Proper and even air balance is more critical to a tunnel sterile process than a
batch oven process. Since the items being sterilized are moving, they are exposed
to different air systems (e.g., heating zone and cooling zone). Air flow
must be balanced in order to provide a gradual decrease in air temperature as
items move along the conveyor. In the absence of a critical balance of air dynamics,
either the items will not be cooled sufficiently once they exit the tunnel
or they will be cooled too quickly, causing the glass to shatter and contaminate
the entire tunnel area with particles. In fact, the major problem in validating tunnel sterilizers is the control of particles. Not only are the items exposed to
great extremes in temperature, but also the conveyor belt is a natural source of
particulates because metal is moving against metal.
Adjustments in the air source should be made to obtain a controlled flow
of air within the tunnel and across the entrance and exit openings. Air must be
particulate-free as it enters the tunnel area; therefore, all high efficiency particulate
air (HEPA) filters in the tunnel must be integrity tested and certified prior
to validation studies.