SOURCES OF CONTAMINATION:
There are a variety of sources that can introduce oil into a compressed air system. Oil lubricated compressors, which are prevalent in manufacturing facilities, use oil to seal, lubricate, and cool during the compression stage. Oil vapors can also be introduced from worn seals, o-rings, or compressors that are overheating and allowing vapors to escape through the system. Because oil is used so abundantly in the compressed air process, the potential for contamination is elevated. Additionally, cleaning solvents and connection glue can also produce oil vapor contamination.
Inappropriate or inadequate filtration can also allow for excess oil to pass through the system. Steve Volkman, of Zorn Compressor & Equipment, explains that an inadequate grade of filtration might not remove the oil properly. If the application requires a 0.01 micron filter, and a 0.1 micron filter is used, then excess oil can pass through the system and impact the product.
Atmospheric air can contribute to oil contamination as well. This air contains anywhere from 0.05 mg/m3 to 0.5 mg/m3 of oil vapor (CAGI, 2012). Car exhausts, industrial processes, facility cleaning, and other environmental factors all contribute to oil vapor in the atmosphere. The compressor intake brings in these hydrocarbons and they can easily pass through the system. For example, intakes near an excess of car exhaust can face a higher risk for contamination.
RISKS OF OIL CONTAMINATION:
Contaminated compressed air systems can result in a decrease of productivity, loss of product, recalls, and even complete shutdown for system cleaning and re-validation. When excess oil is present into the compressed air system, it has adverse effects on the machinery and the end-product. Excess oils could potentially impact the operation of tools or the maintenance of the system (Volkman, 2018). The distribution system is also at risk as excess oil creates a nutrient-rich environment that is particularly suitable for microbiological growth, and can cause damage to the distribution system or equipment (Wilkerson, 2018).
Food that is contaminated with oil will have a bad taste and odor and could affect the consumers’ health. Oil can also create a displeasing visual appearance to the product. Even food packaging manufacturers need to be aware of the effect that oil residue has on their products. If oil is deposited onto the food packaging, then it can transfer to the food product which compromises its quality. No consumer wants to find industrial oil in their coffee in the morning.
A notable case of oil contamination occurred in Germany in 1997. The infamous “oil in the sausage” finding brought attention to the importance of filtration and compressed air testing in the food industry. A consumer-packaging expert released findings of mineral oil in vacuum-wrapped sausages (Smith, 2007). The system lacked filtration and the compressed air had not been tested. As a result, BCAS/BRC Code of Practice recommends testing twice per year to ensure the safety of the product (Smith, 2007).
REGULATIONS AND SPECIFICATIONS
There are four major organizations that have identified compressed air as a Critical Control Point that must be monitored. The International Organization for Standardization (ISO), British Compressed Air Society (BCAS), the British Retail Consortium (BRC), and the Safe Quality Food institute (SQF) all point to the importance of monitoring compressed air quality, as it is a source of potential product contamination.
ISO 8573 is an internationally recognized standard that defines the major contaminants of compressed air. It’s widely used throughout the food and beverage industry and acts as a common language between manufacturers, suppliers, and laboratories. To comply with ISO 8573 classes 1 and 2, both oil vapor and oil aerosol must be considered and monitored. Total oil is defined by ISO 8573 to be “a mixture of hydrocarbons composed of 6 or more carbon atoms”. ISO 8573 also mentions organic solvents which are defined as, “mixture of one or a combination of the following identified groups: alcohols, halogenic hydrocarbons, esters, esters/etheralcohols, ketones, aromatic/alfatic hydrocarbons, and oils”. This type of contamination can result from cleaning products and shows up in oil analyses performed by GC/MS.
ISO 8573-1:2010 defines purity classes for oil based on different risk levels. Total oil is the combination of liquid, aerosol, and vapor. Ensure that your laboratory has the capabilities to test for total oil, rather than just one portion of the contaminant, as they can all have a significant impact. Keep in mind that liquid oil is typically only sampled for when catastrophic failure is suspected, wall flow is present, or total oil results are greater than 5 mg/m3.
BCAS Food and Beverage Best Practice Guide 102 divides specifications between direct, and indirect contact. For direct contact with products, total content oil should be less than or equal to 0.01 mg/m3. If the compressed air is used indirectly with products, the total oil content can be less than or equal to 0.1 mg/m3.
Each individual manufacturer should perform a risk assessment and understand their product to determine the appropriate purity classes. If a company is unsure of what purity classes they should test to, a third-party accredited laboratory can provide baseline or diagnostic compressed air testing to help provide the necessary data to build a monitoring plan.
REMOVING OIL FROM FOOD SYSTEMS:
Many food manufacturers attempt to prevent oil contamination by using oil-free air compressors. Although this is an excellent way to reduce risk of oil contamination, this does not remove the possibility of oil contamination altogether (Shanbhag, 2018). Oil-free compressors do not use oil lubrication, so they greatly reduce the risk, but do not eliminate the need for filtration and testing. Making the switch from a traditional compressor to an oil-free compressor does not account for oil legacy in piping systems (Volkman, 2018). If a system previously used industrial oil, there could be traces of oil left in the piping system. Filtration and regular testing are still an important part of a quality monitoring system.
Another way to protect end-products from dangerous oil contamination is to use food-grade oil in the compressed air process. Unfortunately, for many manufacturers, this is not a cost-effective solution. Traditional industrial oil only needs to be changed 1 or 2 times a year, however food-grade oil requires changing 3-4 times a year and is much more expensive (Compressed Air Systems, 2014).
Both oil-free compressors and food-grade oil greatly reduce the risks of oil contamination, but they should also be used in tandem with appropriate filtration. Paired with frequent maintenance, adequate filtration is the best way to remove oil contamination from a compressed air system (Volkman, 2018). System operating manuals provide projected lifespans for filters and it is critical to change them at the appropriate intervals. As previously mentioned, ensuring the appropriate grade of filtration is another important step in removing oil contamination.
TESTING FOR OIL CONTAMINATION:
ISO 8573 purity classes 1 and 2 require a combination of oil aerosol and oil vapor. Check to make sure that your laboratory provides combined test results. This standard points to infrared spectrometry or spectrometry gas chromatograph to test for oil aerosol. At Trace Analytics, LLC, oil aerosol is determined by gravimetry. This is an alternative, validated method that allows Trace to determine whether oil aerosol contamination is present at > 99.5% recovery at a greatly reduced cost. Filter membranes are pre-weighed, used to collect the compressed air sample, and then analyzed.
Oil vapor is determined using a Gas-Chromatography Mass-Spectrometry instrument (GC-MS). Compressed air is passed through a charcoal tube. The charcoal absorbs oil and can then be extracted by the laboratory for analysis.
Organic solvents are not defined by ISO 8573 as oil vapors and therefore will not be represented in a Pass/Fail. However, it’s worth considering the impact these could have on the product. Because of this, it’s recommended to work with a lab who can test for and report organic solvents, in addition to oil vapors.
Because the risks are so great, it is essential for manufacturers to employ proper filtration and to regularly test their compressed air. Since oil-free compressors and food-grade oil substitutions do not prevent atmospheric or cleaning solvent oils from affecting the system, it is essential to employ preventative measures.
By Jenny Palkowitsh, Trace Analytics, Marketing Manager.
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- Feb 08 2019 07:07 PM
- by Simon