The principle of Clean room design starts from almost 150 years ago when these units were used for bacterial control in hospitals. Today, clean rooms have completed a long way and developed to the modern technology. In earlier day, these clean rooms were designed for fulfilling the requirement of clean environment for industrial manufacturing during 1950s and the same clean rooms are also used for variety of applications in many industries.

A clean room is defined as a place that provides attentively controlled environment that has a low level of environmental pollutants such as airborne microbes, dust, chemical vapors, and aerosol particles. When the air entered in a clean room it is filtered and then continuously circulated through high efficiency particulate air (HEPA) or ultra-low particulate air (ULPA) filters. These filters are used to remove internally generated contaminants. The persons, who work inside the clean room, wear protective clothing while enter and exit through airlocks, while equipment and furniture inside the clean room is specially designed to produce minimal particles.

Today, more than 30 different industry segments utilize clean rooms including semiconductor and other electronic components, pharmaceutical, and biotechnology industries.

Modern clean rooms were developed during the Second World War to improve the quality and reliability of instrumentation used in manufacturing guns, tanks and aircraft. During this time, HEPA filters were also developed to contain the dangerous radioactive, microbial or chemical contaminants that resulted from experiments into nuclear fission, as well as research into chemical and biological warfare.

On the other hand, clean rooms for manufacturing and military purposes were being developed; the importance of ventilation for contamination control in hospitals was being realized. The use of ventilation in a medical setting gradually became standard practice during this time.

The concept of laminar flow was introduced during 1950s and 1960s, when NASAs space travel program was initiated. This marked a turning point in clean room technology and from this time, the evolution of clean rooms gained momentum.

In the late 1950s, the Sandia Corporation (which later became Sandia National Laboratories) began investigating the excessive contamination levels found in clean rooms. Researchers found that clean rooms were being operated at the upper practical limits of cleanliness levels and identified a need to develop alternative clean room designs.

In 1961, Professor Sir John Charnley and Hugh Howorth, showed a tremendous improvement in unidirectional airflow by creating a downward flow of air from a much smaller area of the ceiling, directly over the operating table.

Also in 1961, the first standard written for clean rooms, known as Technical Manual TO 00-25-203, was published by the United States Air Force. This standard considered clean room design and airborne particle standards, as well as procedures for entry, clothing and cleaning.

In 1962, Patent No. 3158457 for the laminar flow room was issued. It was known as an ultra clean room.
By 1965, there have been several vertical down flow rooms were used in which the air flow ranged between 15 m (50 ft)/min and 30 m (100 ft)/min. It was during this time that the specification of 0.46 m/s air velocity and the requirement for 20 air changes an hour became the accepted standard.

By the early 1970s the principle of laminar flow had been translated from the laboratory to wide application in production and manufacturing processes.

The 1980s saw continued interest in the development of the clean room. By this stage, clean room technology had also become of particular interest to food manufacturers.

In 1987, a patent was filed for a system of partitioning the clean room to allow zones of particularly high-level cleanliness. This improved the efficiency of individual clean rooms by allowing areas to adopt different degrees of cleanliness according to the location and need.

In 1991, a patent was filed for a helmet system that can be used in a medical clean room in which the user is protected from contaminated air in the environment, while the patient is protected from contaminated air being exhausted from the users helmet. Such a device decreases the possibility of operating room personnel being contaminated with viruses carried by the patients being operated upon.
The pace of clean room technology transformation has accelerated over recent years. Since the year 2000, there have been significant advances in new clean room technology, which have helped to streamline manufacturing and research processes, while also reducing the risk of contamination. Most of the technological developments of the past decade have been directed towards the manufacture of sterile products, particularly aseptically filled products.

In 2003, Eli Lilly pioneered the development of a new system for the prevention and containment of cross contamination during the manufacture of pharmaceutical powders using a specially designed fog cart. This allows the operator to be covered by an exceptionally fine fog of water on exit from a critical area, virtually eliminating the risk of transferring dust traces beyond their proper confines.

The Future of Clean Rooms
Today, clean rooms are used in variety of applications. The presence of these units can be seen in the manufacturing of semiconductor and other electronic components, as well as in the pharmaceutical and biotechnology industries. Furthermore clean room technology has more recently been applied to micro- and Nano-system processes, and this looks certain to be an area of growth in coming years. The development of clean room technology is likely to continue to be driven by certain key factors including the increasingly technical use of exotic physical and biological phenomena, the central role of increasingly fine structures, the creation and use of materials of the highest purity, and the increasingly broad-based utilization of biotechnology. Given the scale of these challenges, clean room technology looks set to remain indispensable to production in coming years.