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The Major Contaminants in Compressed Aircompressed air contaminants compressed air testing
- 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.