Compressed air contamination can come in various forms, including particles, water, oil, and microorganisms. Non-viable particle contamination is specified in ISO 8573-4:2019 as one of the major contaminants in compressed air to be monitored. Troubleshooting particle contamination with Laser Particle Counters (LPCs) is the focus of this article.
A Valuable Troubleshooting Tool
Because compressed air systems are complicated and dynamic, the sources of particle contamination can be difficult to pinpoint. LPCs, which are an efficient and effective way to troubleshoot particle contamination, can quickly process multiple samples and provide real-time data. Doing so can greatly improve troubleshooting efforts and help to highlight problem areas. The results are only a snapshot of the system at that moment in time, but immediate results mean manufacturers do not have to wait for laboratory analysis which can take several days.
ISO 8573-4:2019 requires particles be sized into four ranges as listed in Table 1.
ISO 8573-4:2019 purity classes for particle contamination.
LPCs are a validated tool for sizing and counting particles instantly. Their ability to size and count particles into ranges can help determine if filters are functioning properly. Third-party companies can then extrapolate the LPC data and report it per the ISO 8573 standard.
These instruments must be calibrated on an annual schedule in accordance with ISO 21501-4 (ISO 8573-4:2019). There are a variety of options available to meet both facility needs and specification requirements.
ISO 8573-4 specifies non-viable particle contamination be monitored in compressed air.
Isolate and Address Problem Areas
LPCs are especially helpful when a problem exists with particles because they help to isolate the problem area. Recent maintenance, leftover construction materials, particle-shedding tubing, and O-ring breakdown can all introduce particle contamination into a compressed air system. Damaged or inappropriate filters can allow particles to pass through systems. No consumer wants metal shavings in their coffee grounds or rust in their canned tomatoes. LPC tests can help ensure preventive measures are working properly at critical control points.
The data provided by an LPC can provide useful information on where contamination is coming from. Collecting multiple sample locations across a system will allow manufacturers to see where the contamination originates. It can help users understand if something in the system is causing particle contamination or allowing it to pass through.
Technicians can compare a passing sampling point to the failing one. A sample can be taken at the source, immediately after the filter, to gain an understanding of the quality of the air at the beginning of the line. Another sample can then be taken at the end of the line to determine if there are any sources of contamination between the two points that might affect end products. Small adjustments can be made and new tests can be immediately taken to determine if that solution fixed the contamination issue.
LPCs take multiple samples quickly and provide instant results, therefore allowing manufacturers to move rapidly through multiple sampling points and compare the results. Trial and error testing allows users to see immediately if they have solved the problem.
Common LPC Applications
There are a variety of situations where LPCs can be effectively used to troubleshoot particle contamination in compressed air systems.
Manufacturers sometimes mistakenly choose a filter made for the wrong industry. For example, a company found they were consistently failing for particles and could not meet their required purity classes. Their LPC results showed an excess of particles in a certain size range. The filter they had purchased was supposed to prevent particles in that size range from passing through. It was eventually discovered they had chosen an automotive industry filter with an inappropriate efficiency rating which was allowing these particulates to move through the filter. Once that filter was replaced with one appropriate for the food industry their results showed the new filter caught particles in the required size ranges.
Sometimes particle contamination comes from an inappropriate hose or old O-ring installed after the filter. In one such case another company used the LPC to identify a problem with their process. They had installed a hose after the filter. They tested the line both before and after the hose placement. The air was of an appropriate quality before the hose but showed particles afterward. They determined the rubber hose was shedding particles. Because it was placed after the filter, the hose was contaminating the air. By changing out the material they corrected the problem.
LPCs can also be useful for troubleshooting during compressed air system validations or qualifications. Some qualification protocols require sampling all points-of-use for three consecutive days. The ability to take samples and get instant results is invaluable during this time. Immediate feedback prevents the validation from stalling or having to be repeated. It is also helpful to test a point immediately after system filtration to determine if the quality of air being produced meets the requirements. This helps to gain an understanding of how the system itself might be affecting results downstream.
When an LPC reveals contamination in a system, cycle purging can be used to “wash the walls” of the distribution system. Cycle purging involves filling the system with filtered dry gas to working pressure, isolating the source and releasing the pressure at the sample point you are trying to remove the particles. The process requires technicians to drop the pressure down to a level that will allow the backfill at the gas source to create a turbulent flow and “wash the walls” as the system is re-pressurized. Depending on the amount of contamination, this process may be repeated as many times as necessary to meet specification. Once these purges have been completed, the LPC can be used to test each branch to ensure that the contamination has been removed.
When testing with an LPC and troubleshooting particle contamination, it is important to remember actions must be taken to remedy the issue. The goal is not to just pass a test, but to make sure the end-product is safe. LPCs can help isolate problem areas and allow for trial and error testing until the contamination is remedied.
The best way to ensure compressed air filters are appropriate and working properly is to perform routine compressed air testing.
Laser Particle Counter Considerations
Though there are other forms of particle analysis, LPCs do not require extensive labor and are not only designed to be used by highly trained technicians. Other forms of particle analysis, such as microscopy or gravimetry, require a user to sample the compressed air and ship the media to a third-party laboratory where trained technicians and specific laboratory equipment perform the analyses. LPCs, on the other hand, provide a real-time, onsite solution.
LPCs are expensive instruments that require yearly calibration. These ISO 8573-4:2019 requirements allow for more precise and accurate particle results from optical particle sizing and counting instruments. Because of this, renting the equipment from an accredited third-party laboratory can ease the burden for manufacturers. Manufacturers can schedule testing, utilize the LPC for analysis, and receive their results for a fraction of the cost of purchasing a new LPC for themselves. Facilities that choose to purchase LPCs for their own use need to create protocols and procedures to validate the instrument and find ways to connect the instruments to their compressed air systems.
It’s also important to note LPCs do not test for total oil or water, which are both major contaminants specified in ISO 8573. LPCs do not recognize water or oil and are not designed to report these contaminants. Water and total oil testing can be completed with a separate kit that is available for rent or purchase. Particle results from the LPC, and water and oil results from the rented or purchased kit, can be combined into one report if an ISO 8573 report is required.
Another challenge with LPCs is that they do not differentiate between liquids and solid particles. If there is excess liquid in the system this could register as a “particle” to the LPC and provide inaccurate data. Some companies, like Trace Analytics, require a pre-test before renting an LPC to ensure the air meets oil and water requirements and that other contaminants will not damage the instrument or cause false readings. It’s also important for companies renting LPCs to have their technicians who perform tests receive training before sampling because an LPC is an accredited method of analysis.
Types of Laser Particle Counters
The 2019 version of ISO 8573-4 specifies two types of LPCs: the Optical Particle Counter (OPC) and the Optical Aerosol Spectrometer (OAS).
A handheld LPC, is an OPC, and is a validated method of particle analysis. Some can size particles down to 0.3 microns and provides an analysis of the particle contamination in the system at a particular point in time. They do it by counting the pulses of scattered light from a particle that is illuminated with a light beam. The size of the particles can be determined by the magnitude of these pulses. Lightweight and user-friendly, the handheld LPC can accommodate multiple sampling points and assist manufacturers in particle troubleshooting efforts.
A handheld LPC is a validated method of particle analysis.
Another type of validated LPC available for rent is a bench LPC, which is also considered an OPC. This instrument is larger and heavier than a handheld instrument, but can size particles down to 0.1 microns, which is sometimes required for sampling particle contamination in high-risk systems. Some devices use an enhanced signal-to-noise ratio to count these small particles. ISO 8573 purity classes 1 and 2 require particle sizing down to the 0.1 to 0.5 micron range.
A bench LPC is sometimes required for sampling particle contamination in high-risk systems.
Manufacturers can use a risk assessment to determine the levels of quality required for their particular use and end-product. A risk assessment looks at the type of piping, the filtration that is installed, dryer types, and the compressed air system as a whole. For high-risk uses, the bench LPC is available.
A Good Choice for Troubleshooting Particle Contamination
With the help of LPCs, manufacturers can more easily troubleshoot particle contamination in their compressed air systems. Depending on the facilities’ unique needs, either a handheld or a bench LPC may be the appropriate choice.
Working with a third-party accredited laboratory allows manufacturers to rent the LPC, train their technicians effectively, and receive real-time results with a validated set-up. This cost-effective method provides them with immediate results ideal for taking multiple samples.
About the Authors
Jenny Palkowitsh is the Business Development Director at Trace Analytics. With a background in marketing and sales, Jenny works diligently with her teams to provide the educational materials and exceptional service that Trace Analytics is known for. Contact Jenny at tel: 512-263-0000 Ext. 5, email: email@example.com.
Gary Ault is a QAR Manager at Quality Assurance Management. Gary has 30-plus years in the analytical and testing industry for the semiconductor, food and life science industries. Contact Gary at tel: 972 331-5805, email: firstname.lastname@example.org.
About Trace Analytics
Trace Analytics, LLC, is an ISO 17025-accredited laboratory specializing in the analysis of compressed air. Testing at Trace includes the analysis of particles, water, oil, and microbial contamination according to ISO 8573 standards through the use of gravimetry, GCMS, microscopy, and Laser Particle Counter (LPC) techniques. To learn more, visit www.AirCheckLab.com.
About Quality Assurance Management
Quality Assurance Management, Inc. headquartered in Carrollton, Texas, is a Trace Analytics, LLC, distributor and leader in providing quality assurance, analytical testing and inspection services for process piping systems in the semiconductor, life science, food and advanced manufacturing industries. With over 25 years of experience, QAM is committed to providing the highest level of quality and integrity while delivering true third-party inspection and testing services. For more information, visit www.QAM.com.
All photos courtesy of Trace Analytics, LLC.
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