A detail often overlooked: goggles in aseptic production

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.

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.

Table 1 Characteristics of the goggles used.

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.

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.

Table 2 Goggles subjected to steam sterilization cycles.

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.

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.

Figure 1

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.

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).

Figure 2

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 progression.

The goggles' 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 goggles could favour the inclusion of the 0.2-μm particles that are in the water used for autoclave feeding and used as washing water prior to analysis. The high temperatures the goggles were subjected to favour 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, as they would not be able to imbed themselves during the autoclave cycles, and were washed away from the goggles' surface.

With the exception of what happens to the particles included in the 0.2–1.0-μm range, with bigger particles, we did not observe a significant variation in their percentage ratio compared with the total calculation. This probably means that the physical degradation of the material in analysis, which leads to particle release, does not vary qualitatively during the autoclave cycles, although there is acceleration after the twentieth cycle.

We concluded that visors subjected to repeated autoclave cycles show an increase in particle release dependent on the number of cycles to which they are submitted. Particles of 0.2-and 0.4-μm diameters increase proportionally in greater measure; those particles that are present on the exterior surface of the sample and not incorporated in the polymer are washed away from the goggles' surface during autoclaving.

Check of the elastic strip particle release. The treatment of elastic strips in autoclave cycles shows a remarkable increase in particle release after five autoclave cycles. The particles then settled until the end of 30 cycles of treatment. The biggest increase is that of the particles of approximately 0.2-μm diameter.

Figure 3 shows the percentage variation of particles of various sizes. There is an interesting absence of variation of particle composition after 30 autoclave cycles. In the 2.0–1.0 μm range, the increase in the particles released for strips follows a linear course proportionate to the number of autoclave cycles. The most important percentage is constituted by 2.0 μm-dimension particles.

The increase in the particle release from the elastic strip in the considered range is related to the number of autoclave cycles to which the strips are subjected. Based on these data, we concluded that elastic strips subjected to repeated autoclave cycles show an increase in the particles released dependent on the number of cycles to which they are submitted. Specifically, the number of 2.0-μm particles increased more than the others. Later, the number of 0.2-μm particles released decreased and the number of larger particles decreased, probably because of the second phase of material degradation.

Conclusion

Based on the data, the goggles that are available have been further developed by the manufacturer, both in the frame colour and in the elastic strip material, to better satisfy pharmaceutical customer needs. These adjustments contribute to a reduction in the particles released, thus improving the goggles' performance and usefulness in controlled contamination areas.

Maurizio Battistini is the General Manager and Qualified Person of Abraxis BioScience Switzerland GmbH. www.abraxisbio.com