Cleanliness refers to the degree of dust content in the air environment. In general, it refers to the number of particles of a certain size or larger contained in a unit volume of air. High dust content leads to low cleanliness, while low dust content leads to high cleanliness.

Cleanliness standard

Basically, it is based on the various versions of the US standard FS-209, with only changes or alterations in the unit system and naming methods. In terms of naming, it can be basically divided into two categories: one is directly named or named with symbols based on the number of particles with a specified particle size or larger per unit volume of air. This naming method is represented by the US FS-209A-E version, which specifies a particle size of 0.5 μ m. The concentration of particles with a particle size ≥ 0.5 μ m in the air is directly named using the imperial system pc/ft3, such as the 100 level standard, which means that the concentration of particles with a particle size ≥ 0.5 μ m in the air is 100pc/ft3, and the number of particles with a particle size ≥ 0.5 μ m in each cubic foot of air is 100. The second is to represent the number of particles with a diameter of ≥ 0.1 μ m per unit volume of air as 10n, and name the level of air cleanliness according to the index n. This naming method is represented by Japanese JISB9920, which specifies a particle size of 0.1 μ m, and the concentration of particles with a diameter of ≥ 0.1 μ m in the air (using the International System of Units) of 10pc/m3 is named as level n.

Cleanliness level

The relationship between cleanliness level and concentration is as follows:

In the formula, N represents the cleanliness level, and the number does not exceed 9. The middle number between cleanliness levels can be increased by 0.1 as the minimum allowable increment;
D – Particle size to be controlled, μ m;

Greater than or equal to the maximum allowable concentration (maximum concentration limit) required to control particle size, pc/m3 (particles/m3), rounded to nearest integer, with no more than 3 significant digits.
For example, in a Level 5 cleanroom, the maximum concentration limit for particles ≥ 0.5 μ m is approximately 3520pc/m3. Due to the origin of clean technology in the United States, the earliest standards were based on the imperial system. The cleanliness level of the imperial system is named based on the imperial concentration of particles ≥ 0.5 μ m. For example, a cleanroom with an allowable concentration of 100pc/ft3 (approximately 3520pc/m3) for particles ≥ 0.5 μ m is referred to as Class 100 cleanroom. In 1984, China’s “Code for Design of Cleanrooms” also used English grade names – Grade 100, Grade 1000, Grade 10000, and Grade 100000, which are still used in engineering. The above four levels are similar to levels 5, 6, 7, and 8 in the GB50072-2001 standard. The lower the cleanliness level of the clean room, the higher the level. Cleanrooms of the same level can control the concentration of 1-2 particle sizes according to process requirements. For example, a Level 6 cleanroom may require a particle concentration of no more than 35200pcs/m3 for particles ≥ 0.5 μ m and no more than 293pc/m3 for particles ≥ 5 μ m.

Monitoring and Management System

The use of clean areas:

(1) Personnel entering the clean area should receive regular training on basic knowledge of microbiology, hygiene, and clean operations;
(2) Personnel entering and exiting the clean area must follow the corresponding level of clean area entry and exit standard operating procedures;
(3) The standard operating procedures for personnel entering and exiting the clean area in each workshop should specify the limit of the number of people entering the clean area and strictly implement it; (4) All materials, equipment, etc. used in the clean area must be cleaned according to the prescribed procedures. Items entering the clean area should be cleaned and processed outside the area, and then enter the area through the transfer window;
(5) The air conditioning in the clean area should be continuously operated. After production is completed, the air conditioning system should continue to operate for 4 hours before stopping. The system must be disinfected before it can be restarted;
(6) Waste should be stored in specialized containers, cleaned up in a timely manner every day, and sent out of the window through the transfer window.

Monitoring of clean areas:

(1) To ensure the purification environment and cleanliness of the clean area, regular monitoring of the clean area is necessary;
(2) If the following situations are found, the high-efficiency air filter should be replaced; a. Airflow velocity ≤ 0.25m/s, even after replacing the primary and medium efficiency air filters, the airflow velocity cannot increase; b. The high-efficiency air filter has irreparable leakage.

Maintenance of clean area:

(1) The clean area should be equipped with safety measures such as safety doors, emergency lights, and alcohol specific cabinets;
(2) The management of clean areas should have records;
(3) In addition to daily personnel management, the air conditioning system and air purification equipment in the clean area should be overhauled once a year. If any abnormal situations occur during production, they should be promptly repaired and verified after the overhaul.

Cleanliness testing

Empty state test: The clean room has been completed, the purified air conditioning system is in normal operation, and the test is conducted without any process equipment or production personnel in the room.
Static testing: The clean room purification air conditioning system is in normal operation, the process equipment has been installed, and there are no production personnel in the room for testing.
Dynamic testing: The clean room has been tested under normal production conditions. The detection of air volume, wind speed, positive pressure, temperature, humidity, and noise in the clean room can be carried out in accordance with relevant general and air conditioning regulations.

Cleanliness testing method

The testing method for air cleanliness in clean work areas should use the light scattering particle counting method for counting dust particles with a particle size greater than or equal to 0.5 microns. For dust particles with a particle size greater than or equal to 5 microns, the membrane microscope counting method can also be used.