How to measure the number of particles in a clean room

A Clean Room is a key environment for controlling air pollution in industrial production, scientific research, and medical fields. To ensure the effectiveness of a modular clean room, particle counting is an essential measurement process. This article will provide a detailed introduction to how to measure the number of particles in a clean room, including measurement methods, equipment selection, standards and specifications, and data calculation.

1. Particle counting principle

Particle counters measure the number of particles in the air based on the principle of laser scattering. When air passes through the counter's beam, the particles scatter light, and the photoelectric detector inside the device captures the scattered light to calculate the number and size of the particles. Common particle counters can be divided into online and offline types. The former is suitable for continuous monitoring, while the latter is suitable for sampling at a specific time point.

According to the ISO 14644-1 standard, the number of particles in a clean room should be classified according to the diameter of the particles, such as 0.5 μm, 1.0 μm, and 5.0 μm. The classification of clean room grades is based on the maximum number of particles allowed per cubic meter of air. The specific requirements are detailed in the table below.

| Cleanroom Class | 0.5 μm Particle Count (Particles/m³) | 1.0 μm Particle Count (Particles/m³) | 5.0 μm Particle Count (Particles/m³) |

2. Selection and Calibration of Measuring Equipment

Choosing the right particle counter is the key to ensuring measurement accuracy. Common particle counters on the market include handheld, portable, and fixed types. Handheld devices are suitable for small-scale and temporary measurements, while fixed devices are suitable for long-term monitoring. When choosing, pay attention to the sensitivity, measurement range and data recording capabilities of the device.

In addition, regular calibration of the particle counter is also an important step to ensure measurement accuracy. According to ISO 21501-4, the calibration cycle of the particle counter is recommended to be once a year, and the calibration process should be carried out using standard particles (such as polystyrene balls) to ensure the accuracy and reliability of the device.

3. Measurement process and data recording

When measuring the number of particles, a certain process should be followed. First, ensure that the environment in the clean room is stable to avoid measurement errors caused by external factors. Next, place the particle counter at the designated measurement location, and usually choose the center area of the air flow direction for measurement.

During the measurement process, sampling usually takes 1 minute to 10 minutes, depending on the sensitivity of the device and the level of the clean room. When recording data, it is necessary to record the measurement time, number of particles and corresponding particle size distribution in detail. By comparing the measurement results with the standard requirements, it can be determined whether the cleanliness of the clean room meets the standard.

4. Data Analysis and Reporting

After data recording is completed, the measurement results should be analyzed. When calculating particle concentration, the following formula can be used:

C = N➗V

Where, \(C\) is the particle concentration (particles/m³), \(N\) is the total number of particles measured, and \(V\) is the measurement volume (m³). For example, if 500 0.5 μm particles are measured in 1 m³ of air, the particle concentration is:

C = 500➗1 = 500 particles/m³

Finally, a measurement report needs to be written, including the purpose of measurement, equipment information, measurement results and analysis, and compared with relevant standards to provide a basis for judging whether it is qualified or unqualified.

5. Related standards and specifications

• 1. iso 14644-1:2015

  This standard specifies the classification of air particle concentrations for modular cleanrooms and related controlled environments, clarifies the particle count limits for each level, and is the basis for Cleanroom design and evaluation.

• 2. ISO 21501-4:2007

  This standard involves performance evaluation and calibration methods for particle counters to ensure the accuracy and reliability of particle counters during use.

• 3. FS209E

  A US Federal Standard that has been replaced by the ISO standard but is still widely used in some industries. It defines the particle count limits for different cleanroom levels to help users understand the levels of cleanrooms.

• 4. GB 50457-2018

  China's national standard "Architectural Design Code for Cleanrooms and Related Environments" provides guidance for the design, construction and operation of cleanrooms.

• 5. iso 14644-2:2015

  This standard specifies the monitoring and inspection requirements for cleanrooms, covering the sampling methods and frequency of particle counting.

• 6. ISO 14644-3:2005

  Provides methods for testing cleanroom performance, including measurement requirements for air flow, particle counts and other related parameters.

• 7. iso 14644-5:2004

  This standard covers the operation and maintenance of cleanrooms, emphasizing the importance of environmental monitoring and particle control.

In modern industry and scientific research, ensuring the cleanliness of cleanrooms is the key to ensuring product quality and the reliability of experimental results. By following the above measurement process, using appropriate equipment and performing data analysis according to relevant standards, the cleanliness of cleanrooms can be effectively evaluated. Regular monitoring and maintenance not only helps to meet industry standards, but also provides data support for continuous improvement of the production process.

In actual operation, enterprises and research institutions should pay attention to the monitoring of clean room environment, regularly train personnel, and ensure that every link meets the regulatory requirements, which is crucial to ensure high-quality production and research results.