Choosing the correct cleanroom clothing may appear a confusing process given the number of different types and style of garment and fabric available. In fact, the choice can be quite logical if taken from the viewpoint of the area of application i.e. the intended use of the cleanroom or area.
Broadly speaking there are two types of cleanroom or controlled area which have a need for cleanroom garments. Industrial cleanrooms (ICR) which encompass electronics and semiconductor manufacturing applications but also include optical and precision engineering cleanrooms and a second type of cleanroom which is the bioscience cleanroom (BCR) comprising pharmaceutical, biotech, medical and medical device applications.
Most ICR’s do not have a defined standard to work to when choosing the correct type of garments and must select a garment on the basis of the grade of cleanroom required or level of air cleanliness as defined by international standard e.g. Federal standard 209e or British standard 5295.
The BCR pharmaceutical cleanroom will have a more rigidly defined requirement for cleanroom clothing and its use which is dictated by the medicines control agency guide to good manufacturing practice (GMP).
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CLEANROOM GARMENT PROPERTIES |
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PROPERTY |
OPTIMUM PERFORMANCE |
ICR |
BCR |
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Filtration Efficiency |
Particles generated from the body and underclothing are prevented from passing through the garment material |
* |
* |
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Abrasion Resistance |
The textile used is non-shedding even after repeated laundering |
* |
* |
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Antistatic |
1. Electrostatic discharge is reduced/prevented tp protect sensitive components 2. Particles are not attracted to a static charge build-up on the garment surface |
*
* |
* |
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Comfort |
1. Perspiration and heat generated are efficiently dissipated to keep the wearer cool 2. Loose fit for freedom of movement 3. Non "see-through" material for modesty 4. Light comfortable feel |
*
* * * |
*
* * * |
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Sterilization |
Resistance to autoclaving or irradiation |
* |
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Durability |
Able to withstand repeated laundering and maintain integrity and filtration efficiency |
* |
* |
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ICR = Industrial/Electronic Cleanroom BRC = Biotech/Pharmaceutical Cleanroom |
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Table 1 above summarises the properties of cleanroom garments which should be considered by both ICR and BCR applications. It can be seen that most of the desired properties are common to both areas of application. Cleanroom managers will place different emphasis or weighting to individual properties according to the intended use for the garment.
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A = air permeability B = particle barrier efficiency C = antistatic behaviour D = water vapour diffusion resistance |
: Data from Institut for Textil Technology, Denkendorf : Data from Institut for Textil Technology, Denkendorf : Data from Institut for Textil Technology, Denkendorf : Data from Hohenstein Institute |
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The closer the line of the graph is to the outer edge of the respective parameter, the better the property of the textile is in this aspect. Please note: A and D are expressed in the negative, that means, the lower the are permeability and the vapour diffusion resistance are, the closer the graph is to the outer edge. |
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All data is determined after 50 washings |
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The difference between the performance of cleanroom garment textiles is illustrated in diagram 1. This data is the result of a study which took place in conjunction with the Denkendorf institute of textile technology and the Hohenstein research institute.
All the textiles tested in this study claim to meet the highest standards attainable for use in cleanrooms but it is clear that some textiles perform better than others when tested in a controlled study. The diagram shows six textiles measured for the four most important criteria for cleanroom use. The nearer the line is to the outer edge of the graph, the better the performance. If the measurement is close to the centre of the graph it indicates a poorer performance for that property. The optimum textile would show a measurement line which would run along the outer edge of the graph and form a perfect square.
A = air permeability
B = particle barrier efficiency
C = antistatic behaviour
D = water vapour diffusion resistance
Having selected a textile with a suitable performance it is important that the finished garment is constructed with the same attention to quality. The style of the garment should be practical and allow free movement of the wearer to reduce stress on the seams, closures and fabric.
As a rule, 20 to 30% more material (than normal clothing) should be used to produce comfortable cleanroom garments which are both easy to wear and if styled and cut with care ensure a secure fit to the wearer.
Double security seams which use a fabric tunnel seam (see diagram 2 above) are used in high performance cleanroom garments to prevent the possibility of a seam opening under daily mechanical stress.
A well constructed high quality garment can only function to its optimum performance if it is used with undergarments specifically designed for cleanroom use. Just as the hepa filter in a cleanroom filtration unit needs a pre-filter to function correctly so the outer garment should be worn with low particle shedding undergarments to reduce the challenge of contaminating particles on the cleanroom fabric.
New synthetic low shedding materials are now available for undergarment construction which act as pre-filters by filtering out particles shed by the wearer.
A further study by the Denkendorf institute for textile technology (see diagram 3) demonstrates the advantage of wearing cleanroom undergarments. In the study three operators were tested wearing the same outer garment but wearing either normal cotton undergarments or high tech cleanroom undergarments.
The number of particles in the size range of 0.5 to 5.0 um found on the surface of the outer cleanroom garment is reduced by over 50% when the high tech cleanroom undergarments are worn.
Undergarments made from these new synthetics also have a capillary action which transports moisture (perspiration) away from the skin surface to the outside of the fabric where it can evaporate, keeping the wearer cool and dry.
Conventional cotton undergarments absorb moisture and the cotton fibres swell which closes up fabric pores forming a barrier against water vapour diffusion. In a short time (less than one hour) this can result in a hot damp feeling which reduces operator comfort.
Influence of the undergarments on the contamination of cleanroom garments |
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Thousand particles/ft2 |
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Particle size: > 5.0m m |
Particle size: > 0.5m m |
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Yellow: DASTEX High-Tech RED:any other fabric |
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Test duration 2.5 days. Coverall, outside ION-NOSTAT-I |
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Working on the well documented basis that 80% of particulate contamination in the cleanroom emanates from the operators working in the room it can be seen how important it is to choose wisely the type and performance of cleanroom garments used. These garments are the final filter between the operator and the product. How well they function will be reflected in the quality and yield of the product made in the cleanroom. Although the major investment in any cleanroom is always seen as the construction cost of the room itself an equal emphasis should be placed on garment choice or the investment will not produce the maximum return.
About the author: Clive Hayler is the managing director of a successful company supplying the cleanroom industry.
