Air quality is mentioned throughout the SQF Code Edition 7.2, in which we are given the guideline: “compressed air used in the manufacturing process and in direct contact with food products, primary packaging, or food contact surfaces, is clean and presents no risk to food safety and that it shall be regularly monitored for purity.” In this case, purity can be understood as “the absence of contaminants that could cause a food safety hazard.” 
SQF also states that, “food processing facilities need to operate from a fundamental assumption that compressed air can be a source of chemical and microbiological contamination.”  Similarly, BRC Global Standard for Food Safety Issue 7, Clause 4.5.4 states that, “Air, other gases and steam used directly in contact with, or as an ingredient in products shall be monitored to ensure this does not represent a contamination risk. Compressed air used directly in contact with the product shall be filtered.” 
What are the potential contaminants in compressed air at your facility? Take a look at the first article in this series titled Compressed Air Contaminants where we identify particles, water, oil aerosol, oil vapor, and microorganisms to be potential risks. Now we will turn our attention on how to sample for particles, water, and oil contaminants. Microorganisms will be covered in a future article. You can also view a recorded webinar on food grade air entitled Navigating the Path to Food Grade Compressed Air Quality at IFSQN.com.
Where to Sample
SQF recommends (in their FAQs) using 0.1um (micron) particle filters or as needed based on a risk analysis. We recommend that you take air samples after point-of-use (POU) filters if you have any installed. Your service distributor or trained maintenance staff should prepare the sampling ports. Setting up a sampling port can be as simple as adapting the pipe or tubing with the correct fittings. However, in some cases, you may need to break into the line to establish the necessary connections. Fully purge the system, as tapping into the distribution line may loosen rusty particles that can break loose from within the pipe. This is also true of metal or plastic shavings from newly threaded pipe, or sealing material.
Establishing a Monitoring Plan
Ultimately, the purpose of any monitoring program is to verify that your compressed air quality is in a state of control and will not contaminate your product. As you probably know, the compressed air system pulls ambient air in through the intake and compresses it for process use. What you may not know is that typical ambient air contains millions of inert particles, 5-25 grams of water, 1-5 micrograms of oil, and tens to hundreds of bacteria per cubic meter. The odds of contamination entering your system are against you from the beginning.
No single monitoring plan exists for all manufacturers. We recommend performing a risk assessment to identify your specific areas of concern and to determine what to test for, frequency of testing, number of sampling points and ultimately, the acceptable purity limits.
Another method used to determine these factors is the performance of baseline analyses. We recommend testing for particles, water, and oil using ISO 8573-1:2010 purity limits at various points throughout your facility. The analytical laboratory classifies your compressed air quality according to the ISO 8573 purity classes. This allows you to verify that the quality of air matches the type of filtration installed at your facility. With sufficient data points, a trend analysis can be performed to make an educated decision on whether the air quality is acceptable for all product lines or if improvements are necessary to ensure food safety.
An excellent source of information is the Food and Beverage Grade Compressed Air Best Practice Guideline 102  from the British Compressed Air Society (BCAS). It recommends testing at least semi-annually, unless otherwise determined by the HACCP process or manufacturers’ recommendations. If an alteration to the design or distribution piping is made, or maintenance is performed that could affect the quality of the air, then additional testing should be performed. For air that comes in direct contact with the product, they recommend ISO 8573-1:2010 [2:2:1], and for indirect contact, purity classes [2:4:2]. (Note the order of the purity classes are always [Particles:Water:Oil] or [P:W:O].)
When selecting a laboratory to provide your compressed air quality assessments make certain that you are getting what you pay for. According to the FDA(4) “Valid analytical results are essential to make informed decisions that impact public health. At its heart, laboratory accreditation is about laboratories’ consistently producing valid results by focusing on assuring 1) management requirements for the operation and effectiveness of the quality management system within the laboratory and 2) technical requirements that address the correctness and reliability of the tests and calibrations performed in laboratory.”
For purity classes 1-5, particles are measured by their size and quantity. ISO 8573-1 establishes three particle size ranges: 0.1 to 0.5 um (microns), 0.5 to 1.0 um, and 1.0 to 5.0 um. Also, there can be no particles greater than 5 um present to qualify for a class 1-5 purity rating. Only purity classes 1 and 2 require all three size ranges. Typically, compressor or filter manufacturers recommend filters for particle and oil removal to meet class 1 or 2 for the food industry.
To measure particles as small as 0.1 um, a calibrated laser particle counter (LPC) is required. For many food manufacturers, this may prove to be impractical due to the availability and expense. While LPCs can be costly if only a few samples are to be taken on an infrequent basis, an LPC is extremely helpful when a particle contamination problem exists. The laser particle counter can be used to rapidly sample multiple locations with on-site test results, and is therefore ideal for troubleshooting. The use of an LPC has played a crucial role in identifying the source of particle contamination from a variety of sources at some of our customers’ facilities. Contamination has been detected from O-rings in valves and filter housings, flexible tubing, distribution piping, and plastic or metal fittings.
On the other hand, particles sized at 0.5 um and larger can be sampled easily and at a significantly lower cost. This is accomplished by using a filter membrane inside a filter housing and passing a known volume of the compressed air over the membrane. Samples are lightweight and easily transportable worldwide, and analyzed using an optical microscope.
For purity classes 6, 7 and X, particles are measured by weight only. These classes are most often used for industrial tools and pneumatically operated machines with filtration by general-purpose filters. Commonly, class 6 limit of 5 mg/m3 is the maximum allowable limit for breathing air used by sport and commercial divers in the U.S. No particle size or quantity is included in these classes. Instead, results are reported by mass weight in mg/m3. Analyses are performed using a calibrated micro-balance. Classes 6, 7, and X are not typically considered food grade air quality by filter or compressor manufacturers.
Trace Analytics offers the LPC Rental Program for our US customers. 
Photo credit: Trace Analytics, LLC
Common Sources of Particle Failure
A common error identified through a monitoring program is the installation of inappropriate tubing or piping after a point-of-use filter. Even a short, brand new, 2-foot length of galvanized piping can be the source of particle contamination.
When the more stringent class 1 particle limit is required (more common in pharmaceutical or electronics) it becomes critical to limit or eliminate the use of quick disconnect fittings, valves, gauges or anything with O-rings because they can lead to sporadic particulate contamination. When a sample is taken from an outlet, it is important to ensure that the sampling process itself isn’t contributing to contamination. The connection between the point of use and the sampling equipment should be short, straight, and preferably made of stainless steel. There should be no elbows, tees, valves or dead ends.
In some cases, where stainless steel piping cannot be used, flexible tubing with low particle shedding properties must be used. Recommended tubing material types, in order of preference, include: stainless steel, conductive polymer, polyester, vinyl (if plasticizer does not interfere), polyethylene, copper, Teflon, and aluminum. 
Water Vapor Testing
There are several ways to measure dew point in compressed air. There are in-line instruments or sensors that provide constant measurements, can transmit data, and/or alarm when results are outside of the required parameters. There are also portable devices that can be used to confirm that the water vapor is in the proper range at use points.
It is important to follow the manufacturer’s recommendations and calibrate the equipment/sensors to assure consistency of results. Another quick and inexpensive method for water vapor determination are length-of-stain (detector) tubes. They are a portable method for determining water vapor for both refrigerated and desiccant dryers. Typically, these require a known quantity of compressed air to flow through the tube at a specific flow rate. A chemical reaction occurs between the water vapor in the sample and the chemicals in the tube. This will be represented by a length of color stain on the tube. Sampling times vary between 2.5 and 12.5 minutes—depending on a variety of factors.
AirCheck Kit K8573NB sampling for water as shown.
Photo Credit: Trace Analytics, LLC
Water Sampling Tips
To prevent the interference of ambient moisture permeating into the compressed air sample stream, select impermeable materials, such as polished stainless steel or PTFE (best known brand is Teflon) . Avoid using hygroscopic materials like rubber, as these materials can allow ambient moisture to permeate into the tubing and affect the results. The use of polished or electro-polished stainless steel is important to prevent any water from collecting on the inner surface of the sampling apparatus.
Any type of connection between the sampling apparatus and the sampling outlet should be short, straight and without dead ends. Avoid the potential for leaks by limiting elbows, tees, and valves.
Total Oil Testing
The terminology used to describe oil can be quite confusing. It is important to understand which form of oil will be tested. Some common terms for oil include: condensed hydrocarbons, oil mist, oil aerosol (these are all aerosols), oil vapor, total gaseous hydrocarbons, and total volatile hydrocarbons (these are all gaseous). Aerosols are usually reported in milligrams per cubic meter (mg/m3) while oil vapors are often noted in parts per million (ppm). ISO 8573 specifies sampling for oil aerosol and oil vapor separately, then combining test results to comply with Total Oil limits for class 1 and 2. Results are reported in mg/m3. Critical control points should be monitored for both oil aerosol and oil vapor for better quality control. This is one of many reasons why testing to ISO 8573 purity classes makes sense for the food manufacturer.
ISO 8573 has a few definitions that help clarify which hydrocarbons are to be tested:
- Oil: A mixture of hydrocarbons composed of six or more carbon atoms (C6+)
- Oil Aerosol: A mixture of liquid oil suspended in a gaseous medium having negligible fall velocity/settling velocity
- Organic Solvent: A mixture of or a combination of the following identified groups: alcohols, halogenic hydrocarbons, esters, esters/ether alcohols, ketones, and aromatic/aliphatic hydrocarbons
- Wall Flow: The proportion of liquid contamination no longer suspended within the air flow of the pipe
Oil Aerosol Testing
A common method for collecting oil aerosols for laboratory analysis is by passing a known volume of air across a pre-weighed filter membrane. The sample can then be analyzed by either infrared spectrometry or gravimetrically.
The path from the point of use to the collection method should be kept short, without bends or drops to avoid the loss of aerosols. The use of cylinders (without a filter membrane) to collect oil aerosols is not recommended because if oil aerosols are present they will adhere to the sides of the cylinder wall.
Oil Vapor and Organic Solvent Content Testing
Oil vapor analysis is suggested for the food industry and required by ISO 8573 for classes 1 and 2. To accomplish analysis for oil vapor consisting of hydrocarbons with six or more carbon atoms (C6+), a charcoal tube must be used to collect the sample. A known volume of air is passed through the collection tube. The sample is lightweight and can be easily shipped to a laboratory for analysis by gas chromatography.
Lighter hydrocarbons composed of five or less carbon atoms are not included in total oil purity classes. These lighter hydrocarbons—as well as other gases like carbon monoxide, carbon dioxide, sulfur dioxide and nitrogen dioxide—are addressed in section 8573-6 Gaseous Contaminant Content. There are no established ISO 8573 purity classes or limits for these other gases. Trace Analytics offers methods to collect the C5- hydrocarbons and other gases upon request.
Common Sources of Oil Failure
Clean, oil-free fittings are critical for a true reading of contamination. Oil aerosol and vapor are detected at very low levels. A slight amount of hydrocarbon contamination in a fitting is enough to produce unacceptably high levels of oil vapor (OV).
The filter cassette holds three layers of membranes for oil aerosol collection, and the charcoal tube collects oil vapors.
Photo Credit: Trace Analytics, LLC
Solvents remain trapped in O-rings and fittings for a long time. Because of this, only solvents that are not C6+ hydrocarbons should be used. Many common cleaning agents are high in C6+ hydrocarbons. Research the solvents you use in your manufacturing area. Ensure that the air compressor inlet is not situated near a source of C6+ materials. This would include cleaning baths, solvent waste cans, process solvents, or other ambient sources of hydrocarbons such as forklift exhaust.
If contamination is expected in the ambient or process air, have the laboratory perform oil vapor (OV) analyses using gas chromatography/mass spectrometry (GC-MS), a technique that readily discerns between OV and other compounds. These other compounds can be reported separately, thus not impacting the OV level as might occur with gas chromatography with a non-specific detector, such as flame ionization detection (FID).
ISO 8573-1:2010 purity classes serve as the foundation for compressed air monitoring to meet certification requirements. As an internationally accepted standard, ISO 8573-1 is a common language available to the food manufacturer, compressed air system supplier, and testing laboratory.
 SQF Code Edition 7.2, http://www.sqfi.com/...code/downloads/
 SQF FAQs, http://www.sqfi.com/...f/faq/sqf-code/
 BRC Global Standard for Food Safety Issue 7, http://www.brcbooksh...378/food-safety
 U.S. Food and Drug Administration, Frequently Asked Questions on FSMA, http://www.fda.gov/F...b_Accreditation
 Particle Measuring Systems, Inc., Basic Guide to Particle Counters and Particle Counting, http://www.pmeasuring.com
 ISO 8573 specifications referenced above are copyrighted and are available for purchase online at http://webstore.ansi.org/.
Ruby Ochoa, President and Co-Owner at Trace Analytics LLC
Ruby has over 30 years of experience in compressed air and gas quality testing. Demand from customers influenced Ruby and co-owner Richard A. Smith into finding a solution for manufacturers needing affordable ISO 8573 testing. Trace Analytics developed the AirCheck Kit™ Model K8573NB specifically to address the needs of today’s manufacturer. The kit captures samples for particles (0.5-5 microns), water, oil aerosol and oil vapor. All samples must be submitted to Trace’s A2LA accredited laboratory for analysis. Trace’s lab accreditation meets ISO/IEC 17025 criteria as established by FSMA. For more information, contact Ruby Ochoa, tel: (512) 263-0000 ext. 211, email: Ruby@AirCheckLab.com, or visit AirCheckLab.com.
See the interview where Ruby answers your questions about major contaminants on “Ask the Expert"
- Oct 10 2016 06:07 AM
- by Simon
- The 7.2nd edition of the SQF Code states:
- “Compressed air used in the manufacturing process shall be clean and present no risk to food safety.”
- “Compressed air used in the manufacturing process shall be regularly monitored for purity.”
- The 7th issue of the BRC Global Standard for Food Safety states:
- “Air, other gases and steam used directly in contact with, or as an ingredient in, products shall be monitored to ensure this does not represent a contamination risk. Compressed air used directly in contact with the product shall be filtered.”
- The 5th issue of the BRC Global Standard for Packaging and Packaging Materials states:
- “Based on risk assessment, the microbiological and chemical quality of water, steam, ice, air, compressed air or other gases which come into direct contact with packaging shall be regularly monitored.”
In the SQF Frequently Asked Questions on their website they state that:
“Food processing facilities need to operate from a fundamental assumption that compressed air can be a source of chemical and microbiological contamination. The site must verify and validate that the compressed air used in the facility is appropriate for use and not a source of contamination.”
With this background set, let’s explore the nature of compressed air contaminants.
Experts like the Compressed Air & Gas Institute (CAGI) and the International Organization for Standardization (ISO) agree that the primary contaminants to monitor are particles, water, and oil (PWO). CAGI also includes micro-organisms in this list. ISO 8573-1:2010 establishes a variety of purity classes for PWO from very clean [1:1:1] to shop air [6:7:X]. These classes are different from air quality specifications for breathing air used by firefighters and divers. ISO 8573-1 focuses on quantifying particles by size, and oil aerosol and oil vapors consisting of hydrocarbons with 6 or more carbons in the chain (C6+).
Breathing air specifications primarily focus on gaseous contaminants like oxygen, nitrogen, carbon monoxide, carbon dioxide, total gaseous hydrocarbons (C1-C10), and oil aerosol. Both ISO 8573-1 and common breathing air specifications provide a variety of limits for water content depending on the usage.
ISO 8573-1 does not have purity classes for other gaseous contaminants but stipulates that if these are a risk for a particular application, they should be monitored.
We can safely generalize that an excess amount of particles, water, oil aerosols, oil vapors, and micro-organisms are contaminants that can affect the quality and safety of most foods. Gaseous contaminants listed in ISO 8573-6 are EPA cited environmental pollutants such as carbon monoxide, carbon dioxide, hydrocarbons C1-C5, nitrogen oxides, and sulfur dioxide. If the food manufacturer determines that these or other gases can adversely affect their product, then limits should be established and air monitoring should include the specific gas(es).
Sources of Contamination
The primary sources of contamination in a compressed air supply include the intake air quality and the compressor itself. Other significant sources include distribution piping, storage receivers, and point-of-use items such as valves, gauges, flexible tubing, and fittings.
The decision about where the intake of the compressor should be located was made at installation. It is prudent to inspect the intake location to verify that air quality conditions have not changed since installation. At any given time the atmospheric air feeding the compressor inlet can have contaminants such as particles (both viable and nonviable), water vapor, oil vapor, and other gases. Careful consideration should be given to the placement of the compressor intake to avoid these contaminants as much as possible. The intake filter as a first defense should be routinely replaced according to the manufacturer’s guidelines.
The intake filter is responsible for removing particles greater than 2.5 microns in size that include solid and liquid aerosols from the outdoor environment and from within the manufacturing facility.
Atmospheric air contains aerosols of various types and concentrations, including quantities of:
• natural inorganic materials: fine dust, sea salt, water droplets.;
• natural organic materials: smoke, pollen, spores, bacteria;
• anthropogenic products of combustion such as: smoke, ashes or dusts; and
• urban ecosystem products: dust, cigarette smoke, aerosol spray cans, car exhaust soot.
Particles – Air pollution is not only a public health and environmental problem, it also contributes contamination in the form of millions of particles per cubic meter. These particles consist of acids (nitrates and sulfates), organic chemicals, metals, and soil or dust particles. Coarse particles are between 2.5 microns and 10 microns in diameter. The finer particles with a diameter of 2.5 microns or smaller are not removed by the intake filter and enter into the compressed air system.
Nonviable particles or micro-organisms such as bacteria and viruses exist in the ambient air and can enter the compressed air system through the intake. The growth of microbes are inhibited when the pressure dewpoint is -26°C / -15°F or better. A refrigerated dryer cannot provide this level of dryness and thus these systems may be more susceptible to microbial growth. It is important to note that although a desiccant dryer can inhibit growth of micro-organisms, it does not kill the microbes. Once the microbes are introduced into a warmer and wetter environment, if present, they will begin to grow again.
The compressor can contribute wear particles from its operation. Wear particles can be metallic or polymeric. Particles can also be generated from a compressed air system that utilizes a refrigerated dryer and iron piping or iron receivers. The combination of water and iron will form rust and pipe scale. Viable particles (micro-organisms) can also grow in this warm, dark, nutrient rich environment. Aluminum piping is a source for fine dust in the form of aluminum oxide.
There seems to be a general agreement that stainless steel along with certain specially manufactured polymers can form a good backbone for the transport of compressed air. Unions and valving of the piping system are critical in that material used for seals can shed particles and have a tremendous negative impact on air quality.
Photo credit: Vaxomatic
Water – Atmospheric air typically contains 1,000-50,000 ppm of water depending on where you live. If left untreated, compressed air with high levels of water is unacceptable for critical applications.
Excess water will cause corrosion in iron piping and storage receivers that can damage equipment used in your production lines and contaminate the final product.
Drops and dead ends in the distribution piping can trap water and create an environment for microbial growth.
Pressure and temperature affect the amount of water in a compressed air system.
Not only can water, the universal solvent, wreak havoc on the piping system, but in a water saturated system, aerosol can be generated from water collected on piping walls and mist the final product.
Oil – Atmospheric air typically contains between 0.05 mg/m3 and 0.5mg/m3 of oil vapor. Common sources are vehicle or motor exhaust and industrial processes.
As oil is comprised not only of liquid and aerosol, but also vapor, the cast of usual suspects is widened to include off-gassing of the more volatile compounds associated with oil, such as solvents used to clean piping and threads and glue used to cement connections. While many of these compounds may not be considered oil in the wider context, the ISO 17025 definition includes C6+ compounds and some of these are indistinguishable from oil components.
Oil lubricated compressors by the nature of their operation introduce liquid oil, oil aerosols and oil vapor from the compression process. However, using an oil-free compressor does not guarantee oil-free air as oil vapors can be drawn in through the compressor intake.
Hydrocarbons and oil (as well as particles) can be introduced by the installation of inappropriate piping. The inside of the distribution piping should be clean, oil-free with low particle shedding properties.
Other – Potential air quality problems can also arise from compressor misuse or mishandling, inattention to maintenance, and of course human error.
The use of flexible tubing should be carefully considered as many types of commonly used polymer tubing in the food industry can shed significant particles. They can also allow ambient water vapor to diffuse into the tubing. This can adversely affect the quality of dry air by raising the vapor levels. There are suitable types of tubing that are designed to have little to no particle shedding or permeability issues. Manufacturers label these types of tubing in a variety of ways.
The proper selection, sizing, and maintenance of compressors and purification packages can eliminate the threat that these major contaminants can pose to your final product. If the food manufacturer must verify the absence of contaminants such as particles, water, oil, and micro-organisms; it must do so by establishing a robust sampling strategy to assure that compressed air is in a state of constant control and will not contaminate the final product.
Ruby Ochoa, President and Co-Owner at Trace Analytics LLC
Ruby has over 30 years of experience in compressed air and gas quality testing. Demand from her customers persuaded Ruby to find a solution for manufacturers needing affordable ISO 8573 testing. Trace Analytics developed the AirCheck Kit™ Model K8573NB specifically to address the needs of today’s manufacturer. The kit captures samples for particles (0.5-5 microns), water, oil aerosol and oil vapor. All samples must be submitted to Trace’s A2LA accredited laboratory for analysis. Trace offers additional samplers and methods for analyzing contaminants outside of the above-mentioned parameters. For more information, contact Ruby Ochoa, tel: (512) 263-0000 ext. 4, email: CDATest@AirCheckLab.com, or visit AirCheckLab.com.
Have questions about contaminants in compressed air?
Submit them to TraceAnalytics@AirCheckLab.com.
Ruby will answer your questions on an upcoming segment of “Ask the Expert". Stay tuned for more details.
- Mar 17 2016 03:22 PM
- by Simon
- The 7.2nd edition of the SQF Code states: