5.1 Introduction
Aerosols consist of particles dispersed in air. The particles may be liquid
droplets or solid particles or include both types of matter. The aerosols of most
concern in food premises are those that include microorganisms. Aerosols may
enter production areas through many routes including doorways, hatches, drains
and any other opening that connects low- and high-care areas (Burfootet al.,
2001). Aerosols can come from many sources, including raw materials, people,
packaging, and moving or rotating equipment. Holahet al.(1995) showed that
cleaning operations are major sources of aerosols that may include micro-
organisms. Cleaning operations such as boot washing, tray washing, equipment
cleaning and floor scrubbing are all potential sources of aerosol.
The best approach to reducing contamination via the airborne route is to
restrict the generation of aerosols. Once particles are airborne it is difficult to
control the movements of every particle because various mechanisms, such as
advection (air movement), turbulent dispersion, gravity and thermal convection
affect the particle motions. However, correct specification and implementation
of air-handling equipment can ensure that the majority of the airborne particles
do not contaminate exposed foods. Such systems rely on three approaches: (i)
using sufficient air exchange rates and filtration to remove the particles from the
air; (ii) providing sufficient air to maintain a positive pressure in the high-care
area and restrict the flow of air from low-care areas; and (iii) ensuring air flows
do not create lower-pressure regions near to doorways, hatches and other
openings that can lead to contamination entering from nearby low-care areas.
These approaches have been developed significantly in sectors that use clean
rooms, such as those for the manufacture of electronics and medical devices.
5 Aerosolsas a contaminationrisk
D. Burfoot, Silsoe Research Institute, UK