Hood, suit, faceplate, cover shoes, gloves: these are the necessary items of clothing when operating in A-and B-grade areas.
The principal purpose of protective clothing is to minimize the risk of microbiological contamination caused by personnel.
But how can we ensure that protective garments themselves are not vehicles of contamination? And how can we ensure that cleaning
and sterilization processes are effective and do not alter the characteristics of the garments? We attempted to answer these
questions, concentrating our attention mainly on goggles.
As goggles are not disposable, stress conditions, such as repeated sterilizations, may compromise their use. They may lose
functionality and the components could become damaged, resulting in the release of contaminating material.
We prepared a study protocol to help verify:
- The goggles' ability to endure repeated sterilization processes without suffering alterations.
- The ability of the sterilization process to obtain a 12 log reduction of the starting microbiological charge.
Table 1 Characteristics of the goggles used.
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We chose to verify only the steam sterilization cycle because this is the process most commonly used in the pharmaceutical
industry, although goggles are also sterilized using other methods, such as g-rays and ethylene oxide.
For our tests, we used goggles with the characteristics outlined in Table 1. Tests were conducted to verify whether it was
possible to subject them to repeated sterilization cycles without causing any alterations that could compromise their usefulness.
Goggles in the trial were subjected to repeated steam sterilization cycles (temperature=121 ±1 °C, time=30 min) according
to the outline in Table 2. At the end of the cycles, the goggles were evaluated for adherence to facial conformation, lens
transmission and particle release.
Table 2 Goggles subjected to steam sterilization cycles.
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The effectiveness of the sterilization process is a probabilistic function that depends on the number of microorganisms present,
the thermic resistance of these microorganisms and the quantity of heat supplied. Therefore, determining the quantity of heat
necessary to obtain the 12 log reduction in the microorganism population to ensure sterility depends on the thermic resistance
of the present microorganisms. The thermic resistance of the microorganisms was evaluated by verifying the D value as the time necessary to reduce 90% of
the population of present microorganisms (1 log) in specific sterilization conditions. Even if the sterilization cycle recommended
by the producer is a typical overkill cycle, it is necessary to evaluate the D value of the microorganism in a trial because
this value strongly depends on the possible interactions between the microorganisms and the material on which they are found.
Figure 1
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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 (Figure 1), which allows the verification of the D value
to one sterilization cycle's specific temperature.
Results
Facial adherence and transmittance checks. The facial adherence did not change after 30 steam sterilization cycles and 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 approximately 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. However, we concluded that the transmittance
did not vary significantly after 30 sterilization cycles. For all tested samples, transmittance was more than 75%, which linked
with a check of the unchanging lenses' surface transparency and guaranteed that high visibility was maintained.
Particle-release check. The particle-release results for goggles subjected to repeated sterilization cycles were analysed separately for the visor
(lenses and support) and the elastic strip.
Figure 2
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Check of the visor particle release. The particles' cumulative calculation, in the 0.2–1.0 μm range, shows a proportional linear growth of the total particles
compared with the autoclave cycles that the goggles were submitted to (Figure 2).
