: The core standard for air cleanliness classification (ISO Classes 1–9).

: The standard is available for viewing and purchase through the IEST Bookstore or the official ISO portal .

: It covered everything from particle counts to complex separative devices.

ISO 14644-6 specifies test methods for evaluating the performance of cleanrooms and associated controlled environments, focusing on airborne particle cleanliness and localized contamination control. It provides standardized procedures for measuring and reporting particle concentrations, testing local leakage and containment (e.g., downflow booths, isolators), and verifying the effectiveness of airflow and filtration systems used in critical processes.

The classification relies on the formula relating the maximum allowable particles per cubic meter of air to the particle size. For example, an cleanroom is roughly equivalent to the old "Class 100" standard, meaning it allows no more than 3,520 particles per cubic meter that are 0.5 micrometers or larger.

Official copies of these standards must typically be purchased through authorised distributors to ensure they are the most recent and valid versions: