Cleanroom certification and testing

A cleanroom is only as good as its last test. Certification is the process of measuring a cleanroom's performance against its specified class and design criteria, and documenting the results. It is done when a cleanroom is first built, at regular intervals afterward and after significant changes.

The core standards are ISO 14644-1, which defines classification by particle concentration, and ISO 14644-3, which describes test methods. Regulated industries add their own requirements, such as EU GMP Annex 1 for sterile pharmaceuticals, USP 797 and the NAPRA model standards for pharmacy compounding and the Canadian Biosafety Standard for containment labs. This guide explains what is tested, how and when.

The tests

ISO 14644-3 describes a range of test methods. Not every cleanroom needs every test; the specification or regulatory framework determines which apply.

Order matters

Tests are performed in a logical sequence because later tests depend on earlier ones. A typical sequence is:

1. Visual inspection of construction, sealing, filter housings and cleanliness.
2. Airflow volume and velocity, after the HVAC system has been balanced.
3. Installed filter leak testing, since leaking filters will distort particle counts.
4. Pressure differentials, with airflows set.
5. Airflow visualization to confirm patterns.
6. Particle count classification in the specified occupancy state.
7. Recovery testing and other optional tests.
8. Temperature and humidity checks where specified.

Running particle counts before airflow and filters are verified wastes time if the room then needs adjustment.

Occupancy states

ISO 14644-1 recognizes three states: as-built, at-rest and operational. Initial certification of a new cleanroom is often done as-built or at-rest, with operational testing once production starts. Regulated facilities generally require testing in both at-rest and operational states. GMP facilities perform operational testing during simulated or actual operations, including aseptic process simulations.

The report must state which state was tested. A room certified at rest has not been shown to meet its class with people working in it.

Key test methods in more detail

Airflow

For non-unidirectional rooms, airflow is measured at each filter or diffuser, usually with a flow hood or by velocity traverse, and summed to calculate air changes per hour. For unidirectional zones, velocity is measured on a grid of points, typically 150 to 300 mm (6 to 12 in.) below the filter face or at the work height, and averaged. Uniformity, often within plus or minus 20 percent, is calculated. Instruments should be calibrated and traceable, using the same practices described in air balancing procedures and instruments.

Filter leak test

A challenge aerosol is introduced upstream and the downstream face and seal of each filter are scanned with an aerosol photometer or particle counter. A common acceptance criterion for HEPA filters is a leak no greater than 0.01 percent of upstream concentration. See HEPA and ULPA filter systems.

Particle counts

Sample locations are determined from the table in ISO 14644-1:2015 Annex A based on room area. Each location is sampled for a volume large enough to give statistically meaningful counts, and each location's average must be at or below the class limit. The ISO 14644 classification guide explains the method.

Airflow visualization

Smoke or fog is released at critical points and the flow observed and often video recorded. The goal is to confirm that air sweeps away from critical areas, that no reverse flow occurs at doors and that equipment does not create dead zones.

Recovery

The room is contaminated with an aerosol, and the time for particle concentration to fall by a factor of 100 is measured. See cleanroom recovery and contamination control testing.

How often to re-certify

Re-certification intervals depend on the standard and the risk.

All frameworks also require re-testing after significant changes, such as filter replacement, HVAC modifications, room reconfiguration or prolonged shutdowns.

Instrument calibration

Particle counters must be calibrated to ISO 21501-4, typically annually. Aerosol photometers, velocity meters, flow hoods and pressure gauges also need current calibration traceable to national standards. Calibration certificates should be included in or referenced by the report.

The certification report

A good report includes:

• Facility and room identification, with a floor plan showing sample locations.
• The standard and edition tested to, and the specified class, particle sizes and occupancy state.
• Test methods and acceptance criteria for each test.
• Raw data and calculated results.
• Pass or fail for each test and room.
• Instrument identification and calibration dates.
• Deviations, failures, corrective actions and retest results.
• Tester identification and qualifications.

Organizations such as NEBB and CETA publish procedural standards and training for cleanroom testing, and owners may require testers qualified under one of these programs.

Common failures and causes

• Particle counts too high: leaking filters, inadequate airflow, poor return locations, construction dust, room not cleaned before testing, or too many people present.
• Filter leaks: damaged media, poorly seated gaskets, damaged gel seals or leaks at housing joints.
• Pressure differentials out of range: changed airflows, door undercuts, unsealed penetrations or controls drift.
• Non-uniform unidirectional flow: unbalanced fan filter units, obstructed plenum or damaged diffusers.
• Slow recovery: low air change rate or poor mixing.

Key takeaways

• Certification measures cleanroom performance against ISO 14644-1 and ISO 14644-3, plus industry-specific requirements.
• Test in sequence: airflow and filter integrity before pressure, visualization and particle counts.
• Always state and test the required occupancy state; at-rest results do not prove operational performance.
• Re-certification intervals range from six months (GMP Grade A and B, USP 797) to annual, plus after significant changes.
• Calibrated instruments and a complete report are essential for regulatory and quality purposes.