|
Class limits (maximum allowable particles) |
ISO |
FED
STD 209 |
0.1 µm |
0.2 µm |
0.3 µm |
0.5 µm |
5.0 µm |
| CLASS
3 |
1 |
1000
/ 35 |
|
|
35 / 1 |
|
| CLASS
4 |
10 |
10,000 / 345 |
75 |
30 |
352 / 10 |
0 |
| CLASS
5 |
100 |
100,000 / 3,450 |
750 |
300 |
3520 / 100 |
0 |
| CLASS
6 |
1,000 |
1,000,000 / 34,500 |
N/A |
N/A |
35,200 / 1,000 |
7 |
| CLASS
7 |
10,000 |
345,000 |
N/A |
N/A |
352,000 / 10,000 |
70 |
| CLASS
8 |
100,000 |
3,450,00 |
N/A |
N/A |
3,520,000 / 100,000 |
700 |
ISO 14644-1 (per cubic meter)
Fed Std. 209 E USA (per cubic foot)
ISO standard requires results to be shown in cubic meters (1 cubic meter = 35.314 cubic feet)
Class 1
- 540 to 600+ air changes per hour (98%+ ceiling coverage)
- ULPA filters (99.9995% on .12 microns)
- Gel/Flush grid ceiling systems with raised floors are required
- Outside/makeup air to be prefiltered with a HEPA filter
Class 10
- 540 to 600 air changes per hour (85-90% ceiling coverage)
- 99.999% on 0.3 microns, with a raised floors
- 90%+ coverage with low wall returns
- Gasketed grids with negative plenums acceptable
- HEPA filters on makeup air
Class 100
- 400 to 480 air changes per hour (60-80% ceiling coverage)
- 99.99% HEPA filters
- Raised floor assures optimal performance. Low wall returns work when they are no further than 12' from the center of the room¹
- Gasketed ceiling grid
Class 1,000
- 120 to 150 air changes per hour (40-50% ceiling coverage)
- 99.99% HEPA filter
- Gasketed ceiling grid
- Raised floor delivers best performance, but low wall returns are very common¹
Class 10,000
- 45 to 60 air changes per hour (10-20% ceiling coverage)
- 99.97% or 99.99% HEPAs
- Low wall or ceiling returns acceptable in most applications¹
Class 100,000
- 20 to 30 air changes per hour (5% ceiling coverage)
- HEPA filters or 95% HEPAs (95%+ ASHRAE box filters²) located downstream of the HVAC unit
- Heat load may require more air changes
1. Room layout with equipment must be evaluated to look for return air paths and possible cross contamination.
2. 95% ASHRAE filters when new may only be 70% and could affect the particle level.
Important point to consider concerning filter coverage
A 300 sq. ft. cleanroom may need 90% coverage (38 HEPAs) for Class 100 at the "operational" mode, 60% coverage (23) in the "at rest" mode, and only 40% (15) to meet Class 100 at "as built". The same rules can and do apply to Class 1,000 and Class 10,000 levels.
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