Particle count & air changes per hour?

Particle Count and Air Changes Per Hour

Particle Count

Measure of airborne particles in a cleanroom, typically expressed as:

1. Particles per cubic meter (particles/m³)
2. Particles per cubic foot (particles/ft³)

ISO 14644-1 Classification

| ISO Class | Particle Count (particles/m³) |
| — | — |
| ISO 1 | ≤10 (0.1 μm), ≤2 (0.2 μm) |
| ISO 2 | ≤100 (0.1 μm), ≤20 (0.2 μm) |
| ISO 3 | ≤1,000 (0.1 μm), ≤100 (0.2 μm) |
| ISO 4 | ≤10,000 (0.1 μm), ≤1,000 (0.2 μm) |
| ISO 5 | ≤100,000 (0.1 μm), ≤10,000 (0.2 μm) |
| ISO 6 | ≤1,000,000 (0.1 μm), ≤100,000 (0.2 μm) |
| ISO 7 | ≤10,000,000 (0.1 μm), ≤1,000,000 (0.2 μm) |
| ISO 8 | ≤100,000,000 (0.1 μm), ≤10,000,000 (0.2 μm) |
| ISO 9 | Not defined |

Air Changes Per Hour (ACH)

Number of times the air in a cleanroom is replaced with filtered air:

1. Calculated: Room volume (m³) / Airflow rate (m³/h)
2. Typical ranges: 10-600 ACH

Relationship Between Particle Count and Air Changes

1. Higher ACH: Lower particle counts
2. Lower ACH: Higher particle counts

Grade A-D Areas Air Changes

1. Grade A: 100-600 ACH
2. Grade B: 50-200 ACH
3. Grade C: 10-50 ACH
4. Grade D: 2-10 ACH

Factors Influencing Air Changes

1. Room size and layout
2. Airflow rate and filter efficiency
3. Occupancy and activity level
4. Equipment and process-generated particles
5. Temperature and humidity control

By controlling particle count and air changes, cleanrooms maintain optimal environmental conditions for sensitive industries.