CDA

Compressed air becomes a utility with quality attributes the moment it contacts product or a product-contact surface. Treatment removes oil, water and particulate; the specification states how much of each is acceptable, and ISO 8573-1 provides the classification framework that most specifications are written against. Untreated plant air carries compressor oil and condensate, which is why the two systems are kept distinct and clearly labelled.

The quality is produced by the treatment train and destroyed by the distribution. Dryers that have stopped regenerating, filters past their service life, and dead legs where condensate collects all degrade air that left the plant room within specification — so sampling belongs at the point of use, as it does for every other utility whose quality can change on the way.

Because it is invisible and continuously available, compressed air is one of the utilities most often left out of a qualification scope, then found blowing down a filling line during an inspection. The question that settles it is simply whether the air contacts product or a surface that will.

• —A product-contact utility when it touches product or product-contact surfaces.
• —ISO 8573-1 is the usual classification framework for oil, water and particulate.
• —Plant air and treated air are separate systems and must be unambiguously labelled.
• —Dryers, filters and dead legs degrade quality downstream of the treatment train.
• —Sample at the point of use; scope it by whether the air contacts product.

ISO 8573-1 for compressed air purity classes; EU GMP Annex 1 (2022) for gases contacting product; EU GMP Part I Chapter 3.