How to Take a Gas Sample Using a Particle Counter

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Oct 19, 2022

Particle counters are powerful tools in a cleanroom – and they can do double duty with the right equipment. High-pressure gas is common in cleanrooms, but can pose a contamination risk. Using a particle counter and a high pressure diffuser, you can test for gas contamination

Cleanroom Gas Sampling Using a Particle Counter

GMP requires you to test compressed gases in clean room applications. These tests are essential because product processing areas in ISO 5 cleanrooms require strict contamination control. Compressed gases, if not properly controlled, can be a source of particulate contamination. This can have an impact on the quality and safety of sterile products. Gas line testing avoids the addition of another source of cleanroom contamination that can impact the defined cleanroom classification based on operating conditions.

ISO 14644-1 indicates the air cleanliness required for different classes of cleanrooms based on a one cubic meter air sample taken from given locations. The result is compared to a table that validates the ISO class of the clean room. For example, ISO 14644-1 requires a cleanroom to have the following limits per cubic meter of sampled air.

How to Take a Gas Sample Using a Particle Counter

In the pharmaceutical industry, sterile processing is mainly carried out in clean rooms classified ISO 5. Therefore, the concentration of particles must be below the limits for the sizes tested. If 0.5 μm and 1.0 μm particles were tested using a particle counter, the limit for each size would be 3520 and 832, respectively, per location.

The number of slots is based on a lookup table (described in ISO 14644-1:2015) and the size of the clean room. If all sampling locations are below the particle sizes per cubic meter at each sample, then the cleanroom would be classified as an ISO 5 cleanroom.

If there was a contaminated gas line, it is possible that the introduction of the gas will further contaminate the part and risk failing ISO 5 classification. This could pose a risk to product safety and quality. ISO 8573 is a standard to follow when testing gas lines. ISO 8573 has several parts, but parts 4 and 7 refer to particulate contamination. ISO 8573-1:2010 describes the maximum number of particles per m3 which is the same concept as ISO 14644-1:2015.

ISO 8573 – Part 4:

1. Provides a method of sampling compressed air.
2. A guide to choosing suitable measuring equipment to determine its particle size and
concentration by number.
3. Establishes a minimum sampling volume of 1000L (1m3).
4. Using an optical particle counter to test sizes from ≥ 0.1 to ≤ 10 μm.

How to Take a Gas Sample Using a Particle Counter

ISO 8573-1:2010 Table for classes of solid particles

For example, a class 5 clean room with a particle diameter of 0.5

Use of an optical particle counter (ISO 8573-4)

  • Isokinetic sampling must be maintained (if particle diameter is > 1 μm, use a high pressure diffuser)
  • OPC particle size range 0.1 μm to 5 μm
  • Sample report to include;
  1. Sterile or non-sterile declaration
  2. Sampling date
  3. Date of measurements
  4. Location

Choose the right HPD

To sample compressed gas, a particle counter will need an accessory called a high pressure diffuser (HPD). The HPD connects the particle counter and the compressed gas line and diffuses the gas as it enters the sample inlet of the particle counter. If high pressure gas enters the sample inlet of the particle counter without the HPD, the sensor inside the particle counter may be damaged and the test results will not be accurate.

There are two types of HDPs offered by Lighthouse Worldwide Solutions: Vented Return HPD and Ported Exhaust HPD. The vented return HPD vents gas to the environment and is best suited for gases such as air. If the gas must not be in the environment, you must use a port vented HPD, which will safely vent the gas out of the environment.

HPD flow adjustment

When using an HPD, it is essential to match the flow rate of the particle counter used to test the compressed gas.

Depending on the model of HDP and particle counter, it is necessary to set the appropriate airflow to verify that the system is set up correctly and that the results are as accurate as possible based on isokinetic sampling. Isokinetic sampling maintains the correct airflow and, with the correct pressure, allows the particle counter to maintain the correct flow rate because flow is critical to accurate sample results. The table below describes the correct setting of the HPD adapter depending on the inlet pressure of the compressed gas to be sampled to maintain ideal flow through the particle counter for accurate sampling.

How to Take a Gas Sample Using a Particle Counter

Configuring the Particle Counter and HPD for Compressed Air Sampling

The HPD connects between the compressed gas line and the particle counter according to the diagram below. Make sure the adapter fittings are tight, the gas line is free from leaks, and air is flowing in the correct direction.

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With the right setup and team on your side, the process is seamless and smooth. Particle counters should be powerful and versatile tools and the Lighthouse team is committed to making sure you get the most out of your particle counter. When working with one of our particle counters, such as the ApexZ50, our team will be standing by your side to ensure proper training and maximization of application.

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