Food productionareas differ fromsuchenvironmentsin that theyare oftenwet,
includemany moresources of aerosol, including morepeople, and the food
sector is moreconcernedwithmicrobialcontaminants ratherthantotalparticle
contaminants. Nonetheless the generalapproachesidentified aboveare adopted
by the foodindustry but oftenat a lower levelof controlthanin other sectors.
It is interestingto comparethe particleconcentrationsfoundin cleanroomsand
high-carefood productionareas.Cleanrooms are classifiedaccordingto various
standards(Mo»ller, 1999) withthe FederalStandard209Ebeingone of the most
commonly used.In this standard,eachcubicfoot of air in a Class100 environment
would not containmore than 100 particlesof 0.5m diameteror larger.Similarly,
the air in a Class 100 000 environment,often knownas a `whiteroom',wouldnot
containmorethan100 000 particlesper cubicfoot withdiametersof0.5m.
These concentrationswould usuallybe measuredwithoutoperatorsin the room. In
comparison,Burfoot and Brown (2004a)foundparticleconcentrationsup to
230 000 ftˇ^3 (8 100 000 mˇ^3 ) nearto an operatingbootscrubberin a high-care
sandwichassemblyarea and downto 9000ftˇ^3 (330 000 mˇ^3 ) duringa periodof
no activity in the same area. Particle concentrations up to 600 000 ftˇ^3
(21 000 000 mˇ^3 ) weremeasuredin a chilleddessertfillingarea.
Filtrationis one of the majorfactors in controllingthe concentrationof
airborne particlesin rooms.A largerangeof filtersand classificationschemes
havebeendevelopedand manyof those of relevance to the high-care/risk
chilled foodindustry are described in a guidancedocument produced by the
Campden& ChorleywoodFood RA (1996). Generally, air-handlingsystems for
some high-careareas would be fitted withF9 filters, some high-careareasand
high-risk areaswithH11filters, whereas cleanrooms woulduse H13or even
higher levelsof filtration. F9 filtersremovealmostall particles of 1m diameter
and above,H11filtersremoveparticles of 0.5m particles and above,and H13
filters removealmostall particlesabove0.3m.
5.2 Factors affecting aerosolcontamination
The risk of foodcontaminationin high-care environments depends on many
factors including the rate of generation of airborne particles, particle sizesand
speeds, the numberof particlesthat includeorganisms,the directionof the air
flow in the roomand the exposure timeand surfaceareaof the food.These
factors are importantbecausetheycontrol the distancetravelled, flighttimeand
spatial distribution of concentrationof the organisms.Methodsare available to
measureeachof theseimportantfactors.In the remainder of this chapter, the
term`particle'will be usedto referto bothdropletsof liquidand solidparticles,
as oftenan aerosolmaycontain both.
5.2.1 Dropletgeneration,size and speed
Mostof the methodsof measuringdropletgeneration, size and speedare based
on lasertechnology.Phase-Doppleranalysershavebeenusedto measure the
94 Handbookof hygiene controlin the foodindustry