Pharmaceutical Compressed Air and Compressed Gases: Microbial Quality Standards and Expectations

Introduction

Compressed gases are used at various steps of the pharmaceutical manufacturing process. Applications include weighing stations process line; use of gas to maintain an inert atmosphere above a liquid or powdered product inside a storage tank, silo, reactor, fermentation and cell culturing processes, process equipment, or other vessel; use of liquid nitrogen for the preservation of biological samples; use of inert gas to pressurize new, repaired, or modified tanks, pipelines, and vessels; and use of inert gas to displace air and contaminants from storage tanks. Furthermore, compressed gases such as air, nitrogen, and carbon dioxide are deployed in operations involving purging or overlaying. Nitrogen is also used in many freeze-drying processes to create lyophilized products.

Compressed gas sampling for microorganisms is an important part of contamination control assessment.1 While sampling is important, the method of sampling can be hindered by the design of the gas system, where sampling is not easily conducted in an aseptic manner, or by the design of the air-sampling instrument. This section reviews the important aspects of compressed air sampling for microbiological assessment and looks at sources of contamination, should any microorganisms be recovered.

Purity is a factor that needs to be maintained with compressed gas; hence the gas should be supplied oil-free (as assessed by measuring Total Hydrocarbon and Total Volatile Hydrocarbons). In addition, a level of microbial control is required, depending on the application and whether the process step is sterile or non-sterile. Sometimes a level of confusion arises with auditors assuming medical grade standards should be applied. This is indeed not necessary and a more considered approach is required, based on the application of the compressed gas.

This article considers the important points for supply, control, and testing as applicable to pharmaceutical facilities.

Achieving the Required Purity

Purity overall is achieved through a combination of filtration, purification, and separation. The process of creating the compressed gas can additionally introduce water vapor; thus, a process must be in place to remove water vapor before the gas is pressured into a critical zone like a cleanroom. Compressed gas is typically discharged from the compressor hot, and it will contain water vapor. Temperature is reduced by using a post-compressor cooler and, as the gas condenses, the water vapor and other impurities can be removed. The risk of water vapor is particularly high with compressed air, which is drawn into a compressor via the atmosphere. Atmospheric air contains a high proportion of water vapor (that is water in a gaseous form). Water removal is achieved through a combination of filtration and dehumidification devices.

Compression is carried out by inducing velocity into the air, where the energy of the air in motion becomes converted into pressure; or compression is created by mechanically reducing the quantity of air in a given space. For larger facilities, interconnected distribution systems are typically in place. The valves and fittings in place must be of a sanitary design, for it is possible to introduce contamination at the point of use through poorly designed connectors and valves.

Contamination Risks

Where the air is drawn in from the outside, the process of drawing in the air also introduces particles and microorganisms (where most microorganisms will be found in association with particles), which require filtering out through the use of a bacteria-retentive filter. The level of filtering depends upon whether ‘sterile’ air is required (absence of viable microorganisms) or air with a low bioburden. Sterility, where required such as with an inhalation product, is achieved through the use of a bacterial retentive membrane filter (0.22 µm pore size), with an appropriate efficiency rating (such as 99.99%). Often a prefilter is in place to remove “gross” larger particulates.

The filter needs to be maintained dry because condensation in a gas filter will most probably cause blockage or lead to microbial contamination. Risks of condensate are controlled by heating and the use of hydrophobic filters (to prevent moisture residues in a gas supply system). Filters should also be changed periodically. As part of ongoing preventive maintenance/quality control, filters must be integrity tested at installation and the end of use.

Compressed Gas Standards

National standards bodies have guidance documents for compressed air sampling, and reference is made within FDA and EU GMPs, the general approach and requirements for compressed gasses are set out in a multi-part ISO standard: ISO 8573.² A separate standard exists for the production of compressed air. This is ISO 12500.³ The different regulatory requirements and standards can appear complicated, especially for pharmaceutical companies working in international markets. The table below sets out a comparison of the requirements, concerning:

• ISO 8573²
• ISO 12500³
• USP <1078><1078>⁴
• USP <1116>⁵
• USP <1229.15>⁶
• ISPE Good Practice Guide: Process gases⁷
• EU GMP Annex 1⁸
• FDA Lyophilization of Parenteral (7/93), inspection guide⁹
• ICH Q7¹⁰
• FDA Guidance for Industry Sterile Drug Products Produced by Aseptic Processing¹¹
• 21 CFR Part 210 (References 6 and 4, Appendix 8)¹²

Based on Table 1, there are choices for the pharmaceutical manufacturer based on the application of the compressed gas and the cleanroom grade within which it is used, in relation to particulate and microbial requirements.

Particles

Particles (such as dirt, rust, and pipe scale) can arise from the mechanical compression process and additional impurities may be introduced into the air system. Generated contaminants include compressor lubricant, wear particles, and vaporized lubricant. Furthermore, fittings and accessories can contribute to particles. Particles will also include microorganisms and the standard does not differentiate between the origin of particulates.

With purity, many parts of the pharmaceutical industry will use class 1 compressed gas based on the maximum number of permitted particulates. The particle limits are:

Microbiological requirements

Although compressed gas and air systems are inhospitable environments, they can aid microbial survival if there are available nutrients. The availability of nutrients is dependent upon the purity of the gas and airline. Nutrients suitable for metabolizing microorganisms include water and oil droplets. Another factor that can affect survival is temperature, especially where temperatures are warmer.¹³ In addition to vegetative cells, bacterial spores are well equipped to survive even harsh environmental conditions. Microbial content itself does not influence the gas purity class assigned, although the standards recommend that microbial levels are assessed. The different requirements in the standards and regulations are set out in Table 2.

For sterile products, for EU GMP Grade A/ISO 14644 class 5 areas, the microbial count would then be ‘no growth’ (what was expressed as < 1 CFU/ m³ until 2022) and the particle levels conform to the area at rest ≤ 3,520 particles per m³). The requirements in Table 2 have been written for sterile medicinal products. For non-sterile products, the consensus is that the microbiological quality of the gas must be at least as good as the cleanroom air quality in which the process is taking place.

Table 3 proposes microbiological requirements and minimum testing frequencies for gas or compressed air microbiological monitoring.

With the action levels set out in the table above, the levels achieved in a practical setting will be far lower. The final user should therefore set alert limits based on a historical review of the data and use these limits for trending purposes. Here limits setting is not dissimilar to approaches used for setting environmental monitoring alert levels.

When sampling compressed air or gas it is important that the air is depressurized and that the flow rate is controlled to ensure that a cubic meter of air is sampled within the required sampling time (this time will be instrument-dependent).¹⁴

Conclusion

Gases and air coming into contact with a pharmaceutical product must be of an appropriate chemical, particulate, and microbial quality. Compressed air sampling should be a key part of an environmental monitoring program, along with cleanroom assessments. The program should consider air points to be tested. This could be every point; points considered to be of greater risk (such as product contact); or representative points along a loop, as defined in a rationale. The frequency of testing must also be considered, and this too would need to tie into risk.

Therefore, the pharmaceutical manufacturer will need to determine the requirements for testing based on the following:

• Cleanroom grade
• Type of product manufactured
• Increased or reduced production schedules,
• Seasonal changes,
• Equipment changes and modifications,
• Replacement of hardware or filters and dryers,
• Inactivity of system.

This will lead to different requirements depending on the cleanroom grade and application and ultimately fit the purpose for the final user.

References

1. Sandle, T. (2013). Contamination Control Risk Assessment in Masden, R.E. and Moldenhauer, J. (Eds.) Contamination Control in Healthcare Product Manufacturing, Volume 1, DHI Publishing, River Grove: USA, pp423-474
2. ISO 8573-1:2010 Compressed Air Contaminants and Purity Classes, International Standards Organization, Geneva, Switzerland (and related parts)
3. ISO 12500-1:2007 Filters for compressed air — Test methods — Part 1: Oil aerosols, International Standards Organization, Geneva, Switzerland
4. USP chapter <1078> Good manufacturing practices for bulk pharmaceutical excipients, 2013, DOI: https://doi.org/10.31003/USPNF_M99797_01_01
5. USP chapter <1116> Microbiology control and monitoring of aseptic processing environments, 2012, DOI: https://doi.org/10.31003/USPNF_M99835_01_01
6. USP chapter <1229.15> Sterilising filtration of gases, 2017, DOI: https://doi. org/10.31003/USPNF_M10797_01_01
7. ISPE Good Practice Guide: Process gases, 2011
8. EU GMP Annex 1 Manufacture of Sterile Medicinal Products, Eudralex Volume IV, 2022, at: https://health.ec.europa.eu/system/fi les/2022-08/20220825_gmp-an1_en_0.pdf
9. FDA Lyophilization of Parenteral (7/93), inspection guide: https://www.fda.gov/ inspections-compliance-enforcement-and-criminal-investigations/inspection-guides/ lyophilization-parenteral-793
10. ICH Q7 “GMP Guide for Active Pharmaceutical Ingredients,” Chapter 20, https://www. complianceonline.com/resources/downloads/QMS-API.pdf
11. FDA Guidance for Industry Sterile Drug Products Produced by Aseptic Processing — Current Good Manufacturing Practice, 2004: https://www.fda.gov/media/71026/download
12. 21 CFR Part 210 (References 6 and 4, Appendix 8)
13. Marquis, R. (1982) Microbial Barobiology, BioScience, 32 (4): 267–271
14. Sandle, T. (2011): Key points for active air samplers, Clean Air and Containment Review, Issue 5, pp8-10

Author Details 

Tim Sandle, Head of GxP Compliance - Kedrion BioPharma, UK; Tommaso Paoli, Senior VP of Global Quality - Kedrion BioPharma

Publication Details 

This article appeared in American Pharmaceutical Review:

 Vol. 27, No. 4 May/June 2024

Pages: 34-39

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