February 24, 2025 | Posted by MICRO
When selecting a particle counter for monitoring air quality, it is essential to determine the specific variables you need to measure. Key factors include air temperature, humidity, particle size, and concentration. If your application requires measuring particle sizes in micrometers (µm) and quantifying particle concentration, particularly for cleanroom classification, an Optical Particle Counter (OPC) is the appropriate choice.
Stationary vs. Mobile Particle Counters
Handheld Particle Counters: These are ideal for random, discontinuous testing in cleanroom environments, research, development, and production. Their compact size and lightweight design make them versatile tools for air quality monitoring. Some mobile units allow for semi-continuous monitoring through adjustable test intervals, but they are not suited for long-term measurement or inline monitoring.
Stationary Particle Counters: Designed for continuous air quality monitoring, these permanently installed systems are suitable for cleanroom qualification and monitoring air quality in operating rooms, pharmaceutical production, and industrial applications. They are also used for filtration efficiency testing and leak detection.
Relevant Standards
An important standard for cleanroom classification is EN ISO 14644-1:2015, which defines cleanroom classes based on detectable particle sizes and concentrations. Particle sizes are categorized between 0.1 to 5 µm.
Additionally, ISO 21501-4 outlines the requirements and calibration protocols for light-scattering particle counters, covering key parameters such as:
- Zero count rate
- Counting efficiency
- Size resolution
- Flow rate
Measuring Principles
Airborne particles can be detected using various methods, including gravimetric techniques, laser diffraction, and the scattered light method. The scattered light method is commonly used in modern particle counters. This method involves particles passing through a detection zone, where they generate scattered light pulses. The intensity of these pulses corresponds to particle size, while concentration is determined by the number of pulses relative to the flow rate.
Zero-Count Rate: This represents the number of particles detected in a channel when particle-free air passes through the measuring volume. Ideally, this value should be zero. A high zero-count rate often indicates contamination in the optical system, requiring maintenance or recalibration.
Counting Efficiency: This measures the accuracy of a particle counter by comparing it to a reference device. According to ISO 21501-4, the counting efficiency in the smallest channel must be within (50 ± 20)%.
Flow Rate: The flow rate in handheld particle counters typically ranges from 2.83 L/min (0.1 cfm) to 28.3 L/min (1 cfm). This rate directly affects test intervals, as measurement times and sampled volumes depend on it. Most devices use isokinetic probes, ensuring uniform airflow into the measurement chamber.
Coincidence Error: When multiple particles are present in the detection volume simultaneously, the system may misinterpret their combined light scattering, leading to an underestimation of particle concentration and an overestimation of particle size. The risk of coincidence errors increases with higher particle concentrations.
Data Storage and Software Integration
For efficient evaluation and documentation, particle counters should have sufficient storage capacity and integrated software for automated reporting. These features simplify data management and enhance compliance with regulatory requirements.
The Importance of Particle Counting in Air Quality Monitoring
Dust is a persistent environmental hazard found in workplaces, homes, and outdoor environments. Fine dust particles are especially dangerous because they are difficult to detect with the naked eye. The smaller the particle, the greater the health risk, as fine particulate matter can penetrate deep into the respiratory system and contribute to severe health conditions, including:
- Respiratory diseases (e.g., asthma, bronchitis, lung cancer)
- Allergic reactions
- Cardiovascular issues
Work environments such as factories, mining sites, textile mills, chemical plants, and construction zones often have high dust concentrations, making continuous monitoring essential. Airborne dust particles are easily transported and inhaled, posing significant health risks.
While the body has natural filtration mechanisms (nose and throat), smaller particles can bypass these defenses and accumulate in the lungs. Long-term exposure to respirable dust increases the risk of serious diseases, underscoring the importance of air quality monitoring.
Mitigating Workplace Dust Exposure
Employers and employees must work together to minimize dust exposure through the following measures:
- Wearing protective gear: Regular use of masks and protective clothing
- Continuous monitoring: Using particle counters to track air quality
- Process improvements: Implementing safer production methods and better materials
- Enhanced cleaning protocols: Regular maintenance and dust removal
- Source identification: Detecting and controlling major dust emission points
By implementing these strategies and utilizing reliable particle counters, workplaces can significantly reduce the health risks associated with airborne particulates, ensuring safer working conditions for employees.
