Peer Review Article

Effective Re-usable Cleanroom Garments and Evaluation of Garment Life

Authors: T Eaton AstraZeneca, Macclesfield, & W Whyte James Watt Building South, University of Glasgow, UK

Summary

Cleanroom garments are used to control the airborne dispersion of contamination from people into the cleanroom. The effectiveness of the garment in controlling the dispersion of contamination is a function of the fabric and design of garments, and test methods used to ascertain the effectiveness of garments are discussed in this article. These test methods can be used when choosing garments for use in a cleanroom but were used in this article to determine the deterioration of garments through use. Cleanroom garments were subjected to increasing numbers of decontamination cycles, which included sterilisation by gamma radiation, up to a maximum of 70. At defined number of decontamination cycles, the garment’s fabric was compared to a new fabric by visual examination, by a scanning electron microscope, and by physical tests of key performance parameters. It was concluded that the performance of the fabric remained acceptable up to 50 decontamination cycles. This conclusion was supported by the low dispersion rate of particles and microbe-carrying particles in a dispersal chamber from personnel wearing the garments. After 50 decontamination cycles, a low dispersion rate of 0.2/s of microbe-carrying particles from personnel wearing the garments was obtained and a 194-fold reduction in the microbial dispersion rate compared to cleanroom undergarments.

Key words: cleanroom garments, garment life, contamination control

Introduction

Cleanroom garments are a key contamination control method used to limit the transfer of particles from personnel into the surrounding environment. A proportion of these particles are microbe carrying particles (MCPs), and for pharmaceutical and healthcare cleanrooms, they present a risk that must be managed. Garments may be single use or reusable and both have the same contamination control requirements. Single use garments are typically used in situations where contamination can occur from harmful biological, chemical, or radioactive substances, or where low numbers of cleanroom garments are required. Following a single use, they are simply disposed. Re-usable garments are used many times, and between uses are subjected to decontamination cycles, which normally consist of controlled washing, drying, packaging and where appropriate, sterilisation. These decontamination cycles should not significantly reduce the contamination control properties of the garment through its life. Whyte and Bailey ¹ ² developed tests for assessing the contamination control properties of cleanroom garments and drew attention to the deterioration of garments during use. They also noted that heavily calandered garments lose their effectiveness much more quickly than lightly calandered garments. Ljungqvist and Reinmuller ³, and Romano et al ⁴, used a dispersal chamber to measure the dispersion rate of airborne contamination from personnel wearing clothing that had been subjected to different numbers of decontamination cycles. They found that the effectiveness of garments reduced during use but was acceptable up to about 50 decontamination cycles. Ljungqvist and Reinmuller ⁵ further investigated garments using a combination of fabric test methods and dispersal chamber results and confirmed their previous conclusions. Different fabrics used to manufacture cleanroom garments deteriorate at different rates and we were interested in studying a fabric that had not been previously investigated but appeared to be very effective in reducing the dispersion of airborne contamination. We also wished to study the deterioration of a fabric with tests that included appearance to the eye and use of an electron microscope, as well as studying the deterioration of fabrics over time in more detail.

2. Requirements for cleanroom garments

Information relating to selection, specification, maintenance, and testing of garments for use in various types of cleanrooms is readily available ⁶ ⁷. For pharmaceutical and healthcare cleanroom applications, there are a number of essential and desirable requirements that need to be considered, and these are summarised in Table 1. Other parameters, such as flame retardancy, chemical resistance, waterproofness, water repellency, and anti-microbial surface properties, may be required for certain applications. The requirements that the authors consider to be the most important are included in Table 1. Table 1 Requirements for effective cleanroom garments   

3. Considerations of choice of fabric for re-usable garments

For re-usable garments, the requirements for garment fabrics that are summarised in Table 1 are discussed in this section. The design and effectiveness of garments are discussed in Section 4.

3.1 Garment fabric A key consideration for effective contamination control is the garment fabric. Popular everyday fabrics are made from either cotton or a mixture of polyester and cotton (polycotton). Polycotton fabrics are woven from yarns made by twisting together the short staple fibres of cotton with the continuous fibres of polyester to form a cohesive yarn. Shown in Figure 1 is the magnified (x 50) image of a polycotton fabric. It can be seen why this fabric, as well as cotton fabrics are not suitable for cleanroom applications as the fibre ends protrude from these yarns and are constantly broken off during normal wear and both fibres and small particles are continually shed into the cleanroom.

Figure 1 Polycotton fabric showing protruding fibre ends (x 50 magnification).

The solution to the problem of the particle and fibre shedding by cotton and polycotton fabrics is to use monofilament plastic thread to produce the yarn. The continuous nature of this yarn ensures that fibre and particle shedding is greatly reduced. The most commonly re-usable woven fabrics used in cleanrooms are currently made from 100% monofilament polyester. Shown in Figure 2 is the integral and continuous nature of this type of fabric.

Figure 2 100% monofilament polyester fabric (x 50 magnification).  

Pores occur in fabrics where the yarns cross and these pores determine the rate at which particles, air, and water vapour, pass through. To minimise the transfer of airborne contaminants from wearer to cleanroom, the fabric must be tightly and reliably woven to produce a small pore size of a consistent size. The tightness of the weave of cotton or polycotton fabric is normally inadequate to control the dispersion of skin and clothing particles from the wearer, including those that carry microbes, as they will easily pass through the space where the yarns cross. However, it is not only cotton and polycotton fabrics that suffer from this problem as fabrics made from monofilament fibres can also be ineffective. Shown in Figure 3 is a fabric woven from monofilament thread which has large pores with an equivalent pore diameter of about 100 µm. This fabric is ineffective in reducing the dispersion of particles and MCPs from personnel as they can easily pass through it. Garments used in cleanrooms should, therefore, be manufactured from a fabric that is tightly woven from monofilament thread.

Figure 3 100% monofilament polyester fabric (x 50 magnification).  Figure 3 Monofilament fabric showing large pores with an equivalent particle diameter of approximately 100 µm.

3.2 Fabric test methods To assess the likely performance of a reusable fabric in a cleanroom, it is necessary to test a range of its properties. It is common to find that the fabric’s properties are provided by the manufacturer but several of these properties may not be directly relevant to the contamination control needs of a pharmaceutical or healthcare cleanrooms. No ISO standard exists that details the relevant properties required for a cleanroom fabric but IEST–RP-003.4 ⁶ includes contamination control property tests developed by Whyte and Bailey ¹,² for use in cleanrooms. Test methods also exist as national standards that cover individual properties of fabrics and these are often combined, although different fabric manufacturers use different tests to describe their fabrics. It is, therefore, important to ensure the fabrics have been subject to relevant test methods, and the tests that the authors consider the most important are given in Table 2.

Table 2 Fabric test methods

4. Fabric investigated

The manufacturer’s specification of the monofilament polyester fabric that was investigated is shown in Table 3 and, where applicable, the test method is included in parenthesis. The fabric investigated was a JG type (WF5505-JG) supplied by Asiatic Fiber Corporation and is widely utilised for garments in the pharmaceutical industry. However, without a detailed knowledge of fabrics and the test methods used, it is difficult to understand from the information given in Table 3 how well the fabric would perform in a pharmaceutical or healthcare cleanroom to the required parameters shown previously in Table 2.

Table 3 Specification for mono filament polyester fabric JG (WF5505-JG)

5. Assessment of fabric performance

The fabric specification shown in Table 3 relates to new garments that have not been subjected to any decontamination cycles. For re-usable garments, it is important to determine the condition of the fabric after a number of decontamination cycles, in order to define an appropriate garment lifetime. To assess the condition of the fabric following decontamination, garments fabricated from JG (WF5505-JG) material were subjected to a number of accelerated standard decontamination cycles (wash, dry, primary pack and gamma radiation sterilisation at 25 kGy) completed by a specialised cleanroom garment laundry company. Fabric from garments that had completed 10, 25, 50 and 70 cycles were tested and compared with new (no decontamination cycles) garment fabric by an independent specialist testing company, using the following test methods, to evaluate key contamination control parameters.

  1. Visual appearance
  2. Equivalent pore diameter (IEST-RP-CC003.4. 2011 ⁶)
  3. Particle removal efficiency (In-house test based on IEST-RP-CC003.4. 2011 method ⁶)
  4. Dry linting propensity (ISO 9073-10 ⁸)
  5. Scanning electron microscopy (SEM) imaging to determine any change to the fabric structure.

6. Results

The results of the testing are shown in Figure 4 to Figure 8 for visual appearance, equivalent pore diameter, particle removal efficiency, dry linting propensity, and SEM imaging parameters, respectively.

Figure 4 Visual appearance of garment fabric after defined number of decontamination cycles

Figure 5 Fabric equivalent pore diameter after defined number of cycles

Figure 6 Average particle removal efficiency of particles ≥0.3µm, ≥0.4 µm, ≥0.5 µm, ≥1 µm after defined number of decontamination cycles.

Figure 4 Visual appearance of garment fabric after defined number of decontamination cycles

With single contact plates the recovery of viable microorganism was poor, and there were differences with the two surfaces examined. Notably, recoveries were higher for vinyl compared with stainless steel, this was wider at the ten second sampling time although this narrowed as the sampling time was extended. In terms of the limitation of the method, the percentage of recovery from the contact plates was relatively low based on the first plate applied to a surface, which matches the way a sample would be taken within the cleanroom environment. For a ten second sampling time the recovery was 13% (stainless steel) and 28% vinyl (mean 20%); for a 20 second sampling time the recoveries were 19% (stainless steel) and 31% vinyl (mean 25%). With the 30 second contact time, recoveries were 17% (stainless steel) and 30% vinyl (mean 24%). The data shows recoveries improved between 10 and 20 seconds, albeit by a small amount from one plate, and to a greater extent when replicate counting was taken into consideration (refer to figures 4 and 5).

Discussions

Extending the sample time to 30 seconds did not make a large difference and it can be argued that extending the time from 20 to 30 seconds does not add value, however, increasing the contact time from 10 to 20 seconds appears to add some value in terms of improving the surface count estimate. This is shown by comparing figure 5 to figure 6.

With the test control, the results showed that the microbial population on the test surface is viable after a drying period of 42 minutes in a unidirectional flow safety cabinet, and that desiccation has no effect on micro-organisms during this test procedure. Based on these results, improvements can be made with sampling time, although microbiologists will still need to be aware that recoveries remain underestimations even with those organisms that can theoretically be recovered using the culture medium, time and temperature combinations used in this study. The findings in this study match some of the concerns about method limitations from literature. A study by Pinto and colleagues, which compared three different brands of contact plates using a similar applicator to the one used in this study (although only for ten seconds and against a stainless-steel surface), showed recoveries for two species of Staphylococcus ranging from 23 to 56% (mean – 38%). There were variations with the recovery of the two species of Staphylococci (S. aureus gave a better recovery than S. epidermidis); this was consistent with the findings of other surface recovery research conducted by Scott and associates ³⁵, and it is of interest given that both species of Staphylococci will be found in cleanrooms (albeit with S. epidermidis more likely to be recovered in higher numbers given this organism’s greater ubiquity on the outer layers of the skin and only a minority of the population being carriers of S. aureus) ³⁶. In assessing the data, the low recovery may be due to the inability of the dried microorganism to transfer to the plate, rather than the inability of the plate to grow the microorganism. While this is interesting, organisms in a drier state will be more representative of what is likely to be found within a cleanroom. Wetness might help in improving recovery. Furthermore, although a common cleanroom bacterium was used this organism may or may not be representative of other typical cleanroom-associated organisms. A more extensive assessment involving other organisms would be required to draw a wider inference. The author has undertaken an assessment of organism recovery from the two surfaces, but not as yet as a time-based study ³⁷. With the differences between surface types, the low total percentage of the microbial population recovered by the stainless-steel samples tested with a 10 second contact time may relate to the rougher surface of the stainless steel when compared with the vinyl surface, which causes difficulty in sampling microorganisms from the surface due to adhesion to microscopic pits in the steel. One observation made during the test procedure was the increase in moisture of the sampling surface when a 20 second contact time was used, which was assessed by visual examination. The level of moisture did not vary between the 20 second and 30 second sampling times. The poor recovery on the previous 10 second recovery test recovery was could be due to the inability of the dried microorganism to transfer to the plate, the moisture on the stainless-steel surface during the 20 second recovery test may have improved recovery Underestimating the microbial contamination of surfaces might have serious consequences on the quality assurance of aseptically prepared pharmaceutical products. Another part of the study looked at recoveries when consecutive samples were taken. Based on the increase to the microbial count as more samples were taken it might be that under specific circumstances consecutive replicate contact plate sampling may represent a more appropriate means of evaluating surface-borne bioburden, perhaps under conditions where high bioburden is likely to be present. However, once the method has been standardized in terms of controlling weight and time has been optimized (balancing what is practical against what provides a greater recovery), microbiologists must remain cognizant that the levels of organisms recovered from a cleanroom surface are likely to be an underestimation of the organisms attached to the surface.

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