Cleanroom Class Limit

Cleanroom Class Limits

Class limits (maximum allowable particles)

ISO FED STD 209E 0.1 µm 0.3 µm 0.5 µm 5.0 µm
CLASS 3 1 1,000 / 35 102 / 3 35 / 1
CLASS 4 10 10,000 / 350 1,020 / 30 352 / 10 0
CLASS 5 100 100,000 / 3,500 10,200 / 300 3,520 / 100 0
CLASS 6 1,000 1,000,000 / 35,000 102,000 / N/A 35,200 / 1,000 7
CLASS 7 10,000 350,000 N/A 352,000 / 10,000 70
CLASS 8 100,000 3,500,000 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)

  • 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
  • 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
  • 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
  • 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
  • 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
  • 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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