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ISO Class 7 describes airborne particle cleanliness. It supplies no universal relative humidity setpoint. Specify the RH band independently from the product, process, materials and equipment, then demonstrate that the room holds it at the critical work locations.
An acceptable return-air reading cannot by itself demonstrate conditions at an exposed product or cold fixture.
Derive a humidity band the process owner can defend
List each operation performed while product is exposed. Collect material handling instructions, instrument environmental limits and any validated process requirements. Identify the overlap, then distinguish the acceptable process range from the narrower control target. If two steps require incompatible conditions, review zoning or local conditioning with the owner.
For illustration, suppose the process owner approves 40–50% RH and the instrument has an uncertainty of ±2 percentage points. A displayed 41% can correspond to 39% at that location. Agree with quality how measurement uncertainty, spatial variation and alarm delay will be handled before promising the process stays inside its band. This range is an example only.
Map the room where decisions are made
- Identify critical locations. Include exposed product, representative work heights, heat sources, supply jets and potentially cold surfaces. Record the return sensor location for comparison.
- Choose operating states. Record equipment status and occupancy. Capture routine door openings or approved process transitions with the monitoring interval specified in the protocol.
- Use independent measurements. Document instrument IDs, calibration, uncertainty and time synchronization. Record temperature and RH together.
- Review the exception. Report the minimum and maximum, time outside the agreed band, recovery time and any condensation observation. Record the operating conditions associated with each excursion.
Keep humidity evidence and particle evidence traceable
ISO 14644-1 covers airborne particle classification and ISO 14644-2 covers particle-monitoring evidence. Maintain the approved particle-monitoring plan alongside environmental trend records. A compliant RH reading cannot establish particle classification. Particle counts likewise cannot establish material moisture, surface dryness or process humidity compliance.
Source · ISO 14644-1 · classification by particle concentration
Source · ISO 14644-2 · particle monitoring
Specify what changes with a humidifier retrofit
Review the installation with facilities and quality before changing the air-handling sequence. Confirm permitted water quality, service access, pressure relationships, filters and available evaporation distance at minimum airflow. Agree how a sensor fault, excess humidity or loss of airflow stops moisture delivery. Repeat the affected qualification checks under the site’s change-control procedure.
