Compressed air pipes

Good practices when manufacturing food supplements

Food supplement manufacturing and packaging operations use automatic machinery to produce products in the form of capsules, tablets, powders, capsules and powdered dosage forms. During manufacturing, compressed air is used for various applications. Some of them include the pneumatic control of automatic capsule filling equipment, tablet compression equipment, tablet coating tanks and packaging equipment. During tablet coating, for example, compressed air creates a fine mist, which is used to coat the tablet in the tablet coating tank. Compressed air is also used on wetted surfaces to dry equipment and utensils after cleaning.

This article primarily focuses on the application of compressed air in the manufacture and packaging of dietary supplements. It discusses parameters that must be monitored and controlled to ensure product quality and compliance with compressed air quality regulatory requirements with respect to good manufacturing practices (GMP) for dietary supplements.

Parameters to monitor and control

According to the FDA Good Manufacturing Practices for Dietary Supplement Regulations (21 CFR part 111.27 (7)), “compressed air or other gases that you mechanically introduce into or over a component, a dietary supplement or a contact surface or that you use to clean any contact surface should be treated so that the component, dietary supplement or contact surface is not contaminated.


In air compressors, common types of particulate contamination are dust and rust particles. The source of particulate contamination is the air compressor intake air, storage tanks, piping, valves, pressure gauges and other fittings. These particles can be controlled by installing filters at the air compressor inlet before the receiving tank and at the point of use. The rating of the typical filter installed at the air compressor inlet is between 1.0 and 10 µm, and the rating of the coalescing filter installed at the point of use is between 0.5 and 1.0 µm .


The main source of moisture in compressed air is the intake air. In atmospheric air at normal temperature pressure (NTP) conditions, water vapor molecules are dispersed in ambient air. When air is compressed, a large amount of water vapor is collected in a small volume of compressed air and thus converts the water vapor into condensed water. The presence of moisture in the compressed air can affect the permanence of the air compressor by causing corrosion in storage tanks, piping, valves, pressure gauges and other fittings. Repairs and spare parts are expensive, not to mention time. The presence of moisture could also be a potential source of microbiological contamination in food supplements, which could result in a very expensive process or product recall. Therefore, controlling humidity in compressed air is vital. This can be accomplished by installing adsorption dryers, which are cylindrical vessels filled with silica to absorb moisture generated in the air compressor.


Air compressors require lubricating oil to prevent friction, wear and tear of moving parts, unless the compressor is an oil-free compressor. When manufacturing dietary supplements, hydrocarbon contamination is more common with oil-based air compressors. Hydrocarbons are oily liquids and vapors that can be hazardous to consumers and products. If dietary supplements are ingested, for example, the hydrocarbons can cause illness in the consumer. The main source of this contamination is the compressor itself. Overheating of the air compressor can cause lubricants to convert to vapors, which can slide through the piston rings and mix with compressed air. Appropriate point-of-use filtration will minimize oil contamination.

Compressed air quality test methods


According to ISO 8573-4 (Measurement of contaminants in compressed air Part 4: Particle Content), there are three different methods for determining particle size and concentration:

  • Sampling of sampling discs and dimensioning / counting by light optical microscopy
  • Sampling of sampling discs and dimensioning / counting with an electron microscope
  • Optical particle sizing and counting instrument

An optical particle sizing and counting instrument is the most widely used method for determining particle size and concentration. According to ISO 8573-4, two types of instruments are used: the optical aerosol spectrometer (OAS) and the optical particle counter (OPC). These instruments are highly specialized electronic devices and can be used efficiently to analyze air samples of different particle size ranges. This method is advantageous over filter collection with microscopy, as it provides documented qualitative data and rapid results on particle concentrations of air samples.


According to ISO 8573-3 (Compressed air Part 3: Test methods for measuring humidity), there are four different methods for measuring humidity:

  • Spectroscopic methods
  • Refrigerated mirror (condensation)
  • Chemical reaction using direct reading tubes (glass) with hygroscopic content
  • Electrical sensor based on capacitance or conductivity or resistance

Although ISO 8573-3 describes several methods for measuring humidity, the most widely used technique for determining humidity in compressed air is to measure the dew point temperature. The dew point temperature is the temperature at which the air will be cooled to become saturated with water vapor. When still cooled, water vapor condenses to form liquid water. It is very important to measure the dew point temperature in a compressed air line as it gives an indication of the dryness level of the compressed air. The instrument used to measure the dew point temperature is a hygrometer. There is a wide range of hygrometers available, and the selection will depend on different factors: specification range, ability to calibrate, instrument accuracy and precision, and pressure and volumetric flow rate requirements of the compressed air. .

Oil vapor

In accordance with ISO 8573-5 (Compressed air – Part 5: Test methods for the content of oil vapor and organic solvents), two methods are available. The choice depends on the range of oil vapor content in the compressed air.

  • Gas chromatography is applicable for an oil vapor content of the order of 0.001 mg / m3 at 10 mg / m3
  • The chemical indicator tube is a preliminary method and mainly used to conduct an initial survey


According to ISO 8573-7 (Compressed Air Part 7: Test Method for Viable Microbiological Contaminants Content), the appropriate test method to distinguish viable colony-forming microbiological organisms from other solid particles which may be present in compressed air is to expose the nutrient from agar with compressed air sample. There are different instruments for collecting samples of compressed air on the petri dish with agar. The choice of instrument depends on the pressure of the compressed air line and the volumetric flow.


The installation of a well-designed filtration system at the point of production and the installation of filters at the point of use where the compressed air comes into contact with the product are the best defenses against cross-contamination. The most common types of contamination (particulates, moisture and oil) can cause destructive damage to products and consumers, leading to product recalls, as well as negatively affecting the life of equipment requiring compressed air.

Monitoring the quality of compressed air in the manufacture of dietary supplements can help ensure compliance with 21 CFR Part 111 regulations. Documented quality controls are the only way to prove that the system is operating in accordance with the regulations of the FDA Good Manufacturing Practices for Food Supplements (21 CFR Part 111.27 (7)). These checks can help diagnose problems such as a heavy build-up of particles, moisture, and oils that tend to clog and corrode components in a compressed air system.

Karthik Maniam is an independent GMP and EHS consultant. Maniam is a licensed professional environmental engineer in New York, Vermont, and Massachusetts, and holds a master’s degree in environmental technology from the New York Institute of Technology and a master’s degree in chemical engineering.

The references

  1. ISO 8573-3 (First edition, 1999-06-01) Compressed air – Part 3: Test methods for the measurement of humidity. Retrieved from the Swedish Standards Institute:
  2. ISO 8573-4 (Second edition, 2019-02) Compressed air – Measurement of contaminants – Part 4: Particle content. Retrieved from the Swedish Standards Institute:
  3. ISO 8573-5 (First edition, 2001-12-15) Compressed air – Part 5: Test methods for the content of oil vapors and organic solvents. Retrieved from the Swedish Standards Institute:
  4. ISO 8573-7 (First edition, 2003-05-01) Compressed air – Part 7: Test method for the content of viable microbiological contaminants. Retrieved from the Swedish Standards Institute:
  5. Ochoa R. “Sampling and analysis of compressed air contaminants. ” Best Practices in Compressed Air. Accessed here.
  6. 21 Code of Federal Regulations, Part 111. Subpart D – Equipment and Utensils. Updated April 1, 2020. Accessed at: