Standard clean room

The International Standards Organization (ISO) has defined standards for  international standards clean rooms. The first standard of a clean room is dust content, ie the content of dust particles suspended in the air is controlled (of course, the dust must be cleaned up). If you imagine an image, the diameter of a human hair is about 100μm, the dust in the room can be from 0.5 to 50μm in diameter.
✔ The ISO 14644-1 standard was released in 1999 called “Classification of air cleanliness”. The clean room type is specified based on the expression: Cn=10N[0,1D]2,08
with:
– Cn¬ maximum concentration limits (particles/m3) of suspended dust in air greater than or equal to the size considered.
– N is an ISO classification index, does not exceed 9 and the minimum permitted index is 0.1
– D is the particle diameter calculated by μm
0,1 here is the constant with the dimension being μm.
Thus, it is easy to determine the dust concentration limits from the above formula and easily classify each clean room level 
✔Class 8 (3,520,000 particles size 0,5 micron in one cubic meter of air)
Commonly applied to a computer room. In addition to restricting access and being pressurized, special clothing or special procedures are not needed..
✔Class 7 (352,000 particles size 0,5 micron in one cubic meter of air)
Commonly applied in hospital operating rooms. Some types of plants use this clean room level. Clean clothes, hoods and shoes are required. Air enters the room through HEPA filters. (High particle accumulation efficiency). Restricting access. Room is using strong pressure and related to the surrounding space.
✔Class 6 (35,200 particles size 0,5 micron in one cubic meter of air)
Commonly used in disc production factory or computer hardware or other sensitive materials. There are also rules when using such as a clean room at level 7 but workers must wear gloves and a full hood as part of a clean room wardrobe. More frequent air changes in the room. Again, all the air is constantly being filtered through HEPA filters and the amount of air change per hour is huge.
✔Class 5 (3,520 particles size 0,5 micron in one cubic meter of air)
Commonly used for semiconductor-intensive plants such as computer memory production. It is also used in pharmaceutical manufacturing technology. Same rules as above, but more stringent. With a clean room of this level it is required to use a full body mask.

✔ Level 4 and beyond (352 and fewer particle size 0,5 micron in one cubic meter of air)
Especially good for use in large semiconductor fabrication areas where even a small pollution will cost a lot. Workers are required to wear full clean room clothes with masks. Breathing is done through a mask to filter workers’ breath and avoid breathing of polluted air in the space.