An autoclave known as a BIER-vessel must be used to evaluate the D value. The most important characteristic of this autoclave is its ability to produce a sterilization graphic to wave quadrant
(see Figure 2), which allowed the verification of the D value to one sterilization cycle's specific temperature.
Figure 2: Sterilization graphic to wave quadrant that enables us to verify the D value to one sterilization´s specific temperature.
Facial adherence and transmittance checks. The facial adherence did not change after 30 steam sterilization cycles. The goggles maintained their adherence without any
shape modification caused by steam.
Even if the transmittance variations are minimal and can be attributed to measurement uncertainty, we verified that the transmission
increased slightly with the increase in the number of sterilization cycles. The 84.1% transmittance value of the lenses increased
to about 2 points after 20 cycles. After 30 cycles, transmittance decreased slightly under the starting value because of the
appearance of superficial sediment and slight blurring of the lenses' surface. In any case, we concluded that after 30 sterilization
cycles, the transmittance does not vary significantly. In fact, for all tested samples, transmittance was more than 75%, which
linked with a check of the unchanging lenses' surface transparency, guaranteed that high visibility was maintained.
Particle-release check. Particle-release results for glasses subjected to repeated sterilization cycles were analyzed separately for the visor (lenses
and support) and the elastic strip.
Check of the visor particle release. The particles' cumulative calculation, in the range between 0.2 and 1.0 μm, shows a proportional linear growth of the total
particles compared with the autoclave cycles to which the glasses were submitted (see Figure 3).
Figure 3: Percentage of particles in the 0.2–1.0 mm range released by the frames during the autoclave cycles.
The contribution is given by the particles with diameters smaller than 0.2 µm that reach values greater than 90% of the total
after 10 sterilization cycles, with exponential growth. The 0.4, 0.6, 0.8, and 1.0-μm diameter particles decrease with analogous
The glasses' particle release, in the considered dimensional range, may be attributed to pollution of the sample obtained
after repeated autoclave cycles. The polymer reticule of the glasses could favor the inclusion of the 0.2-μm dimension particles
that are in the water used for the autoclave feeding and used as washing water before the analysis. The high temperatures
to which the glasses were subjected favor plastic material expansion and the introduction of particles with smaller dimensions.
The 0.4–1.0-μm particles that quickly decrease to values lower than 10% of the total after 10 sterilization cycles were present
on the sample's surface and not inside the polymer, because they would not be able to imbed themselves during the autoclave
cycles and were washed away from the glasses' surface.