Article : Two-way protection for cleanroom environments
Article : Two-way protection for cleanroom environments
Figure 1 : Tyvek® protective clothing helps to prevent wearers from contaminating production processes and products, whilst at the same time protecting the wearer from potential hazards which may also arise in cleanrooms.
Single-use protective suits (so-called disposable protective apparel) can form a barrier between the human body and products, samples, preparations or processes in cleanroom areas and in doing so, perform two important functions. Firstly, they can protect the wearer from contamination and secondly, they can protect products and processes from human contamination.
Cleanrooms, typically encompassing industries such as pharmaceuticals, medical engineering, electronics, the optical industry and the food industry, frequently require products to be manufactured to extremely high standards of quality and purity. Alongside the controlled temperature and maximum permissible particle load in the air (see Table 1), special equipment and tools, corresponding work techniques and last but not least, appropriate clothing are useful tools to meet cleanroom class conditions.
Protecting processes from human contamination
Humans are a major source of particles inside a cleanroom (figure 1). Every minute, humans shed an average of 100,000 particles (dead skin, hair, perspiration) from just standing, and this can rise to millions of particles depending on how much they are moving around.*
Therefore suitable protective apparel is helpful to maintain the maximum permissible particle limit values per cleanroom class (as in Table 1). Cleanroom apparel acts as a filter, holding back the wearer’s bodily particles, and in doing so protecting the environment from human contamination.
Protecting humans from contamination.
Protecting products and processes in cleanrooms against human contamination is just one side of the coin. At the same time it is often necessary to protect the wearer from hazardous substances such as chemicals typically used in cleanroom environments. The risk of contamination does not just exist in chemical, pharmaceutical and microbiological work areas, but may also arise in the manufacture of computer chips where surfaces of silicon wafers have to be treated with certain chemicals over and over as part of a multi-stage process.
To protect employees from exposure to hazardous substances typically encountered in cleanroom applications, protective clothing must also assume the role of chemical protective apparel and be CE-certified accordingly.
Materials for cleanroom apparel : lint-free and anti-static
Cleanroom garments are generally made from synthetic materials that do not release many particles, but at the same time are air and water-vapour permeable. Frequently these are polyester filaments, particularly in the case of reusable cleanroom apparel. TYVEK® protective apparel from DuPont consists of a lightweight, air and water-vapour permeable nonwoven made from extremely fine and strong polyethylene filaments.
Alongside the capacity to hold back particles, other important criteria that come into the equation are abrasion resistance, the ability to be decontaminated and sterilised as well as the material’s antistatic properties. Without electrostatic charge dissipation capacity, static charges may build up on the surface of cleanroom apparel when worn. This is particularly true of synthetic materials. Electrostatic discharge is a major concern in cleanroom applications as it poses both an uncomfortable feeling for the wearer and can easily harm sensitive products. To counter this problem, conductive carbon yarns are often woven into polyester cleanroom materials. TYVEK® already comes with an anti-static treatment on both sides, applied when the nonwoven material itself is manufactured. This anti-static finish satisfies the requirements of EN 1149-5.
TYVEK® protective apparel : a highly effective particle barrier …
TYVEK® material used in the manufacture of protective garments provides a liquid and a particle barrier, low specific weight and good tear and abrasion resistance, in addition to air and water-vapour permeability (table 2). The material is made from very fine 100% high-density polyethylene fibres (HDPE) interwoven during the spinning process itself, and then bonded together by heat and pressure to form a sheet.
TYVEK® protective garments can help to reduce human contamination of cleanrooms. Different models are available for a diverse range of applications, including coveralls with integrated socks and elasticated waistband (figure 3).
DuPont offers the TYVEK® Classic and TYVEK® Classic Plus protective coveralls as single-use (disposable) garments. This means that on the one hand the garment’s high barrier performance and protective effect is maintained at a consistently high level, whilst on the other hand it also simplifies logistics, as cleaning cycles and any repeated sterilisation and validation of the protective apparel are no longer required.
As TYVEK® protective garments do not incorporate any additives (e.g. halogens), users will incur lower disposal costs. Contaminated protective garments should of course be disposed of after use in the same way as the corresponding hazardous substance (corresponding national/regional legislation and regulations apply accordingly).
Additional chemical protection
In addition to acting as a particle barrier between humans and products, TYVEK® protective garments also meet the requirements of Type 6 to Type 4 chemical protective apparel :
TYVEK® Classic is typically used to protect against liquid mist (Type 6) and against solid particle exposure (Type 5).
TYVEK® Classic Plus is a Type 4 chemical protective suit. This means it offers protection against liquid aerosols in addition to Type 6 and Type 5 protection. TYVEK® Classic Plus coveralls have over-taped seams (see figure 3) and so offer the same barrier performance as the base fabric at these critical points.
Protection against highly concentrated inorganic or organic chemicals is provided by the DuPont Tychem® product range.
Table 1 : Cleanroom classification with associated particle limit values (source : EN ISO 14644-1 ; US Fed. Std. 209E)
* The previous cleanroom classification in accordance with US Federal Standard 209E defined the limit value as the maximum number of particles > 0.5 μm per cubic foot of ambient air (1 ft³ corresponds to 28.3 l) – e.g. cleanroom class 10,000 (a cleanroom class used in many sectors) means that 1 ft³ may contain a maximum of 10,000 particles > 0.5 μm.
For comparison : 1 ft³ (28.3 l) of urban air contains 15 to 100 million particles > 0.5 µm, cleaner mountain air at an altitude of 2,000 m contains up to 10 million of these particles (Source : H. Kück : Partikelkontamination in der Luft. Institut für Zeitmesstechnik, Fein- und Mikrotechnik, Universität Stuttgart 2003).
Table 2 : Physical properties of Tyvek® protective apparel material
MD : machine direction, XD : cross direction
* Tyvek® can be printed in colour. Some values of this colour-printed protective apparel material may deviate slightly from the values stated for white Tyvek®.
Particle barrier efficiency data for Tyvek®
Body Box test results for Tyvek® Classic Plus
Figure 1 : Sources of particulate contamination in cleanrooms
Figure 3 : The hardwearing and ergonomically designed protective suits made of Tyvek® Classic (left) and Tyvek® Classic Plus with sealed seams (shown on right of photo with integrated socks and elastic thumb loops) are air and water-vapour permeable. They feature the same extremely high barrier performance against particles and are, at the same time, capable of repelling lower-risk water-based chemicals.