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Industry – Health: What is a Clean Room?
Nov 25, 2008

Just what is involved in a “clean room” above and beyond the obvious fact that it is just that – clean? A clean room has a very specific definition, stated in the NF EN ISO 14644 standards, as follows:

“Room in which the concentration of airborne particles is controlled, which is built and used so as to minimize the entry, production and retention of particles inside the room and in which other relevant parameters such as temperature, humidity and pressure are also controlled.”

 

 What are clean rooms for?

Clean rooms meet the need for an environment that has a low level of environmental pollutants. There can be two categories for such environments.

  • Category 1 covers situations where the presence of inert particles below the size of a micron could affect the operation or the lifetime of a product. 
  • The second category covers the requirement for controlling transmission of micro-organisms contained in dust to a product, or a person (such as in a hospital) and providing total absence of contamination.

Clean rooms, or environments with controlled levels of contamination, are used in many sectors, including: 

  • electronics: manufacturing of computer, television screens, magnetic tape;
  • semi-conductor manufacturing: circuit boards (processors, memories);
  • micro-mechanics: gyroscopes, micro-supports and cds;
  • optics: lenses, laser and photography film;
  • biotechnology: antibiotics and genetic engineering;
  • pharmacy: sterile products;
  • surgery: cardiac bypass systems and valves;
  • food: non-sterilized food and beverages;
  • hospitals: surgery wards, immune-deficient therapies, isolation of contagious disease.

 Clean room classifications

Clean rooms are classified according to the number and size of particles permitted per volume of air. The simplest, most widespread method is the Federal Standard 209E method which counts the number of particles of size 0.5 µm or larger permitted per cubic foot of air (classes 1 to 100,000).

The European reference, adapted to the metric system, is the EN ISO 14644 standard which classifies into ISO classes 1 to 9 based on the maximum concentration of particles per cubic meter of air.

The following states examples of the work done in the ISO classes of clean rooms:

  • ISO 3 class: manufacturing of certain types of circuit boards;
  • ISO 4 class: semi-conductor manufacturing; 
  • ISO 5 class: manufacturing of sterile products and injection ampoules; 
  • ISO 6 class: manufacturing of high-precision opticals, assembly and testing of precision gyroscopes, wafer assembly; 
  • ISO 7 class: assembly of precision pneumatic and hydraulic equipment, control valves, precision clockmaking, precision mechanisms; 
  • ISO 8 class: general opticals, assembly of electronic, hydraulic and pneumatic components.
 Clean room characteristics

There are two types of clean rooms distinguished by the type of air flow which ventilates the room:

  • Conventional flow clean rooms with turbulent, non-laminar air flow – here, air cleanliness depends on the quality of the filtered air, the volume of the recycled air and the amount of new air..
  • Clean rooms with uni-directional air flow (laminar air flow, or ultra-clean rooms).

Another characteristic of clean rooms involves the type of finishing on the inside surfaces. Clean rooms are built with materials which do not generate particles and which are easy to clean. Surfaces are designed to be easily accessible for cleaning purposes, and do not hold dust or dirt. Clean rooms have smooth flooring and flush lighting.

Contamination protection

Clean rooms are used to protect a product from contamination. And yet, there are frequently processes which involve toxic chemical products or dangerous bacteria which have to be controlled in the clean environment. This is the case for example in the pharmaceutical industry, where highly active products such as hormones must not come into contact with the operator. There are other examples, such as in the biotechnology industry, where each zone must confine certain micro-organisms produced by genetic engineering. Microbiology laboratories which work on infectious micro-organisms must protect personnel from infection. Clean rooms can therefore contain protected zones within their controlled environment.

Contamination is also impacted by particles emitted from machines and people inside the room. People working in clean rooms wearing unsuitable clothing such as lab jackets produce an average of 2 million 0.5-micron particles, 300,000 5-micron particles and 160 bacteria every minute. When clean room workers are dressed in clean room suits, which include coveralls, booties and mob caps made of dense mesh weave, emission of 0.5 and 5-micron particles is reduced by 50 to 88 %, and bacterial contamination is reduced by 92 %.