Using ISO 8573 to Test Compressed Air
Compressed air is used in the production of pharmaceuticals, food, beverages, medical devices and other products. Worldwide, it is used in more than 70 percent of all manufacturing activities ranging from highly critical applications that may impact product quality, to basic uses such as simple air lines to provide power for tooling.
Here at IATT, we can help clear up some of the confusion surrounding the standard and also provide best practices for setting up a compressed air monitoring programme.
What exactly are the Contaminants in Compressed Air?
ISO and other major authorities state that there are 3 major contaminants that typically need to be removed or reduced from compressed air used in manufacturing. The 4th mainly concerns breathing air which we will cover in another section.
- Particles (from pipe scale, wear particles and atmospheric dirt)
- Water (liquid, vapour and aerosol)
- Oil (liquid, vapour and aerosol)
- Microorganisms
The international standard ISO 8573-1:2010 is a compressed air quality specification that addresses
these very same specific contaminants by providing a range of purity classes for particles, water and oil. It does not include classes for gases or microorganisms.
How to Designate ISO 8573-1 Purity Classes
The designation of ISO 8573.1 Purity Classes for compressed air includes the specification name and edition date, followed by the purity class number(s) in brackets. The designation is presented in the following order and separated by a colon: ISO 8573-1:2010 [Particles:Water:Oil]*
Where:
P is the Purity Class for Particles (Classes 0 to 7, X)
W is the Purity Class for Water (Classes 0 to 9, X)
O is the Purity Class for Oil (Classes 0 to 4, X)
*ISO 8573-1 actually uses the letters ABC, but for this purpose, PWO makes is easier to remember the correct order.
Specification Example #1: ISO 8573-1:2010 [2:2:1]
This indicates Class 2 for particles, Class 2 for water, and Class 1 for oil.
Specification Example #2: ISO 8573-1:2010 [2:-:1]
When a class for any particular contaminant (either P, W, or O) is not specified, the designation shall be replaced by a hyphen (as seen in Example 2). This indicates that water is not classified.
Specification Example #3: ISO 8573-1:2010 [1:2:0 (0.001)]
The use of the term Class 0 is frequently misunderstood and misused. When specifying air quality that meets Class 0, the limit MUST be included in the designation, AND it must be more stringent than Class 1 (Refer to Example 3). Class 0 does not mean that there are zero contaminants. This indicates Class 1 for particles, Class 2 for water, and Class 0 for oil with a limit of 0.001 mg/m 3 . When requesting filtration or analysis to Class 0, always provide a limit that is more stringent than Class 1.
Is there any guidance on selecting Purity Classes?
Clean, dry air is typically needed by food, beverage, pharmaceutical and other industries manufacturing a consumable product.
As a voluntary code of practice, BCAS Food and Beverage Grade Compressed Air Best Practice Guideline 102 stipulates compressed air that is in direct contact with the product should meet or exceed ISO 8573-1:2010 [2:2:1] and [2:4:2] for indirect contact. It also states that compressed air purity shall be tested and verified at least twice per year and whenever maintenance work or an activity occurs that may affect the air quality (www.bcas.org.uk)
The effects of particles, moisture and oil in your compressed air system
The contaminants can harm your production in three main ways. Specifically, they can reduce the performance of your compressed air system itself; negatively impact your air-powered equipment and impact the integrity and quality of your end products. Individually, each of them can negatively impact your system. In combination, however, they can be even worse. For example; the oil and moisture in your compressed air can allow the microorganisms contained in the intake air to grow and thrive.
This poses a serious challenge. After all, one cubic meter of ambient air can contain more than 140 million particles from dust to microorganisms like bacteria, viruses and bacteriophages. In fact, they are so small (microorganisms range from 0.0.4 µm to 4 µm) that they can’t be caught by an inlet filter.
Because they are living organisms, they would multiply if the conditions are right, such as in non-dried compressed air.
This is particularly bad in the food & beverage, medical and pharmaceutical industries and could have catastrophic consequences if microorganisms like bacteria and fungi were to contaminate food and pharmaceuticals.
Particles
Some manufacturing processes include flexible tubing or hoses after the point-of-use filters. Common rubber, nylon and other flexible tubing, can shed numerous particles that can affect product quality. This is a good example why particle testing samples should be taken at the point of use.
While the compressed air quality might be perfect, adding a hose to the operation can adulterate the quality of the air being used on the final product. It is important to specify tubing or hose with low particle shedding and low water permeation properties.
Other common causes for particle count failures can be attributed to fittings, gauges or other items using O-rings or rubber gaskets. The O-rings will deteriorate due to friction and/or age. Everyone involved — from the end user; service distributor and compressor manufacturer to the filter manufacturer and the testing laboratory — must use a common language when discussing clean, dry air. ISO 8573-1 Purity Classes make that easy to accomplish and the standard is proving to be the preferred language.
What can IATT offer to detect Particles?
Particle Counter
A laser particle counter – a highly specialised electronic device – can be used to sample according to ISO 8573 compressed air quality standards. This method can effectively analyse air samples for particles of all size ranges.
The use of a laser particle counter is advantageous as it provides rapid analysis of particle concentrations of air samples (typical running time is about 10 minutes) and provides information on air quality via screen readouts. As a result, laser particle counters are particularly useful when multiple samples are to be checked for quality within a short timeframe. The particles are counted in microns (µm) and our testing equipment is calibrated to find 5µm, 0.7µm, 0.5µm & 0.3µm.
Moisture
Moisture is constantly contained in our ambient air. It enters the compressed air piping system through the intake in the form of water vapor. This water vapor is the most prominent contaminant found in compressed air in total volume terms and it forms most of the liquid contamination that can be found in any air system.
The water content is measured in terms of the dewpoint. It is the temperature at which the compressed air is still able to handle its water vapor content before the moisture forms condensate. If the moisture is not removed, it can reduce the service lives of pneumatic equipment through corrosion. In addition, it could lead to bacterial growth which could adversely impact the quality of final products. This is especially problematic in applications in the food and beverage and pharmaceutical sectors.
While air quality is not as important for some processes, it is crucial to applications in the food &
beverage and pharmaceutical sectors, where bacterial growth would be particularly harmful.
What can IATT offer to detect Moisture?
Detection Tubes and Hygrometers
This air testing method detects water vapour impurities in compressed air samples. The following methods utilise either the physical properties of water or elicit chemical reactions to measure water vapour saturation.
Hygrometers used for ISO 8537 air quality testing come in various sizes and specifications. There are key features which all good quality hygrometers must possess:
• Must be easily calibrated
• Hygrometers should be easily modifiable to sample air from pressurised sources
• The exact accuracy and degree of measurement precision for the device must be known
Typical Detection Tube devices work by creating a chemical reaction which manifests as a measurable colour change in the hygrometer column when a certain level of moisture-saturated air is passed through it.
A Portable Hygrometer gives a precise calibrated figure of the dewpoint present. This is used by allowing air to pass over a ceramic plate which measures the content of the moisture and then calculates the dewpoint giving an instant readout on a LCD screen. These can be used for either Atmospheric Dewpoint or Pressure Dewpoint.
Oil
The quantity of oil in compressed air depends on several factors, including the type of machine, design, age and condition. There are two main types of compressor design in this respect: those that function with lubricant in the compression chamber and those that function without lubricant. In lubricated compressors, oil is involved in the compression process and also is included in the (fully or partially) compressed air. However, in modern, lubricated piston and screw compressors, the quantity of oil is very limited.
Oil testing is done for many varied types of hydrocarbon compounds which include:
• Oil
• Condensed hydrocarbons
• Oil vapour
• Total gaseous hydrocarbons
The presence of these oil fractions is reported in parts per million
What can IATT offer to detect Oil Vapour and Aerosol Detection Tubes?
Oil vapour testing is done for hydrocarbon compounds. This method employs either a Chemical Test Tube or an Oil Impactor which takes a sample of the air as it passes through the system. The chemical compound will change colour and the impactor will show dark spots.
IATT Monitoring Programme
What Constitutes a Monitoring Programme?
The goal of any compressed air quality monitoring programme should be to assure that air used in the manufacturing process is in a state of constant control and will not add contamination to the product. Steps to establish a monitoring programme include:
• Document the current compressed air system in place. Include the type of compressor (oil- free, oil lubricated); type of system filtration for particle, water and oil removal; storage tank capacity; type of point-of-use filters; and material used for distribution piping (stainless steel, copper, aluminium, galvanised, etc.). Include: make, model, serial, and part numbers. This information will provide insight as to the quality of air expected.
• Create a diagram of the compressor system, piping and outlets. Indicate type of usage for each outlet, including direct or indirect product contact, and non-product contact. If point-of-use filters are installed, indicate their location and the type of filter. This will identify which product lines must be tested and aid in preparation and selection of a representative number of sampling outlets.
• Document air compressor maintenance. This should include filter changes, compressor maintenance, changes or additions to the distribution piping, emergency repairs, etc. This could be useful troubleshooting information in the event of a failure. It can also be a guide in determining sampling intervals.
• Perform air quality testing for particles, water, oil, and microorganisms over a period of time to gather sufficient data points for a trend analysis. Ensure that a variety of points of use are sampled at various times throughout the year and are representative of air used during a production cycle.
• This variety in sampling is intended to catch irregularities that may occur due to weather conditions or other unknown procedures. It is also recommended to include sampling immediately before point-of-use filter changes to determine if air quality was acceptable at the end of the filter life.
• Review trend analysis results. This will provide valuable information to either confirm or establish purity classes appropriate for product safety.
• A monitoring programme for compressed air is not about checking an item off an audit checklist. A monitoring programme should be designed to either a) confirm that air quality is meeting levels specified in corporate quality control documents or b) identify over time the appropriate compressed air quality for the product being manufactured so that purity classes can be selected and documented.
ISO 8573-1:2010 is an internationally accepted language that can be used between the compressor manufacturer, filter manufacturer, product manufacturer and analytical laboratory to confirm the safety of compressed air used in the manufacturing process.
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