Don’t be floored by contamination

Published: 16-Nov-2010

The right flooring is integral to ensuring that contamination is kept under control. Graham Lewis, corporate account manager, Forbo Flooring Systems, looks at how to ascertain the suitability of a flooring product, based on the individual demands of different applications

The right flooring is integral to ensuring that contamination is kept under control. Graham Lewis, corporate account manager, Forbo Flooring Systems, looks at how to ascertain the suitability of a flooring product, based on the individual demands of different applications

Four types of contamination need to be kept under control in a cleanroom environment – airborne particles, gaseous molecules (also known as volatile organic compounds or VOCs), micro-biological (bacteria and moulds) and electrostatic i.e. static electricity – and depending on the sector, the requirements will differ.

The electronic industry, for example, is largely concerned with airborne particles, VOCs and electrostatic dissipation, whereas within a healthcare environment infection control is also crucial. Whatever the situation, the potential effect any element of a cleanroom’s construction may have on its performance must be taken into account.

The suitability of a product for use in a cleanroom or clean area is greatly influenced by its material composition. It is therefore necessary to know what impact a building material will have on a specific environment and to what extent.

In particular, specifiers should be aware of any potential problems that could be caused by particle emissions under frictional stress or outgassing. It is also important to ensure that any materials used won’t serve as a nutrient for micro-organisms, so offering biological resistance. Due to the nature of the environment, the integrity of any material should also withstand vigorous cleaning and chemicals.

The industrial alliance ‘Cleanroom Suitable Materials’ (CSM) of the Fraunhofer IPA Institute in Germany has developed procedures for determining the cleanroom suitability of materials.

The comprehensive tests are carried out in a standardised way and in compliance with relevant national and international norms. The results obtained provide an objective and substantiated basis for comparison and should be referred to when selecting suitable materials for specific production environments and fields of application. Looking at potential particle emission under frictional stress, the test is simulated by a PA6 nylon wheel travelling over a given specimen, at three different load forces. This determines the level of particulate contamination emitted during the application, in terms of the detected number and size of any released particles. The results should lie within the permitted values of the Air Cleanliness ISO Class 4, in accordance with ISO 14644-1.

Airborne molecular contamination, or outgassing, is tested using a method of analysis called thermo-desorption, gas chromatography or mass spectrometry, which provides a qualitative and quantitative analysis suitable for measuring the emission of VOCs. In particular, the test looks at outgassing of particular substances – amines, organophosphates, siloxanes, phthalates and semi-VOCs – all of which could have a detrimental effect on a cleanroom environment. Industries such as aerospace, microelectronics and pharmaceuticals are particularly sensitive to these types of airborne contaminants.

According to the cGMP (Good Manufacturing Practices) floors in life science and pharmaceutical production environments, in particular, need to take special precautions to reduce micro-biological contamination risk. The aim of a biological resistance test is therefore to assess the action of bacteria and moulds on a specific material. For vinyl flooring, for example, tests are carried out in line with procedures laid down in the international standard ISO 846 “Plastics – Evaluation of the action of micro-organisms, Procedure A (moulds) and C (bacteria).”

In this test, samples of a material are inoculated with suspensions containing different moulds and bacteria, incubated over a period of four weeks and the growth intensity measured – with the ideal result being ‘0’ – no growth visible under microscopic inspection.

Materials can also be tested against 14 typical chemicals, representative of the chemical substance categories present today in most cleaning products, disinfecting products and bio-decontamination procedures, to ascertain product resistance under these stresses. In addition, there are tests under ISO 14644-9 ISO and 14698-1 respectively, which determine the level of cleaning success possible using a standard surface cleaning procedure and the potential adhesion of micro-organisms.

Finally, with the increasing amount of sensitive electrical equipment in the workplace, electrostatic discharge (ESD) is becoming more of a problem, as it can cause damage to expensive and in some cases life saving equipment.

Consequently, there are also standards regulating the performance of conductive floors in cleanrooms and associated controlled environments found in several industrial sectors, such as semicon manufacturing, pharma and life science.

Reducing the generation of electrostatic charges is the main scope of comprehensive control measures in ESD protected areas (EPA) and the right floorcovering plays a crucial role here. It not only drains electrostatic charges from personnel and equipment, but also reduces the generation of charges where they occur, at the interface between the shoe soles and the floor.

The applicable tests for ESD measurement are EN1081 and IEC61340-4-1. These two tests describe how to measure an electrical charge, and performance levels and requirements for EPA areas are regulated by IEC 61340-5-1.

In addition, in terms of flooring it is also worthwhile understanding the actual make-up of the product, as the production process can have an impact on its overall performance.

There are two basic construction types of vinyl ESD flooring, those with chemical additives and those with pressed conductive chips.

The production process of the former means that the tiles have generally been cut down from sheets, which have a high plasticiser content as the initial production process has had in mind a need to be flexible and able to be rolled. However, this plasticiser also ‘outgasses’, and so may prove a problem in relation to the issue of airborne molecular contamination, discussed earlier.

During the production, anti-static chemical additives (surfactants) are added. However, these rely on a relative air humidity of 40% or above to gain their ESD performance – which in some cases is not practical for the environment in which they are placed. These surfactants also migrate, reducing product performance.

Alternatively, products manufactured under pressed chip production, such as Colorex SD/EC, for example, offer a highly compressed tile with a compact surface. The special production process starts with vinyl sheets being cut into small chips, which are then coated with a conductive substance. By very high pressure and high temperature, these conductive, coated chips are compressed into solid blocks of homogeneous material that are subsequently sliced into single tiles.

In the finished product, the conductive coating of the chips forms a dense network of tiny black veins. These are “conductor paths” for the secure drainage of electrostatic charges through the thickness of the tiles.

The optimised composition and highly compressed nature of Colorex SD/EC makes it ideally suited for use in cleanrooms. In addition, it has been certified by the Fraunhofer IPA Institute and satisfies the highest requirements in particle release behaviour, contributing to reduced contamination by airborne particles.

As demonstrated, there are a number of complex and demanding design considerations for engineers to contend with for the technical application of flooring in a cleanroom environment.

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