A tour of any modern manufacturing facility will uncover the extensive use of compressed air.
Production managers and quality managers may not be aware of the potential hazards associated with this common utility. Untreated, compressed air entering a wet air receiver and distribution system contains many contaminants, and one of the most problematic is water. Water not only causes corrosion, but it also promotes the growth of harmful micro-organisms.
Whether compressed air comes into direct contact with a product, or is used to automate a process, provide motive power, package products, a clean, dry and reliable source of compressed air is essential to maintain a safe, efficient, and cost-effective production process.
This blog examines sources of microbial contamination, factors that contribute to microbial growth, risks associated with untreated compressed air, and the most effective methods of control.
To learn more about the risks of micro-organism contamination in a compressed air system, testing methods, examples of microbial growth, technology recommendations, and best practices for cost-effective system design, download the white paper.
Ambient air is the air we breathe and it’s all around us. It’s also the air that is drawn in by air compressors. One cubic meter of ambient air typically contains between 140 and 150 million dirt particles — and anywhere up to 100 million of these could be micro-organisms. Eighty percent of these particles are smaller than 2 micron in size and not visible to the human eye. The images below show examples of the types of micro-organisms and their sizes found in ambient air.
Large volumes of ambient air are drawn into the compressor intake as the compressor is running. Particles the size of micro-organisms are too small to be captured by panel and intake filters, so they travel freely into the compressed air system.
When the air is compressed, it is "squeezed" down into a smaller volume. Since the compression process raises the temperature of the air, the air needs to be cooled before use. This process condenses water vapor into water aerosols and droplets, fully saturating the compressed air. As the wet compressed air enters the storage and distribution system, it provides the ideal environment for microbial growth.
If compressed air directly or indirectly contacts products, packaging materials, instrumentation, or production machinery, contamination is likely. Microbial contamination from compressed air can:
Untreated compressed air exhausted from pneumatic tools, valves, cylinders or machinery can also contain micro-organisms. If this exhausted air is inhaled by employees working nearby, it can lead to workforce illness. Workers should wear personal protective equipment (PPE) when handling compressed air condensate as it can also contain micro-organisms. Caution should be taken as condensate discharges. The condensate (containing micro-organisms) can be easily be inhaled, especially when timed solenoid drains or manual drains are used because these can aerosolise.
ISO 8573-7 is the international standard used to test compressed air for micro-organisms. It is used in conjunction with ISO 8573-4 (solid particulate).
First, the air is tested in accordance with ISO 8573-4 for solid particles. Next, samples are taken using a slit sampler to distinguish between a particle and a micro-organism. The slit sampler passes compressed air over an agar plate. The plate is then taken to a laboratory, incubated, and checked for growth. This test determines if the air is sterile or non-sterile and if required, provides a count of colony-forming units (CFUs).
Partial flow test equipment required
To control microbial growth, a combination of very dry compressed air and high-efficiency filtration should be used.
First, all traces of liquid water and water aerosols must be eliminated from the compressed air.
Next, the dewpoint of the compressed air must be reduced to a level known to inhibit the growth of micro-organisms. A dewpoint of <-26°C inhibits growth but is not available from dryer manufacturers who use the 3 dewpoints from ISO 8573-1 to classify dryer outlet dewpoint; therefore ≤ -40°C is used. The lower the pressure dewpoint, the more effective the control. Achieving the right dewpoint will stop the growth but micro-organisms can still survive and flourish again if exposed to moisture.
Combining the optimal dewpoint with high-efficiency dry particulate filters (particulate reduction down to 0.01 micron at 99.9999% efficiency) located at the point of use will significantly reduce microbial concentrations down to acceptable levels.
If sterile air is required for critical applications, such as pharmaceutical manufacturing, additional absolute rated air sterilization filters should be used to achieve 100% removal of micro-organisms and particles.
There are many different drying technologies available, but not all are able to deliver the outlet dewpoint required to inhibit the growth of micro-organisms. Types of dryers include:
The table below shows the six ISO 8573-1:2010 dewpoint classifications and typical dryer technologies used to achieve the required dewpoint.
The recommended pressure dewpoint to control the growth of micro-organisms is ≤ 40°C, equivalent to ISO8573-1:2010 Class 2 for water. The recommended specification for point of use dry particulate filtration is a high-efficiency grade providing particle reduction down to 0.01 micron with a removal efficiency of 99.9999%, equivalent to ISO 8573-1:2010 Class 1:2:1 or ISO 8573-1:2010 Class 1:2:0.
The warm, dark, moist air found in a compressed air system provides the ideal environment for microbes to grow and flourish. Untreated compressed air contains many potentially harmful or dangerous contaminants that must be removed or reduced to acceptable levels to protect consumers, employees, the brand, and provide a safe and cost-effective production process. The most effective way to control the growth and proliferation of micro-organisms is with a combination of very dry compressed air and high-efficiency filtration. For applications requiring sterile air, absolute rated air sterilization filters should be used.
Parker Oil-X filter range and modular dryer ranges have been designed to provide quality that meets or exceeds the levels shown in all editions of ISO 8573-1 and the BCAS Food and Beverage Grade Compressed Air Best Practice Guideline 102. Parker filtration and dryer performance have been independently verified by Lloyds Register.
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Download the white paper to learn more about the risks of micro-organism contamination in a compressed air system, testing methods, examples of microbial growth, technology recommendations, and best practices for cost-effective system design.
This article was contributed by Mark White, compressed air treatment applications manager, Parker Gas Separation and Filtration Division EMEA