Microbial / ISO 8573-7

ISO 8573-7 Micro Testing of Compressed Air

Micro Testing of Compressed Air or Bioburden Testing per ISO 8573-7 is generally conducted by the pharmaceutical, medical device and food industries. Microbial contaminants found in the compressor or compressed air lines can be devastating to a final product in these industries. A regular Micro Testing program can provide insight to a potential problem long before it brings production to a halt.

Microbiological Compressed Air Sampling per ISO 8573-7

Most pharmaceutical, medical device, and food manufacturing environments have environmental air sampling programs in place. However, compressed air or process air is frequently overlooked. Compressed air and process gases can be sampled using specialized samplers that use contact plates to capture any microorganisms present. Micro testing is imperative to avoid microbial contaminants inside controlled environments including production areas and clean rooms.

Microorganisms include bacteria, yeasts, molds and viruses. Millions of microorganisms enter the air system through the compressor intake. Intake filters do not remove these viable particles. Modern compressor systems, which are properly maintained, should have properly sized filtration and point-of-use filters to remove these contaminants. A monitoring program is essential to verify that filtration and routine maintenance is providing the protection required to keep your products safe. For more information about contaminants, visit our web page about Compressor Contamination Sources.

Compressed air systems can harbor the nutrients required for microbes to grow; namely water, oil, and warm temperatures. Maintaining a dry water level of -40°F can inhibit the growth of microbes but will not eliminate them. Bacterial spores can be resistant to U.V., desiccation or heat and can remain dormant for long periods, thus creating the potential for a reccurring problem. Further, there is another nasty contaminant known as biofilm. Biofilm can have negative effects on the compressed air quality as well. Biofilm creates a safe haven for bacteria and can provide nutrients to bacteria under conditions that might normally be considered too harsh. To learn more about biofilm, read this Microbiology Online article by Fabio Pacheco.

A microbial monitoring program as suggested by the International Society of Pharmaceutical Engineers’ (ISPE) Good Practice Guide – Process Gases, is a practice that any manufacturer using critical air or gas in their process should consider. The Guide goes on to state in Chapter 7, Risk Assessment, Table 7.1:
Microbial Count (Non-sterile applications) – Guideline limits to be established based on product bioburden limits. Typical level NMT 5 cfu/m3
Microbial Count (Sterile Applications) – As per viable particle requirements for Grade area where the product is exposed to the compressed gas (e.g. Grade A, Grade A/B, Grade B or Grade C)
(from US FDA 2004 Aseptic Processing Guidance.)

Due to the lack of definitive limits for microorganisms, many refer to the limits established for cleanroom classifications shown below.

Cleanroom Classifications a

Clean Area Classification
(0.5 µm particles/ft3)
ISO Designation b ≥0.5 µm particles/m3 Microbiological Active Air Action Levels c
Microbiological Settling Plates Action Levelsc,d
(diam 90mm; cfu/4 hours)
100 5 3,520 e e
1,000 6 35,200 7 3
10,000 7 352,000 10 5
100,000 8 3,520,000 100 50
  1. All classifications based on data measured in the vicinity of exposed materials/articles during periods of activity.
  2. ISO 14644-1 designations provide uniform particle concentration values for cleanrooms in multiple industries. An ISO 5 particle concentration is equal to Class 100 and approximately equals EU Grade A.
  3. Values represent recommended levels of environmental quality. You may find it appropriate to establish alternate microbiological action levels due to the nature of the operation or method of analysis.
  4. The additional use of settling plates is optional.
  5. Samples from Class 100 (ISO 5) environments should normally yield no microbiological contaminants.

Recommended Limits for Microbial Contamination a

Grade Air Sample cfu/m3 Settle Plates
(diameter 90mm)
cfu/4 hours b
Contact Plates
(diameter 55mm) cfu/plate
Glove Print
5 fingers
A < 1 < 1 < 1 < 1
B 10 5 5 5
C 100 50 25 -
D 200 100 50 -
  1. These are average values.
  2. Individual settle plates may be exposed for less than 4 hours.
Air & Gas Specifications referenced above may be viewed and/or purchased from: ANSI - American National Standards Institute

ISO 8573-7:2003 is an excellent source for establishing sampling methods although it does not provide limits. On the subject of microbial contamination in compressed air used in food plants, “Drying the air to a low dew point is an effective way to inhibit this microbial growth. Inhibit – not kill”, is what Parker Hannifin’s Lee Scott has to say. Read more from Lee Scott on Reducing Contamination Risks of Compressed Air in Food Plants: Benchmarking Good Manufacturing Practices.

The BCAS Food Grade Compressed Air, A Code of Practice states, “6.2 Microbiological contaminants HACCP shall establish the risk of contamination by microbiological contaminants. The level of viable microbiological contaminants in the compressed air shall not be detectable using the method described in clause 7.6.” Clause 7.6 refers to ISO 8573-7 test method for viable microbiological contaminant content.

The SQF Code, Edition 7 states that compressed air “shall be regularly monitored for purity”. On their website they go on to say, “Food processing facilities need to operate from a fundamental assumption that compressed air can be a source of chemical and microbiological contamination. Food facilities must verify and validate the compressed air used in their facility is appropriate for use and not a source of contamination.” Read more on air purity testing from SQF.

Trace Analytics offers the AirCheck Kit™KPSII Microbial Impaction Sampler in addition to offering the AirCheck Kit™ K8573NB and K8573NX models for the testing of particles, water, oil, and gases, in compressed air and process gases.

All AirCheck Kits™ are available for rent or purchase. For more information about compressed air quality testing for the manufacturing industry, contact us today. We are happy to discuss your needs and assist you with testing for your operation.

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