GMP cleanroom grades A to D

Pharmaceutical manufacturers working on sterile products use a grading system, Grade A to Grade D, rather than ISO classes alone. The grades come from Annex 1 of the EU and PIC/S Good Manufacturing Practice guides, "Manufacture of Sterile Medicinal Products". The current Annex 1 was revised in 2022, with most requirements taking effect in August 2023.

Health Canada is a member of PIC/S, and its GMP guidance for drug products draws on the PIC/S guide and its annexes, including Annex 1 for sterile products. Canadian manufacturers exporting to Europe must also meet EU requirements directly. This guide explains each grade, how it is defined and what it means for the HVAC system. Manufacturers should always confirm current regulatory expectations with Health Canada and their quality unit.

What each grade is for

The background required for a Grade A zone depends on the technology. An open Grade A zone or restricted access barrier system (RABS) normally sits in a Grade B room. An isolator can usually sit in a Grade C or D background, because the isolator itself provides the separation. That choice has a large effect on HVAC size and operating cost.

Particle limits

Annex 1 sets maximum airborne particle concentrations for each grade at rest and in operation. The 2022 revision aligned the limits with ISO 14644-1.

Values are maximum particles per cubic metre at or above the stated size. Annex 1 notes that 5 um classification may still be considered for Grades A and B where the contamination control strategy or historical trends indicate it. For Grade D in operation, the manufacturer sets limits based on risk assessment.

In ISO terms, Grade A corresponds to ISO 5 both at rest and in operation; Grade B to ISO 5 at rest and ISO 7 in operation; Grade C to ISO 7 at rest and ISO 8 in operation; and Grade D to ISO 8 at rest. The ISO 14644 classification guide explains the ISO system.

Microbial limits

Unlike ISO classes, GMP grades also limit viable (microbial) contamination. Annex 1 action limits for routine monitoring are:

Microbial control depends on more than HVAC, including gowning, cleaning and disinfection, and operator behaviour. But airflow patterns, pressure relationships and humidity all contribute.

HVAC design implications by grade

Grade A

Grade A zones use unidirectional airflow from HEPA filters. Annex 1 gives a guidance range of 0.36 to 0.54 m/s (about 70 to 105 fpm) at the working position, and the actual velocity must be justified in the contamination control strategy. Airflow visualization (smoke studies) must show that air sweeps over and away from critical areas without turbulence or reflux from surrounding rooms. Equipment, operators' hands and arms, and product containers all disturb airflow, so smoke studies are performed under dynamic conditions. See unidirectional vs non-unidirectional airflow.

Grade B, C and D

These rooms use non-unidirectional airflow with ceiling HEPA filters and low-level returns. Annex 1 does not set fixed air change rates. Instead, rooms must achieve their grade and meet recovery expectations. Air change rates are therefore derived from expected particle generation, room size and recovery time, then confirmed by testing.

Grade B rooms in operation must meet ISO 7, so they typically need high air change rates, particularly with several gowned operators present. Grade D rooms can often achieve their limits with much lower rates.

Pressure differentials

Annex 1 requires cleaner grades to be at higher pressure than adjacent lower grades, with a guidance value of 10 Pa between rooms of different grades. Airlocks separate grades, and the final stage of an airlock should be at the same grade at rest as the room it leads to. Where products are potent or hazardous, the cascade may be adjusted with pressure sinks or bubbles to protect both product and people. See cleanroom pressurization cascades.

Monitoring

Grade A zones require continuous particle monitoring throughout critical processing, and Grade B areas require monitoring at a frequency and sample size that will detect interventions and excursions. Room pressures must be continuously monitored with alarms. Data integrity requirements apply to monitoring systems.

Temperature and humidity

Annex 1 does not set numeric temperature or humidity limits; these come from product requirements and operator comfort in full aseptic gowning. Heavily gowned operators shed more particles when hot, so Grade A and B areas are usually kept cooler than normal occupied rooms.

Qualification and requalification

GMP cleanrooms are qualified through documented protocols that include classification, filter integrity testing, airflow volume and velocity, pressure differentials, airflow visualization, recovery testing and temperature and humidity checks. Annex 1 calls for requalification of Grade A and B areas at least every six months and Grade C and D areas at least every 12 months, and after any significant change. See cleanroom certification and testing.

Frequently asked questions

Is Grade A the same as ISO 5?

For particle limits at 0.5 um, Grade A matches ISO 5. But Grade A also requires unidirectional airflow, microbial limits of no growth, continuous monitoring and airflow visualization, which ISO 5 classification alone does not require.

Do non-sterile pharmaceutical facilities use these grades?

Annex 1 applies to sterile products. Non-sterile manufacturing, such as oral solid dosage, follows the general GMP requirements, and many sites define their own cleanliness levels, often referencing Grade D or ISO 8 as a benchmark.

Key takeaways

• GMP grades A to D come from EU and PIC/S GMP Annex 1, revised in 2022, and are reflected in Health Canada's approach to sterile manufacturing.
• Grades set both particle limits, at rest and in operation, and microbial limits.
• Grade A needs unidirectional airflow, typically 0.36 to 0.54 m/s, proven by dynamic smoke studies.
• Background room grade depends on technology; isolators allow less demanding backgrounds than open RABS or Grade A zones.
• Annex 1 does not fix air change rates; designs must achieve the grade and recovery expectations, proven by testing.