ISO Classification of Particulate Matter in Air and PEC or Secondary Engineering Controls
| ISO class | Particle count/m3 of air | PEC or secondary engineering controls |
| 3 | 35.2 | |
| 4 | 352 | |
| 5 | 3,520 | PEC |
| 6 | 35,200 | |
| 7 | 352,000 | Buffer area, secondary engineering control |
| 8 | 3,520,000 | Anteroom, radionuclide generator elution |
| Unclassified | Ambient room air | Segregated radiopharmaceutical processing area |