Active and Passive Air Sampling in Controlled Areas

Learn the requirements for active and passive air sampling in controlled areas, including methods, differences, applications, monitoring strategy and GMP considerations.

Active and Passive Air Sampling in Controlled Areas: Requirements, Methods and Differences

Air sampling is an important component of environmental monitoring in pharmaceutical controlled areas and cleanrooms. It helps assess the presence of viable microorganisms in the surrounding environment and provides information that supports contamination control.

The two commonly used approaches are active air sampling, also called volumetric air sampling, and passive air sampling, generally performed using settle plates. They provide different types of information and are therefore often used together as part of a risk-based environmental monitoring program.

However, an important distinction should be made: both methods should not automatically be described as universally mandatory for every controlled area. For sterile medicinal-product manufacturing, curren

t EU/PIC/S GMP Annex 1 expects environmental monitoring to use an appropriate combination of methods, including settle plates and volumetric air sampling where justified by the contamination-control strategy and the nature of the operation.

Quick Answer: Are Active and Passive Air Sampling Required?

Active and passive air sampling are complementary environmental-monitoring techniques, but they should not automatically be considered universally mandatory for every controlled area. Their use, frequency, locations and duration should be established through a scientifically justified, risk-based environmental monitoring program and applicable GMP requirements.

What Is Air Sampling in Pharmaceutical Environmental Monitoring?

Air sampling is the collection or assessment of airborne microorganisms in a controlled environment to evaluate the microbiological state of the area.

In pharmaceutical microbiological environmental monitoring, air monitoring primarily concerns viable microorganisms, such as bacteria, yeasts and moulds. The results can help detect changes in environmental conditions and determine whether contamination-control measures remain effective.

Air monitoring should be considered together with other environmental monitoring activities, such as:

• Surface monitoring
• Personnel monitoring
• Settle plates
• Volumetric air sampling
• Non-viable particle monitoring
• Monitoring of critical processing areas

A suitable monitoring program should be scientifically justified and incorporated into the facility's overall Contamination Control Strategy (CCS) where applicable.

Is Active and Passive Air Sampling Mandatory in Controlled Areas?

Not universally. The requirement depends on the type of facility, product, cleanroom classification, process, contamination risk and applicable regulatory framework.

For sterile manufacturing, EU/PIC/S GMP Annex 1 states that microbial monitoring during aseptic operations should use a combination of methods, such as settle plates and volumetric air sampling, together with personnel and surface monitoring. The selected methods should be justified within the Contamination Control Strategy.

Therefore, it is more accurate to say:

Active and passive air sampling are complementary environmental-monitoring techniques. Their use, frequency, locations and duration should be established through a scientifically justified, risk-based monitoring program rather than assuming that both methods are automatically mandatory in every controlled area.

This distinction is important because regulatory expectations are increasingly focused on risk-based contamination control, rather than applying identical monitoring practices to every controlled area.

What Is Active Air Sampling?

Active air sampling is a volumetric method in which a defined volume of air is actively drawn through a microbial air sampler and directed onto an appropriate culture medium.

The purpose is to estimate the concentration of viable microorganisms in a known volume of air.

Active Air Sampling Procedure

1. Select the sampling location according to the approved environmental monitoring plan.
2. Prepare and disinfect the sampling equipment according to the applicable procedure.
3. Place the microbial air sampler at the defined location.
4. Set the required sampling volume or sampling duration.
5. Draw a known volume of air through the sampler.
6. Allow microorganisms present in the sampled air to be captured on or in the culture medium.
7. Remove the exposed medium according to the approved procedure.
8. Incubate the medium under validated or established conditions.
9. Count and record the recovered colonies.
10. Evaluate the result against applicable environmental monitoring limits and alert/action levels.

What Does Active Air Sampling Measure?

Active air sampling provides a volumetric measurement of viable microorganisms in the sampled air.

Results are commonly expressed in relation to the volume of air sampled, such as:

CFU/m³

CFU means colony-forming units.

Advantages of Active Air Sampling

• Provides a quantitative estimate of viable airborne contamination.
• Uses a defined or measured volume of air.
• Can be useful for monitoring areas where airborne microbial contamination must be closely controlled.
• Allows comparison of results over time when sampling conditions are appropriately standardized.
• Can provide relatively rapid microbiological monitoring compared with approaches requiring prolonged exposure.

However, the sampling volume and frequency should be scientifically justified. The sample volume used for environmental monitoring does not necessarily have to be the same as the volume used for cleanroom classification.

What Is Passive Air Sampling?

Passive air sampling is an environmental monitoring technique in which exposed culture media, commonly called settle plates, are placed at defined locations for a specified exposure period.

Instead of actively drawing a measured volume of air through a device, the method allows microorganisms associated with airborne particles to settle naturally onto the exposed culture medium.

The exposed plates are subsequently incubated and examined for microbial growth.

How Does Passive Air Sampling Work?

1. Select the monitoring location.
2. Prepare the required culture medium.
3. Place the settle plate at the defined monitoring position.
4. Remove or open the lid according to the approved procedure.
5. Expose the plate for the predetermined period.
6. Close or remove the plate according to the procedure.
7. Incubate the exposed medium.
8. Count the resulting colonies.
9. Record and evaluate the result.

What Does a Settle Plate Measure?

A settle plate does not directly measure the concentration of microorganisms per cubic metre of air.

Instead, it provides information about microorganisms that settle onto the exposed surface during the exposure period.

This makes passive monitoring useful for assessing contamination deposition over time.

Active vs Passive Air Sampling: What Is the Difference?

The fundamental difference is how microorganisms are collected.

Parameter	Active Air Sampling	Passive Air Sampling
Basic principle	A defined volume of air is actively sampled	Microorganisms settle naturally onto exposed medium
Common method	Volumetric microbial air sampler	Settle plate
Air volume	Defined/measured sampling volume	No defined sampled air volume
Typical result	CFU/m3 or equivalent volumetric result	Colonies recovered from an exposed plate over a defined period
Main information	Viable airborne contamination in sampled air	Microbial deposition over exposure time
Equipment	Requires microbial air-sampling equipment	Requires suitable culture plates and exposure setup
Exposure	Usually relatively short and controlled	Can provide longer-duration monitoring
Monitoring value	Quantitative volumetric assessment	Deposition/settling assessment
Limitation	Sampling can potentially affect airflow if poorly designed	Does not directly provide airborne concentration

The two methods should therefore not be treated as interchangeable.

Why Use Both Active and Passive Air Sampling?

The main reason for using both approaches is that they provide different information.

Active sampling answers a question similar to:

How many viable microorganisms are present in the volume of air sampled?

Passive sampling addresses a different question:

What viable microorganisms settle onto an exposed surface during a defined period?

Using complementary methods can provide a broader understanding of environmental microbiological conditions.

For aseptic operations, Annex 1 describes a combination of environmental-monitoring methods, including settle plates and volumetric air sampling, alongside other monitoring methods.

Active Air Sampling vs Settle Plates: Which Is Better?

Neither method is universally better.

They measure different aspects of environmental contamination.

Active air sampling is more appropriate when the objective is to obtain a volumetric assessment of viable airborne microorganisms.

Passive monitoring using settle plates is valuable when the objective is to evaluate microbial deposition during an exposure period.

For sterile manufacturing, using complementary monitoring methods can provide a more meaningful assessment than relying on a single technique.

The choice should therefore be based on risk, process knowledge and the facility's contamination-control strategy, rather than simply selecting the cheaper or easier method.

Why Is Environmental Air Monitoring Important in Pharmaceutical Manufacturing?

Air can act as a potential pathway for microbial and particulate contamination.

Potential sources of contamination in pharmaceutical environments include:

• Personnel
• Raw materials and components
• Equipment
• Water systems
• Air and HVAC systems
• Manufacturing processes
• Cleaning activities
• Facility surfaces

Personnel are particularly important sources of contamination because movement, gowning, interventions and other activities can influence the cleanroom environment.

Environmental monitoring provides information that can help a pharmaceutical manufacturer determine whether environmental controls continue to perform effectively.

How Are Air-Sampling Results Interpreted?

Air-monitoring results should not be interpreted as an isolated number.

A robust environmental monitoring program considers:

• Sampling location
• Sampling method
• Sampling volume or exposure time
• Cleanroom grade/classification
• Manufacturing activity
• Personnel presence
• Historical environmental monitoring data
• Alert and action levels
• Organisms recovered
• Repeated excursions
• Other environmental monitoring results

Why Is Trend Analysis Important?

A single result may not provide the complete picture.

For example, repeated recovery of microorganisms from a particular location may indicate a developing environmental-control problem even if individual results do not exceed an established action level.

Trend analysis can help identify:

• Increasing microbial recovery
• Repeated contamination at a specific location
• Seasonal patterns
• Changes associated with personnel or processes
• Recurring environmental excursions

The monitoring program should define how results are reviewed, trended and investigated.

Important Considerations for Active Air Sampling

Active air sampling in controlled areas should be carefully designed.

Sampling Location

Locations should be selected using a documented risk assessment that considers:

• Critical processing activities
• Airflow patterns
• Personnel movement
• Equipment configuration
• Material transfer
• Intervention points
• Historical contamination data

Sampling Volume

A defined volume should be selected and justified according to the monitoring objective and sampling method.

It should not simply be assumed that every environmental monitoring application requires the same sampling volume.

Equipment

The microbial air sampler should be appropriately qualified, maintained and controlled according to the site's procedures.

Impact on Airflow

Sampling equipment should not introduce an unacceptable disturbance to critical airflow patterns.

This is particularly important in Grade A and Grade B environments used for aseptic processing.

Important Considerations for Passive Air Sampling

Settle plates are simple to use, but their application still requires careful control.

Important considerations include:

• Defined sampling locations
• Defined exposure periods
• Appropriate culture medium
• Prevention of accidental contamination
• Correct plate handling
• Appropriate incubation
• Clear identification and traceability
• Defined acceptance criteria
• Timely evaluation of results

Why Does Exposure Time Matter?

A settle plate provides information associated with its exposure period. It should therefore not be treated as though it were a direct measurement of CFU/m³.

The exposure period should be defined and scientifically justified as part of the environmental monitoring program.

For critical aseptic processing, the applicable GMP requirements should be followed for viable air monitoring throughout critical processing activities.

Common Mistakes in Pharmaceutical Air Sampling

1. Treating Active and Passive Sampling as the Same Method

They provide different information and should not be interpreted in the same way.

2. Assuming Every Controlled Area Requires Identical Monitoring

Monitoring should reflect the contamination risk and process requirements.

3. Calling Every Air-Sampling Result CFU/m³

This is inappropriate for settle plates because they do not directly sample a defined volume of air.

4. Ignoring Sampling Location

The location of sampling can strongly influence the usefulness of the result.

5. Focusing Only on Individual Results

Environmental monitoring should also include trend analysis and assessment of recurring patterns.

6. Treating Regulatory Requirements as Universal

Requirements differ according to product type, process, regulatory framework and cleanroom grade. A site should identify the requirements applicable to its operations rather than applying a generic rule to every controlled area.

Are Active and Passive Air Sampling Both Required in Grade A Areas?

For sterile manufacturing, Grade A environments require particularly stringent viable and non-viable particle monitoring.

EU/PIC/S Annex 1 requires continuous viable air monitoring in Grade A during critical processing, using an appropriate monitoring system. The monitoring strategy must also consider the risk of the sampling method affecting airflow.

The exact system, sampling approach, sample volume and monitoring configuration should be justified within the site's Contamination Control Strategy.

What About Grade B, C and D Areas?

The monitoring strategy should be based on the applicable cleanroom grade, operation and contamination risk.

It is therefore inappropriate to assume that Grade B, C and D areas must all use exactly the same sampling frequency, sampling volume or combination of methods.

The environmental monitoring program should establish:

• Sampling locations
• Sampling frequency
• Sampling methods
• Sampling duration and/or volume
• Alert levels
• Action levels
• Trending requirements
• Investigation requirements

These parameters should be supported by documented risk assessment and applicable GMP requirements.

Key Takeaways

• Active air sampling uses a microbial air sampler to collect a defined volume of air and provides a volumetric assessment of viable airborne contamination.
• Passive air sampling commonly uses settle plates to detect microorganisms that settle onto exposed culture media over a defined period.
• The two methods provide different but complementary information.
• Active sampling results may be expressed as CFU/m³, whereas settle-plate results should not automatically be converted into CFU/m³.
• Both methods can form part of a pharmaceutical environmental monitoring program.
• Current EU/PIC/S GMP Annex 1 emphasizes a risk-based combination of monitoring methods rather than a universal rule that every controlled area must always use both methods.
• For sterile manufacturing, monitoring should be integrated into the facility's Contamination Control Strategy (CCS) and should consider the effect of sampling on critical airflow.

Frequently Asked Questions

What is active air sampling in pharmaceuticals?

Active air sampling is a volumetric environmental-monitoring technique in which a microbial air sampler actively collects a defined volume of air onto an appropriate culture medium. After incubation, recovered microorganisms are counted to assess viable airborne contamination.

What is passive air sampling?

Passive air sampling generally uses settle plates exposed for a defined period. Microorganisms associated with airborne particles can settle naturally onto the exposed culture medium, which is subsequently incubated and examined for microbial growth.

What is the difference between active and passive air sampling?

Active sampling actively draws a defined volume of air through a sampling device, while passive sampling relies on natural microbial deposition onto an exposed settle plate. Active sampling provides volumetric information, whereas passive sampling provides information about microbial settling during exposure.

Are both active and passive air sampling mandatory?

Not automatically for every controlled area. The applicable requirement depends on the type of manufacturing operation, regulatory framework and contamination risk. For sterile manufacturing, EU/PIC/S Annex 1 expects an appropriate combination of environmental-monitoring methods, with the approach justified within the Contamination Control Strategy.

Does passive air sampling measure CFU/m³?

No. A settle plate does not directly sample a defined volume of air. It measures microbial deposition onto the exposed culture medium during the specified exposure period. Therefore, settle-plate results should not automatically be reported as CFU/m³.

Why is active air sampling used in cleanrooms?

Active air sampling provides a defined-volume assessment of viable airborne microorganisms and can therefore be useful for monitoring microbiological air quality in controlled environments.

Why are settle plates used in pharmaceutical cleanrooms?

Settle plates provide information about viable microorganisms that deposit from the environment onto an exposed surface during a defined period. They can therefore complement volumetric air sampling.

What is the purpose of environmental monitoring?

Environmental monitoring helps assess whether the controlled manufacturing environment remains within the expected state of microbial and particulate control. Results can also support trend analysis, contamination investigations and verification of the effectiveness of contamination-control measures.