### 2.3.4 Cleanliness

Dust poses a significant hazard to the equipment. Dust on the enclosure causes electrostatic adhesion, leading to poor contact of the metallic joints. Electrostatic adhesion is more likely to occur in an indoor environment with relatively low humidity, not only affecting the service life of the equipment, but also causing communication faults. The following table lists the requirements for dust concentration and particle size in the equipment room.

Table2-3 Requirements for Dust

Particle Diameter | Unit | Concentration
≥ 0.5 μm | Particles/m3 | ≤ 3.5 x 106
≥ 5 μm | Particles/m3 | ≤ 3 x 104

Apart from dust, there are also requirements on the salt, acid, and sulfide in the air of the equipment room. These harmful substances will accelerate metal corrosion and component aging. Therefore, the equipment room should be properly protected against harmful gases, such as sulfur dioxide, hydrogen sulfide, nitrogen dioxide, chlorine gas, and so on. The following table lists the limits on harmful gases.

Table2-4 Requirements for Gases

Gas | Average (mg/m3) | Maximum (mg/m3)
Sulfur dioxide (SO2) | 0.3 | 1.0
Hydrogen sulfide (H2S) | 0.1 | 0.5
Nitrogen dioxide (NO2) | 0.5 | 1.0
Chlorine gas (CI2) | 0.1 | 0.3

Note

Average refers to the average value of harmful gases measured in a week. Maximum refers to the upper limit of harmful gases measured in a week for up to 30 minutes every day.