Cleanroom classification vs routine monitoring: what's the difference?

Freshers often mix up two activities that both involve particle counters: classification and monitoring. They answer different questions, follow different rules and produce different documents. Experienced people mix them up too, usually by copying classification locations straight into a monitoring SOP.

This article explains both, with the numbers you need and the mistakes auditors look for.

Classification answers "what is this room capable of?"

Classification is a formal qualification test under ISO 14644-1. It is done at defined occupancy states and confirms that the room meets its grade's particle limits.

• Sampling locations: the minimum number comes from ISO 14644-1 Table A.1, based on the room area.
• Particle sizes: 0.5 µm and 5.0 µm are used for EU GMP grades.
• States: "at rest" (equipment installed and running, no people) and "in operation" (normal activity, often simulated).

How many locations?

ISO 14644-1 Table A.1 gives the minimum number of locations for a given room area. A few examples:

Room area (m²) up to	Minimum locations
2	1
4	2
6	3
8	4
10	5
24	6
32	8
52	10
76	15
108	17
156	20
232	22

Divide the room into that many sections of roughly equal area and sample in each. Add more locations where risk is higher, for example near filling points.

How much air per location?

The volume per location must be large enough to detect at least 20 particles if the room were exactly at the limit for the largest particle size considered. For Grade A at 5.0 µm this would mean very large volumes, which is one reason Annex 1 no longer sets a 5.0 µm classification limit for Grade A. In practice, at least 1 m³ per location is common for Grade A and B, and many counters sample 1 m³ in about 36 minutes at 28.3 L/min or 10 minutes at 100 L/min.

Annex 1 (2022) maximum limits for classification, total particles per m³

Grade	At rest, 0.5 µm	At rest, 5.0 µm	In operation, 0.5 µm	In operation, 5.0 µm
A	3,520	Not specified	3,520	Not specified
B	3,520	Not specified	352,000	2,930
C	352,000	2,930	3,520,000	29,300
D	3,520,000	29,300	Not predetermined	Not predetermined

So Grade A and Grade B at rest are both ISO 5 for 0.5 µm particles; in operation, Grade B corresponds to ISO 7, Grade C to ISO 8, and Grade D at rest to ISO 8.

How often

Annex 1 expects Grade A and B areas to be requalified at least every 6 months, and Grade C and D areas at least every 12 months, plus after major changes such as HVAC modifications or layout changes.

Monitoring answers "is it still in control today?"

Monitoring is the routine, ongoing collection of particle and microbial data during normal work. Its locations and frequency come from a risk assessment and your contamination control strategy, not from a formula.

• Grade A should have continuous particle monitoring for the full duration of critical processing, including equipment assembly and set-up.
• Grade B monitoring should be frequent enough to detect changes, and is often continuous in practice.
• Microbial monitoring (active air, settle plates, contact plates and personnel) runs alongside, against the limits in Annex 1 Table 6.

Annex 1 (2022) limits for monitoring, total particles per m³ (Table 5)

Grade	At rest, 0.5 µm	At rest, 5.0 µm	In operation, 0.5 µm	In operation, 5.0 µm
A	3,520	29	3,520	29
B	3,520	29	352,000	2,930
C	352,000	2,930	3,520,000	29,300
D	3,520,000	29,300	Set by the site	Set by the site

Notice that monitoring keeps a 5.0 µm limit for Grade A and B, even though classification does not. Repeated or sustained counts of large particles in Grade A can be an early sign of a contamination event, even when they are low.

Choosing monitoring locations

A risk-based monitoring plan considers:

• Proximity to exposed product and product-contact surfaces
• Airflow patterns, ideally from smoke studies, to find where contamination would travel
• Personnel movement and interventions
• Hard-to-clean areas and places where water collects
• Transfer points such as pass boxes, airlocks and material entry
• Historical data: locations with past excursions

Record the reasoning for each location, show them on a layout drawing, and review the plan at least once a year or after any change. A monitoring plan that has never changed in five years is a warning sign.

Alert and action levels

Action levels for monitoring come from Annex 1 Tables 5 and 6. Alert levels should be set by the site based on historical data, usually lower than action levels, so that adverse trends are spotted before limits are exceeded. For particles, many sites also define an alert for a defined number of consecutive counts above a level, because a single brief spike can be an artefact of the counter.

Other qualification tests

Classification is only one part of cleanroom qualification. Expect also:

• HEPA filter integrity (leak) testing with an aerosol challenge, usually every 6 or 12 months
• Airflow velocity under unidirectional airflow, typically 0.36–0.54 m/s at the working height as guidance
• Air change rate and airflow volume for non-unidirectional rooms
• Pressure differentials between rooms of different grades, typically 10–15 Pa
• Airflow visualisation (smoke studies) in Grade A and at critical interfaces, recorded on video
• Recovery time after a particle challenge, often with a guidance value of 15–20 minutes
• Temperature and humidity within the defined range

Common audit findings

• Monitoring locations copied from the classification grid without a risk assessment
• Grade A particle monitoring not covering equipment set-up
• 5.0 µm counts ignored because "they're not in the classification limit for Grade A", even though repeated low counts at 5.0 µm can be an early sign of contamination
• Smoke studies that do not cover real interventions, or are not on video
• Requalification overdue, or done after major changes without assessment
• Alert levels unchanged for years

Getting the difference right is simple once you see it: classification is a periodic snapshot of capability, monitoring is a continuous record of control. You need both, and each needs its own justification.