Validation of Aseptic Room Garments
- Purpose of garment validation tests
Introduction
Sterile pharmaceutical products are manufactured in cleanroom environments, which are designed to meet the high standard of freedom from contaminants – dust, pathogens etc. It is therefore crucial to prevent potential contamination of this aseptic environment by working personnel. Thus, aseptic room garments are specially manufactured and tested to meet high standards for properties such as bioburden, barrier strength, etc.
Contamination from personnel
Every activity in the clean room generates particles. The extent of which is shown in the following table
Activity / Number of Particles generated(0.5m and larger per min)
Sitting or standing still / 100000
Sitting, with small movements of arms or head / 500000
Sitting, moving arms, legs or head / 1000000
Standing up / 2500000
Walking slowly / 5000000
Walking normally / 7500000
Walking with speed (2.5m/s) / 10000000
Table 1: Relationship of activity to the number of particles shed from a human body1.
The types of particles generated include the following:
1) From the human body
- Skin flakes from all parts of the body, including hair
- Bacteria, parasites, viruses and pyrogens (from skin and breath)
- Chemical components from cosmetics and skin care products
2) From normal street wear
- Dust, bacteria, parasites, viruses and pyrogens that collected on clothing
- Fibres such as cotton
- Chemicals (e.g. dyes)
- Electrostatic charges which may cause particle contamination due to attraction of particles of opposite charges or repulsion of similar charges
What constitutes a garment?
The complete garment should be able to cover the whole body surface area. It comprises a combination of the following:
- coverall with elasticized arm and leg cuff closures
- cap or hood that can cover the whole head (including hair) with a transparent faceplate
- eye protection
- suitable gloves
- trousers, jacket or coat
- covered shoes, shoe covering, long legged boots
The garment should be elasticized in order to close any gaps as tightly as possible to minimize the leakage of particles.
Different classes of clean rooms require different types of garments, as illustrated by the following picture:
Figure 1: Examples of different types of aseptic room garment (a) Garments for lower classification clean rooms: shoe cover, trousers, apron, and complete hair protection. (b) Garments for use in higher classification clean rooms: coverall, gloves, hood, facial protection and long-legged boots. (c) Garments as in (b) but with the addition of a helmet which replaces the face mask1.
Validation tests overview
After being manufactured, aseptic garments are validated to ascertain their quality. This report focuses on validation tests for the fabric quality of aseptic garments (leaving out goggles, hood, cap, shoes).
Low bioburden / Bioburden test / Sterility of garment
Strength / Grab tensile and tear test / Durability
Fabric’s static dissipativeness / Electrostatic discharge test* / Static buildup on fabric may cause an electrical discharge and operative machinery failure
Barrier efficiency / Body Box Test*( Particle Containment method),
Barrier test*
Pore size test / Prevent contaminants from personnel from entering the aseptic environment
No moisture buildup / Moisture vapour transmission rate test / Moisture buildup causes personnel discomfort due to the increase in humidity between the fabric and the body
Air filtration efficiency / Particle penetration test / Airflow in heating and cooling processes, such as the cooling process of the body, contains contaminants that can be transferred to the product.
The lower the permeability, the lower the risk of contaminating the product.
Fabric cleanliness (Insignificant release of particles from garments) / Primary Test Procedure
(modified from ASTM F51 test)*
Helmke Drum test* / To test fabric material quality
Fabric splash resistance absorbance / Water repellency test / Ensure personnel is well protected from spillage
Do not absorb and transfer residues / Liquid extraction test*,
Particle transfer test / Can be washed and reused safely
Table 2: Overview of validation method 1, 2, 3, 4
*The highlighted tests are more commonly used, thus would be further explained in part B of this report.
- Details on commonly employed validation tests
- Body Box Test (Particle Containment Test) 4,5,6,7
Purpose of test
To qualify the relative cleanliness of cleanroom garment fabrics under controlled conditions that simulate the routine movements encountered during the actual usage of garments
Description
The test consists of a test subject performing a predetermined mobility protocol, such as the "March and Touch" and the "Deep Knee Bend" activities, in an enclosed Class 10 room about the size of a telephone booth. The activities include arm extensions for three minutes, walking for three minutes and doing five deep knee bends in one minute.
Air is blown downward on the subject and released particles are then counted by a laser particle counter. The data is reported as the average number of particles 0.5m and larger counted per minute during the ten-minute test period.
Interpretation of results
The total number of particles is a function of the cleanliness of the garment, the openness of the fabric weave and the garment design.
In general, the lower the number of particles, the better the performance of the fabric/garment combination.
Test limitations
Due to the high variation in particle generation between individuals, one can only compare the relative performance of garment systems if the test person and test parameters are identical. A performance classification does not exist.
This test can be improved by adding strategically located, multiple probes with aerosol concentrators and automated data acquisition to determine particle release at different locations. This would facilitate real-world assessment of operator/garment system aerosol releases and their location at actual point of entry into the cleanroom8
- Helmke Drum test
Purpose of test
To determine the number of easily releasable particles (≥0.3m and ≥0.5m) on the garment surface6
Description
The garment is folded and placed in a stainless steel rotating drum open at one end and rotated at 10rpm ± 1 rpm. An optical or laser automatic particle counter is used to sample the air within the drum to determine the average particle (≥0.3 µm) release rate in particles per minute.
The particle counts and size spectra are determined at ten-minute intervals. Alternatively, the air from the drum may be drawn through a filter cassette placed in line between the drum and vacuum pump, and analysed microscopically8.
Interpretation of results
The number of particles counted by the Helmke Drum can determine if the fabric has been properly laundered. It can also show if the fabric is degrading3. The lower the number of particles released, the better the quality of the garment and the more suitable they are for use in cleanrooms with more stringent requirements.
Test limitations
One limitation of this test is that it does not discriminate between particles and fibres, and the release of contaminants from the interior and exterior sides of the garment7.
Also, there has been extreme statistical variation in the data. This variation is probably due to a combination of factors including different drum designs, different brands of Particle Counters, the tendency of the garment to roll up during tumbling, sleeves or legs falling out of the drum during tumbling, the garment getting stuck on the sampling probe, and the effects of electrostatic charging9.
- Primary Test Procedure/ Modified ASTM F51 Test
Purpose of test
To evaluate shedding properties of the garment by determining the number of particles and fibres (≥5.0µm) on the garment surface
Description
The primary test procedure is a non-destructive particle-count test modified from the ASTM F51: Alternate Method (Woven Fabrics). It is widely used and still the accepted test method in the pharmaceutical, medical devices and other health care-related industries.
An area of one square foot (929 cm2) (compared to 46.5 cm2 for original ASTM F51) of the garment is vacuumed and particles are collected on a (0.8 µm pore size) membrane filter. Particles and fibres greater than or equal to 5.0µm in size are retained on the membrane filter and then counted using a microscope or by using an automatic particle counting unit (e.g. based on the laser scattering principle).
Interpretation of results
The greater the number of particles/fibres, the less acceptable the garment is.
Class / Contamination per square footA / Less than 1,000 – (≥5 µm particle length)
Maximum - 10 fibres
B / Less than 5,000 – (≥5 µm particle length)
Maximum - 25 fibres
C / Less than 10,000 – (≥5 µm particle length)
Maximum - 50 fibres
Table 3: Particulate cleanliness classes (maximum counts per square foot)
Test limitations
It only allows for the testing of apparels which have the required one-square-foot seamless surface i.e. only coveralls
- Liquid extraction
Purpose of test
To determine if residual elements (e.g. anions, cations, non-volatile residues, volatile residues, silicone, and antibiotics) are present in garments after laundering
Description
A one-square-foot sample of the garment is immersed in boiling solvent for a specified period of time and the solvent is passed through a membrane filter to remove particles and fibres. The amount of extractables in the solvent filtrate is then determined by gravimetric techniques.
Interpretation of results
Garments found to contain significant amounts of certain residual elements are not suitable for applications that are sensitive to the relevant residues.
Test limitations
The test is destructive; hence, it relies on a statistical confidence for each batch of garments produced.
- ESD (electrostatic discharge) tests 8,9,10,11
Purpose of test
To evaluate the ability of the garment to dissipate static electricity
(Conductive thread e.g. Beltron is often woven in a grid or stripe pattern into garments to reduce electrostatic discharge.)
Description
Most commonly used ESD tests:
-Static Electricity Decay measures the time taken for a fabric to reduce an electrical charge of e.g. 500 volts to 50 volts.
-Surface Resistivity quantifies the resistance of a fabric to pass an electrical charge through it (measured in Ohms from point to point). Under defined conditions of relative humidity and temperature, a one-square-foot patch is probed and measured for its ability to conduct electricity.
-
Interpretation of results
Static Electricity Decay: The less time taken for the garment to reduce electrical charges, the better its performance. Extremely fast decay times indicate that the material is a conductor and may be a safety hazard. Slow decay times indicate that the charge does not dissipate well and may discharge through a spark, damaging electronic devices.
Surface Resistivity: When the resistivity of the garment is within the electrostatic dissipative range of 105 ohms/sq. to 1011 ohms/sq., any electrical charge will be quickly broken down to 0 volts and no charge will enter the product.
Test limitations
Static Electricity Decay measurements can currently only be performed destructively on small samples of fabric.
Surface Resistivity test does not have good repeatability.
- Barrier Test
Purpose of test
To test the integrity of barrier after withstanding penetration under known pressure
Description
The test material is wrapped over the end of a glass tube of known uniform internal diameter. The tube could be marked at 100 mm and filled with microbial suspension, containing either 106 number of E. coli or a similar microorganism, to this level.
The height of the suspension column represents the pressure with which the barrier is stressed. The tube and its affixed barrier material stand vertically on a sterile, dry Petri plate, suspended by a ring stand so that it can be observed from below.
Interpretation of results
If liquid penetration of the affixed material is seen, the study is aborted.
If no obvious breach of liquid barriers has taken place in the prescribed time, the Petri dish is removed and a pour plate is prepared.
After 24 and 48-hour incubation, the pour plate is examined and colony counts are made. The colonies can then be subcultured or inspected after a Gram's stain to confirm that barrier penetration is by the test organism rather than a contaminant.
Test limitations
This test does not test for the penetration of microorganisms when the fabric is in dry conditions, or exposed to external stresses like stretching and temperature changes.
- Summary of other methods3,11,12,14,15
Bioburden
Measures the number of viable microorganisms on garment / Samples of water and materials are tested using standard microbiological techniques (contact plates, pour plates)
Particle Penetration Method
Measures the efficiency of fabric as a barrier / Air is drawn through a cleanroom garment fabric at specific pressure
An airborne particle counter is used to obtain particle counts upstream & downstream of fabric sample
The data is used to calculate filtration efficiency of the fabric
Liquid Filtration Efficiency
Measures the fabric's barrier properties in a wet environment / Pass water with a known quantity of particles through the fabric.
A liquid particle counter is used to determine the number of particles passing through the fabric
Moisture Vapour Transmission Rate / Measure how much water vapor passes through a cleanroom garment fabric in a 24-hour period
Particle Cleanliness Wet Test
Measures the number of insoluble particles on the sample's surface / Portion of fabric is rinsed with ultrapure deionised water
Rinsed water is subsequently tested for particles:
> 0.2µm using Scanning Electron Microscope(SEM)
> 0.3 µm using Liquid Particle Counter
> 0.5 µm and fibres using Optical Microscopy
The number of particles per unit area is determined
Particle Transfer Test
Measures an item's tendency to shed particles when subjected to moderate adhesive force / A clean piece of tape is applied to the garment surface for a specific time and mass placed on top of it
Tape is then removed and the number of particles more than 0.5 microns and fibres are counted microscopically
Pore Size Evaluation / SEM is used to measure the size of pores in the fabric weave
Fibres are also examined at high magnification for defects (e.g. cracks) that could shorten garment lifespan
Water Repellency (Spray Test)
Measures resistance of fabric to wetting by water / The higher the spray rating the higher the water resistance
Conclusion
Test standards and methodology for cleanroom garments are set forth in non-mandatory guidelines published by the Institute of Environmental Sciences (IES)(UK), the Association for the Advancement of Medical Instrumentation (AAMI)(USA), and the American Society for Testing and Materials (ASTM) 4.
Tests such as those outlined by the Institute of Environmental Science-- modified ASTM F51: Primary Test Procedure, body box, liquid extraction, Electrostatic Discharge Test and the Helmke Drum -- are more widely and routinely employed 13.
Aseptic garment validation tests are often limited by a lack of uniformity in the application of methods and instrumentation, a lack of repeatability and a lack of correlation of the data to actual cleanroom classification.
Standard tests for comparison of garment systems are still non-existent, and the search continues for better and more reliable methods.
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