MICROBIAL CONTAMINATION OF COMPRESSED AIR
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 recurring 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 (CFU/M3) | MICROBIOLOGICAL SETTLING PLATES ACTION LEVELSC,D (DIAM 90MM; CFU/4 HOURS) |
|---|---|---|---|---|
| 100 | 5 | 3,520 | 1 e | 1 e |
| 1,000 | 6 | 35,200 | 7 | 3 |
| 10,000 | 7 | 352,000 | 10 | 5 |
| 100,000 | 8 | 3,520,000 | 100 | 50 |
| All classifications based on data measured in the vicinity of exposed materials/articles during periods of activity.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.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.The additional use of settling plates is optional.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 CFU/GLOVE |
| A | < 1 | < 1 | < 1 | < 1 |
| B | 10 | 5 | 5 | 5 |
| C | 100 | 50 | 25 | – |
| D | 200 | 100 | 50 | – |
| These are average values.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 |