The classification of a cleanroom is not a static result achieved once and for all. It is a process that must be continuously monitored and maintained over time, ensuring that the same operating conditions required for manufacturing are always in place. A fundamental element of this process is particle monitoring. Environmental quality must be constantly monitored to prevent any contamination that could compromise product quality and, in regulated sectors, GMP compliance.
ISO 14644-1 is the standard that establishes the criteria for classifying air in cleanrooms based on the number and size of particles present. In this article, we explore how to comply with this standard, how to select the appropriate instruments, and how to correctly apply acceptance criteria to ensure process quality and safety.
ISO 14644-1: An Operational Guide for Particle Classification
ISO 14644-1 provides a clear framework for cleanroom classification. It defines the particle concentration per cubic metre of air, dividing rooms into cleanliness classes based on the number of particles at specific sizes (e.g. 0.5 μm, 1.0 μm, 5.0 μm). Cleanrooms are classified from ISO 1 (the cleanest) to ISO 9 (for less critical environments).
This classification is essential for ensuring contamination control, but the challenge does not end with the initial qualification. It is necessary to continuously monitor air quality inside the cleanroom, in accordance with ISO 14644-2 and GMP requirements. This monitoring relies on particle counters and requires a carefully defined sampling strategy.
Choosing the Right Particle Counter
When it comes to particle monitoring, selecting the right particle counter is a critical step for ensuring correct cleanroom classification. Not all particle counters are suitable for all applications. It is essential to choose a device that meets the following criteria:
- Calibration and certification: counters must be calibrated in accordance with national or international standards (ISO 17025) and provide reliable, traceable data for audits.
- Particle size range: the instrument must be able to measure the specific particle sizes required by the cleanroom’s cleanliness class.
- Flow rate and sampling time: instruments must have an adequate sampling flow rate and allow continuous monitoring, especially in high-criticality areas.
- Reliability and accuracy: the particle counter must be reliable and capable of detecting very small particles with minimal error.
Portable Counters vs Fixed Systems
One of the most common decisions involves choosing between portable counters and fixed systems. Portable counters are ideal for spot inspections and monitoring specific environments at particular points in time. However, for reliable continuous monitoring, fixed systems represent the best solution. These can be integrated into an environmental monitoring network and provide real-time data that can be automatically archived and analysed.
Common Errors in Particle Monitoring
Even though particle monitoring is an established practice, there are common errors that can compromise data quality and regulatory compliance:
- Incorrect placement of measurement points. The choice of sampling points is critical. It is important to avoid non-representative locations and distribute points so as to cover the entire critical area.
- Lack of periodic instrument calibration and verification. Particle counters must be regularly calibrated and verified, including after modifications or maintenance.
- Failure to respect actual operating conditions. Calibration and monitoring must be carried out under real operating conditions — with the production environment active and personnel present.
- Undervaluing monitoring data. Monitoring data must be periodically analysed to ensure ISO class limits are maintained. It is essential to integrate particle data with other environmental measurements (such as temperature, humidity and pressure).
