Particle Count Test in Pharmaceutical Cleanrooms
A practical guide to non-viable airborne particle testing, cleanroom classification, sampling plans, acceptance limits, and routine monitoring.
The particle count test in pharmaceutical cleanrooms provides objective evidence of airborne particulate cleanliness. It helps confirm that a room or clean zone is suitable for its intended use and can reveal deterioration in filtration, airflow, cleaning, equipment condition, or personnel practices. The result is meaningful only when the room state, particle sizes, sampling locations, and acceptance criteria are defined before testing.
A particle counter does not tell you whether a detected particle is a fiber, powder, skin flake, or microorganism. That distinction matters: non-viable particle testing is one part of contamination control, alongside viable environmental monitoring, cleaning, personnel controls, and qualified HVAC performance. This article explains how to plan and interpret the test within a broader cGMP system.
What is a cleanroom particle count test?
A cleanroom particle count test is a measurement of the concentration of airborne particles equal to or larger than selected particle sizes in a defined volume of air. Portable or installed optical particle counters draw air through a sensing chamber. As particles pass through a light beam, the instrument estimates their size and counts them in configured size channels.
Results are normally expressed as particles per cubic metre (particles/m³) or particles per cubic foot (particles/ft³). Pharmaceutical cleanroom classifications commonly use threshold sizes such as 0.5 µm and 5.0 µm, subject to the applicable standard and grade requirements.
Why particle counting matters in pharmaceutical facilities
Particle-count results should be interpreted with the room’s intended use and contamination-control strategy. For sterile processing, a particle classification result alone cannot demonstrate microbiological control or assure sterility.
Particle classification: ISO classes and GMP grades
ISO 14644-1 classifies air cleanliness by airborne particle concentration at defined particle sizes. It is a classification standard, not a complete pharmaceutical GMP program. The ISO scope concerns airborne particles with threshold sizes from 0.1 µm to 5 µm; it does not characterize their physical, chemical, radiological, or viable nature.
Pharmaceutical sterile manufacturing may also use GMP grades, such as Grades A to D, with specified at-rest and in-operation particle limits. Do not treat an ISO class and a GMP grade as interchangeable labels without confirming the applicable requirements and room state. FDA explains that ISO 14644 classifications are useful for non-viable particle cleanliness, but aseptic facilities should not rely on ISO classification alone because sterile manufacturing has additional microbiological and operational considerations.
Illustrative airborne particle limits used in EU GMP Annex 1
The table below summarizes the familiar Annex 1 maximum concentrations for sterile cleanroom grades, in particles/m³. Confirm the current applicable Annex and its definitions before writing or approving a protocol. Grade D in-operation limits are not predefined in the table and should be established by the manufacturer based on risk and routine data.
| Grade | At rest ≥0.5 µm | At rest ≥5.0 µm | In operation ≥0.5 µm | In operation ≥5.0 µm |
|---|---|---|---|---|
| A | 3,520 | 20 | 3,520 | 20 |
| B | 3,520 | 29 | 352,000 | 2,900 |
| C | 352,000 | 2,900 | 3,520,000 | 29,000 |
| D | 3,520,000 | 29,000 | Not predefined | Not predefined |
At rest versus in operation
The test state changes the meaning of the result:
- At rest: The room is complete and operational, with equipment installed and running as specified, but without personnel present. The exact definition should follow the applicable standard or GMP annex.
- In operation: The room is functioning in its normal production configuration, with the defined personnel, equipment, and activities present.
A room may pass at rest and show higher counts during operation because people, materials, and process activity generate or resuspend particles. In-operation sampling should therefore represent actual or justified worst-case activity without creating unnecessary risk to the operation.
How to perform a particle count test
1. Approve the protocol and define the objective
State whether the study is for initial classification, requalification, an investigation, or routine monitoring. Identify the room boundaries, classification target, particle sizes, room state, equipment, sampling plan, and acceptance criteria. Link the test to the facility’s HVAC validation and qualification lifecycle.
2. Verify the particle counter
Before use, confirm the counter is suitable for the required size range and flow rate, has current calibration, passes the required operational checks, and has adequate battery or power. Check the sampling probe, tubing, instrument zero-count status where applicable, and data export or printout settings.
Use a probe and tubing arrangement suitable for the particle sizes being measured. Long or sharply bent tubing can affect particle transport, especially for larger particles. Document counter ID, calibration due date, flow rate, software or firmware information when relevant, and any accessories used.
3. Prepare the cleanroom
- Confirm cleaning is complete and the room has reached the defined stabilization or recovery period, if required by the protocol.
- Record room state, HVAC status, differential pressure, doors, equipment state, personnel, and production activity.
- For at-rest classification, ensure the room is unoccupied and meets the stated at-rest definition.
- For in-operation sampling, use trained personnel and avoid disrupting aseptic or critical operations.
4. Select representative sampling locations
Determine locations according to the applicable classification standard and risk assessment. Consider room area, layout, process exposure points, airflow patterns, work height, equipment, doors, and locations where contamination could threaten product. Add justified locations around critical operations where an overall room classification sample alone would not represent local risk.
Document a marked floor plan or location list. Each point should have a unique ID and a defined probe position or height so that repeat tests are comparable.
5. Collect samples using the defined volume and sequence
At each location, sample the required volume at the counter’s validated flow. Use a consistent sequence and avoid placing the probe where it samples directly from a diffuser unless that is the intended test point. For in-operation sampling, record what was happening when each sample was taken.
Follow the standard’s sample-volume and location rules; do not substitute an arbitrary short sample for the required classification method. Where the counter reports concentration directly, preserve the raw particle counts and instrument output along with the calculated result.
Particle concentration = number of particles counted ÷ sampled air volumeExample: 120 particles counted in 0.0283 m³ of air = approximately 4,240 particles/m³.
6. Review data and determine pass or fail
Compare results to the pre-approved classification limits at each required location and size threshold. Apply any statistical evaluation required by the governing classification standard. Do not average away an individual failing location unless the standard explicitly permits that calculation and the protocol defines it in advance.
Review unusual particle-size distributions, abrupt spikes, instrument alarms, missing records, and differences between at-rest and operational results. The report should provide enough data for an independent reviewer to reproduce the conclusion.
Sampling plan and location selection
The number and placement of sampling locations depend on the applicable standard, cleanroom area, process risk, and study purpose. A sound plan should combine the minimum standard-based locations with additional points justified by risk. Consider:
- Where exposed product, components, or product-contact surfaces are handled.
- Locations near operators, material transfer, open equipment, and interventions.
- Air supply and return locations, airflow direction, and potential dead zones.
- Room geometry, equipment obstruction, and recurring maintenance or cleaning issues.
- Whether the purpose is classification, trending, or an investigation of a specific event.
Sampling locations should be representative of the room and its airflow system; ISO 14644-1 includes a defined approach for selecting classification locations.
Classification versus routine particle monitoring
| Feature | Classification test | Routine monitoring |
|---|---|---|
| Purpose | Assign or confirm a cleanliness class in a defined state | Detect trends and conditions that may affect ongoing control |
| Plan | Follows the selected classification standard and its location/sample rules | Risk-based points, frequency, and operating conditions from the contamination control strategy |
| Result use | Pass/fail against classification limits | Trend review, alert/action evaluation, investigations, and process oversight |
| Frequency | Initial qualification and periodic or change-triggered requalification as defined | Defined by risk, process exposure, monitoring strategy, and historical performance |
Classification demonstrates a room’s airborne particulate class under specified conditions. Routine monitoring asks whether the facility remains in a state of control during actual operations. One cannot replace the other.
Non-viable particle counts are not microbial results
A non-viable particle counter measures particles, not whether they are alive. A particle may be inert, biological, or a carrier of microorganisms, but the counter cannot identify that from optical size data. Viable monitoring requires appropriate microbiological methods such as active air sampling, settle plates, or surface sampling as defined by the site program.
For sterile manufacturing, integrate particle-count data with viable monitoring, personnel monitoring, process simulations, airflow visualization, cleaning, and the Contamination Control Strategy. FDA notes that ISO classification should not be the sole basis for aseptic facility qualification because it does not address all microbiological concerns of sterile manufacture.
Common causes of elevated particle counts
- High personnel traffic, poor gowning practice, or excessive movement.
- Cleaning residues, incomplete cleaning, or resuspension from floors and surfaces.
- Damaged, poorly seated, or leaking HEPA filters and seals.
- Incorrect air balance, reduced airflow, blocked diffusers, or altered pressure cascade.
- Construction, maintenance, packaging debris, or uncontrolled material transfer.
- Particle counter setup problems, contaminated tubing, probe disturbance, or poor handling.
Trending by size channel, location, room state, shift, and activity can help distinguish a room-control issue from a one-off sampling artifact.
What to do when a result exceeds a limit
- Secure the original instrument record and verify the sample location, volume, size channel, time, and room state.
- Check the particle counter’s status, calibration, zero check, probe, tubing, and handling conditions.
- Review adjacent locations, HVAC alarms, pressure differentials, filter integrity, cleaning records, and activity at the time.
- Assess the potential impact on exposed product, components, or critical operations with Quality and process owners.
- Repeat sampling only when scientifically justified and documented; a passing retest does not erase an initial valid failure.
- Open a deviation and initiate investigation or CAPA when required by the quality system.
Use the approved SOP to define responsibilities, escalation, product impact, and documentation. Ensure raw records remain complete and attributable in line with ALCOA+ data integrity principles.
Particle count test report: essential contents
- Protocol number, room name/ID, classification target, date, and personnel.
- Applicable standard or GMP requirement and its edition/version.
- Room state: at rest, in operation, or other specifically defined state.
- Particle counter manufacturer, model, serial number, calibration status, flow rate, and probe/tubing details.
- Sampling-point diagram, location identifiers, sample volume, duration, and particle size channels.
- Raw particle counts, calculated concentrations, and any required statistical analysis.
- Acceptance criteria, deviations, invalid samples, retests, and rationale for exclusions.
- Conclusion, reviewer approvals, and required follow-up actions.
Key takeaways
- A particle count test measures airborne non-viable particles by size and concentration.
- ISO classification and pharmaceutical GMP grades are related but not interchangeable; state and jurisdiction matter.
- Classification testing and routine monitoring have different objectives and sampling strategies.
- Particle counts do not identify organisms or prove microbial control.
- Use calibrated counters, justified representative locations, pre-approved criteria, and complete raw-data records.
- Investigate valid excursions; do not dismiss a failure solely because a later sample passes.
Conclusion
A well-designed particle count test in pharmaceutical cleanrooms does more than produce a pass/fail number. It verifies airborne cleanliness under a defined room state, supports a credible classification, and provides useful evidence for ongoing contamination control. The strongest program combines an appropriate ISO or GMP framework, calibrated particle counters, risk-based sampling locations, in-operation understanding, microbiological monitoring where applicable, and disciplined excursion investigations.
Frequently asked questions
1. What does a particle count test measure?
It measures the number or concentration of airborne particles at or above selected size thresholds in a known volume of air. It does not identify particle composition or viability.
2. Which particle sizes are counted in pharmaceutical cleanrooms?
Common classification thresholds include 0.5 µm and 5.0 µm, but the applicable sizes depend on the classification scheme, room grade, and current regulatory requirements.
3. What is the difference between ISO classification and GMP grading?
ISO 14644-1 classifies airborne cleanliness by particle concentration. GMP grades add pharmaceutical manufacturing context, including room state and contamination-control expectations. They should not be assumed equivalent without checking the applicable requirements.
4. What does “at rest” mean in particle counting?
At-rest testing is performed when the room is complete and operating as specified, with no personnel present. Follow the exact definition in the applicable standard or GMP annex and approved protocol.
5. What does “in operation” particle counting mean?
It means sampling while the room is functioning in a defined production configuration, with specified personnel, equipment, and activities present.
6. Does a particle count test detect bacteria?
No. A non-viable particle counter reports optical particle sizes and counts. It cannot determine whether a particle contains or supports a living microorganism; microbiological methods are needed for viable monitoring.
7. How often should cleanrooms undergo particle classification?
Requalification frequency should follow applicable requirements and the site’s approved program. Risk, classification, room performance, changes, and historical trends can affect the schedule.
8. Can a cleanroom pass at rest but fail during operation?
Yes. Personnel, equipment, and process activity can increase particle generation or resuspension. That is why the test state must match the classification requirement and actual room use.
9. What should be done after an out-of-limit particle result?
Preserve the original data, verify instrument and sampling conditions, investigate room and process factors, evaluate product impact, and document the event through the quality system. Retesting should have a documented scientific rationale.
10. Can routine environmental monitoring replace cleanroom classification?
No. Classification and routine monitoring serve different purposes. Classification verifies a cleanliness class under defined conditions; monitoring evaluates ongoing control during operations.
- ISO 14644-1:2015 — Cleanrooms and associated controlled environments: Classification of air cleanliness by particle concentration
- U.S. FDA — Questions and Answers on CGMP: production and process controls, including use of ISO cleanroom classifications
- U.S. FDA — Sterile Drug Products Produced by Aseptic Processing: Current Good Manufacturing Practice
- European Commission — EudraLex Volume 4, EU Guidelines for Good Manufacturing Practice
Educational content only. Confirm the current applicable standard, regulatory annex, and approved site procedures before using limits or procedures in a GMP protocol.
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