The location of the monitoring points should be based upon a formal risk assessment (FMEA, FMECA or other risk analysis tools) using data from the certification and qualification testing. Other factors, such as equipment interference, mounting points, operator impedance and operator intervention contribute to selecting the final location for the sample probe.
During a post-analysis assessment of the sample point, it may be determined that a location is directly in line with where the operator needs to make routine system adjustments, thus impeding operator activities. In such a case, the sample point must be moved, and the second-highest ranking sample point should be selected.
The isokinetic sample probe should face into the air stream and the minimum length of tubing should be used. Although different manufacturers claim specific lengths of tubing can be used with their particle counter, this is typically a function of vacuum pump dynamics, and not of particle transportation. Particles of 0.5 µm move freely in long lengths of tubing. However, 5.0 µm particles do not have this same mobility. As 5.0 µm particles are a greater concern, the tubing should be maintained at its shortest recommended lengths1.
Particle Measuring Systems quotes maximum tubing lengths based upon the same conditions of airflow and has a recommended maximum length of 3 m. However, for pharmaceutical particle systems we advise a reduced recommended length of 2m to ensure transportation of the larger particles.
Learn more now by downloading: Choosing the Most Suitable Particle Sample Point Locations in the Cleanroom.