Sterile and Nonsterile Cleanroom Garments, Particle Emission Testing, Sterile and Nonsterile Gowning: Part 3 – Aseptic Facility Requirements

This series of articles is intended to provide an overview of cleanroom gowning divided into four parts:

• Part 1: Materials and Components
• Part 2: Operational Aspects
• Part 3: Aseptic Facility Requirements
• Part 4: Aseptic Operational Aspects

Sterile Cleanroom Garments

Sterile cleanroom garment systems consist of a coverall, hood and boots. Gamma radiation sterilization is the most common method of sterilization of cleanroom apparel. Gamma radiation sterilizes the garments using Cobalt 60 ionizing energy. This method has a high penetration of material and lethal effects on microbial populations at very low levels of radiation. Gamma radiation sterilization is a reproducible and reliable process that is based on the exposure time of the product to the gamma source. All reusable, woven and disposable, single use nonwoven cleanroom garments used in sterile cleanroom manufacturing are validated to a sterility assurance level of 10^-6 SAL (sterility assurance level).

Gamma Sterilization Validation

Gamma sterilization validation consists of determining the average device bioburden, bacteriostasis/fungistasis testing and establishing the dose. ANSI/AAMI/ISO 11137-1 (Sterilization of Heath Care Products – Requirements for Development, Validation and Routine Control of a Sterilization Process for Medical Devices) provides the guidance for gamma sterilization validation.

Determination of Average Device Bioburden

ANSI/AAMI/ISO 11737-11 (Sterilization of health care products – Microbiological methods – Part 1: Determination of the population of microorganisms on product) provides guidance on determination of the average device bioburden. Three lots of 10 reusable, laundered or disposable, single use cleanroom garment devices are sent to a contract laboratory to undergo an exhaustive extraction for bioburden. It is recommended that the contract laboratory achieves and maintains ISO 17025 (Testing and Calibration Laboratories) certification as well as having been qualified as a supplier by the company.

The bioburden testing consists of testing for aerobic bacteria, molds and yeasts. The total number of colony forming units (CFUs) are counted for the bacteria, molds and yeasts after incubation and multiplied by the recovery factor determined in the detailed bioburden analysis. In addition to the bioburden analysis, an initial bacteriostasis/fungistasis analysis is performed to provide documented evidence that there isn’t a microbial inhibiting agent in the sample.

Establishing the Sterilization Dose

ANSI/AAMI/ISO 11137-2 (Sterilization of health care products – Radiation – Part 2: Establishing the sterilization dose) and ANSI/AAMI/ISO TIR 13004 (Sterilization of health care products – Radiation – Substantiation of a selected sterilization dose: Method VDmaxSD) provides guidance on establishing the sterilization dose based on the average device bioburden. The contract laboratory submits the required number of devices to the gamma sterilizer with instructions to irradiate the samples at the calculated verification dose.

Sterility Testing

ANSI/AAMI/ISO 11737-2 (Sterilization of medical devices – microbiological methods – Part 2: Tests of sterility performed in the definition, validation and maintenance of a sterilization process) provides guidance for the sterility tests that verify and validate the established dose will achieve a 10^-6 SAL. The samples are subjected to a test of sterility.

The validated sterilization dose continues to be used as long as the quarterly dose audits continue to pass for reusable cleanroom garments, the process stays in control and no specifics of the process or product changes. Any change in the process or product whether reusable or disposable, single use cleanroom garments require an evaluation of the potential impact that the change may have on the product bioburden and may require a complete re-validation.

Dose Mapping

Once the established dose has been verified, the gamma subcontractor will perform a dose mapping of the product to determine sites of minimum and maximum dose ranges. The dose is variable with respect to the density of the packaged product and the dimensions and weight of the transport container. Therefore, the density of the packaged product and the weight and dimensions of the transport container should remain uniform in the mapped product each time the product is gamma radiated. The contract sterilizer performs an initial dose mapping of each product (reusable cleanroom garments or disposable, single use cleanroom garments) and also at each source loading. This ensures that the correct radiation dose is delivered to the product every time.

Routine Monitoring of Gamma Radiation

Colorimetric indicators may be used as a visual aid to show that the garments have been exposed to gamma radiation. Indicators for gamma radiation change from yellow to red and are typically placed on inner and outer packaging.

Note that if an indicator is exposed to isopropyl alcohol (IPA) such as during decontamination of the external surface of the packaging (wiping) prior to placing the garment item in the sterile gowning area, the IPA can cause the red indicator (one that has been exposed to gamma radiation) to turn back to yellow. Therefore, care must be taken with IPA exposure.

Certificate of Sterility

Each lot of cleanroom garments that are gamma processed is accompanied by a certificate of sterility based on the evaluation of the dosimetry data results from the gamma subcontractor. A certificate of sterility should contain the following information:

• Product description or catalog number
• Lot number
• Gamma radiation run number
• Date of irradiation
• Statement of how the product was sterilized and how the process was validated
• Minimum and maximum specified dose
• Minimum and maximum delivered dose
• Signature, date and title of the individual performing the dosimetry testing
• Signature, date and title of the individual performing the review of the test data

It is in the best interest of the cleanroom garment laundry and the manufacturer of disposable, single-use nonwoven cleanroom garments to reduce the average bioburden levels during the laundering and manufacturing process to in turn reduce the level of gamma radiation required to terminally sterilize the product.

Documentation and Records Retention

1. Gamma sterilization validation of both reusable and disposable, single use cleanroom garments consist of a design qualification (DQ), installation/operation qualification (IOQ), performance qualification (PQ) and change control (CC). All validation documentation, including dose audit results, should be reviewed and trended. Periodic reviews of all documentation and trends should evaluate the gamma sterilization program to determine if re-validation is required or the established validation is representative. Revalidation of the sterile reusable and disposable, single use cleanroom garment validation is performed if there is a change in the process or the product. All validation documentation including the dose audit results should be retained for the longest period required by the regulations in the market being served—at least five years per US Title 21 Chapter I Subchapter C Part 211 Subpart J.

Particle Emission Testing

The cleanliness of cleanroom garments is a function of their shedding particles, fibers and extraneous unwanted contaminants in the cleanroom. All garment testing is performed by trained and experienced personnel wearing cleanroom garments and conducted in a cleanroom environment, the cleanliness level of which the is equal to or higher than that which the garments are processed in. Particle emission testing is performed based on user’s requirements. Factors to be considered are:

• Particle size – ASTM F51(Alternative In-Plant Method for Particulate Sampling of Clean Room Garments) measures particles at 5.0µm and larger, plus fibers. The Helmke drum test measures submicron particles equal to and larger than 0.3µm and 0.5µm.
• Frequency of testing and sampling plan
• Type of data required for qualification, comparison, repeatability, consistency or trend analysis
• Quality control requirements or specifications
• Cost

Releasable large particle test

The ASTM F51 (Alternative In-Plant Method for Particulate Sampling of Clean Room Garments) is used to determine the shedding of particle 5.0µm and larger and fibers. This test is limited to reusable cleanroom fabrics designed with some porosity. This test is less reproducible due to technician variability over various laboratory settings.

Figure 1 Releasable Particle Garment Cleanliness (from IEST-RP-CC003 Garment System Considerations for Cleanrooms and Other Controlled Environments) – IEST-RP-CC003 (Courtesy of IEST)

Particle dispersion test (body box test)

The cleanroom garment system to be tested is donned by a volunteer in a controlled change area. The volunteer then enters a dispersion test chamber (body box), where specific exercises are performed while the chamber air is sampled to determine the particle dispersion rate for viable and non-viable particles released from the garments under test. This test is useful in determining different cleanroom garment systems but is limited by the efficiency of containment of the particle burden generated by the wearer and the reproducibility of their movements.

Helmke drum test (woven, nonwoven, and coated fabrics)

The Helmke drum test method is used to quantify particles released from cleanroom garments while tumbling in a calibrated rotating drum over 10 minutes. The drum is attached to an automatic, discrete-particle counter which is used to sample the air within the drum to determine the average particle concentration of the air during the test. This particle concentration is used to compute a particle emission rate, which is used to determine a garment cleanliness classification for the particular type of garment.

The Helmke drum test is specially designed to test the particle shedding of a garment over time. This test evaluates the integrity of the garment as well as the overall ability of the cleanroom garment laundry to render the garment item “particulately clean.”1^, 2^, 3^, 4^, 5^, 6^, 7^, 8

Figure 2 Helmke Garment Cleanliness Classification (Courtesy of IEST)