What is a Cleanroom? Classification under ISO 14644 and GMP A/B/C/D

The "cleanroom" concept has long featured in Vietnamese industry — alongside FDI pharma and electronics plants. But not everyone understands how a cleanroom differs from an enclosed room, or what A/B/C/D and Class 100/1,000/10,000 actually mean. This article gives the fullest and most accessible overview of the definitions, classifications, and characteristics of modern cleanrooms.

1. What is a cleanroom?

In plain terms, a cleanroom is a room that is not dirty — no dust, no bacteria — while also controlling temperature, humidity, and pressure.

That said, the term "cleanroom" means different things in different industries and environments. For example:

• Healthcare (hospitals): operating rooms, negative-pressure isolation rooms.
• Pharmaceuticals: injectable compounding rooms, vaccine vial-filling rooms.
• Electronics companies: photolithography rooms, chip-assembly rooms.
• Premium food: infant-formula filling rooms, probiotic production rooms.
• Cosmetics: lipstick and cream filling rooms.

Each industry has its own standard, but all rest on two major standards systems: ISO 14644 and GMP-WHO/EU.

2. Cleanroom classification

Cleanrooms are classified along several axes:

a. By cleanliness

You can split them into:

• Absolute cleanrooms (below Class 100) — semiconductor production, vaccines, biologics.
• Relative cleanrooms (Class 100 and above) — standard pharma, food, cosmetics.

b. By function (application)

You can split them into:

• Hospital cleanrooms (OR, ICU, microbiology lab).
• Pharmaceutical cleanrooms (compounding, primary packaging).
• Electronics cleanrooms (chips, hard drives, optical pickups).
• Cosmetics cleanrooms.

c. By standard

You can split by US (FS 209E — withdrawn but still referenced), Japan (JIS B 9920), Europe (EU GMP), Germany (VDI 2083)… European standards now dominate, with cleanrooms graded A, B, C, D.

3. The ISO 14644-1 classification

This is the current international standard — classifying by the number of particles ≥ 0.5 µm per m³ of air:

ISO class	Particles ≥ 0.5 µm/m³	FS 209E equivalent
ISO 1	~10	—
ISO 2	~100	—
ISO 3	1,020	Class 1
ISO 4	10,200	Class 10
ISO 5	102,000	Class 100
ISO 6	1,020,000	Class 1,000
ISO 7	10,200,000	Class 10,000
ISO 8	102,000,000	Class 100,000
ISO 9	1,020,000,000	Ambient air

4. The GMP classification (EU GMP Annex 1)

In pharmaceuticals, GMP-WHO and EU GMP classify cleanrooms by 4 letter grades: A, B, C, D. Each grade has 2 measurement states: at rest (no people, no operating equipment) and in operation.

Grade A — High-risk operating area

• Sterile compounding and vial filling, cell-culture handling.
• Requirement: ISO 5 in both states, with laminar flow at 0.36-0.54 m/s.
• Final filter: HEPA H14 + ULPA U15/U17 inside a LAF box.

Grade B — Background to Grade A

• The area surrounding Grade A, in the same room but not directly inside the LAF.
• Requirement: ISO 5 at rest, ISO 7 in operation.
• Final filter: HEPA H14 + ULPA U15 in the FFU.

Grade C — Lower-risk area

• Non-sterile compounding, intermediate processing.
• Requirement: ISO 7 at rest, ISO 8 in operation.
• Final filter: HEPA H14.

Grade D — The lowest GMP area

• Secondary packaging, pharma warehouse.
• Requirement: ISO 8 at rest; no in-operation requirement.
• Final filter: HEPA H13.

5. Common cleanroom characteristics

Whatever the grade, cleanrooms share four core characteristics:

• Very low dust, near-zero microbial counts.
• Particle control down to 0.3 µm (and lower for high-end cleanrooms).
• High airflow and recirculation — 20-60 air changes per hour depending on grade.
• Minimal influence from the outside environment — maintained by filtration + differential pressure + airlocks.

6. Technical structure of a standard cleanroom

A complete cleanroom has 7 main components:

a. Envelope

• 50-100 mm EPS / PU / rockwool sandwich panels with powder-coated or stainless surfaces.
• Gasketed airtight doors with observation windows.
• Walkable or T-grid ceilings for FFUs.

b. Floor

• Anti-static vinyl, or raised floor for vertical-laminar cleanrooms.
• Coved corners (cove) for easy cleaning.

c. HVAC system (AHU/MAU)

• Pre Filter G4 + Medium F8/F9 + HEPA (if not at the terminal).
• Cooling coil, heating coil, humidifier/dehumidifier.
• Temperature, humidity, and pressure controllers.

d. Final-stage air supply

• Terminal HEPA Box or FFU.
• Filter grade per the cleanroom requirement.

e. Return air

• Raised-floor return (for vertical laminar cleanrooms) or low-wall return slots.

f. Airlocks and anterooms

• Buffer zones between cleanroom grades, maintaining a 10-15 Pa differential.

g. Monitoring system (BMS)

• Differential-pressure, temperature, humidity, and online particle sensors.
• Threshold-based alarms.

7. Differential pressure — an inviolable principle

Each cleanroom grade must be at least 10-15 Pa higher than the less clean grade. Example GMP cascade:

Production area (D) +15 Pa → Compounding area (C) +30 Pa → Sterile area (B) +45 Pa → LAF (A) +60 Pa

This ensures dust and bacteria do not "flow back" into cleaner areas when doors open. Negative-pressure rooms (such as infectious-disease isolation rooms) work the other way — they are lower in pressure than their surroundings to keep pathogens contained.

8. Four operating variables to control

• Particles — measured with a particle counter, with thresholds per class.
• Microorganisms — measured by settle plates and air samplers (CFU/m³).
• Temperature and humidity — typically 20±2°C and 45-60% RH (industry-dependent).
• Differential pressure — continuously measured by DP sensors.

Conclusion

A cleanroom is not a "sealed box" — it is an integrated system of architecture, HVAC, filtration (Pre + Medium + HEPA / ULPA), environmental control, and operating procedure. Understanding ISO 14644 and GMP A/B/C/D properly is the first condition for designing, operating, and validating any pharma, electronics, food, or hospital cleanroom successfully.

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About Green Filter

Green Filter supplies filters for every cleanroom grade end-to-end, from ISO 8 (Class 100,000 / GMP D) to ISO 3 (Class 1): HEPA, ULPA, Medium, Pre Filters, and FFUs. Green Filter's technical team will help you design the right filter chain per room from your drawings.

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See also: GMP cleanrooms for pharma plants · Cleanrooms for electronics & semiconductors · AHU/MAU and the 3-stage filter train.