Especially after Secont World War, products and services became more and more complicated and the effects of the environment on product process qualty became more visible which has led to the emergence of clean room concept and the need for classfying rooms with different cleanliness has led to the emergence of clean room standards. Although a variation of different standads have appeared over time, there are three standards used commonly: Amercian/English, ISO and Metric standards. Holding the need for appropriate validation and documentation, the requirements for a clean room roughly are as follows:

• A unique function defined for every location - For example, granulation and tablet production cannot be at the same room.
• Controlled entrance-exit - Clean room entrance procedures, air-locker and etc.
• Surfaces that are easy to clean, that do not allow antistatic electric accumulation and that do not produce or catch dust.
• Controlled heat / humidity
• Controlled number of particles
• Appropriate form of air flow and approriate difference of presssure between locations.

The clean room class to be used should be dtermined according to the objective. For example, sterile production and an aseptic tablet cannot be produced in the same conditions. Most commonly used ISO and FDA standards are as follows:

Numbers of particles according to the classes ( particles / m3) are as follows:

According to ISO 14644-2, it is obligatory to validate these amounts of particles, forms of flow and difference of pressures in the time intervals that follow:

To verify the mentioned classes, the choice of flow forms ( laminar or turbulenced ), air conversion coefficients, air holes, position of anemostates, approriate selection of air velocities, equipment and channel design and production and tests are more complex and require experience and care compared to the comfort applications. If there is a problematic situation, it can be very time-consuming and expensive to undo or correct the applications.