What contaminants are lurking in your compressed air supply? Compressed air testing can tell you what type of contaminants are present in your compressed air and in what quantities - including dry particulate, oil carryover, moisture and microbes. Understanding your compressed air quality can help you avoid big problems down the road when it comes to compressor maintenance, product quality and regulatory compliance.
Why Test Compressed Air?
Compressed air testing is recommended for any application that requires air to meet certain quality standards - and may be required for some regulated industries. It can also be used to detect impurities that may cause problems with products or equipment. Compressed air testing:
- Ensures compliance with regulatory requirements or application specifications for compressed air quality.
- Provides an indicator of potential problems within the compressed air system that should be addressed, such as excessive oil carryover or bacterial growth.
Air used in food processing, medical applications, pharmaceuticals, chemical production and other sensitive applications may need to meet certain purity standards to meet regulatory requirements and ensure product quality and safety. In these cases, air testing may be required by law to ensure compliance and safety.
But what about “dirty” applications such as compressed air use in automotive service centers, metalworking facilities, manufacturing plants or packaging lines? While these applications may not face the regulatory pressures of the “cleaner” industries, compressed air testing can still provide valuable insights into the health of the compressed air system and prevent problems down the line. For example, excessive moisture can cause corrosion in pneumatic tools and equipment as well as in the compressed air distribution system. Oil carryover may indicate a problem with the compressor oil pump or inline filtration. Understanding your air quality can help you diagnose and address issues before they cause problems in your compressed air system, air-using tools or final products.
Understanding Compressed Air Quality
Compressed air quality is determined by measuring the levels of contamination. Under ISO 8573, air is classified along three variables: dry particulate, humidity and liquid water, and oil concentration. Purer air has lower concentrations of these contaminants. For some applications, it may also be necessary to test for microbial contamination and gas-phase contaminants.
Types of Contamination in Compressed Air
There are four main types of contaminants to be concerned about in the compressed air system.
Dry particulate includes particulate matter (PM) such as pollen, dust, combustion byproducts (e.g., soot), smoke, and rust.
The EPA classifies particulate matter by size. PM10 includes particulate of 10 microns or smaller and is considered to be inhalable. PM2.5 includes particulate of 2.5 microns and smaller.Dry particulate in the compressed air supply may contaminate final products (e.g., food, pharmaceuticals, paints and coatings) or foul pneumatic tools and equipment.
- Moisture includes both aerosolized liquid droplets of water and water vapor. Moisture in compressed air can lead to corrosion in the distribution system or pneumatic tools and equipment. Excess moisture can also lead to product quality issues in many applications. (Here’s why Moisture in Your Compressed Air System Is a Bad Deal).
- Oil carryover includes aerosolized or vaporized oils and lubricants. Depending on their origin, these may include mineral oil and petroleum-based motor oils, food-grade oil or synthetic lubricants. Oil - especially petroleum-based oil - is an unwelcome additive in food, pharmaceutical or medical applications. Oil can also mix with dry particulate to form a sludge that builds up in the compressed air system or pneumatic tools, creating maintenance issues.
- Microbial contamination includes bacteria, viruses, and molds. If molds and bacteria are breeding within the compressed air system, that can create a health and safety issue for workers or consumers, especially in food or pharmaceutical production. Viruses tend to be less of a problem inside the compressed air system, as they are not able to replicate without a living host.
Sources of Contamination in Compressed Air
Contaminants in the compressed air system may come from both external and internal sources.
- Intake air can contain many different types of contaminants, including dust and pollen from the outdoors, particulate or chemical vapors created by production processes, combustion engine exhaust, and other material.
- Almost all of the moisture inside the compressed air system also comes from intake air. The amount of moisture will depend on the humidity level (dew point) of the intake air. In a warm, wet climate, intake air will contain more water vapor than air in cooler, dryer conditions. As air is compressed, the water vapor is compressed, too, creating saturated air. Because cool air can’t hold as much moisture as warm air, this excess moisture falls out of the air as condensate as the air cools in the distribution system.
- Oil carryover may come from both internal and external sources. In an oil-flooded rotary screw, rotary vane or reciprocating (piston) air compressor, a lubricant is used to reduce friction between moving parts and create a seal in the air end. Some of this oil can end up in the compressed air supply. Oil can also enter the system through intake air, especially if the compressor intake is near industrial processes that create aerosolized oils and lubricants (e.g., metalworking fluids).
- Microbial contamination comes into the system through intake air, but molds and some kinds of bacteria can grow inside the compressed air system if conditions are right. Moisture in the air or liquid pooling in the compressed air distribution system can create a breeding ground for certain kinds of bacteria and molds.
Compressed Air Quality Standards
The International Standards Organization (ISO) has created the most widely used and recognized standard for compressed air quality. ISO 8573 lays out purity classes for compressed air according to its concentrations of particles, water and oil.
ISO purity classes follow an [A]:[B]:[C] format, with A being dry particulate, B humidity and liquid water, and C total oil concentration (aerosol, liquid and vapor). Air may have different purity classes for each constituent. For example, air classified as 1:2:1 has a purity class of 1 for dry particulate, 2 for moisture and 1 for oil. Purity classes range from 1 to 10 (or X), with 1 being the cleanest. Class 0 air must be even cleaner than class 1 but does not have specific standards; instead, it must meet application-specific criteria (for example, for use in cleanroom conditions).
- Dry particulate is measured by number and size (number of particles in different micron ranges) for classes 1 – 6 and by mass (mg/m3) for classes 6 – X.
- Moisture is measured by Vapor Pressure Dewpoint for classes 1-6 and by liquid mass (g/m3) for classes 7 and up.
- Oil is measured in mass (g/m3) at all purity classes.
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What Is ISO 8573 Compressed Air Quality Standard?
Chart from Trace Analytics used with permission.
ISO 8573 does not have purity classes for gas-phase contaminants (such as volatile organic compounds (VOCs), carbon monoxide, carbon dioxide, sulfur dioxide or nitrogen oxides) or for microbial contaminants. However, industry- or application-specific standards may apply for these types of contaminants.
Other standards may apply to certain industries, such as food and pharmaceuticals. For example:
The SQF Code , from the Safe Quality Food Institute, provides additional guidance for food and beverage manufacturers on compressed air quality. SQF 126.96.36.199 and 188.8.131.52 require air that comes in contact with food or food contact surfaces to be clean and to be regularly monitored and maintained.
- The British Retail Consortium (BRC) requires compressed air monitoring to ensure that there are no contaminants that may provide a health or food safety risk.
How to Test Compressed Air
Compressed air testing should be conducted by a qualified and accredited laboratory. Some kinds of testing are done on-site, and other types of testing require taking samples of compressed air from your system and sending them back to a laboratory for analytical testing. The type of testing required will depend on how compressed air is used; breathing air requires more stringent testing than non-breathing air, and regulated industries such as food and pharmaceutical production require more stringent testing than general manufacturing.
Types of Compressed Air Testing
There are several different SQF Code that can be conducted on compressed air. ISO 8573 outlines Compressed Air & Gas Testing Specifications. Other standards include NFPA 1989, NFPA 99, OSHA, CGA and CSA, among others. Make sure that the laboratory you select is fully accredited for your application. If you’re not sure what kind of testing you need, talk to a compressed air testing specialist.
The goal of particulate testing is to determine the particle size distribution and concentration in compressed air. These tests can be used to assign a purity class for dry particulate according to ISO 8573. Tests may include:
- Laser particle counter (LPC): This test can be used on-site, which is a big advantage for troubleshooting the source of contamination. It provides a count of particles at all three size ranges specified by ISO 8573 and can be used to measure purity down to Class 1.
- Filter collection with microscopy: This method collects particulate on a filter, which is later examined under a microscope to provide a particle count. It is necessary to know the pressure and flow rate for sampling to get an accurate estimate of particulate concentrations.
- Mass concentration: This method is typically used for air of Class 6 or above. It provides a total mass of particulate in a certain volume of air, reported in mg/m3. It does not provide particle counts or size distribution.
Water Vapor Testing
Moisture content can be measured in a couple of different ways.
- Hygrometers determine the dew point of air, which provides a measure of moisture content. A wet/dry bulb thermometer is one form of hygrometer. Others use electrical sensors. Hygrometer readers may be done on-site or in the lab. Some compressed air systems incorporate fixed-mount hygrometers for continual monitoring of dew point.
- Spectroscopy can be used to measure water content directly in the laboratory. Spectroscopy is widely used to identify different kinds of molecules in a sample.
- Detection tubes can be used for water vapor testing using the chemical-length-of-stain method.
Oil may be present in a sample as an aerosol (liquid droplets suspended in air) or a vapor. Testing methods depend on the level of contamination and the purity class requirement for the sample.
- Heavier concentrations of oil aerosols are typically measured using a membrane system that separates the oil from the air. Oil concentrations are determined by weighing the amount of oil captured by the membrane.
- Oil vapor and organic solvent content testing (usually used for purity classes 1 and 2) is usually done using gas chromatography.
Analytic testing can be used to determine what types of microbes are present and in what quantities. Testing is usually focused on microbes that cause particular problems, such as foodborne illnesses or respiratory diseases. These may include bacteria such as Listeria, E.Coli and Salmonella and fungal species such as Candida and various molds and yeasts. Microbial testing may be either qualitative or quantitative.
- Qualitative testing simply reports the presence or absence of specific microbes.
- Quantitative testing tells us the number of microbes present in a specified volume. ISO 8573-7 requires quantitative results and provides guidance on validated sampling methods.
Microorganisms can be identified using a variety of analytical methods, including visual macroscopic and microscopic identification and molecular methods.
- The sample is usually cultured, using a petri dish to allow organisms to grow into a colony. Identification may be made by looking at both macroscopic characteristics (colony shape, color, borders, etc.) and microscopic characteristics (physiology, Gram staining reaction, etc.).
- Identification may be completed or confirmed using molecular methods. These methods include genetic testing and other forms of molecular analysis that “fingerprint” organisms based on various characteristics.
Sampling Compressed Air
Sampling methods depend on the type of analytical testing that will be conducted. It is important to get a clean sample that is not contaminated by ambient air, which may result in false positives for all types of contaminants. For microbial testing, aseptic techniques must also be used to ensure that sampling equipment and containers are not contaminated by contact with hands or surfaces.
Samples may be taken at the outlet of the air compressor, at the point of use, or at other points in the distribution system. Taking multiple samples at different points may be useful in identifying the source of contamination in the system.
Depending on the type of testing that will be conducted, sampling may involve:
- Collecting a volume of compressed air into a clean container to send to a lab.
- Running a defined volume of compressed air through a filter or membrane to collect particulate, microbes or oil aerosols.
Always follow laboratory instructions exactly when collecting compressed air samples for analytical testing. Your laboratory will send you a sampling kit for the test(s) you want to have conducted. Alternatively, you may want to have a trained technician come to your facility to collect the samples for you.
How Often Should Compressed Air Be Tested?
Your compressed air sampling schedule will depend on how you are using air and what issues you are seeing in your facility.
- Breathing air should be tested at least every three months.
- Air used for regulated industries such as food and pharmaceutical production should be tested at least annually (some experts recommend every six months).
- For non-regulated industries, there are no specific requirements for compressed air testing intervals. However, annual testing for particulate mass, dew point and oil carryover can help to identify emerging problems in the compressed air system and avoid problems with tools, equipment and finished products. Testing should also be conducted if a problem is identified with compressed air (visible particulate, bad odor, etc.).
Need Help with Compressed Air Testing?
Fluid-Aire Dynamics works with Trace Analytics as our partner for compressed air testing. Trace Analytics provides a full range of compressed air testing services and is fully accredited by the American Association for Laboratory Accreditation in accordance with ISO/IEC 17025:2017. Our service technicians have been trained to collect compressed air samples using Trace Analytics test kits for laboratory testing.
Whether you’re having problems with your air or just need to set up a regular air quality monitoring program, we can help to connect you to the service you need. We can also help you identify the right air treatment strategy to achieve your purity class requirements, including air dryers and inline filtration. With proper treatment and monitoring, you can be sure that your air is clean, dry and oil-free.