To remain in compliance with ISO 14644, you need a testing certificate. Frequency is dictated by application and ISO classification. In pharmaceutical manufacturing, more frequent testing (around every 6 months) is common, whereas general manufacturing usually tests only once a year.

ISO classification also plays a role in determining this. In rooms classed as ISO 5 or cleaner, calibration should take place every 6 months at maximum. In rooms classed ISO 6 and up, calibration should occur at least once every year.

First and foremost, frequent calibration and maintenance is part of regulatory compliance. More than that, though, it is a part of maintaining confidence in your equipment. You need to know that something as critical as your particle counter is functioning properly and giving accurate readouts.

ISO 17025 calibration covers size setting error, counting efficiency, sampling flow rate error, size resolution, and false count in the actual equipment. 

Size Setting Error

The size setting error tells you the deviation from the particle counter’s programmed sizes. Per ISO 21501-4:2018 certification guidelines, the particle size must be ±10% to pass the calibration. The Uncertainty of each particle size will be stated in microns.

Counting Efficiency

This metric will be determined by comparing a particle to a National Institute of Standards and Technology (NIST) traceable particle with higher sensitivity. The ISO 21501-4:2018 standard allows for a tolerance of 50% (± 20%) of the minimum detectable size, and 100% (± 10%) of a size 1.5 – 2 times larger than the minimum detectable channel size. The Uncertainty is stated in percent counting efficiency.

Sampling Flow Rate Error

The sampling flow rate tolerance is ±5% of the stated rate for the unit and refers to the amount of air that flows through the laser block of the particle counter. The flow value uncertainty is stated in liters per minute (LPM).

Size Resolution

The size resolution will be stated with the particle size used in microns and the criteria of less than 15% as stated per ISO 21501-4:2018. The uncertainty will be stated in percent size resolution.

False Count

This is also known as the zero-count test. It is the number of particles detected on the minimum detectable channel in a certain volume of air with a 95% confidence level. We also state the false count rate in accordance with JIS B 9921, which gives a limit of one count per five minutes. Both values are stated as average observed counts in five minutes.