Compressed Air System Qualification is an important pharmaceutical utility and may directly or indirectly affect product quality, equipment performance and manufacturing operations. This article explains a practical GMP-based approach for qualifying a compressed air system, including responsibilities, prerequisites, sampling, testing for moisture, oil, particles and microbiological quality, acceptance criteria, documentation, change control and requalification.
Objective for Compressed Air System Qualification
The objective of this procedure is to establish a systematic approach for the qualification of the compressed air system and its associated components.
The qualification shall demonstrate that the compressed air system operates consistently and reliably throughout its intended operating range and produces air of suitable quality for its defined application.
Where compressed air comes into direct contact with the product, product-contact surfaces or primary packaging components, the quality requirements shall be established according to the intended use and applicable regulatory or compendial requirements.
Scope
This procedure applies to the qualification and periodic verification of compressed air systems used in pharmaceutical manufacturing and associated operations.
The procedure covers:
- Qualification of the compressed air generation and distribution system.
- Evaluation of compressed air used for product-contact applications.
- Testing for moisture and oil contamination.
- Non-viable particle monitoring.
- Microbiological quality assessment where applicable.
- Review of operating parameters and system performance.
- Acceptance criteria and evaluation of qualification results.
- Change control and requalification requirements.
- Periodic monitoring and trending of compressed air quality.
The extent of qualification and testing shall be based on the intended use and quality risk associated with the compressed air system.
Regulatory and Quality Considerations
Compressed air should be treated as a critical utility whenever its quality can have an impact on product quality.
FDA GMP guidance states that utilities capable of affecting product quality, including compressed air, should be appropriately qualified and monitored. FDA inspection guidance also specifically considers monitoring of product-contact process gases for particulates, moisture, oil and bioburden.
For sterile manufacturing operations, compressed gases used in areas where they may affect sterile materials should have an appropriate purity level. FDA guidance indicates that compressed gas used in such applications should have suitable microbiological and particle quality after filtration.
ISO 8573-1 provides a framework for specifying compressed-air purity based primarily on:
- Particles
- Water
- Oil
The applicable purity class should therefore be selected according to the intended application rather than assigning the same specification to every compressed-air point.
Responsibilities
| Designation | Responsibility |
| Officer/Executive Engineering | Provide the required technical support during qualification. Ensure availability of the compressed air system and associated utilities. Provide system drawings, equipment details and operating parameters. Ensure that the compressor, dryer, filters, receiver and distribution system are maintained in qualified condition. Support troubleshooting and investigation of abnormal results. Provide calibration status of critical instruments. Support execution of approved qualification activities. Maintain appropriate maintenance and service records. |
| Officer/Executive Production | Provide the required production support during qualification. Ensure that the compressed air system is operated under normal intended conditions during testing. Support identification of representative points of use. Record operational observations and qualification data. Ensure that qualification activities do not adversely affect manufacturing operations. |
| Officer/Executive QC | Provide analytical and microbiological testing support. Perform sampling according to the approved qualification protocol. Test compressed air samples using approved and validated or verified methods. Record and review test results. Inform QA and Engineering of any abnormal or out-of-specification result. Maintain appropriate laboratory records. |
| Officer/Executive QC | Review and approve the qualification protocol. Review qualification data and supporting documentation. Verify compliance with approved acceptance criteria. Review deviations and investigations associated with qualification. Approve applicable change controls. Review and approve the final qualification report. Ensure that requalification requirements are established and followed. Periodically review this procedure. |
Description of the Compressed Air System
The compressed air system generally consists of an air compressor, air intake filtration, compression assembly, oil or oil-free compression arrangement, air receiver, cooling system, dryer, downstream filtration and distribution network.
In an oil-lubricated compressor, atmospheric air enters through the intake system and is compressed along with the lubricating medium. The compressed mixture passes through an oil separation stage, where the oil is separated from the compressed air.
The compressed air then passes through suitable filtration and cooling stages before entering the distribution system. Depending on the system design, additional dryers, coalescing filters, particulate filters and point-of-use filters may be installed to achieve the required air quality.
The final configuration shall be verified against the approved system drawing and equipment documentation.
Strategy for Compressed Air System Qualification
Qualification of the compressed air system should be performed using a documented and risk-based approach.
Depending on the system and site qualification program, qualification may include:
- Design Qualification (DQ)
- Installation Qualification (IQ)
- Operational Qualification (OQ)
- Performance Qualification (PQ)
For an existing qualified system, periodic verification and performance monitoring may be sufficient where justified by documented risk assessment and historical performance.
The qualification protocol should clearly identify:
- System identification
- Equipment and component details
- Critical operating parameters
- Sampling locations
- Sampling frequency
- Test methods
- Acceptance criteria
- Responsibilities
- Deviation handling
- Reporting requirements
Pre-Requisites for Qualification
Before beginning the qualification study, verify the following:
- Approved qualification protocol is available.
- Current compressed-air system schematic or P&ID is available.
- Compressor and associated equipment are identified.
- Calibration status of pressure gauges, temperature indicators, flow meters and other critical instruments is valid.
- Air filters and dryers are installed and operational.
- Preventive maintenance status is satisfactory.
- Sampling points are properly identified.
- Sampling equipment is clean and suitable for use.
- Microbiological media are approved and within expiry.
- Sterile membrane filters are available where required.
- Qualified personnel are available for sampling and testing.
- Applicable SOPs are approved and effective.
- Previous qualification and monitoring data are available for review, where applicable.
Selection of Sampling Points
Sampling points should represent the actual use of compressed air throughout the distribution network.
The sampling plan should consider:
- Compressor outlet
- After dryer
- After major filtration stages
- Long distribution branches
- Points with the greatest potential for contamination
- Remote points of use
- Frequently used points
- Points directly contacting product or primary packaging
- Points associated with critical manufacturing operations
A risk assessment should be used to justify the number and location of sampling points.
For large systems, sampling all points during every qualification cycle may not always be necessary if a scientifically justified, representative sampling plan has been established.
Parameters to be Evaluated in Compressed Air System Qualification
Depending on the intended application, the following parameters may be evaluated:
| Parameter | Purpose |
| Pressure | Verification of adequate system operation |
| Flow | Verification of supply capability |
| Moisture / Water | Detection of excessive moisture |
| Oil | Detection of oil contamination |
| Non-viable particles | Assessment of particulate contamination |
| Microbiological quality | Assessment of microbial contamination |
| Specific contaminants | Where required by product or process risk |
The final test panel should be defined in the approved qualification protocol.
Determination of Moisture
Moisture in compressed air can adversely affect equipment, filters, product-contact operations and downstream processes.
The moisture test shall be performed using a scientifically justified and validated or verified method.
Where a Karl Fischer-based method is used, the sample volume, sampling duration, flow rate, solvent volume, blank correction and calculation shall be established in the approved analytical procedure.
The original procedure specifies approximately 150 mL of dry methanol and sampling at approximately 5 L/min for 4 minutes and 30 seconds. This corresponds to approximately 22.5 L of sampled air.
The moisture calculation shall be performed using the currently approved laboratory method and the applicable Karl Fischer factor.
Determination of Oil
Oil contamination shall be evaluated at representative compressed-air sampling points where oil contamination could affect the product, packaging material or manufacturing process.
An appropriate validated or verified oil detection method shall be used.
Where a visual filter-paper method is used as an in-house screening test, clean suitable filter paper may be exposed to the compressed air for a defined period and subsequently inspected for visible oil contamination.
The observation should be documented and, where applicable, supported by a photograph.
For critical applications, a quantitative or more sensitive analytical method should be considered rather than relying solely on visual observation.
The compressed-air oil specification should be linked to the selected compressed-air purity class and intended use. ISO 8573-1 specifically addresses oil as one of the major compressed-air contamination categories.
Non-Viable Particle Monitoring
Non-viable particle monitoring should be performed using a calibrated particle counter suitable for the intended compressed-air application.
The following should be controlled:
- Particle counter calibration status.
- Sampling flow rate.
- Sampling volume.
- Sampling pressure and pressure-reduction arrangement, where applicable.
- Sampling location.
- Particle sizes evaluated.
- Number of replicate samples.
- Environmental conditions during testing.
- Data recording and review.
The particle specification should be established based on the intended compressed-air quality class and process requirements.
The limits of 90,000 particles/m³ for particles ≥0.5 µm and 1,000 particles/m³ for particles ≥5 µm appearing in the original draft should not be described as universal GMP compressed-air limits. If these values are retained at a particular facility, they should be clearly identified as site-specific acceptance criteria and scientifically justified.
Microbiological Evaluation
Microbiological testing should be performed when compressed air has a potential impact on product quality, product-contact surfaces, primary packaging or sterile operations.
The sampling method should be scientifically justified and capable of recovering microorganisms from compressed air.
Possible approaches include validated compressed-air microbial sampling equipment or an appropriate membrane filtration method.
Where a liquid impingement or collection method is used, the sampling volume, flow rate, collection medium, exposure time and subsequent recovery procedure should be validated or verified for the intended application.
The original procedure proposes passing approximately 1,000 L of compressed air through 100 mL of Soyabean Casein Digest Medium followed by membrane filtration and incubation. This approach should only be retained if it has been demonstrated to be suitable for the site’s compressed-air system and validated or verified for microbial recovery.
A commercially available or validated compressed-air microbial sampler may provide a more controlled approach for routine qualification and monitoring.
Microbiological Testing Procedure – Compressed Air System Qualification
A typical microbiological evaluation may include the following steps:
- Ensure that sampling equipment and accessories are clean and suitably sterilized.
- Verify the calibration or qualification status of the sampling equipment.
- Sanitize the compressed-air sampling connection using an approved disinfectant procedure.
- Allow the compressed air to flow for a defined stabilization period.
- Connect the qualified sampling device to the compressed-air point.
- Collect the predetermined volume of compressed air.
- Process the sample according to the approved microbiological method.
- Incubate the recovery medium or membrane under specified conditions.
- Record the number of recovered colonies.
- Report the result in the appropriate unit, such as CFU/m³.
- Investigate any result exceeding the established alert or action limit.
Detection of Specified Microorganisms
Where required by the risk assessment, compressed air may be evaluated for specified microorganisms.
Examples include:
- Escherichia coli
- Salmonella species
- Pseudomonas aeruginosa
- Staphylococcus aureus
The media and confirmation procedures should be based on the current approved microbiological method.
A typical screening approach may include:
| Target Organism | Example Selective Medium |
| Escherichia coli | MacConkey Agar |
| Salmonella spp. | Brilliant Green Agar or another validated selective medium |
| Pseudomonas aeruginosa | Cetrimide Agar |
| Staphylococcus aureus | Mannitol Salt Agar |
Presumptive colonies should not be identified solely on colony appearance. Appropriate confirmation, such as Gram staining, biochemical identification or a validated identification system, should be performed where required.
Colony Observation
Typical colony characteristics may provide preliminary information but should not be treated as definitive organism identification.
Examples include:
- Cetrimide Agar: colonies of Pseudomonas aeruginosa may show greenish pigmentation or other characteristic reactions.
- Mannitol Salt Agar: presumptive Staphylococcus aureus colonies may produce yellow coloration associated with mannitol fermentation.
- MacConkey Agar: lactose-fermenting organisms may produce pink to red colonies.
- Brilliant Green Agar: presumptive Salmonella colonies may show characteristic colony appearances depending on the formulation and incubation conditions.
The current manufacturer’s instructions and approved laboratory method should always take precedence over generic colony descriptions.
Acceptance Criteria – Compressed Air System Qualification
Acceptance criteria shall be established in the approved qualification protocol before execution of the study.
A typical site specification may include the following parameters:
| Test | Example Acceptance Requirement |
| Moisture | Within approved site specification |
| Oil | Within specified compressed-air purity class / site limit |
| Non-viable particles | Within approved particle purity specification |
| Microbiological quality | Within approved alert/action limits |
| Specified pathogens | Absent where required by risk assessment |
The original draft specifies NMT 0.25% moisture, absence of visible oil, 90,000 particles/m³ at ≥0.5 µm, 1,000 particles/m³ at ≥5 µm, an alert level of 75 CFU/m³ and an action level of 90 CFU/m³.
These values should be retained only if they are supported by the site’s approved specifications, intended application, risk assessment, historical data and applicable standards. They should not be presented as universal regulatory limits.
FDA inspection guidance specifically expects manufacturers to establish appropriate specifications and monitoring programs for product-contact process gases, including evaluation of particulates, moisture, oil and bioburden.
Evaluation of Qualification Results
All qualification results shall be reviewed against the approved acceptance criteria.
The evaluation should include:
- Individual test results.
- Sampling locations.
- Date and time of sampling.
- Equipment identification.
- Instrument identification and calibration status.
- Test method.
- Deviations, if any.
- Previous results and trend data.
- Any abnormal observations.
Any result outside the approved acceptance criteria shall be documented and investigated through the applicable deviation or OOS/OOT procedure.
The compressed air system shall not be considered qualified solely because individual test results pass. The overall system performance, sampling coverage and consistency of results should also be evaluated.
Qualification Acceptance
The compressed air system may be considered qualified when:
- All required qualification activities have been completed.
- All critical acceptance criteria have been met or deviations have been scientifically justified and approved.
- Required sampling points have been evaluated.
- Test instruments were within calibration.
- No unresolved critical deviation remains.
- The system demonstrates reproducible performance.
- The compressed air quality is suitable for its intended application.
- The qualification report has been reviewed and approved by QA.
Requalification shall be done
Requalification shall be performed when required by risk assessment, historical performance or changes to the system.
Requalification should be considered following:
- Major modification to the compressor or distribution system.
- Replacement of critical components that may affect compressed-air quality.
- Modification of the compressed-air distribution network.
- Replacement or relocation of critical filters.
- Major changes to dryer configuration.
- Changes in the intended use of compressed air.
- Significant adverse trends.
- Repeated excursions from established limits.
- Major maintenance activities that could affect air quality.
- Prolonged system shutdown where justified by risk assessment.
- Significant contamination events.
- Regulatory or quality-system requirements.
The original statement of automatic three-year requalification should be changed to a risk-based periodic requalification frequency, unless the site’s approved validation master plan or quality system specifically establishes a three-year interval.
Annual Verification
Where justified by the site’s monitoring strategy, annual verification may include testing of critical compressed-air quality attributes such as:
- Moisture/water
- Oil
- Non-viable particles
- Microbiological quality, where applicable
The exact frequency should be defined through the site’s qualification and utility-monitoring program.
Trending of historical data is important because a gradual deterioration in compressed-air quality may indicate filter blockage, dryer performance problems, compressor deterioration, moisture ingress or distribution-system contamination.
- Change in intended application.
- Modification of pressure or flow requirements.
The change-control assessment shall determine whether partial or complete requalification is necessary.
References
- ISO 8573-1, Compressed air — Part 1: Contaminants and purity classes.
Suggested SOP Abbreviations
| Abbreviation | Full Form |
| SOP | Standard Operating Procedure |
| QA | Quality Assurance |
| QC | Quality Control |
| OQ | Operational Qualification |
| PQ | Performance Qualification |
| DQ | Design Qualification |
| IQ | Installation Qualification |
| GMP | Good Manufacturing Practice |
| P&ID | Piping and Instrumentation Diagram |
| SCDM | Soyabean Casein Digest Medium |
| CFU | Colony Forming Unit |
| IPA | Isopropyl Alcohol |
| KF | Karl Fischer |
| NMT | Not More Than |
| NLT | Not Less Than |
| OOS | Out of Specification |
| OOT | Out of Trend |
History of Change
| Effective Date | Change Control No. | Description of Change |
| — | — | New SOP / Initial Issue |
Related Article