How Is Cleanroom Particle Count Testing Conducted? A Step-by-Step Field Guide
🌱 Last updated: July 28, 2026
How Is Cleanroom Particle Count Testing Conducted? A Step-by-Step Field Guide
A cleanroom can look spotless and still contain an unacceptable concentration of airborne particles.
Particles released by people, garments, equipment, packaging, maintenance work or uncontrolled air movement may be too small to see. Cleanroom particle count testing measures these airborne particles at defined locations to assess whether the room meets its specified cleanliness requirement.
However, a technically reliable cleanroom particle count testing procedure involves much more than entering the room, switching on a particle counter and taking a few readings.
The monitoring team must establish:
why the room is being tested;
which cleanliness class or acceptance criteria apply;
whether the room is as-built, at-rest or operational;
how many sampling locations are required;
where those locations should be placed;
how much air must be sampled;
whether the instrument is suitable and properly calibrated;
what activities occurred during testing; and
whether every result is technically traceable.
A particle-count value is meaningful only when its location, sample volume, room condition, instrument status and acceptance criteria are also known.
This guide explains how cleanroom or Server Room particle counting is planned, conducted, reviewed and reported, with practical observations based on the industrial environmental monitoring experience of Perfect Pollucon LLP.
What Does Cleanroom Particle Count Testing Measure?
Cleanroom particle counting measures the number of airborne particles equal to or larger than selected particle sizes within a known volume of air.
A light-scattering airborne particle counter draws air through a sampling inlet. Individual particles passing through the sensing chamber scatter light. The instrument detects these signals and classifies the particles into defined size channels.
The result may be shown as:
the raw number of particles in the sampled air;
particles per cubic metre;
particles per cubic foot;
cumulative counts at specified particle sizes; or
differential counts within individual size ranges.
ISO 14644-1:2015 classifies air cleanliness according to airborne particle concentration. For classification purposes, it covers cumulative particle populations at threshold sizes from 0.1 µm to 5 µm and uses light-scattering airborne particle counters at designated sampling locations.
Particle count testing is also commonly described as:
airborne particle counting;
non-viable particle monitoring;
cleanroom classification testing;
cleanroom particle monitoring; or
particle counter testing in a cleanroom.
The term non-viable particle count distinguishes this measurement from microbiological air sampling. A particle counter measures the physical number and size of airborne particles. It does not establish whether those particles contain living microorganisms.
Cleanroom Classification and Routine Monitoring Are Different Activities
Before planning the test, the facility and monitoring agency must determine whether the work is for formal classification or routine monitoring.
Cleanroom classification
Classification determines whether a room or clean zone complies with a specified ISO cleanliness class under a clearly defined occupancy state.
A classification exercise typically requires:
a defined cleanroom boundary;
an intended ISO class;
a documented occupancy state;
a calculated minimum number of sampling locations;
a defined sample volume;
measurements at all required locations;
comparison with the applicable class limits; and
a formal classification report.
Routine particle monitoring
Routine monitoring determines whether the cleanroom continues to perform within an established state of control after classification.
A monitoring plan may focus on:
critical production areas;
locations where products are exposed;
high-traffic zones;
material-transfer points;
areas near particle-generating equipment;
locations with recurring excursions; and
trends in particle concentration over time.
ISO 14644-2:2015 specifies minimum requirements for a monitoring plan related to cleanroom performance and airborne particle concentration.
Classification asks whether the room achieves a stated cleanliness class. Routine monitoring asks whether the room continues to perform as expected between formal classifications.
Routine readings at a few critical locations can be valuable for process control, but they should not automatically be presented as classification of the entire cleanroom.
Step 1: Confirm Why the Room Is Being Tested
A reliable test begins by defining its purpose.
Cleanroom particle counting may be required for:
initial classification of a new cleanroom;
periodic reclassification;
verification after HEPA-filter replacement;
assessment following HVAC modification;
investigation of a contamination event;
verification after shutdown or maintenance;
routine environmental monitoring;
customer qualification;
audit preparation;
process validation support; or
investigation of recurring particle excursions.
The purpose determines how the room should be prepared, where samples should be taken and how the results should be interpreted.
For example, measurements near a suspected leakage point may help investigate a local problem. Those measurements alone do not establish the classification of the complete room.
Before fieldwork begins, the monitoring team should obtain or confirm:
room identification;
room dimensions and area;
intended use;
required cleanliness class;
applicable particle sizes;
occupancy state;
cleanroom layout;
critical process locations;
supply- and return-air locations;
equipment operating status;
recent maintenance history;
previous test results; and
any known problem areas.
Where the target class or acceptance criteria have not been defined, the testing agency should not invent a convenient pass-or-fail limit.
Step 2: Confirm the Intended Cleanliness Class
The intended ISO class establishes the maximum allowable airborne particle concentration at the particle sizes selected for classification.
The applicable class should come from an approved source such as:
cleanroom design documents;
process requirements;
product-quality requirements;
customer specifications;
validation protocols;
regulatory expectations; or
internal quality standards.
A request such as “check whether the room is clean” is not sufficiently precise.
A better test objective would be:
“Assess whether Cleanroom CR-02 complies with the specified ISO Class 8 particle concentration limits under operational conditions.”
The monitoring plan should identify:
the intended ISO class;
the particle sizes to be evaluated;
the room occupancy state;
the units in which results will be reported; and
any additional site-specific limits.
The current authorised copy of the applicable standard and the facility’s approved protocol should be consulted when finalising the procedure.
Particle concentration can change considerably depending on whether people, materials and equipment are present.
ISO cleanroom assessments commonly refer to three occupancy states.
As-built
The cleanroom installation is complete and operating, but production equipment, materials and personnel are not present.
At-rest
The cleanroom is complete, services are operating and production equipment is installed. Personnel required for routine operation are absent.
Operational
The cleanroom is functioning with the agreed number of personnel performing the specified activities.
ISO 14644-3:2019 recognises performance testing in as-built, at-rest and operational states for cleanrooms with unidirectional and non-unidirectional airflow.
The selected state must be recorded in the report because a room that passes at-rest may behave differently when:
operators enter;
doors are opened;
equipment begins operating;
products are transferred;
trolleys move;
garments release particles; or
packaging materials are handled.
The monitoring team should not combine readings taken under different room states and present them as one uniform dataset.
Step 4: Review the Room Area and Layout
The cleanroom area should be verified from an approved drawing or actual measurements. An informal estimate can lead to an incorrect number of sampling locations.
The layout review should identify:
cleanroom boundaries;
length and width;
irregular sections or recesses;
internal partitions;
doors and airlocks;
pass boxes;
supply-air diffusers;
return-air grilles;
workstations;
major equipment;
personnel movement routes;
material movement routes; and
critical operations.
Where a room contains separately classified areas or distinct clean zones, each zone may require an independent sampling assessment.
Why a location-coded layout is important
Every particle-count result should be linked to a clearly marked sampling point.
For example:
Location code
Representative area
L1
Personnel entrance area
L2
Central production zone
L3
Main worktable
L4
Material pass-box area
L5
Rear corner
L6
Near return-air grille
A room layout makes the report easier to review and helps the facility investigate any location that produces an abnormal result.
Step 5: Determine the Minimum Number of Sampling Locations
For classification testing, the minimum number of sampling locations should be determined from the applicable ISO 14644-1 procedure.
A commonly used initial calculation is:
Minimum number of sampling locations = √A, rounded up
Where:
A is the cleanroom area in square metres.
The calculated value must still be checked against the applicable location table and other provisions of the standard.
Illustrative example
For a cleanroom of 64 m²:
√64 = 8
The initial minimum number of sampling locations would be eight.
For a room of 70 m²:
√70 = 8.37
The value would be rounded up to nine locations.
This represents a minimum sampling basis. Additional locations may be needed where the cleanroom has:
an irregular shape;
isolated corners;
several entrances;
large fixed machinery;
separate operational zones;
unusual airflow patterns;
multiple critical workstations; or
known contamination risks.
The calculated minimum should not prevent the monitoring team from using technical judgement where the room layout demands broader coverage.
Step 6: Select Representative Sampling Points
After the minimum number of locations has been established, the room is divided into approximately equal sections and a representative point is selected within each section.
The selection should consider:
exposed-product locations;
operator positions;
production workstations;
particle-generating equipment;
airflow direction;
supply-air distribution;
return-air positions;
doors and pass boxes;
material-transfer routes;
previous high-count locations; and
areas that may have poor air mixing.
Why convenient spot readings are inadequate
A technically planned test should represent the room, not the convenience of the engineer.
Sampling only in easily accessible open areas may miss:
the actual process zone;
a location behind equipment;
a material entry point;
an area with weak airflow;
a high-traffic position; or
a corner where particles accumulate.
A few convenient spot readings may be useful for an initial investigation, but they do not necessarily demonstrate the classification of the entire cleanroom.
Step 7: Calculate the Minimum Sample Volume
A particle counter assesses only the volume of air drawn through the instrument. It does not measure all the air in the cleanroom.
The required sample volume depends on:
the intended ISO class;
the largest particle size being considered;
the applicable concentration limit;
the instrument flow rate;
the minimum sampling duration; and
the requirements of the approved procedure.
A commonly applied ISO 14644-1 sample-volume calculation is:
Vs = (20 ÷ Cn,m) × 1,000
Where:
Vs is the minimum single-sample volume in litres; and
Cn,m is the class limit in particles per cubic metre for the largest considered particle size.
The calculated volume remains subject to the minimum-volume and minimum-duration provisions of the applicable standard.
Why testing time depends on flow rate
Sampling time is calculated as:
Sampling time = required sample volume ÷ instrument flow rate
This means two particle counters with different flow rates may require very different times to collect the same air volume.
A fixed one-minute sample should therefore not be used automatically at every location. The required air volume must be determined first.
Why sample volume matters
An insufficient sample volume may:
fail to represent the required concentration;
increase the effect of random variation;
produce unstable results in cleaner environments;
prevent a valid comparison with the class limit; or
make the reported conclusion difficult to defend.
The approved sampling time and volume should be recorded for every location.
Step 8: Verify Instrument Suitability and Calibration
The instrument must be suitable for the particle sizes, concentration range and purpose of the assignment.
Before testing, the monitoring team should verify:
instrument identification;
serial number;
particle-size channels;
nominal flow rate;
sampling mode;
calibration status;
calibration due date;
battery condition;
memory availability;
date and time settings;
inlet condition;
tubing condition, where used;
flow alarms; and
instrument cleanliness.
ISO 21501-4:2018 describes calibration and verification requirements for light-scattering airborne particle counters used in clean spaces. Its scope includes parameters such as size-setting error, counting efficiency, size resolution, false count, maximum particle-number concentration and sampling-flow-rate error.
The applicable 2023 amendment should also be considered when reviewing the current calibration basis.
Calibration certificate review
A valid calibration sticker alone is not enough. The certificate should be reviewed for:
correct instrument identification;
calibration date;
traceability;
flow-rate performance;
counting efficiency;
size resolution;
false-count performance;
maximum concentration or coincidence characteristics;
test results;
acceptance criteria;
environmental conditions; and
authorised signatory details.
Calibration confirms instrument performance under defined conditions. It does not compensate for poor sampling locations, insufficient air volume or an uncontrolled room state.
Step 9: Prepare the Cleanroom Before Sampling
The cleanroom should be brought to the agreed condition before particle counting begins.
Pre-testing checklist
Check
What should be confirmed
Room identification
Correct room and zone
Intended class
Applicable classification or limit
Test state
As-built, at-rest or operational
HVAC status
Operating under normal test conditions
Room stabilisation
Agreed period completed
Cleaning
Planned cleaning completed
Maintenance
No unplanned maintenance underway
Doors
Normal control arrangement established
Personnel
Number and activity agreed
Garments
Appropriate cleanroom garments used
Equipment
Operating condition documented
Materials
Unnecessary packaging removed
Layout
Sampling locations marked
Instrument
Calibration and pre-use checks completed
Recent disturbances
Recorded before testing
Unless they are intentionally part of an operational assessment, the following activities should be avoided immediately before or during testing:
sweeping or dry dusting;
movement of cardboard packaging;
drilling or civil work;
ceiling access;
filter replacement;
aggressive surface cleaning;
compressed-air cleaning;
repeated unnecessary door opening; and
uncontrolled personnel movement.
The monitoring team should document unusual conditions rather than silently waiting for particle levels to reduce and reporting only the later readings.
What Our Monitoring Team Checks Before Switching On the Instrument
Before taking the first reading, the Perfect Pollucon monitoring team checks:
whether the room identification matches the approved scope;
whether the intended cleanliness class is documented;
whether the required particle sizes are known;
whether the room is as-built, at-rest or operational;
whether the HVAC system is operating normally;
whether cleaning or maintenance has recently occurred;
whether doors are being operated under the agreed condition;
whether the number of personnel matches the test plan;
whether the full classified area is represented;
whether critical work areas are included;
whether the instrument and calibration records are traceable;
whether the sample volume and duration have been calculated;
whether the sampling inlet can be positioned without disturbing airflow; and
whether every reading can be linked to a field observation and location code.
These checks help prevent avoidable disputes after testing.
Step 10: Position the Sampling Inlet Correctly
The sampling inlet should normally be placed at or near the level of the activity being assessed, unless the approved procedure specifies another position.
Depending on the cleanroom process, this may be:
product-exposure height;
workbench level;
filling-line height;
equipment-opening height;
a critical process plane; or
another representative sampling height.
In a unidirectional airflow system, the inlet should normally face the direction of airflow. In a non-unidirectional or mixed-airflow room, positioning should follow the approved procedure and the intended assessment point.
Long, sharply bent or unsuitable sampling tubing can contribute to particle losses, particularly for larger particles. Direct sampling should be used where practical.
Why operator position matters
The person conducting the test is also a possible particle source.
Readings may be influenced when the operator:
stands directly upstream of the inlet;
speaks over the sampling point;
reaches across the inlet;
handles paper nearby;
blocks a supply-air path;
touches garments or hair;
moves abruptly; or
directs exhaled air towards the inlet.
The operator should stand away from the incoming airflow, minimise movement and avoid unnecessary interference with the sampling point.
Step 11: Record Particle Counts and Field Conditions
At each location, the monitoring engineer should:
confirm the location code;
position the inlet at the defined height;
confirm the selected particle channels;
confirm the sample duration or volume;
complete the sampling cycle;
check for alarms;
save or record the result;
document activity during the sample; and
move carefully to the next point.
The field record should retain:
date;
time;
room identification;
location code;
sampling height;
sample number;
sampled volume;
sampling duration;
particle-size channels;
raw count;
normalised concentration;
instrument identification;
occupancy state;
personnel present;
equipment status;
door activity;
field observations; and
any interruption or deviation.
Sample field-observation sheet
Field
Example entry
Room
Component Assembly Cleanroom
Room code
CR-02
Intended class
ISO Class 8
Test state
Operational
Location
L4 – Material pass-box area
Sampling height
1.0 metre
Personnel present
Four operators and monitoring engineer
Equipment status
Assembly activity in progress
Door activity
Material door opened once
Sample duration
As per approved sampling plan
Observation
Operator crossed behind sampling position
Review status
Result retained with disturbance noted
A field sheet should record what happened. It should not be adjusted later to make the result easier to explain.
Step 12: Review Abnormal Locations
A high particle count should not be deleted merely because nearby locations passed.
The monitoring engineer should review:
door openings;
personnel movement;
operator position;
instrument alarms;
inlet obstruction;
equipment operation;
material transfer;
airflow patterns;
return-air proximity;
recent cleaning;
recent maintenance;
visible leakage;
damaged seals; and
previous results at the same location.
When repeating a sample may be justified
A repeat sample may be appropriate where:
the sampling cycle was interrupted;
an accidental disturbance was documented;
the instrument reported a fault;
the inlet was displaced;
the wrong location code was entered;
the required room condition was not maintained; or
the result requires further technical investigation.
The original result, the reason for repetition and the repeat result should remain traceable.
Repeated testing should not become a process of taking readings until one happens to pass.
An abnormal particle count is information. The first responsibility is to understand it, not remove it.
Coincidence Loss at High Particle Concentrations
At high particle concentrations, more than one particle may pass through the sensing zone at almost the same time.
The instrument may then:
count multiple particles as one;
assign an incorrect particle size; or
under-report the actual concentration.
This effect is known as coincidence loss.
Instrument suitability should therefore be reviewed during heavily contaminated conditions, post-maintenance investigations or other situations where particle levels may approach the instrument’s maximum specified concentration.
A low displayed count should not automatically be accepted when there is evidence that the instrument may be operating outside its validated concentration range.
Borderline Results and Measurement Uncertainty
Results close to an acceptance limit require careful technical review.
Interpretation may be influenced by:
sampling-flow accuracy;
counting efficiency;
particle-size resolution;
calibration performance;
sample volume;
repeatability;
location selection;
environmental instability; and
measurement uncertainty.
A borderline result should not be casually rounded down and declared compliant.
The report should state the measured value clearly and apply the decision rule required by the facility’s quality system, client protocol, accreditation framework or applicable contract.
Where no formal decision rule has been defined, this should be communicated instead of making an unsupported claim.
Stabilisation Time Is Not the Same as a Recovery Test
A cleanroom may need time to stabilise after:
cleaning;
maintenance;
shutdown;
filter work;
door opening;
personnel movement; or
process interruption.
The necessary stabilisation period should be defined by the facility’s approved procedure, validation data or operating experience.
This should not be confused with a formal cleanroom recovery test.
A recovery test evaluates how quickly a cleanroom returns from a controlled elevated particle concentration to a selected target condition. Recovery testing is covered as a separate supporting test method under ISO 14644-3.
Waiting for a room to stabilise before classification and formally measuring its recovery performance are therefore different activities.
Step 13: Compare the Results With the Applicable Criteria
After sampling, the data should be reviewed for:
correct particle-size channel;
correct units;
correct air volume;
correct concentration calculation;
correct cleanliness class;
correct occupancy state;
inclusion of all required locations; and
proper treatment of repeated or invalid samples.
Results should normally be evaluated location by location.
A low room average should not be used to conceal an unacceptable location where the applicable classification procedure requires each location to comply.
The report should distinguish between:
valid samples;
invalid samples;
compliant locations;
non-compliant locations;
repeat samples;
investigative measurements; and
observations requiring corrective action.
What Should Happen After a Failed Result?
A failed result should trigger a structured investigation.
Verify the validity of the test
First check:
calibration status;
instrument alarms;
sample volume;
sampling duration;
location;
occupancy condition;
unit conversion;
data entry;
door activity; and
any recorded disturbance.
Determine the extent of the problem
The pattern of failure can provide useful clues.
One high location may indicate a local airflow, activity or equipment issue.
Several nearby high locations may indicate a zone-level problem.
High readings across the complete room may indicate a broader filtration, pressure, cleaning or operating-control problem.
Investigate likely causes
Possible causes include:
damaged or incorrectly seated HEPA filters;
leakage around filter frames;
poor airflow distribution;
pressure imbalance;
blocked supply- or return-air paths;
frequent door opening;
excessive personnel;
unsuitable garments;
inadequate cleaning;
particle-generating equipment;
uncontrolled packaging;
maintenance residue; or
insufficient stabilisation.
Implement corrective action
Corrective actions may include:
HEPA-filter integrity testing;
filter or gasket repair;
airflow balancing;
pressure-cascade correction;
improved cleaning;
equipment maintenance;
personnel-control changes;
gowning improvements;
material-transfer controls; or
operator training.
Retest under controlled conditions
After corrective action, the room should be returned to the defined state and retested under an approved plan.
The retest report should remain linked to:
the original failure;
the investigation;
corrective actions; and
the final conclusion.
A passed retest does not, by itself, explain why the original result failed.
Step 14: Prepare a Traceable Technical Report
A particle count report should contain enough information for a client, auditor or technical reviewer to understand exactly how the conclusion was reached.
A table containing only numbers and the word “Pass” is not sufficient for a technically defensible assessment.
Recommended report contents
Report section
Information to include
Client details
Client name and site
Room details
Department, room name and room code
Test purpose
Classification, monitoring or investigation
Reference basis
Applicable standard or protocol
Intended class
ISO class or other criteria
Occupancy state
As-built, at-rest or operational
Room description
Area, use and important equipment
Sampling plan
Basis and number of locations
Layout
Numbered sampling-point diagram
Test date and time
Start and completion details
HVAC condition
Status during testing
Personnel
Number and activities
Instrument details
Make, model and serial number
Calibration
Certificate and validity information
Particle channels
Measured and evaluated particle sizes
Sample volume
Volume and duration at each location
Raw results
Original particle counts
Normalised results
Concentration in required units
Acceptance limits
Applicable criteria
Compliance status
Location-wise and overall result
Field observations
Doors, movement, maintenance and activities
Deviations
Departures from the approved method
Repeat samples
Original and repeat data with justification
Conclusion
Clear, scope-limited technical statement
Authorisation
Responsible technical personnel
Example of a scope-limited conclusion
“Based on the location-wise airborne particle measurements obtained under the documented at-rest condition, Cleanroom CR-02 complied with the specified ISO Class 8 particle concentration limits at the evaluated particle sizes on the date of testing.”
A particle-count test alone does not establish:
microbiological cleanliness;
HEPA-filter integrity;
air velocity;
air-change rate;
pressure differential;
recovery performance;
temperature compliance; or
humidity compliance.
These require separate tests where applicable.
Practical Mistakes PPS Has Observed During Industrial Monitoring Work
Perfect Pollucon’s monitoring experience has shown that particle-counting errors often begin before the instrument is switched on.
1. The room area is estimated
The number of locations is calculated from an approximate figure rather than the actual classified area.
Better practice: Verify the room dimensions and classification boundary before preparing the sampling plan.
2. Locations are chosen for convenience
Open and easily accessible areas are tested while critical process zones are missed.
Better practice: Use an area-based layout and include locations that represent operations, airflow and contamination risk.
3. The intended class is not documented
The monitoring team is asked to determine whether the room is “acceptable” without being given any acceptance criteria.
Better practice: Confirm the cleanliness class and particle sizes before beginning fieldwork.
4. Different room states are mixed
Some readings are taken without personnel and others during production, but all are presented under one result table.
Better practice: Maintain one defined room state or report each state separately.
5. The same duration is used everywhere without calculation
Every location is sampled for a fixed duration regardless of the required volume.
Better practice: Calculate the required air volume and determine sampling time from the verified flow rate.
6. The operator influences the sample
The engineer stands upstream of the inlet or moves directly beside the sampling point.
Better practice: Position the operator away from the airflow path and minimise movement.
7. Door activity is not documented
A high reading follows a material transfer or door opening, but no observation is recorded.
Better practice: Record door events and other disturbances during each sample.
8. Only converted values are retained
The report contains final particles-per-cubic-metre figures, but the raw count, volume and duration are unavailable.
Better practice: Preserve both raw data and normalised results.
9. Failed readings are replaced
Sampling continues until a lower result is obtained and only the lowest value is reported.
Better practice: Retain the original reading and document the technical reason for any repetition.
10. Calibration is checked only from the sticker
The certificate scope, instrument serial number and calibration results are not reviewed.
Better practice: Link the exact instrument used to a valid and technically relevant calibration certificate.
11. Particle count is confused with particulate mass
PM2.5 or PM10 mass concentrations are treated as interchangeable with cleanroom particle number concentrations.
Better practice: Use direct particle-count measurements at the required size channels. Do not rely on a generic mass-to-count conversion.
12. Indicative readings are presented as classification
A small number of spot measurements are described as an ISO-classification exercise.
Better practice: Clearly state whether the assignment is classification, routine monitoring, troubleshooting or an indicative survey.
How Long Does Cleanroom Particle Count Testing Take?
There is no single testing duration applicable to every room.
The time depends on:
room area;
number of classified zones;
minimum number of sampling locations;
additional risk-based locations;
intended cleanliness class;
particle sizes;
required sample volume;
instrument flow rate;
room stabilisation;
access and gowning arrangements;
production conditions;
abnormal results; and
field-documentation requirements.
Illustrative example
Suppose a room requires nine sampling locations and the approved plan requires five minutes at each location.
Direct sampling time would be:
9 locations × 5 minutes = 45 minutes
The total site time would also include:
entry and gowning;
room verification;
layout review;
marking of locations;
equipment checks;
movement between points;
field observations;
investigation of unusual readings; and
exit procedures.
Nine readings should therefore not automatically be treated as a nine-minute assignment.
What Should the Facility Arrange Before Testing?
The facility should ideally arrange:
an approved room layout;
verified room dimensions;
intended ISO class;
applicable protocol;
access permission;
cleanroom garments;
a responsible site representative;
normal HVAC operation;
the agreed occupancy state;
completion of planned cleaning;
completion of maintenance;
access to previous reports; and
information about production or equipment status.
The monitoring agency should also be informed about:
recent HEPA-filter replacement;
pressure or HVAC alarms;
ongoing civil work;
abnormal production activities;
contamination incidents;
changes in personnel numbers; and
previous failure locations.
Why Choose Perfect Pollucon LLP?
Perfect Pollucon LLP has more than 25 years of experience in environmental monitoring and field assessments across industrial facilities in India.
Our cleanroom particle count assignments are planned around four principles:
Representative sampling
The sampling plan should represent the complete room and its critical activities, not merely the easiest accessible locations.
Traceable measurements
Each reading should be connected to a room, location, sample volume, time, occupancy state and instrument record.
Field observations
Door movement, personnel activity, equipment operation, cleaning and maintenance conditions are recorded because these factors can directly influence the result.
Technically restrained reporting
The report should state what the test demonstrates without claiming that particle counting alone proves HEPA integrity, microbiological control or complete cleanroom qualification.
The minimum number depends on the classified area and the applicable ISO procedure. Additional locations may be required because of room shape, critical processes, equipment arrangement or known risks.
Is one reading enough for a small cleanroom?
Only where the applicable procedure permits it and the point adequately represents the complete classified zone. Additional risk-based locations may still be appropriate.
How long should each sample run?
The duration depends on the required air volume and the verified instrument flow rate. A fixed one-minute sample is not automatically suitable for every class or particle size.
Can testing be performed during production?
Yes, where operational testing is required. Personnel, equipment, activities and door movement must be controlled and documented.
Why do particle counts rise when people enter?
People release particles from skin, hair and garments. Movement can also disturb settled material and change local airflow.
Does passing a particle-count test prove that the HEPA filters are leak-free?
No. HEPA-filter integrity testing is a separate assessment.
Can PM2.5 readings be converted into cleanroom particle counts?
Not reliably through a generic formula. PM2.5 is normally expressed as mass concentration, while cleanroom classification uses particle number concentration at defined size thresholds.
What should happen if only one location fails?
The reading should be retained and investigated. The team should review airflow, door activity, personnel, equipment, maintenance, cleaning, sampling conditions and instrument status before deciding on corrective action and retesting.
How often should particle counting be performed?
The frequency depends on the cleanliness class, process risk, facility monitoring plan, customer or regulatory requirements, changes to the room and previous performance. ISO 14644-2 provides the framework for establishing a monitoring plan related to air cleanliness by particle concentration.
Final Takeaway
Reliable cleanroom particle count testing is not defined by the number of readings displayed by the instrument.
It is defined by whether the test was properly planned and whether the results can be traced to:
the correct room;
the intended cleanliness class;
a documented occupancy state;
representative locations;
a sufficient sample volume;
a suitable calibrated instrument;
controlled field conditions;
recorded room activities; and
a technically clear report.
A few convenient readings may provide a quick indication. They do not necessarily demonstrate cleanroom classification.
A well-conducted assessment helps the facility understand where the cleanroom is performing correctly, where contamination risks may exist and what should be investigated when a result is outside the applicable criteria.
