Differential Pressure Gauge for an ISO Class 6 Cleanroom

ISO Class 6 cleanrooms are used in industries such as medical-device manufacturing, electronics, precision components, optics, pharmaceuticals, laboratories and processes requiring strict airborne-particle control. An ISO Class 6 room may also provide the background environment for an ISO Class 5 zone, Clean Booth, Mini-environment or localized unidirectional airflow system.

Maintaining the required condition involves more than filtration. The HVAC system must control airflow volume, direction and pressure relationships between the ISO Class 6 room, airlocks, corridors and adjacent spaces.

A differential pressure gauge helps operators determine whether the intended airflow direction remains effective. It can also reveal an open door, airflow imbalance, fan-performance deterioration, increased filter resistance or another HVAC abnormality.

ISO 14644 does not prescribe one gauge model, one measuring range or one fixed pressure differential for every ISO Class 6 cleanroom. Instrument requirements should reflect the manufacturing application, background environment, HVAC configuration, contamination risk and monitoring plan.

What is an ISO Class 6 cleanroom?

ISO Class 6 is an airborne-cleanliness classification defined by ISO 14644-1. The standard classifies cleanrooms and clean zones according to airborne-particle concentration at specified particle sizes rather than by differential pressure, air-change rate or the installed filter type.

Positive pressure or HEPA filtration alone does not prove that a room meets ISO Class 6. Classification must be performed by measuring airborne-particle concentration at defined sampling locations.

Differential pressure is a supporting parameter. It helps maintain the controlled condition but does not directly establish the ISO class.

ISO Class 6 may be provided as:

• A complete cleanroom.

• A background room for an ISO Class 5 zone.

• A room containing a Clean Booth or Mini-environment.

• A precision-component assembly area.

• A medical-device production room.

• An electronics or semiconductor room.

• A support area for pharmaceutical processing.

• A clean zone served by FFUs.

Each configuration may require a different airflow arrangement, pressure relationship and monitoring strategy.

Why is differential pressure important?

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

Under a conventional positive-pressure arrangement, the ISO Class 6 room is maintained above the pressure of a corridor or lower-cleanliness area. When a door opens or leakage occurs, air tends to move outward from the cleaner room.

This arrangement reduces the probability of particles, fibres, microorganisms or chemical contaminants entering from a less-controlled environment.

ISO Class 6 may also serve as the background for an ISO Class 5 zone. Stable background pressure helps protect the performance of the Clean Booth, LAF, Mini-environment or other localized clean-air system.

Some applications require negative pressure to contain chemicals, powders, biological agents or hazardous materials. In such cases, the intended airflow direction is toward the room.

Positive pressure is therefore not universally correct. The pressure arrangement should meet the product-protection, personnel-protection and environmental-containment objectives of the process.

Does ISO 14644 require 10 Pa for ISO Class 6?

ISO 14644 does not require every ISO Class 6 room to maintain a 10 Pa pressure difference.

ISO 14644-1 addresses air-cleanliness classification by particle concentration, while ISO 14644-2 specifies minimum requirements for a monitoring plan based on parameters that measure or affect airborne-particle concentration.

Ten pascals is commonly referenced in certain industry-specific standards and guidance, particularly for pharmaceutical cleanrooms. It should not be applied automatically to every ISO Class 6 electronics, semiconductor, optical or medical-device facility.

The required pressure should be based on:

• Cleanliness of adjacent spaces.

• Intended airflow direction.

• Leakage through panels, ceilings and doors.

• Door gaps and other openings.

• Supply, return and exhaust airflow.

• Door-opening frequency.

• Personnel and equipment loads.

• Product-protection requirements.

• Containment requirements.

• Cross-contamination risk.

• HVAC balancing and test results.

A facility may use 5 Pa, 10 Pa, 15 Pa, 20 Pa or another justified value where testing confirms that the intended airflow direction is maintained.

Two adjacent ISO Class 6 rooms may also use a pressure difference to separate processes, control material movement or reduce cross-contamination.

Is ISO Class 6 equivalent to Grade B or Grade C?

ISO Class 6 and pharmaceutical Grades A, B, C and D should not be treated as fully equivalent concepts.

ISO 14644-1 classifies air cleanliness according to airborne-particle concentration. Pharmaceutical grades may additionally depend on occupancy state, process use, microbiological control, monitoring strategy and the applicable GMP requirements.

An ISO Class 6 room does not automatically become Grade B or Grade C. A GMP area may also need to meet a particular ISO class under a specified condition while complying with additional regulatory controls.

The project should therefore identify whether it applies only ISO 14644 or also EU GMP, WHO GMP, PIC/S GMP or another industry-specific requirement.

Identify the measurement purpose

Before selecting an instrument, the measurement duty should be defined.

Typical ISO Class 6 monitoring points include:

• ISO Class 6 versus ISO Class 7.

• ISO Class 6 versus a corridor.

• Cleanroom versus an airlock.

• ISO Class 6 versus an unclassified area.

• ISO Class 5 Clean Booth versus its ISO Class 6 background.

• Mini-environment versus the production room.

• Isolator or enclosure versus the background.

• Across a HEPA or ULPA filter.

• Across AHU pre-filters or intermediate filters.

• On an FFU, Pass Box, Air Shower or cleanroom device.

Room-pressure measurement and filter differential-pressure measurement have different purposes.

Room pressure indicates airflow direction between areas. Filter pressure indicates resistance and filter operating condition. These duties normally require different ranges and alarm limits.

Select a suitable measuring range

The range should match the actual operating pressure.

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

For pressure between an ISO Class 6 room and an adjacent space, 0–25 Pa or 0–50 Pa may be considered where these ranges match the design. They are engineering examples rather than mandatory ISO 14644 values.

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

• Pressure reversal is possible.

• Both positive and negative pressure must be monitored.

• The system has multiple operating modes.

• The room is used for containment.

• The reference pressure may change.

The selected range should consider:

• Target operating value.

• Normal operating range.

• Alert level.

• Action limit.

• Door-opening transients.

• Maximum credible pressure.

• Sensor overpressure capability.

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

Accuracy should support the operating limits

ISO 14644 does not specify one accuracy class for all ISO Class 6 differential pressure gauges.

Required accuracy should reflect the separation between the normal value, alert level and action limit.

Where a room operates at 15 Pa and has a 10 Pa action limit, the combined error of the sensor, signal transmission, input module and display system should be small enough to distinguish reliably between the two conditions.

Instrument assessment should include:

• Accuracy within the working region.

• Repeatability.

• Zero drift.

• Long-term stability.

• Temperature and humidity effects.

• Resolution.

• Overpressure resistance.

• Calibration uncertainty.

• Zero-adjustment method.

Zero stability is especially important for low-range sensors. A shift of only a few pascals can represent a significant percentage of the room pressure.

A resolution of 0.1 Pa or 1 Pa may be appropriate depending on the span. Display resolution does not necessarily represent actual measurement accuracy.

Mechanical gauge or electronic transmitter?

A mechanical differential pressure gauge may be appropriate for local indication or periodic manual recording.

It is simple, requires no electrical supply and is easy to observe.

A basic mechanical gauge normally cannot:

• Record data automatically.

• Generate remote alarms.

• Store event time stamps.

• Display pressure trends.

• Communicate with a BMS or EMS.

• Detect signal failure.

An electronic transmitter or digital gauge is generally more suitable where the pressure relationship directly affects the ISO Class 6 condition or an ISO Class 5 zone located within it.

ISO 14644-2 requires the monitoring plan to consider parameters that measure or affect airborne-particle concentration. Monitoring frequency should therefore be established through the monitoring plan and risk assessment rather than through the ISO Class 6 designation alone.

Output signals and central-system integration

Electronic instruments may provide:

• 4–20 mA.

• 0–10 V.

• Modbus RTU.

• Modbus TCP.

• BACnet.

• Alarm relays.

• Ethernet communication where available.

A 4–20 mA output is widely used because it is suitable for practical transmission distances and can be integrated with a PLC, BMS, EMS or SCADA system.

Where the central-system value is used to determine room status, the complete loop should be verified from applied pressure through to the displayed and stored value.

The system should also identify:

• Sensor power loss.

• Open signal wiring.

• Out-of-range signals.

• Frozen readings.

• Communication failure.

• Zero-adjustment or sensor faults.

An instrument failure should not result in a false normal indication.

Establishing ISO Class 6 pressure alarms

Alarm limits should not be copied from another room or based on one universal value.

A practical alarm strategy normally includes:

• Target operating value.

• Normal operating range.

• Alert level.

• Action limit.

• Alarm delay.

• Reset hysteresis.

• Defined operator response.

If the room normally operates at 15 Pa and has a 10 Pa action limit, the alert level may need to be higher than 10 Pa so deterioration is identified before control is lost.

Alarm delay can prevent nuisance events caused by brief door openings. An excessive delay may conceal a genuine loss of segregation.

Alarm settings should be established after HVAC balancing and review of operational data. The alarm should be challenged by creating an unacceptable pressure condition or by simulating the relevant input signal.

Suitability for the ISO Class 6 environment

A cleanroom-mounted instrument should minimize particle accumulation and permit effective cleaning.

The front surface should preferably be flush or nearly flush with the wall panel. Gaps around the instrument should be sealed using materials compatible with the cleanroom construction.

The housing, display and seals should withstand the cleaning agents, disinfectants or process chemicals used in the area.

For electronics and semiconductor applications, additional considerations may include:

• Particle-shedding materials.

• Chemical emissions.

• Electrostatic-discharge requirements.

• Airborne molecular contamination.

• Corrosion resistance.

• Process-material compatibility.

• Magnetic or ionic contamination where relevant.

ISO 14644-4 covers the process of creating a cleanroom from requirements through design, construction and start-up. Instrument location, functionality and acceptance criteria should therefore be established during the URS or design stage.

Pressure-tap location and tubing

The pressure tap should measure representative room static pressure.

It should not be installed:

• Directly in a supply-air jet.

• In a high-velocity airflow region.

• Too close to a return-air grille.

• Directly at a door gap.

• Near a fan or pressure disturbance.

• Where it may be obstructed.

• Where liquid may accumulate.

The high- and low-pressure ports must be connected correctly. Reversing them will produce an incorrect sign or airflow direction.

Tubing should be leak-tight and protected against kinking, crushing and liquid accumulation. Both lines should be clearly identified to prevent incorrect reconnection during installation or maintenance.

Where a reference port is located in a ceiling void or wall cavity, the designer should verify that the space represents the intended reference pressure.

Calibration requirements

The instrument should be calibrated before use and at approved intervals.

Calibration should not be limited to zero. Test points should cover:

• The normal operating range.

• Alert level.

• Action limit.

• The upper part of the working span where relevant.

The reference instrument should have suitable accuracy and metrological traceability.

The calibration certificate should state individual test results, errors, acceptance criteria and calibration uncertainty where applicable.

Calibration frequency should reflect measurement criticality, manufacturer recommendations, environmental conditions and historical drift.

Where an instrument is found out of tolerance, the facility should assess the effect on previous pressure data and the ISO Class 6 condition during the affected period.

Complete 4–20 mA loop verification

Where the official reading is taken from the BMS or EMS, the transmitter calibration certificate alone does not verify the complete measuring system.

Loop testing should confirm:

• Reference pressure.

• Local transmitter display.

• Output current.

• PLC analogue-input value.

• HMI, BMS or EMS indication.

• Relay status.

• Alarm operation.

• Historical data record.

Error can originate in the sensor, converter, signal wiring, analogue-input module, software or scaling configuration.

Acceptance testing in cleanroom occupancy states

ISO 14644-3 provides test methods for cleanrooms and clean zones, including both unidirectional and non-unidirectional airflow systems in as-built, at-rest and operational occupancy states.

Differential pressure acceptance testing should consider:

• Stable HVAC operation.

• Door opening and closing.

• Pressure recovery time.

• Personnel and equipment effects.

• Airlock operation.

• Fan failure or reduced airflow.

• Sensor-signal loss.

• Power failure and restoration.

• Alarm operation.

• Agreement between local and central values.

The required occupancy state and acceptance criteria should be specified in the URS, design documents or acceptance plan before testing.

Required documentation

The ISO Class 6 differential pressure documentation package should include:

• User Requirement Specification.

• Technical datasheet.

• Model, serial number and measuring range.

• Installation-location drawing.

• High- and low-pressure connection diagram.

• Electrical wiring diagram.

• Calibration certificate.

• On-site test results.

• Signal-loop test record.

• Alarm-challenge record.

• Operating and maintenance instructions.

• Inspection and calibration procedure.

• Maintenance history.

• Setpoint-change records.

• Impact assessment following an out-of-tolerance result.

Common mistakes

Common errors include:

• Assuming ISO Class 6 always requires 10 Pa.

• Selecting an excessively wide range.

• Using one range for room and HEPA-filter pressure.

• Reviewing only percentage-of-full-scale accuracy.

• Ignoring zero drift.

• Positioning a pressure tap beside a supply diffuser.

• Reversing the high- and low-pressure ports.

• Failing to check tubing leakage.

• Calibrating the transmitter without checking the loop.

• Failing to challenge alarms under operating conditions.

• Failing to determine recovery after door opening.

• Assuming pressure monitoring replaces particle classification.

FAQ: ISO Class 6 differential pressure gauges

Must an ISO Class 6 room maintain 10 Pa?

No. ISO 14644 does not define one universal pressure difference for every ISO Class 6 room. The value should be based on airflow direction, background cleanliness, HVAC configuration, manufacturing application and risk assessment.

Does ISO Class 6 require continuous pressure monitoring?

The ISO class alone does not determine monitoring frequency. The monitoring plan should define the frequency according to the effect of differential pressure on cleanroom performance. Critical points or background rooms supporting a higher-class clean zone are often suitable for continuous monitoring.

Can a mechanical gauge be used?

Yes, for local observation or periodic manual recording. A point directly affecting the ISO Class 6 condition should normally use an electronic transmitter with alarms and signal output.

Does a differential pressure gauge prove ISO Class 6 compliance?

No. ISO Class 6 is determined by airborne-particle concentration testing under ISO 14644-1. Differential pressure is a supporting parameter used to maintain the controlled state.

Can a room-pressure gauge measure HEPA-filter pressure?

Only where its range, accuracy and overpressure capability are suitable. Filter pressure loss is generally higher than room-to-room differential pressure and normally requires a separate range.

ISO Class 6 differential pressure solutions from VCR Cleanroom Equipment

VCR Cleanroom Equipment supplies and supports the selection of differential pressure gauges, transmitters and monitoring solutions for ISO Class 6 and ISO Class 5 cleanrooms, Clean Booths, Mini-environments, FFUs, LAF units, Pass Boxes, Air Showers, Dispensing Booths, HEPA Boxes and HVAC systems.

VCR can assist with defining the measurement purpose, range, accuracy, 4–20 mA output, Modbus communication, alarm functions, calibration requirements and acceptance documentation for each project.

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