Cleanroom clothing has to meet several criteria to be effective. Ulrike Koster and Steve Marnach, DuPont Personal Protection, look at a combination of personal and product protection requirements.
Contamination protection for products and processes in cleanrooms requires an effective particle barrier on cleanroom clothing, while personal protection from hazardous substances requires effective defence against biological and chemical substances.
The Health & Safety Regulations of the German Employers’ Liability Insurance Association, BGR 189, section 2 “Definitions of terms”1 says: “Cleanroom clothing covers workwear that protects the environment against influences coming from the wearer of such clothing, including skin particles and textile fibres; it is not the same as protective clothing”.
Protective clothing, on the other hand, is defined in the same regulations as: “... personal protection equipment that protects a person’s body, arms and legs against harmful influences at work. Different types of clothing may protect a person against one or more influences.”
Cleanroom clothing primarily functions as a personal filter that protects products and processes from contamination by people as the most serious source of particle emission in a cleanroom. Some cleanroom work, on the other hand, requires the protection of people from hazardous substances, such as liquid or solid chemicals and indeed from biological agents. These hazards may occur not only in chemical, pharmaceutical and microbiological environments, but also, for instance, in the production of computer chips or while painting.
In such cases the workers are inadequately protected with traditional cleanroom clothing. Instead, they need to use chemical protective clothing in combination with further personal protection, such as gloves, respiratory equipment, etc.
Particle retention
Both cleanroom clothing and chemical-protective clothing need to meet the same basic criteria for use in a cleanroom: the material must be low-linting; the design must be sufficiently tight; and the danger of collecting particles on the surface of the garment must be minimised. Furthermore, such clothing must be comfortable to wear, must have good electrostatic charge derivation and – if it is required to be germproof – sterilisation must be possible.
The potential effectiveness of clothing as particle filters to protect products and processes, and as barriers to protect the wearer, can be demonstrated using Tyvek protective clothing from DuPont Personal Protection as the example.
The clothing and its materials are subjected to a range of checks to ensure their suitability for use in a cleanroom. Particle retention capacity is ascertained under an ITV test method (established by ITV Denkendorf), using a test facility certified under VDI 39262 and simulating the filtering effect (barrier) of the material used in the relevant garment. Air charged with a defined quantity of particles is absorbed through the test fabric, followed by the determination of the permeation and retention factors in relation to particle size.
The Martindale test under ISO 129473> serves to model particle migration while wearing the cleanroom suit. When used in real life, the wearer’s movements inevitably lead to undergarments and cleanroom clothing rubbing against each other. This means that any fibres released by the undergarments – and thus any skin particles released by the wearer – may leak through the material of the cleanroom clothing. Table 1 summarises the results of these two tests for Tyvek protective clothing material.
A person’s movements will affect the particle emission of the clothing fabric. The tests seek to simulate this through the creation of controlled particle charging conditions.
The Helmke drum test4 involves placing the entire garment in a rotating drum as a way of testing the extent to which particles come off the surface of the clothing. After a period of 10min a particle counter identifies the average particle concentration of the air in the drum. Depending on particle emission, cleanroom clothing is divided into three categories (see Table 2). The results of these tests for untreated Tyvek clothing can be found in Table 3.
The test method that comes closest to genuine wearing conditions, which allows an assessment of particle emission, is the so-called body-box test5. A person wearing cleanroom clothing is placed in a test chamber and makes a number of defined movements and sequences of movements. At the same time particle counters are in place, continually recording the particles emitted by the wearer/suit.
However, as different people usually emit different quantities of particles despite conducting the same activities, these absolute values are not sufficient as an assessment criterion. Nevertheless, if the same test person is used, the body-box test does allow comparisons of different clothing systems, as can be seen for the three types of Tyvek suits in Table 4.
The comparison shows that, as expected, the Classic Plus with its tight seams, zip covers and chin covers has the lowest particle emission values and best particle retention capacity.
As shown above, there are several standardised tests to provide comparative data on the barrier properties and particle emission of the fabric and the clothing. So far, however, there have been no standards or authorised recommendations as to which performance classes or categories of material and clothing should be used in which cleanroom classes. This means that users have to follow their own assessments of cleanroom clothing. They need to decide on the extent to which readings (barrier properties and particle emission) are relevant to their specific cleanroom processes.
Based on the readings compiled in this paper and also on general experience, DuPont Personal Protection recommends the use of Tyvek clothing for specific cleanroom classes as shown in Table 5.
Washed and sterilised Tyvek protective clothing can be used up to cleanroom class ISO-5. These suits not only provide product protection but also meet the requirements on type 4B, 5 and 6 chemical protective clothing: • The Industry and Classic series are typically used as protection from liquid mist (type 6) and solid airborne particles (type 5). • The Classic Plus suits offer type 4B, 5 and 6 protection, as they have tight seams, providing additional protection from liquid aerosols. This type of suit can also be used when dealing with biological agents, as it offers an effective barrier against biologically contaminated dust under EN 14126:20036. A wide range of accessories is also available.
Static charge
A further vital criterion for usability in a cleanroom is electrostatic charge derivation. Electrostatic discharges cause considerable concern as they pose a health hazard to the workforce and may have a destructive effect on sensitive products.
It is a known fact that synthetic materials are particularly charge-prone. Tyvek is therefore given a full-surface antistatic coating on both sides and indeed as early as the production of the nonwoven. This antistatic coating meets the requirements of EN 1149-1:1995 and EN 1149-1:2006 with EN 1149-5:20087.
The latest research, commissioned by DuPont with independent test facility, the Explosion Proofing Unit (Mining Exploration Drift) of Dekra Exam in Germany, showed that this protection suit material does not transmit any charges (i.e. explosive brush discharges) that might pose a hazard to an explosive mixture of gas and air.
Provided that the suit and its wearer are properly earthed and in an atmosphere with relative humidity of at least 25%, Tyvek protective suits can be used in EX-zones. This even applies to the most hazardous EX-zone 0: according to ATEX directive 1378 “an area in which a potentially explosive atmosphere, consisting of a mixture of air and flammable substances – in the form of gas, vapour or mist – is present constantly for long periods or is frequently present.”
Reliability
Used by DuPont for all its protective clothing, Tyvek has a low specific weight, a high level of resistance to tear, tear growth and abrasion, while also allowing air and steam permeability (Table 6). The material consists of extra-fine filaments made of 100% high-density polyethylene (PE-HD), condensed into a nonwoven under heat and pressure.
This protective clothing is provided for limited-duration applications (i.e. dispos-able protective clothing). This ensures a consistently high barrier and the protective effect of the material. Moreover, it also simplifies logistics procedures in relation to protective clothing as there is no need for cleaning cycles.
To conclude, it is worth noting that Tyvek protective clothing is inexpensive in terms of waste disposal as it does not have any critical (halogenic) additives, thus allowing disposal via ordinary municipal incinerators. Obviously, where the clothing has been contaminated by hazardous substances, it should be disposed of in the same way as the actual substances. The relevant national laws and regional regulations thus apply.
Contact
Ulrike Koster, Life Sciences Marketing Manager, and Steve Marnach, Life Sciences Sales Specialist DuPont Personal Protection Luxembourg .(JavaScript must be enabled to view this email address) .(JavaScript must be enabled to view this email address) www.dpp-europe.com