June 12, 2024
WWW.STOCK.ADOBE.COM
Technicians can achieve contamination control during aseptic operations by applying two methods: gowning workers to minimize microorganism “shedding” and surrounding products with localized protection to minimize human contact. Gowning includes both disposable and relaundered suits (both circular and noncircular cleanroom textile solutions). Many organizations use relaundered suits for operator comfort. But the control of relaundered garments is a difficult compliance challenge, especially in relation to the number of times they can be reprocessed through laundry and associated controls. Whyte and Bailey established deterioration over time as a factor of garment reprocessing (1). Addressing such deterioration is crucial to facility contamination-control strategies.
In the European Union (EU) good manufacturing practice (GMP) Annex 1, points 7.11 and 7.13 describe how cleanroom garment reuse should be subjected to formal studies for integrity and particulate control.
For sterilised garments and eye coverings, particular attention should be taken to ensure they have been subject to the sterilisation process, are within their specified hold time and that the packaging is visually inspected to ensure it is integral before use. Reusable garments (including eye coverings) should be replaced if damage is identified, or at a set frequency that is determined during qualification studies. The qualification of garments should consider any necessary garment testing requirements, including damage to garments that may not be identified by visual inspection alone.
The protective clothing should minimize shedding of fibres or particles and retain particles shed by the body. The particle shedding and the particle retention efficiencies of the garments should be assessed during the garment qualification. (2)
How often gowns can be relaundered (which involves washing and sterilization) is a key question in contamination control. Material fibers weaken over time, reducing a gown’s bacteria-filtering efficiency. Facility managers and microbiologists must understand what testing is conducted on relaundered gowns and what the procedures are for rejecting gowns when integrity loss is detected. Here I present the main criteria to consider when establishing qualifications of cleanroom-garment relaundering.
People and Contamination Risks
Human operators are the main source of microorganisms and particulates in cleanrooms. Contamination occurs through the release and shedding of particles, such as those that carry microorganisms. The proportion and types of microorganisms released depends upon the region of the body they come from, as the analysis of the human microbiome has revealed (3). Whyte’s research indicates that about 10% of the human microbiome contains microorganisms (4).
Sources of particles include skin flakes and oil, cosmetics and perfumes, spittle, clothing debris (lint and fibers), and hair. Fast movements increase particle release quantitatively (Table 1). Operator movement inside a clean zone should be performed at a slow, controlled speed. Working too quickly inside a clean zone can create turbulence, which can increase rates of particle release (5). The relationship between particle release (and subsequent dispersal within a cleanroom) and movement has been established for several decades (6).
Table 1: Relative differences in human particle generation based on movement.
Actions such as coughing, talking, and sneezing also affect rates of particulate release (7). Despite our enhanced knowledge and application of controls, personnel-related contamination remains the most frequent type of biological contaminant (8). In addition, operators transfer contaminants when touching and moving objects. Thus, correct gowning procedures, materials, and training are essential to contamination control. Operators must consider both human behavior and gown quality when creating contamination-control strategies.
Gown Quality: The most important critical quality attribute (CQA) for cleanroom gowns is fabric filtration efficiency, which must conform to International Organization of Standardization (ISO) guidance 9073 (9) along with garment design specifications for controlling particle capture and dispersion (10). Filter efficiency (defined as the factor of the garment’s water vapor pressure across the fabric as 10-cm water beads) and user comfort have a trade-off relationship: the better the filtration efficiency, the poorer the comfort experienced by the user. Textile fabrics determine comfort. Tighter weaves have reduced breathing capacity, making a garment less comfortable to wear. Particles can penetrate gowns through contact pressure and abrasion as workers move against solid objects. Cleanroom gowns should capture >90% of particles ≥0.3 µm in diameter. Therefore, a balance should be struck between operator comfort and filtering efficiency.
In addition, gowns must be sterile, prevent shedding, and cover skin and hair (e.g., through face masks, hoods, facial hair covers, protective goggles, and elastic gloves). Wearing gowns of the correct size is important. Those worn too close to the skin increase moisture levels on textiles, which can decrease filtration efficiency. If gowns are too large, then excess air will escape, leading to particulate increases.
Gown Relaundering Time: All cleanroom garments must undergo qualification studies to assess particle shedding and retention efficiencies over their life cycles. Qualification studies have definitive limits that vary among facilities (11). Such studies depend on several factors such as gown material, number of relaundering cycles permitted, sterilization processes, and degree of potential damage or soiling on gowns. Gown suppliers can provide generic data sets for cleanroom operators to use in qualification studies; however, facility-specific studies may be required to qualify cleanroom garments.
To guide assessment processes, the Institute of Environmental Sciences and Technology (IEST) and ASTM International provide two test methods for cleanroom garment assessments:
• IEST-RP-CC003.4 — “Garment Systems Considerations for Cleanrooms and Other Controlled Environments” (Helmke drum test method)
• ASTMF51/52M — “Standard Test Method for Sizing and Counting Particulate Contaminant in and on Clean Room Garments.”
Of those two approaches, the Helmke drum method can detect and track problems with laundered fabric and wear cycles.
Case Study
To understand how operators can establish maximum gown relaundering cycles, consider a case study from an aseptic manufacturer in the United Kingdom. The assessed cleanroom garments were made of a tightly woven 98% polyester/2% carbon fabric with a density of 114 g/m2. The garment provider performed qualification studies for particle counts, relative pore size, and air permeability. An assessment was required to determine how often a gown could be “recycled” — the maximum number of laundering and irradiation cycles before material deterioration or other impacts on measured efficiencies.
To assess particle shedding and retention, the aseptic facility requested that the garment provider perform validation studies of the supplied cleanroom garments. All fabric testing was performed over time after exposure to 25 kGy of gamma radiation. The garment provider conducted validation studies on three garment types of different age ranges and tested particle counts over time, air permeability, and relative pore size.
Air permeability is the rate of air flow passing perpendicularly through a known area under a prescribed pressure differential between two surfaces of a material. Permeability allows air to pass through a garment and is quantified by a volume/time ratio per area. Lower air permeability rates within a garment result in lower contamination levels to products. Influences on air permeability include material density, fabric weave, yarn raw material, and yarn sets.
Relative pore size is the shape and value of fabric pore sizes to determine barrier efficiency. Smaller pore sizes can trap greater numbers of particles. Therefore, pore size evaluation is crucial to determine which fabrics should be used in cleanroom garments.
Three types of sample garments were evaluated on 10 occasions in the case study:
• Sample 1 — unworn, unprocessed, and nonirradiated
• Sample 2 — laundered through ISO 14644-5 cleanroom and irradiated for 40 processes
• Sample 3 — laundered through ISO 14644-5 cleanroom and irradiated for 70 processes.
Particle Count Studies: Particle count studies were performed according to the IEST-RP-CC003.4 Helmke drum test method, which is a widely accepted method used by cleanroom laundries to determine the efficiency of cleaning processes. It measures microcontamination levels to certify cleanroom garments for use in controlled environments (12).
Typical coverall garments entered a trial period of 70 laundry processes, which represented a worst-case duration exceeding the established 50-process limit (11). Garment deterioration was measured by particulate shedding over time, and a visual inspection was conducted at each laundry process to look for visible effects on the fabric and proper functioning of the zips and fasteners.
Size distributions from Helmke drum tests correlate to a power law equation, which is expressed as
N(d) = Ad(–B)
where N(d) is the cumulative concentration greater than or equal to d, d is particle diameter, and A and B are statistically determined coefficients (13).
In that study, garments were tumbled in a drum for a set duration. Air was extracted from the drum interior and passed across a counter that measured particles of ≥0.5 µm. The allocated specification was <1,200 particles of ≥0.5 µm per IEST recommendations. Air permeability studies were conducted in line with ISO 9237:1995 (14). In those studies, particle penetration increased with higher velocity and particle sizes of <1 μm. The relative pore-size test was conducted in line with British Standard (BS) 3321:1986 (15).
Results and Discussion
Tables 2 and 3 outline data for pore size alteration and air permeability tests. Pore size slightly increased after 70 gown recycles. Air permeability was adjusted but did not cause excessive particulate release.
Table 2: Pore size results.
Table 3: Air permeability results; CV = coefficient of variation.
Figure 1 shows results for the Helmke drum tests across 70 cycles. The rate of particle release increased proportionally with the number of washes but stayed within the maximal permitted value of 1200 particles.
Figure 1: Particle counts recorded by the Helmke drum test over time, where S is a
standard deviation, R2 is the coefficient of determination, and R2 (adj) is an adjusted
coefficient of determination.
Auditing Gown Suppliers: An approval process for a garment supplier should feature the elements examined above. When auditing a gown supplier to create a technical agreement, clients must ask important questions from a contamination-control perspective. Questions should include the following:
• How are suits cleaned and laundered?
• How long can suits be laundered for?
• How is suit laundering tracked?
• How is suit cleanliness assessed?
• What sterilization method is used, and what are the dose and time parameters for that method?
• What is the maximum number of times that a suit can receive sterilization doses?
Garment suppliers may provide data from generic studies. However, facilities must ensure that those data describe gowns that have been subjected to the same types of processing. Facilities also must establish controlled garment use to ensure traceability, such as assigning barcodes to each gown.
Conclusion
The observed particle counts from the air permeability tests show that garment shedding increases over time. The trial involved full processing of garments, including an irradiation procedure at each wash session. Irradiation is known to affect garment material and is the most destructive event during laundry preparation. However, the observed particle counts remained within normal loading while showing a steady range through 70 wash processes. The counts slightly increased between 30 and
40 wash processes. However, that did not constitute a shift from the acceptance criteria. Garments tend to fade in color around that point.
The case study primarily used the Helmke drum test method. It quantifies dislodged particles by applying mechanical energy under dry conditions to simulate shedding from the surface of garments during use. They tumble in a rotating drum to release particles from their fabric while a discrete-particle counter samples air within the drum.
Relative pore size remained stable up to 70 wash processes. That factor verified the air-permeability results and confirmed the choice of material used in gowning. Air permeability increased with the number of laundry processes conducted. However, measurements were recorded as mean values over
10 sampling events and therefore gave slightly irregular results (increasing at 40 washes and decreasing again at
70 washes). From those results, garment deterioration with respect to pore size integrity remained constant, even at the excessive processing frequency of
70 washes.
The aseptic-manufacturing company selected the methods described here because of their easy use. However, other technologies could yield more precise results. One such method is a dispersal chamber or “body box,” which captures the actual particles shed from a human during gown wear (16). Electron microscopy also can be used to study textiles in greater detail to find variations in wear and tear.
Although the identified measures were acceptable for the case study, many other aspects of relaundered gown management require detailing within a facility contamination-control strategy. Examples include whether repairs are permitted and, if so, to what extent. Another factor is the duration that gowns can be worn and how that length of time is assessed (such as capturing maximum operator occupancy time in simulation studies). Furthermore, how gowns are folded and packaged also influences the process of donning the garments, especially when users must prevent gowns from touching changing-room floors. And developments in textiles technology, such as microfibers, might bring improvements in maximum wash and sterilization times without limiting operator comfort.
Gown-quality assessment plays an important part in contamination control, not least because of risks for microbial release into cleanrooms by personnel. The gown is the first line of defense in aseptic processing — therefore, technicians need a robust method to verify the suitability of cleanroom garments.
References
1 Whyte W, Bailey PV. Reduction of Microbial Dispersion by Clothing. J. Parenter. Sci. Technol. 39(1) 1985: 51–60; 3973804.
2 Annex 1: Manufacture of Sterile Medicinal Products. European Commission: Brussels, Belgium, 2022.
3 Grice EA, et al. Topographical and Temporal Diversity of the Human Skin Microbiome. Science 324(5931) 2009: 1190–1192; https://www.doi.org/10.1126/science.1171700.
4 Whyte, W. Settling and Impaction of Particles into Containers in Manufacturing Pharmacies. J. Parenter. Sci. Technol. 35(5) 1981: 255–261; 7299604.
5 Whyte W, Hejab M. Particle and Microbial Airborne Dispersion from People. Euro. J. Parenter. Pharma. Sci. 12(2) 2007: 39–46; https://eprints.gla.ac.uk/84357/1/84357.pdf.
6 Austin PR, Timmerman SW. Design and Operation of Cleanrooms. Business News Publishing Company: Birmingham, MI, 1965.
7 Ramstorp M, Gustavsson M, Gudmundsson A. Particle Generation from Humans — A Method for Experimental Studies in Cleanroom Technology. Indoor Air 2005: 1572–1576; https://lup.lub.lu.se/search/publication/8ddb6980-1de2-48e8-b7c7-298c4934ce37.
8 Sandle T. A Review of Cleanroom Microflora: Types, Trends, and Patterns. PDA J. Pharm. Sci. Technol. 65(4) 2011: 392–403; https://www.doi.org/10.5731/pdajpst.2011.00765.
9 ISO 9073 Textiles Test Methods for Nonwovens, Part 10: Lint and Other Particles Generation in the Dry State. International Organization for Standardization: Geneva, Switzerland, 2003.
10 Whyte W, Bailey P. Particle Dispersion in Relation to Clothing. J. Environ. Sci. 32(2) 1989: 43–49; https://doi.org/10.17764/jiet.1.32.2.n36876j86475626k.
11 Ljungqvist B, Reinmüller B. People as a Contamination Source: Cleanroom Clothing After 1, 25, and 50 Washing/Sterilizing Cycles. Euro. J. Parenter. Pharm. Sci. 8(3) 2003: 75–80.
12 Elion J, et al. Improving the Repeatability and Reproducibility of the Helmke Drum Test Method. J. IEST 44(4) 2001: 28–31; https://doi.org/10.17764/jiet.44.4.y295378177h76761.
13 Ensor D, Elion J, Eudy J. The Size Distribution of Particles Released by Garments During Helmke Drum Tests. J. IEST 44(4) 2001: 24–27; https://doi.org/10.17764/jiet.44.4.33j2557006581633.
14 ISO 9237:1995 Textiles: Determination of the Permeability of Fabrics to Air. International Organization for Standardization: Geneva, Switzerland, 2023.
15 BS 3321:1986: Method for Measurement of the Equivalent Pore Size of Fabrics (Bubble Pressure Test). British Standards Institute: London, UK, 1986.
16 Ljungqvist B, Reinmüller B. People as a Contamination Source: Dispersal Chamber Evaluation of Clothing Systems for Cleanroom and Ultra Clean Operation Rooms. Chalmers University of Technology: Göteborg, Sweden, 2014.
BPI editorial advisor Tim Sandle is head of GxP compliance and quality risk management at Bio Products Laboratory (part of Kedrion) in Elstree, UK, and a visiting tutor at University College London and the University of Manchester;
You May Also Like
