sources(e.g.low-risk production,packing, outside). For high-riskareas, the goal
of the air-handlingsystemis to supply suitably filteredfreshair, at the correct
temperature and humidity,at a slightoverpressureto prevent the ingressof
external air sources,particularlyfromlow-riskoperations.
The cost of the air-handlingsystems is one of the majorcosts associated with
the constructionof a high-riskareaand specialist advice shouldalwaysbe
soughtbeforeembarkingon an air-handling designand construction project.
Following a suitable risk analysis, it maybe concludedthat the air-handling
requirementsfor high-care areas maybe less stringent, especially relatedto
filtration levelsand degreeof overpressure.Onceinstalled, any changes to the
constructionof the high-risk area(e.g.the rearrangementof walls,doorsor
openings) shouldbe carefullyconsideredas they will havea majorimpact on the
air handlingsystem.
Air qualitystandards for the foodindustry werereviewedby Brown (2005)
and the designof the air-handlingsystemshould nowconsiderthe following
issues:
∑ Filtrationof air is a complex matterand requires a thoroughunderstandingof
filtertypesand installations. Thechoice of filterwillbe dictated by the
degreeof microbial and particleremovalrequired (BS EN 779).For high-
careapplications,a seriesof filtersis required to provideair to the desired
standard and is usuallymadeup of a G4/F5panelor pocketfilterfollowedby
an F7-9rigidcell filter.For somehigh-riskoperationsan H10or H11final
filtermaybe desirable.
∑ The pressure differentialbetweenlow and high risk shouldbe between5 and 15
pascalsor, through openings,an air flowof 1.5 m sˇ^1 or greatermaybe
required to ensure one-way flow is maintained. The desired pressure
differentialwill increaseas boththe numberand size of openings, and also
the temperaturedifferentials,betweenlow and high risk increases. As a general
rule,openingsinto high-riskareasshouldbe as smalland as few as possible.
Generally5±25air changesper hourare sufficientto removethe heatload
imposedby the processingenvironment(processesand people)and provide
operativeswithfreshair, thoughin a high-riskareawithlargehatches/doors
that are frequently opened,up to 40 air changesper hourmaybe required.
∑ The requirementsfor positive pressurein high-care processing areasare less
stringentand ceiling-mounted chillers togetherwithadditionalair make-up
maybe acceptable.
∑ As wellas recirculating temperature-controlled air, the systemmayneedto
be designedto dumpair directlyto wasteduring cleaningoperationsand to
recirculate ambient or heated air after cleaning operations to increase
environmentaldrying.Withrespectto drafts, the maximumair speedcloseto
workers to minimise discomfort through'wind-chill' shouldbe 0.3ms-1. This
is typically achievedwith airsocks, positioneddirectlyoverthe product lines.
∑ UK governmentsponsored work at the Campden& ChorleywoodFood
Research Association (CCFRA) and the Silsoe Research Institute has
Improvingzoningwithinfoodprocessingplants 163