Several terms are currently used to describe controlled environments, but they are most often referred to as clean zones, or just ‘cleanrooms’. The key role of this type of rooms is to ensure that the air there has certain precisely specified parameters that are necessary to ensure the repeatability of production, regardless of the industry, be it pharmaceutics, electronics or the automotive industry.
DEFINITION OF CLEANROOMS
The currently used definition of a cleanroom is stated in the ISO 14644-1 standard titled ‘Cleanrooms and other associated controlled environments’ and is worded as follows: ‘A cleanroom is a room where the concentration of particles in the ambient air is controlled and which is designed and operated so as to minimise the introduction, generation and retention of particles in the room’.
Today, the cleanroom technology is used in a variety of industries, both to reduce the amount of particles (e.g. in electronics, optics and semiconductor industries) and to reduce the number of micro-organisms that can pose a threat to humans and products (pharmaceutics, biotechnology, production of medical devices, food, beverages). In order to obtain a product of the highest and most repeatable quality, it is necessary to comply with the strict guidelines stipulated in the regulations and with the ISO standards, namely the already mentioned ISO 14644 1 standard.
THE PURPOSES OF CREATING A CLEANROOM
The purpose of creating cleanrooms is to:
WHAT AFFECTS THE AIR QUALITY IN CLEANROOMS?
The air quality in cleanroom areas is directly related to the presence of particles, such as dust, dirt, and sand that are visible to the naked eye. In addition, in a cleanroom, particles can originate from human skin, clothing, materials, equipment, as well as bacteria or fungi that cannot be observed macroscopically. The level of these contaminants is largely determined by the care taken to properly use such rooms and keep them clean.
HOW A CLEANROOM WORKS
Most cleanrooms are positive pressure spaces designed to prevent contaminants from getting inside. Usually, air is introduced into the cleanroom at the ceiling level, after passing through HEPA filters that remove particles that are as small as 0.3 microns. In this way, a positive pressure room is obtained. The air and contaminants are pushed towards the floor and eventually exhausted through openings in the lower parts of the room walls. This means that the air and contaminants from the processes carried out in the room are constantly flowing outwards. It is recommended to maintain an overpressure of at least 10 Pa with respect to the adjacent zone.
In addition, the air leaving the room, both through the ventilation openings and when the door is opened, has sufficient pressure to prevent contaminants from entering through these openings.
Negative pressure cleanrooms
Cleanrooms can also be negatively pressured. Negative pressure rooms are designed to keep the contaminants inside the room. A negative pressured room is used when dealing with infectious diseases, pathogens, bio-contaminants and certain processes involving chemicals, flammable or explosive liquids and powders. What is important is not what enters the room, but what gets out of it. In a negative pressure room, air is drawn out of the room through inverted HEPA filters, thus creating negative pressure inside the room (which prevents the contaminants from escaping). The force of the incoming air prevents the contaminants from escaping – this solution is mainly intended to ensure the safety of production processes.
In the electronics industry, both models can be used, depending on the produced components and the production process, which may or may not generate additional chemical contamination. However, it is more common for positive pressure to be used in cleanrooms in the electronics industry.
ISO 14644 STANDARD
Cleanrooms are classified according to the degree of air cleanliness in a controlled environment. The ISO EN 14644-1 classification system defines the number and size of particles per cubic metre of air. This ISO standard includes the following cleanroom classes: ISO 1, ISO 2, ISO 3, ISO 4, ISO 5, ISO 6, ISO 7, ISO 8 and ISO 9. ISO 1 is the “cleanest” class, while ISO 9 is the “dirtiest” one. However, it is worth noting that ISO 9 rooms are still cleaner than the spaces we stay in on a daily basis.
The most common classes of cleanrooms are ISO 7 and ISO 8.
Contamination is measured as the ‘number of particles of a certain size per cubic metre’. For example, an ISO 6 class cleanroom should have no more than 35,200 particles that are larger than 0.5 microns per cubic metre. These are particles that are invisible to the naked eye. The counting of particles in a cleanroom takes place at the working surface level.
CLEANROOM EQUIPMENT
Only products and materials that meet specific air cleanliness, quality and safety requirements can be used in controlled environments. Products entering the cleanroom must be packaged properly so as to minimise the risk of contamination and to keep the air in the room clean. Usually, special packaging is used, such as bags, films, boxes and containers that are specifically designed to transport materials, tools and equipment for this type of rooms.
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Cleanroom clothing
In a controlled environment, special clothing is used as one of the important elements to reduce the emissions of particles and micro-organisms, and to protect products from contamination. The following types of clothing are used in such rooms:
Coveralls are typically made of materials which minimise particle emissions (polyesters, polypropylene or anti-static fabrics). They may have snap fasteners or a zip fastener, while the sleeves and legs are elasticated to prevent the ingress of air and contaminants.
Aprons are typically made of anti-static fabrics that are easy to clean and disinfect. Such aprons typically have rubberised cuffs to prevent the ingress of air and dirt.
Gloves for cleanrooms are made of materials that minimise the emissions of particles and micro-organisms (latex, neoprene or nitrile) These gloves are anti-static and are available in elbow- or forearm length variants.
Hair nets and face masks are made of anti-static fabrics that prevent hair and micro-organisms from being released into the environment. These nets are usually disposable, while masks provide protection against inhaling contaminants.
Shoes for cleanrooms should have non-slip and anti-static soles, and their design should minimise the emissions of particles and micro-organisms. Shoes are usually disposable or manufacturers provide an option to disinfect them.
Cleanroom clothing is available in a variety of air cleanliness classes, depending on the requirements. When making a choice, it is important to choose garments that are suitable for the air cleanliness level, ensure minimal particle emissions, and provide protection from contaminants. Anti-static clothing used in cleanrooms is particularly important in the electronics industry. It is also important to ensure that the clothing, despite meeting strict requirements specified in the ISO standard, is comfortable for the employees.
Cleanroom equipment.
Cleanrooms need to be equipped with special chairs which are adapted to work in such environments. Such chairs have to meet certain requirements in terms of air cleanliness, and they have to be easy to clean, disinfect, and comfortable to use. This is guaranteed by the compliance with the standard. The same applies to all kinds of materials used during work – office supplies, containers or cleaning products used in cleanrooms.
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