Differential Pressure Gauge for Grade C Under EU GMP

Grade C is widely used in sterile medicinal-product manufacturing facilities. Although it is not a critical Grade A zone or a conventional Grade B aseptic background, Grade C may be directly involved in operations that affect the particulate, microbial and endotoxin burden of a product before sterilizing filtration or terminal sterilization.

Maintaining an appropriate pressure relationship between Grade C and adjacent Grade D rooms, corridors, airlocks or unclassified areas helps control the direction of air movement.

A differential pressure gauge supports this control by showing whether the room remains within its qualified pressure range. The resulting data may also be used for routine operation, preventive maintenance, deviation investigations and periodic requalification.

EU GMP does not require every Grade C pressure point to use the same range, alarm setpoint or monitoring method. Instrument selection should be based on the room function, the criticality of the pressure relationship and the facility Contamination Control Strategy.

What is Grade C under EU GMP Annex 1?

EU GMP Annex 1 describes Grade C and Grade D as cleanrooms used for less critical stages in the manufacture of aseptically filled sterile products. They may also serve as backgrounds for isolators or be used for the preparation and filling of terminally sterilized products. terminally sterilized products, Grade C may be required where preparation presents a high or unusual microbial-contamination risk. Ointments, creams, suspensions and emulsions should also be prepared in at least Grade C before terminal sterilization. Filling before terminal sterilization should normally be carried out in at least a Grade C environment. re the product is unusually vulnerable because filling is slow, the container has a wide opening or the product remains exposed for an extended period, filling may need to be performed in Grade A with at least a Grade C background. aseptic processing, Grade C may be used for preparing solutions that will subsequently be filtered, including sampling and dispensing activities. se applications show that Grade C is not merely a support corridor. Its pressure, airflow and cleanliness condition can influence the initial contamination burden presented to later process-control stages.

Why is differential pressure important in Grade C?

Differential pressure establishes the intended direction of air movement between spaces.

In a conventional positive-pressure cleanroom cascade, the cleaner room is maintained at a higher pressure than the lower-grade background. When a gap is present or a door opens, air tends to move from the cleaner space toward the less-clean space.

A Grade C room may therefore be maintained at a positive pressure relative to Grade D or an unclassified corridor.

A reduction or reversal of pressure may be caused by:

• A door that is not fully closed.

• Failure of a supply or extract fan.

• Changes in filter resistance.

• Incorrect damper position.

• Increased room leakage.

• HVAC power interruption.

• Damaged or leaking pressure tubing.

• Zero drift of the differential pressure sensor.

The gauge or transmitter helps operators identify these conditions before they develop into a prolonged loss of control.

What differential pressure does EU GMP require for Grade C?

EU GMP Annex 1 requires cleanrooms to receive filtered air that maintains positive pressure and/or appropriate airflow relative to a lower-grade background under all operational conditions.

Adjacent rooms of different cleanliness grades should have a minimum pressure difference of 10 Pa as a guidance value. pascals is not a universal mandatory setpoint for every Grade C pressure point. The design value should consider:

• Whether the adjacent rooms have different grades.

• The intended airflow direction.

• Room construction and leakage.

• Door-opening frequency and duration.

• Supply, return and exhaust airflow.

• Personnel and equipment loads.

• Cross-contamination risk.

• Product-containment requirements.

• Airflow-visualization results.

• The facility CCS and risk assessment.

A Grade C room may be designed to operate at 10 Pa, 15 Pa, 20 Pa or another scientifically justified value relative to an adjacent space.

Where two adjacent rooms are both Grade C, a pressure difference may still be established to control cross-contamination or process flow. However, the Annex 1 guidance value for adjacent rooms of different grades does not automatically apply.

Pressure recommendations may also need to be modified where pathogenic, highly toxic, radioactive or live biological materials require containment. Where containment requires air to enter a controlled zone, the source air should come from an area of the same or a higher cleanliness grade. Does Grade C require continuous pressure monitoring?

EU GMP Annex 1 requires pressure-difference indicators to be installed between cleanrooms and, where relevant, between isolators and their backgrounds. Setpoints and the criticality of individual pressure relationships should be considered in the CCS. ssure differences identified as critical should be continuously monitored and recorded. A warning system should indicate air-supply failure or a reduction below the established pressure limit.

Other pressure differences should be monitored and recorded at regular intervals. is therefore incorrect to assume that every Grade C room automatically requires continuous electronic pressure recording. The required approach depends on the criticality assessment.

A Grade C pressure relationship may be considered critical when:

• The room serves as a background for an open isolator.

• Loss of pressure could directly increase product-contamination risk.

• Filling before terminal sterilization is performed in the room.

• The pressure cascade controls cross-contamination.

• The process involves a particularly vulnerable product.

• A pressure excursion could affect multiple batches.

• The value is used for room release or production authorization.

The rationale should be documented in the CCS, URS or an approved quality-risk assessment.

Mechanical or electronic differential pressure gauge?

A mechanical differential pressure gauge may be suitable for local observation and periodic manual recording.

Its advantages include simple construction, no requirement for electrical power and clear local indication. For a noncritical Grade C point, a mechanical gauge may be acceptable when supported by an approved inspection and recording procedure.

However, a basic mechanical gauge usually cannot:

• Record data automatically.

• Transmit a remote alarm.

• Communicate with a BMS or EMS.

• Store event time stamps.

• Generate pressure trends.

• Detect communication-circuit faults.

For a pressure relationship identified as critical, an electronic transmitter or digital gauge should normally be selected. A mechanical gauge may still be installed as a supplementary local indicator.

When should a 4–20 mA output be selected?

A 4–20 mA output is commonly used in cleanroom monitoring because it integrates readily with a PLC, BMS, EMS or SCADA system.

The current signal is suitable for practical transmission distances and may support the detection of some wiring or signal faults.

Other available outputs may include:

• 0–10 V.

• Modbus RTU.

• Modbus TCP.

• BACnet.

• Alarm relays.

• Ethernet-based communication.

The URS should identify which value is treated as the official GMP record.

Where the BMS or EMS value is used for room-status decisions, the complete measurement loop from the sensor to the central system should be verified, calibrated where applicable and placed under change control.

Selecting the measuring range

The measuring range should be based on the design pressure and the qualified operating window.

An excessively wide range makes small changes difficult to observe. A range that is too narrow may overrange during door opening, HVAC start-up or temporary imbalance.

For a Grade C room operating around 10–15 Pa relative to an adjacent area, a range of 0–25 Pa or 0–50 Pa may be considered. These are engineering examples rather than mandatory EU GMP values.

A bidirectional range such as ±25 Pa or ±50 Pa may be appropriate when:

• Pressure reversal is possible.

• The room uses different operating modes.

• Negative pressure is used for containment.

• Both positive and negative conditions must be detected.

HEPA-filter differential pressure normally requires a higher range than room-to-room pressure. One measuring span should not be used for both duties unless its suitability has been demonstrated.

The normal operating value should fall within a clearly readable portion of the span while leaving sufficient capacity for credible abnormal conditions.

Accuracy, resolution and zero stability

EU GMP does not prescribe one universal accuracy class for Grade C differential pressure gauges.

Accuracy should be selected according to the intended use and the separation between the normal operating value, alert level and action limit.

For example, where a room operates at 15 Pa and the action limit is 10 Pa, the total measurement error must be sufficiently small to distinguish reliably between the two conditions.

For low-range sensors, the following characteristics should be evaluated:

• Accuracy within the operating region.

• Repeatability.

• Zero drift.

• Long-term stability.

• Temperature effects.

• Overpressure resistance.

• Calibration uncertainty.

• Zero-adjustment method.

A display resolution of 0.1 Pa or 1 Pa may be appropriate depending on the range. Displaying additional digits does not necessarily indicate better measurement accuracy.

Establishing Grade C pressure alarms

For pressure points identified as critical, the warning system should rapidly alert operators when pressure falls below the established limit or the air supply fails.

A warning signal should not be overridden without assessment, and the required actions should be defined in an approved procedure. ractical alarm strategy commonly includes:

• A target operating value.

• A normal operating range.

• An alert level.

• An action limit.

• An alarm delay.

• Reset hysteresis.

• Defined operator-response instructions.

The low alarm should not automatically be set at 10 Pa. If a room is designed to operate at 15 Pa, the alert level may need to be above 10 Pa so deterioration is detected before the action limit is reached.

Alarm delays can reduce nuisance events caused by short door openings. However, any delay should be assessed and justified in the CCS. Airlocks leading to Grade C

EU GMP Annex 1 states that entry and exit doors of personnel airlocks, material airlocks and pass-through hatches should not be opened simultaneously.

For airlocks leading to Grade C or Grade D areas, a visual and/or audible warning system should be provided as a minimum. Where segregation must be maintained, a delay may be established between the closing of one door and the opening of the other. s means an electronic two-door interlock is not stated as the universal minimum requirement for every Grade C airlock. However, an interlock may still be necessary based on the facility design, pressure-recovery performance and risk assessment.

Qualification should consider:

• Door-open and door-closed status.

• Warning operation.

• Interlock function where installed.

• Pressure recovery after door use.

• Time-delay settings.

• Personnel and material flow.

Correct installation of the gauge

The high- and low-pressure ports must be connected to the correct spaces.

Pressure tubing should be leak-tight and protected against kinking, crushing and liquid accumulation. Pressure taps should not be located directly in a supply-air jet, close to a high-velocity diffuser or immediately beside a frequently opened door.

The objective is to measure representative room static pressure rather than a local dynamic-pressure effect.

The instrument face should preferably be flush or nearly flush with the cleanroom wall panel. This minimizes ledges and difficult-to-clean gaps.

The housing, seals and exposed surfaces should be compatible with the cleaning agents and disinfectants used in Grade C.

Following installation, the qualification team should verify:

• Pressure polarity.

• Zero indication.

• Tubing integrity.

• Signal stability.

• Local display value.

• BMS or EMS value.

• Alarm operation.

Calibration and loop verification

Calibration should cover the actual operating range rather than only the zero point.

Test points should include the normal operating value, alert level and action limit.

For a 4–20 mA transmitter, the complete loop should be verified from the applied pressure through to:

• The local display.

• Output current.

• Controller input.

• BMS or EMS display.

• Alarm relay.

• Historical data record.

Where an instrument is found out of tolerance, the site should assess the potential effect on previously recorded pressure data and associated manufacturing activities.

IQ and OQ qualification

EU GMP Annex 15 states that Installation Qualification should confirm correct installation against approved drawings and specifications. It should also include the collection of supplier instructions, verification of construction materials and calibration of instrumentation. rational Qualification should demonstrate that the system operates as designed and should test upper and lower operating limits or relevant worst-case conditions. Grade C pressure-monitoring qualification package should normally include:

• Approved URS and datasheet.

• Model, serial number and range.

• Installation location.

• Pressure-port diagram.

• Calibration certificate.

• Zero and multipoint testing.

• Output-signal verification.

• Comparison of local and central values.

• Alarm and delay testing.

• Signal-loss and power-failure simulation.

• Operating, calibration and alarm-response procedures.

Grade C requalification

EU GMP Annex 1 requires periodic cleanroom requalification to include, at a minimum, particle classification, final-filter integrity testing, airflow-volume measurement and verification of room-to-room pressure differences. maximum interval between Grade C and Grade D requalification activities is 12 months.

Requalification should also be performed following changes or events that may affect the qualified state, such as HVAC design modifications, interruption of airflow or replacement of final filters. 12-month requalification interval does not automatically determine the pressure-gauge calibration interval. Instrument calibration frequency should be established separately according to criticality, manufacturer recommendations and historical drift.

Common mistakes

A common mistake is specifying one wide measuring range for every cleanroom without considering the actual design pressure.

Some projects use only a mechanical gauge at a pressure point classified as critical, with no alarm or continuous data recording.

Other systems include an electronic transmitter but fail to verify the complete measurement loop.

Additional problems include:

• Reversed high- and low-pressure ports.

• Poorly positioned pressure taps.

• Kinked pressure tubing.

• Undetected leakage.

• Alarm settings equal to the minimum operating limit.

• Excessive alarm delays.

• Uncontrolled alarm-setpoint changes.

• Failure to assess historical data after an out-of-tolerance calibration.

FAQ: Grade C differential pressure gauges

Must Grade C maintain exactly 10 Pa?

Ten pascals is a guidance value for adjacent rooms of different cleanliness grades. The actual operating value should be established from the HVAC design, CCS, risk assessment and qualification results. Does every Grade C room require continuous pressure monitoring?

No. Critical pressure relationships should be continuously monitored and recorded. Other pressure differences may be monitored and recorded at defined regular intervals. Can Grade C use only a mechanical gauge?

A mechanical gauge may be suitable for a noncritical point supported by periodic manual monitoring. Critical points should normally use an electronic transmitter with alarms and data recording.

How frequently should Grade C be requalified?

The maximum interval for Grade C requalification is 12 months. Verification of room-to-room pressure differences forms part of the minimum requalification scope. Grade C differential pressure solutions from VCR Cleanroom Equipment

VCR Cleanroom Equipment supplies and supports the selection of differential pressure gauges, transmitters and monitoring solutions for Grade C, Grade A, Grade B, Grade D, isolators, airlocks, Pass Boxes, Dispensing Booths and cleanroom HVAC systems.

VCR can assist with measuring-range selection, accuracy requirements, 4–20 mA output, Modbus communication, alarm settings, calibration documents and IQ/OQ records for EU GMP projects.

Hotline: 090.123.9008
Email: [email protected]
Website: vietnamcleanroom.com