Particle Monitoring in Sterilizing Tunnels
aerosol particle counters are designed to sample ambient air at 1 cubic foot
per minute (1 cfm) and no greater than 35 oC. There are however applications
which are based on ambient temperatures much greater than this, such as
pharmaceutical sterilizing tunnels. Sterilizing tunnels are used to ensure
sterility off glassware (vials, syringes, bottles) prior to their entry onto an
aseptic filling line, where internal temperatures can reach up to 200єC.
question of monitoring particle levels within these class 100 (ISO Class 5)
areas, to prove that the area remains within specification raises two separate
issues: do we need to monitor in these areas? if so, how do we monitor in these
for Monitoring within Sterilizing Tunnels
tunnels are typically classified as the first part of the aseptic environment,
and therefore class A (ISO 5).
classified environment it therefore must be monitored on a regular basis to
prove that it meets the requirements. However one of the functions of a non-viable
particle monitoring system is to act as a barometer to the potential of viable
particles, and it is these which most of the legislation is designed to
control. As the environment is sterile, the high temperatures confirming this,
then this part of the particle counter function is negated.
critical part to monitor a sterilizer tunnel is therefore within the cooling
zone, where temperatures drop to that which may support viable organisms.
of a sterilizing tunnel should be based upon the cold classification of the
filters and their installed integrity. This classification should be performed
at regular intervals, during routine shutdowns and room classification
exercises. This data is then used to support the stability of the tunnels in
operation. The particle counter in the cold zone will identify if particles are
migrating into the tunnel from the cleanroom and the pressure differential used
to prove that particles did not ingress into the system from outside the
Must be Done If sampling must be performed then the sample must be cooled to a
temperature acceptable by the particle counter; this is typically less than
35єC. The only method of cooling the sample down is to use a cooling probe.
Various other methods exist but do not meet ideal criteria: Dilution: The
amplification of errors due to dilution dramatically affect the statistical
value of the data being reviewed. Either long sample intervals should be used
to ensure sufficient ‘real’ particles are being seen or very low dilution rates
which may cause particle counter temperatures to rise. Cooling loops: Cause
significant losses due to particle entrainment in the loop mechanism.