsusedin the low-riskareaof the factory
togetherwithany pathogensthat had enteredlow risk fromsoil associatedwith
people or vehicular movements. To protect the product being further
manipulatedin the high-risk areafromsuch pathogens, the philosophy is
undertakento:
∑ provideas manybarriers as possible to prevent the entryofListeriainto the
high-riskarea;
∑ preventthe growthand spread of anyListeriapenetratingthesebarriers
duringproduction;
∑ after production,employ a suitablesanitationsystemto ensure that all
Listeriaare removedfromhighrisk priorto productionrecommencing.
Together withthe buildingstructure, the thirdlevelbarrieris builtup by the
use of combinationsof a numberof separate components or sub-barriers,to
controlcontamination that couldenterhighrisk fromthe following routes:
∑ Structural defects.
∑ Product enteringhighrisk via a heatprocess.
∑ Product entering highrisk via a decontaminationprocess.This mayinclude
product enteringhighrisk that has beenheatprocessed/decontaminatedoff-
site but whose outerpackagingmayneeddecontaminatingon entry to high
risk.
∑ Otherproduct transfer.
∑ Packaging materials.
∑ Liquidand solidwastematerials.
∑ Foodoperatives, maintenance and cleaning personnel,etc., entering highrisk.
∑ The air.
∑ Utensils that mayhaveto be passedbetweenlow and highrisk.
8.4.1 Structure
Structurally,creatinga thirdbarrier levelcan be described as creatinga box
withina box. In otherwords,the high-riskarea is sealedon all sides to prevent
microbial ingress. While this is an idealsituation, we still needopeningsto the
box to allowaccessfor people, ingredientsand packagingand exit for finished
product and wastes.Openings shouldbe as few as possible, as small as possible
(to bettermaintain an internal positive pressure)and should be controlled (and
shutif possible) at all times. Similarly,the perimeter of the box shouldbe
inspected frequently to ensure that all jointsare fullysealed.
The design of the high-risk food processing area must allow for the
accommodationof five basic requirements,i.e.:
∑ processed materials and possibly some ingredients;
∑ processing equipment;
Improvingzoningwithinfoodprocessingplants 157