Verification of the EDA Concept Through an Assessment of Theoretical Failure Modes, Failure Mode Analysis, and Case Studies with Real Data - Good Cascade Impactor Practices, AIM and EDA for Orally Inhaled Products - page 251

Fig. 9.3 Situation 1 for
potential failure of EDA:
change of shape in LPF alone
but the same absolute LPM
before and afterwards ( From
[ 3 ] —used with permission )

broadening occurs, which by changing the values of both SPM and LPM affects
LPM / SPM , making the change detectable by EDA.
Particles that come into contact can agglomerate (Chap. 3 ). Typically, four
processes that will potentially bring aerosol particles together need to be considered
during the lifetime of an OIP aerosol:

1. The larger particles can sweep out smaller particles along their settling path,
because the former settle more rapidly under the infl uence of gravity which is the
dominant force affecting micron-sized particles if no other processes, in particu-
lar turbulence in the fl ow, are operating.
2. Brownian (molecular) motion can move particles across the streamlines of fl ow
so that they intersect other particles. This process only becomes important for
particles whose size approaches the mean-free path of the surrounding air
[0.068 m at ambient pressure (101.3 kPa)] and can therefore be largely ignored

with OIP aerosols.
3. Particles can experience diffusion in random directions as the result of localized
turbulence, resulting in collisions with neighboring particles.
4. Larger particles, unable to respond to acceleration of the gas phase around bends
and/or obstructions, will cross the streamlines of the fl ow and thereby intersect
other particles, resulting in inertial-induced agglomeration.

μ

Agglomeration, being a particle number—as well as a time-dependent stochastic
process, results in a smooth change to the whole APSD as particle growth occurs,
most evident at the fi ne end as there are many more fi ner than coarser particles on a
number-weighted basis in a typical APSD. Aerosol removal/depletion processes such
as gravitational sedimentation to nearby surfaces or inertial impaction to obstructions
will have most infl uence on the large sizes of the APSD, with a smooth steadily
decreasing effect throughout the remainder of the APSD. Similarly, de-agglomeration