Article: Particle Counting Basics: Using Airborne-Particle Counters For ISO Certified Cleanrooms

By Bill Belew

The sensitivity of an airborneparticle counter is determined by the size of the smallest particle the unit can detect. Modern particle counters used for cleanroom certification typically have sensitivities of 0.1, 0.3, or 0.5 µm. Particle counters with greater sensitivity can count smaller, and thus many more particles. For example, under ISO (International Organization for Standardization) conditions (1), a particle sensor with a sensitivity of 0.1 µm can count 28 times more =0.1-µm sizeparticles than a 0.5-µm instrument can count of =0.5-µm size. (There are many more smaller particles than larger ones.)

The flow rate of a particle counter is simply the rate at which its pump draws the sample air through the sample chamber. The higher its flow rate, the more data a counter collects per time period, or the faster it can collect a specified volume. Historically, flow rates of particle counters used in cleanroom certification were 0.1 ft3 per minute (cfm) and 1.0 cfm. However, recent EU GMP regulations now require a 1.0 m3 sample to certify Class A or B rooms for aseptic drugs. This has significantly increased the value of higher flow rates.

Reprinted with permission from BioProcess International 4(8):48-53 (September 2006)