Upper Limit of the Cleanliness Class (Upper class limit of the cleanliness class)

The air cleanliness class is used to distinguish the degree of air cleanliness, and is determined by the maximum allowable number of particles per cubic meter (or, when necessary, per liter) of air. This maximum allowable particle number is called the upper class limit of the cleanliness class.

[Reference] Since the pattern of particle distribution on log-log paper was mastered, the U.S. standard adopted the method of drawing parallel lines on log-log paper to establish cleanliness classes for different types of locations.

[Reference] U.S. standard (Table 1.2).

Table 1.2 U.S. Federal Standard 209E

Class Class Upper concentration limit of the class Upper concentration limit of the class Upper concentration limit of the class Upper concentration limit of the class Upper concentration limit of the class Upper concentration limit of the class Upper concentration limit of the class Upper concentration limit of the class Upper concentration limit of the class Upper concentration limit of the class
0.1μm 0.1μm 0.2μm 0.2μm 0.3μm 0.3μm 0.5μm 0.5μm 5μm 5μm
Per unit volume Per unit volume Per unit volume Per unit volume Per unit volume Per unit volume Per unit volume Per unit volume Per unit volume Per unit volume
SI units English units m³ ft³ m³ ft³ m³ ft³ m³ ft³ m³ ft³
M1 350 9.91 75.7 2.14 30.9 0.875 10.0 0.283 — —
M1.5 1 1 240 35.0 265 7.50 106 3.00 35.3 1.00 — —
M2 3 500 99.1 757 21.4 309 8.75 100 2.83 — —
M2.5 10 12 400 350 2 650 75.0 1 060 30.0 353 10.0 — —
M3 35 000 991 7 570 214 3 090 87.5 1 000 28.3 — —
M3.5 100 — — 26 500 750 10 600 300 3 530 100 — —
M4 — — 75 700 2 140 30 900 875 10 000 283 — —
M4.5 1 000 — — — — — 35 300 1 000 247 7.00
M5 — — — — — 100 000 2 830 618 17.5
M5.5 10 000 — — — — — 353 000 10 000 2 470 70.0
M6 — — — — — 1 000 000 28 300 6 180 175
M6.5 100 000 — — — — — 3 530 000 100 000 24 700 700
M7 — — — — — 10 000 000 283 000 61 800 1 750

Note: The particle counts in the table all refer to particles ≥ the indicated particle size. [Reference] China's national standards and ISO standards (Table 1.3).

Table 1.3　National Standard GB50073-2001 and International Standard ISO14644-1

Class Class limit Class limit Class limit Class limit Class limit Class limit
0.1μm 0.2μm 0.3μm 0.5μm 1.0μm 5.0μm
m³ m³ m³ m³ m³ m³
1 10 2
2 100 24 10 4
3 1 000 237 102 35 8
4 10 000 2 370 1 020 352 83
5 100 000 23 700 10 200 3 520 832 29
6 1 000 000 237 000 102 000 35 200 8 320 293
7 352 000 83 200 2 930
8 3 520 000 832 000 29 300
9 35 200 000 8 320 000 293 000

Note: The particle counts in the table all refer to particles ≥ the indicated particle size.

[Reference] The Institute of Environmental Sciences (IES) of the United States, the developer of the U.S. Federal Standard FS209, has repeatedly emphasized and noted in the standard that class limits do not necessarily represent the particle size distribution in any specific situation, because the quantitative distribution of dust particles of different sizes in the air depends on many factors, such as the density, shape, and volume of the dust particles, the airflow state they are in, the height of the location above the ground, the energy they receive (kinetic, thermal, electromagnetic), and the viscosity of the air. Since the nature of indoor and outdoor dust sources, the particle size distribution and emission rates of the particles released, and the airflow states are different, the particle size distributions of indoor and outdoor aerosol particles also differ.