How to Use Particle Counters for Gas Sampling

Compressed gases are common in cleanrooms but also carry contamination risks. Properly using particle counters with high-pressure diffusers can detect contamination in compressed air.

I. Using Particle Counters for Cleanroom Gas Sampling

GMP requirements mandate testing compressed gases in cleanroom applications. This testing is critical because ISO 5 cleanroom product process areas require strict contamination control. Compressed gases can cause particulate contamination if not properly tested, affecting the quality and safety of sterile products. Testing gas pipelines can mitigate another source of increased cleanroom contamination, which may also affect cleanroom classification.

ISO 14644-1 specifies the required air cleanliness for different cleanroom levels, based on air samples collected at given locations. Results are compared with tables for validating cleanroom ISO classes. For example, ISO 14644-1 requires the following limits for air sampling per cubic meter in cleanrooms:

Figure 1: ISO 14644-1:2015 Air Cleanliness by Particle Classification

In the pharmaceutical industry, sterile processing primarily occurs in ISO 5 level cleanrooms. Therefore, particle concentration should be below the test size limits. If 0.5 μm and 1.0 μm particles are tested using a particle counter, the limits for each size would be 3,520 and 832 respectively per location.

The number of locations is based on a lookup table (outlined in ISO 14644-1:2015) and the size of the cleanroom. If all sample locations are below the particle size per cubic meter sample, the cleanroom will be classified as an ISO 5 cleanroom.

If gas pipelines are contaminated, this will result in further gas contamination of the room, potentially failing to meet ISO 5 requirements. This can lead to product safety and quality risks. ISO 8573 is the standard to follow when testing gas pipelines. ISO 8573-1:2010 outlines the maximum number of particles per cubic meter, the same concept as ISO 14644-1:2015.

ISO 8573 – Part 4:

1. Provides methods for compressed air sampling.

2. Guidelines for selecting appropriate measuring equipment to determine particle size and concentration.

3. Establishes a minimum sampling volume of 1000L (1m³).

4. Uses optical particle counters for testing particle sizes ≥0.1 to ≤10 μm.

II. ISO 8573-1:2010 Solid Particle Table

For example, a Class 5 cleanroom must have fewer than 100,000 particles per cubic meter sample for particle sizes 0.5<d≤5.0µm. For Class 4, this value is ≤10,000. Class 3 should be ≤1,000, Class 2 ≤100, and Class 1 will be ≤10.

Figure 2: ISO 8537-1:2010 Classifications

Using an Optical Particle Counter (ISO 8573-4):

• Isokinetic sampling should be maintained (using a high-pressure diffuser if particle diameter >1μm)

• OPC particle size range 0.1μm to 5μm

• Sample reports include:

• Sterile or non-sterile declaration

• Sampling date

• Measurement date

• Location

III. Selecting the Correct HPD

To sample compressed gas, the particle counter needs an accessory called a High Pressure Diffuser (HPD). The HPD connects the particle counter and the compressed gas line, and diffuses the gas entering the particle counter sample inlet. If high-pressure gas enters the particle counter inlet without an HPD, the sensors inside the particle counter may be damaged, and test results will be inaccurate.

Figure 3: Port Exhaust HPD

Figure 4: Exhaust Return Flow HPD

IV. Setting HPD Flow Rate

When using an HPD, it is critical to match the flow rate of the particle counter used for testing compressed gas. The diagram below outlines the correct HPD adapter adjustments based on the inlet pressure of the compressed gas to be sampled, in order to maintain the ideal particle flow.

Figure 5: Isokinetic High Pressure Diffuser Adjustment Diagram

V. Setting Up the Particle Counter and HPD for Compressed Air Sampling

The HPD connects the compressed gas line and particle counter according to the diagram below. Ensure adapter fittings are secure, gas lines have no leaks, and air flow direction is correct.

Figure 6: Compressed Gas to Remote Particle Counter Flow

Maintaining Your Cleanroom Environment with Wipestar

While proper gas sampling is essential for cleanroom compliance, maintaining overall cleanliness is equally important. Wipestar's premium cleanroom wipes are specifically designed to complement your contamination control strategy. Our low-particle, lint-free wipes are ideal for ISO-classified environments, including the critical ISO 5 areas discussed in this article.

Wipestar wipes feature:

• Ultra-low particulate generation to maintain ISO classification standards

• Excellent solvent compatibility for effective cleaning around sampling equipment

• Available in multiple grades to match your specific cleanroom requirements

• Sterile options for the most demanding applications

Protect your compressed gas sampling results by ensuring your cleanroom surfaces remain contaminant-free with Wipestar's trusted cleanroom wipes. Learn more about our complete range of contamination control solutions HERE.

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