Grade B is the room around an aseptic filling line. It is classified as ISO 5 at rest and ISO 7 in operation, and those two numbers are the source of most of the confusion in the specification. A supplier who quotes a single particle count is quoting half the requirement.
Two states, two counts
At rest means the room is complete, the equipment is running and no operators are present. In operation means the room is doing the work it was built for, with the people, the movements and the particle generation that go with it. The same room can pass one and fail the other, which is the point of measuring both.
For particles ≥0.5 µm, ISO 5 allows 3,520 per cubic metre and ISO 7 allows 352,000. For particles ≥5 µm the limits are 29 and 2,930 respectively. Those are classification limits under ISO 14644-1:2015, not action limits. A room that runs at half the limit is not twice as clean; it is simply not close to the boundary.
| ISO class | ≥0.5 µm / m³ | ≥5 µm / m³ | Typical role |
|---|---|---|---|
| ISO 5 | 3,520 | 29 | Grade A/B at rest, laminar zone |
| ISO 7 | 352,000 | 2,930 | Grade B in operation, Grade C background |
| ISO 8 | 3,520,000 | 29,300 | Grade D, support areas |
The sampling plan is part of the claim
ISO 14644-1:2015 sets a minimum number of sample locations based on the area of the room, and requires the locations to be distributed where the risk is, not where the pipework is convenient. A classification report with three sample points in a 40 m² suite is not a classification, it is an illustration.
Sample at the height where the work happens. A count taken at 1.8 m in an empty room tells you about the air handling unit; a count taken at the filling point, with the line running, tells you about the process. Both have a use, but they answer different questions.
What it means for consumables
A Grade B room cannot be maintained with a consumable that sheds. The wipe is inside the controlled space, handled by the people who are the largest particle source, and it is used on the surfaces that matter most. Two properties decide whether it belongs there: particle release from the cloth, and extractables left on the surface.
For the critical zone, the usual reference is a sealed-edge polyester or a sterile pre-wetted microfibre, packed so the outer surface can be transferred without contaminating the inner. For the surrounding Grade B area, a lower-cost sealed-edge cloth is often adequate. The mistake is to use one reference everywhere because it simplifies purchasing; the cost is paid in particle counts and deviations.
Classification is not monitoring
Classification happens once, or after a change. Monitoring happens continuously, or at an agreed frequency, and it uses different limits: alert and action levels set by the site, based on trend data, not on the ISO table. A room can be classified ISO 5 and still be drifting out of control, which is why the trend matters more than the certificate.
Review the trend monthly. If the count at a critical location is moving up while the room is stable, look for a new source: a changed wipe, a new garment, a maintenance activity, a door that no longer seals. The number is a symptom; the cause is usually a recent change nobody recorded.
Is Grade B the same as ISO 5?
Only at rest. In operation Grade B corresponds to ISO 7. The EU GMP grade and the ISO class are related but not interchangeable, and the state must always be stated.
How often should a Grade B room be classified?
The interval is set by the site's quality system and the applicable regulation, typically annually for a mature facility and more often after a change. Monitoring runs between classifications.
Do consumables need to be sterile in Grade B?
Not automatically. Sterility is required where the consumable enters the critical zone or contacts a sterile surface. In the surrounding Grade B area, a non-sterile sealed-edge wipe may be acceptable if the bioburden and particle data support it.
