What is a clean room? Definitions, functions and classes.

A clean room is a room that has a very or even extremely low concentration of airborne particles. Airborne particles are all particles and substances that float in the air and which for the most part cannot be seen with the naked eye.

Clean rooms are required where particles in the ambient air would interfere with the work, such as in the production of pharmaceutical products, sterile medical devices, certain foods, semiconductor manufacturing or in optics and laser technology and more. It is important for all these products that they are not contaminated by the smallest particles.

Since the standards and classifications for clean rooms differ between different industries and areas of activity, there are different rules and requirements. Here are some general principles for clean rooms with a focus on the production of plastic based medical devices that AMB mainly works with.

What then is a clean room?

A clean room is designed in such a way that the number of airborne particles that enter the room or occur there, is as low as possible. Different processes and techniques are used to create the necessary conditions.

Depending on the use and the desired clean room classification (see below), the number of particles in the clean room is measured. If the products from a clean room are also to be sterile-packaged, the number of microorganisms (called bioburden) must also be checked.

The classification can take place according to different standards. AMB’s both clean rooms are classified according to the international standard ISO 7-8.

Other parameters such as temperature, humidity and pressure are usually kept constant to have comparable conditions at all times.

General conditions for a clean room

The entrance to a clean room is divided into one or more areas where the degree of cleanliness increases gradually. In other words, the clean room class gradually decreases because a low ISO rating means a cleaner room. A common step in the beginning is to change into clothes and shoes that are adapted to the clean room requirements. Stick mats help to clear shoe soles. In general, it also applies that the staff working in the clean room with the production of medicines or medical devices must be free from certain diseases.

The staff who work in the clean room are responsible for the largest proportion of particles or other pollutants because movement causes, for example, skin and clothing particles to come loose and spread. To minimize these, special work clothes and shoes as well as protective covers are used in the room. In addition, some approaches and techniques are needed that must be trained.

After changing and hand washing, one or more locks are passed into the clean room itself, where pressure differences prevent further contaminants from being introduced from the outside. Usually there is a certain overpressure in the clean room to prevent particles from penetrating, but there are also clean rooms where negative pressure is used to prevent dangerous or disease-causing substances from penetrating.

All tools, materials and production equipment must be adapted to the clean room and cleaned before being taken into the room. They must also meet the requirements for the desired particle content in the clean room. For common materials such as paper, pencils and fabrics made of natural fibers, alternatives must be used. The materials used for the surfaces in the clean rooms must be abrasion resistant as they must be cleaned regularly and be disinfectable. Everything that is to be brought into the clean room must pass at least one lock.

The clean room floor is an industrial floor and must be seamless. Low wear and freedom from cracks are also some of the features. The floors must be easy to clean and disinfect.

Clean rooms are not sterile

Clean rooms are not sterile in themselves, that is, they are not free of microbes. The number of airborne particles in the room is mainly limited and controlled. The particle levels can be tested with the help of a particle counter and the microorganisms and their number can be detected, for example, by different nutrient substrates that are placed in the room for a certain time. By minimizing the number of particles, the number of microbes is often also reduced. This is also the precondition for a subsequent sterilization of the parts produced in the clean room.

Air flow principles for clean rooms

Together with one, or usually several, filtration steps and a large air flow, the purity of the air is ensured. There are different principles for airflow. Either a low turbulent laminar flow or a turbulent flow.

In a laminar flow, the clean air flows into the clean room with low turbulence and usually vertically, which ensures that the sensitive work surfaces and machines are polluted as little as possible. The air then leaves the room on the opposite surface, often through a perforated double floor, and is returned to the circulating air device for repeated filtration.

In a turbulent or mixed flow, the filtered clean air is introduced into the room in a swirling manner and creates a constant dilution of the particle concentration. The turbulent air tries to trap particles that may be in the air and push them towards the floor. In order to meet the requirements for the desired clean room class, it is then particularly important that the staff follow the routines that apply to the air flow principle and to ensure that the number of objects and processes that generate particles in the clean room is minimized.

Air filters

The minimized proportion of particles in the air is achieved by using high-efficiency HEPA (High-Efficiency Particulate Air) particulate filters. HEPA filters are normally also present in modern vacuum cleaners and must be able to filter out at least 99.97% of the airborne particles that are 0.0003 millimeters in diameter in size.

Climate control

The climate in the clean room is controlled via air conditioning where humidity, temperature and pressure can be regulated. The humidity in particular must be balanced because too low a humidity can cause electrostatic problems and, for example, plastic components produced in the room then become statically charged.

On the other hand, too high humidity provides better conditions for bacteriological growth. To avoid the latter, additional equipment that ionizes the air may be needed to avoid electrostatic discharge.

Clean room standards

There are different standards for classifying clean rooms. The most common are:

• ISO 14644-1 (particles)
• ISO 14698 (biological contamination)
• EU GMP

The main purpose of the standards when it comes to clean rooms is to protect people through the quality assurance of the production.

Different clean room classes

Clean rooms are classified according to the number and size of particles allowed per unit volume of air.

Air in a typical urban environment contains about 35 million particles per cubic meter that are 0.0005 mm and larger in diameter, which corresponds to the clean room class ISO 9. The most demanding clean room class is ISO 1 and there are no particles of that size at all.

ISO is an international standard and it generally does not apply as a law but is complied with voluntarily. However, some countries have chosen to apply certain ISO standards in their laws.

GMP (Good Manufacturing Practices). The standard was developed in the United States by the FDA (Food and Drug Administration) in the mid-1960s and is valid as a law there, but it is not a certified standard. The standard is mainly used for the manufacture of food, cosmetics and medicines through the practical application of quality systems to companies and it must also be taken into account for exports to the USA.