Introduction

Temperature, Relative Humidity (RH), and Pressure Differential (PD) are three fundamental environmental parameters used to control pharmaceutical manufacturing environments.

They are sometimes treated simply as HVAC parameters displayed on a Building Management System (BMS) or Environmental Monitoring System (EMS). In a GMP facility, however, their significance is much broader.

Proper control of these parameters can influence:

• Product quality
• Product stability
• Powder flow
• Granulation
• Compression
• Coating
• Capsule filling
• Microbial control
• Cross-contamination prevention
• Sterile manufacturing
• Packaging performance
• Warehouse conditions
• Equipment performance
• Operator comfort
• Cleanroom performance
• HVAC efficiency
• Containment
• Data integrity
• Regulatory compliance

US GMP requirements specifically recognize the need for adequate control of air pressure, microorganisms, dust, humidity and temperature when appropriate to manufacture, process, pack or hold drug products.

WHO HVAC guidance similarly emphasizes that HVAC design affects room pressure, pressure differentials, pressure cascades, filtration, humidification/dehumidification, heating and cooling, and that environmental conditions should be appropriate for the storage, manufacture and use of materials, products, equipment and instruments.

The key GMP principle is therefore:

Temperature + RH + Pressure Differential + Airflow + Filtration + Monitoring + Qualification + Risk Management = Controlled Pharmaceutical Environment

There is, however, an important distinction: there is no single universal temperature, RH or pressure-differential value that applies to every pharmaceutical facility, dosage form or manufacturing process.

The appropriate limits should be scientifically justified based on the product, process, facility design, HVAC system, regulatory expectations and quality risk assessment.

1. What Are Temperature, RH and Pressure Differential?

1.1 Temperature

Temperature is a measure of the thermal condition of the environment.

In pharmaceutical manufacturing, temperature is commonly expressed in:

• °C
• °F

Temperature affects physical, chemical and biological phenomena throughout the manufacturing process.

It can influence:

• Product stability
• Chemical reaction rates
• Moisture transfer
• Drying
• Viscosity
• Solubility
• Microbial growth
• Powder behavior
• Coating performance
• Equipment operation
• Packaging performance

Temperature can also influence Relative Humidity. Therefore, temperature and RH should not be evaluated independently.

2. What Is Relative Humidity?

Relative Humidity is the ratio between the actual amount of water vapor present in air and the maximum amount of water vapor the air can hold at that temperature, normally expressed as a percentage.

For example:

50% RH means the air contains approximately half of the moisture it could hold at that temperature before reaching saturation.

RH is temperature-dependent.

This is extremely important in pharmaceutical manufacturing because the same quantity of water vapor can correspond to different RH values at different temperatures.

Therefore:

Temperature change → Moisture-holding capacity changes → RH changes

This is one reason why pharmaceutical HVAC systems need integrated temperature and humidity control.

3. Absolute Humidity, RH and Dew Point

Three terms are frequently confused.

Relative Humidity

Percentage of saturation at the existing temperature.

Absolute Humidity

Actual quantity of water vapor present in a given volume or mass of air.

Dew Point

The temperature at which air becomes saturated and condensation begins under the relevant conditions.

Dew point is particularly useful for:

• HVAC engineering
• Dehumidification
• Compressed air systems
• Cold rooms
• Condensation-risk assessment
• Moisture-sensitive processes

A pharmaceutical facility may therefore monitor temperature and RH while HVAC engineers may also use dew point for system design and troubleshooting.

4. What Is Pressure Differential?

Pressure Differential is the difference in air pressure between two adjacent spaces.

It is normally expressed in:

• Pascal (Pa)
• millimeter water gauge (mmWC)
• inch water gauge (in. w.g.)

For example, if Room A is at a higher pressure than Room B, air tends to move from Room A toward Room B when a leakage path exists.

This creates an important GMP principle:

Pressure difference → Airflow direction → Contamination-control strategy

Pressure differential is therefore not an isolated number. Its real purpose is to support the intended direction of airflow.

5. Positive, Negative and Neutral Pressure

5.1 Positive Pressure

A room is maintained at higher pressure than the adjacent less-clean area.

Typical objective:

Protect the product or clean environment from ingress of less-clean air.

Common applications may include:

• Clean manufacturing areas
• Certain packaging areas
• Clean corridors
• Certain sterile processing environments

5.2 Negative Pressure

A room is maintained at lower pressure than adjacent areas.

Typical objective:

Contain contaminants within the room.

It may be appropriate for:

• Potent compounds
• Toxic compounds
• Certain cytotoxic operations
• Hazardous materials
• Dust-generating processes
• Containment applications

Negative pressure should not be interpreted as automatically providing adequate containment. Containment effectiveness depends on the complete system, including airflow, pressure cascade, exhaust, room integrity, equipment containment and process design.

5.3 Neutral Pressure

A space may be operated close to the pressure of an adjacent area where no significant pressure cascade is required.

The appropriate pressure strategy depends on the facility’s contamination-control and containment strategy.

6. Why Temperature, RH and PD Matter in GMP Manufacturing

The three parameters address different but interconnected risks.

The pharmaceutical HVAC system integrates these controls.

7. Relationship Between Temperature, RH and Pressure Differential

A simplified relationship can be represented as:

AHU → Temperature Control → Humidity Control → Airflow → Room Pressure → Contamination Control

For example:

1. AHU conditions incoming air.
2. Cooling/heating controls temperature.
3. Dehumidification or humidification controls moisture.
4. Supply and return/exhaust airflow are balanced.
5. The airflow balance establishes room pressure.
6. The pressure cascade controls the direction of air movement.
7. HEPA filtration and airflow patterns support cleanliness.

This is why changing one HVAC parameter can affect others.

For example:

Cooling coil performance decreases → Temperature rises → RH may change → Air density/airflow conditions change → Room pressure may fluctuate.

8. Scientific Principles Behind Environmental Control

8.1 Sensible Heat

Sensible heat changes air temperature without changing its moisture content.

Example:

An AHU cooling coil removes sensible heat and reduces air temperature.

8.2 Latent Heat

Latent heat is associated with moisture removal or addition.

Dehumidification removes moisture from air.

Humidification adds moisture.

8.3 Psychrometrics

Psychrometrics is the study of the thermodynamic properties of moist air.

Important parameters include:

• Dry-bulb temperature
• Wet-bulb temperature
• Relative humidity
• Humidity ratio
• Dew point
• Enthalpy

Psychrometric analysis is particularly important for HVAC design and troubleshooting.

9. Effect of Temperature and RH on Oral Solid Dosage Manufacturing

Oral Solid Dosage (OSD) manufacturing is one of the areas where environmental conditions can have a significant effect on processing.

Major OSD processes include:

• Dispensing
• Sieving
• Milling
• Granulation
• Drying
• Blending
• Compression
• Coating
• Capsule filling
• Packing

9.1 Dispensing

Temperature and RH can affect:

• Powder flow
• Hygroscopic materials
• Electrostatic charging
• Material sticking
• Weighing operations
• Material handling

Highly hygroscopic APIs or excipients may require tighter environmental control than relatively stable materials.

9.2 Granulation

Environmental conditions can affect:

• Binder behavior
• Granule moisture
• Drying performance
• Powder flow
• Granule strength

However, process parameters such as:

• Binder quantity
• Granulation endpoint
• Mixing time
• Impeller speed
• Drying temperature
• Product moisture

are usually more directly related to granulation performance than room RH alone.

9.3 Fluid-Bed Drying

Temperature and humidity affect:

• Drying rate
• Final moisture
• Product temperature
• Drying efficiency

The process itself should therefore be controlled using qualified process parameters rather than relying solely on room environmental conditions.

9.4 Compression

RH can have a significant influence on certain formulations.

Possible effects include:

• Sticking
• Picking
• Capping
• Lamination
• Poor flow
• Static charge
• Weight variation
• Compression behavior

The relationship is product-specific.

A high RH does not automatically cause every compression problem, and low RH does not automatically cause every static or flow problem.

Investigation should consider formulation, equipment, tooling, process parameters and environmental conditions together.

10. Capsules and RH

Capsules can be particularly sensitive to moisture.

Environmental conditions may influence:

• Shell flexibility
• Brittleness
• Dimensional behavior
• Filling performance
• Locking
• Defects

The appropriate environment should therefore be established based on:

Capsule material + formulation + process + equipment + product requirements.

11. Coating Operations

Environmental conditions may influence:

• Coating solution/suspension behavior
• Drying
• Film formation
• Tackiness
• Tablet appearance
• Coating defects

Potential defects include:

• Picking
• Sticking
• Twinning
• Roughness
• Cracking
• Orange peel
• Poor film formation

However, coating defects should not automatically be attributed to room RH or temperature. Investigations should also consider:

• Spray rate
• Atomization
• Inlet temperature
• Outlet temperature
• Pan speed
• Airflow
• Exhaust
• Coating formulation
• Solvent system
• Product bed temperature

12. Liquid Dosage Forms

Liquid dosage forms include:

• Solutions
• Syrups
• Suspensions
• Emulsions
• Oral liquids

Temperature can influence:

• Viscosity
• Solubility
• Mixing
• Suspension stability
• Emulsion stability
• Microbial growth
• Preservative behavior

RH is generally less directly critical to an aqueous bulk product than to hygroscopic powders, but it can still be important for room conditions, packaging materials, microbial control and personnel/environmental requirements.

13. Semisolid Dosage Forms

Examples include:

• Creams
• Ointments
• Gels
• Lotions
• Pastes

Temperature can affect:

• Viscosity
• Melting behavior
• Mixing
• Homogeneity
• Filling
• Product consistency

Environmental conditions should be established based on the formulation and process.

14. Sterile Pharmaceutical Manufacturing

Sterile manufacturing requires a much more comprehensive environmental-control strategy.

Areas may include:

• Sterile compounding
• Aseptic filling
• Terminal sterilization
• Vial filling
• Ampoule filling
• PFS filling
• BFS
• Component preparation
• Sterile corridors
• Gowning areas
• Personnel airlocks
• Material airlocks

For sterile manufacturing, Temperature/RH/PD must be considered together with:

• Cleanroom classification
• Airflow pattern
• HEPA filtration
• Airflow visualization
• Air changes
• Personnel movement
• Material movement
• Cleaning
• Disinfection
• Environmental monitoring
• Contamination Control Strategy (CCS)

The EU GMP framework for sterile medicinal products is therefore not simply a question of maintaining a particular temperature or RH value.

15. Grade A, B, C and D Areas

In sterile manufacturing, environmental controls are linked to cleanroom grades.

The grades should not be interpreted as temperature/RH classifications.

They primarily relate to the required level of environmental cleanliness and associated controls.

For example:

• Grade A: critical zone
• Grade B: background to Grade A in traditional aseptic processing
• Grade C: less critical stages
• Grade D: less critical controlled areas

The applicable environmental conditions must be established within the facility’s overall CCS, process design and regulatory framework.

16. Biologics and Vaccine Manufacturing

Biological products can have highly specific environmental requirements.

Examples include:

• Cell culture
• Fermentation
• Purification
• Formulation
• Filling
• Cold storage
• Vaccine manufacturing

Temperature can be particularly important because biological materials may be sensitive to:

• Temperature excursions
• Protein denaturation
• Aggregation
• Biological activity loss

For such products, environmental limits should be derived from product knowledge, process requirements and stability data rather than applying generic cleanroom values.

17. API Manufacturing

API facilities can involve:

• Powder handling
• Milling
• Drying
• Solvent handling
• Intermediate processing
• Dispensing
• Crystallization
• Final API processing

Environmental control may be required for:

• Product quality
• Moisture control
• Dust control
• Containment
• Cross-contamination prevention
• Operator protection

For potent or hazardous materials, negative-pressure containment strategies may be appropriate.

18. High-Potency, Cytotoxic and Hazardous Products

Special products may require enhanced containment.

Examples include:

• Cytotoxic compounds
• Highly potent APIs
• Hormonal products
• Sensitizing compounds
• Certain beta-lactams
• Other hazardous materials

Potential engineering controls include:

• Dedicated HVAC
• Negative pressure
• Dedicated exhaust
• Airlocks
• Safe-change filters
• Containment equipment
• Pressure cascades

The pressure strategy should be based on a documented containment and contamination-control assessment.

19. Packaging Areas

Packaging may involve:

• Blister packing
• Strip packing
• Bottle filling
• Sachets
• Cartoning
• Labeling

Environmental conditions may affect:

• PVC
• PVDC
• Aluminium foil
• HDPE
• PET
• Rubber components
• Adhesives
• Labels

For moisture-sensitive products, packaging-room environmental control can become particularly important.

20. Warehouses and Storage Areas

Environmental controls may apply to:

• Raw materials
• APIs
• Excipients
• Packaging materials
• Finished products
• Quarantine materials
• Released materials
• Rejected materials
• Cold rooms
• Controlled-temperature rooms

Warehouse environmental control should be based on the specified storage conditions for the materials/products.

21. Temperature Mapping

Temperature mapping demonstrates how temperature is distributed throughout a defined space over time.

It can identify:

• Hot spots
• Cold spots
• Temperature gradients
• Areas affected by doors
• Areas affected by HVAC supply
• Seasonal variation

A typical mapping program includes:

1. Define the area.
2. Review the layout.
3. Conduct risk assessment.
4. Determine logger quantity.
5. Identify locations.
6. Calibrate loggers.
7. Install loggers.
8. Record the mapping conditions.
9. Conduct mapping.
10. Analyze data.
11. Identify hot/cold spots.
12. Determine routine monitoring locations.
13. Prepare the report.
14. QA review/approval.

22. RH Mapping

RH mapping follows similar principles.

It can identify:

• High-RH zones
• Low-RH zones
• Seasonal variation
• Moisture gradients
• Areas influenced by doors
• HVAC distribution problems

Temperature and RH mapping should be considered together because RH is temperature-dependent.

WHO guidance specifically recognizes temperature and relative humidity as HVAC parameters requiring consideration and qualification, alongside room pressures and airflow patterns.

23. Seasonal Mapping

Depending on facility location and risk assessment, mapping may need to consider:

• Summer
• Winter
• Monsoon/wet season
• Transitional periods

For facilities in humid climates, seasonal humidity variation can be especially significant.

Mapping strategy should be scientifically justified rather than based solely on a generic frequency.

24. Pressure Differential and Pressure Cascade

Pressure cascade is the planned relationship between the pressure of interconnected rooms.

A simplified product-protection cascade may be:

Cleanest area
↓
Cleaner corridor
↓
Less-clean area
↓
Unclassified area

The objective is to establish airflow in the intended direction.

A containment strategy can intentionally reverse the relationship around a hazardous process.

25. Typical Pressure Differential

One of the most frequently misunderstood pharmaceutical HVAC questions is:

“What is the GMP requirement for room pressure differential?”

There is no universal GMP value applicable to every room.

ISO 14644-4:2022 addresses cleanroom design and start-up and does not prescribe one universal technological method for achieving cleanroom performance.

The commonly referenced industry design range for adjacent cleanrooms of different cleanliness levels is approximately 5–20 Pa, but this should be treated as a design/reference concept, not as a universal pharmaceutical GMP mandate.

The actual site value should consider:

• Room classification
• Leakage
• Door configuration
• Airflow balance
• Airlock design
• Process requirements
• Containment
• Personnel movement
• Material movement
• HVAC design
• Risk assessment

Too little differential can risk unstable airflow direction.

Too much differential can create:

• Door-opening difficulties
• Excessive leakage
• Turbulence
• HVAC energy consumption
• Personnel discomfort
• Unstable room control

26. Temperature and RH: Typical Industry Ranges

A major GMP mistake is to state:

“GMP requires 20–25°C and 40–60% RH.”

This is not a universal GMP rule.

Such ranges may be used as site-specific or industry design/operating conditions, but the actual values must be scientifically justified.

A practical reference framework is:

WHO HVAC guidance deliberately avoids prescribing one fixed value for every facility because multiple parameters affect clean-area conditions.

27. HVAC System Components

A pharmaceutical HVAC system may include:

• Fresh-air intake
• Return air
• Exhaust
• AHU
• Pre-filters
• Fine filters
• HEPA filters
• Cooling coils
• Heating coils
• Humidifiers
• Dehumidification systems
• Supply fans
• Return fans
• Exhaust fans
• Dampers
• VFDs
• Ductwork
• Terminal HEPA units
• Sensors
• Controllers

The system should be designed as an integrated environmental-control system.

28. Temperature Control Through HVAC

Temperature can be controlled through:

• Cooling
• Heating
• Reheat
• Airflow adjustment
• Mixing
• VAV/CAV strategies where appropriate

The control system should maintain the defined operating range under expected load and environmental conditions.

29. RH Control Through HVAC

Humidity can be controlled by:

Dehumidification

Often achieved through cooling below the air dew point followed by appropriate reheating or other engineered methods.

Humidification

Can involve:

• Steam humidification
• Clean steam systems where applicable
• Other validated humidification technologies

The humidification system should be designed to avoid introducing contamination.

30. Pressure Control

Room pressure depends largely on the relationship between:

Supply Air – Return Air – Exhaust Air – Leakage

If supply airflow exceeds return/exhaust plus leakage, room pressure generally tends to increase.

If return/exhaust exceeds supply, room pressure generally tends to decrease.

This is why pressure control is closely linked to HVAC air balancing.

31. Airflow and Pressure Are Not the Same Thing

A common mistake is to assume:

“High pressure differential means good airflow.”

Not necessarily.

Pressure differential indicates a pressure relationship.

Airflow direction and performance must also be demonstrated.

For cleanroom systems, appropriate testing may include:

• Airflow measurements
• Airflow visualization
• Pressure differential testing
• Recovery testing
• HEPA filter integrity testing
• Particle classification
• Other applicable cleanroom qualification tests

32. Sensor Selection

Temperature Sensors

Common technologies include:

• RTD
• Thermocouple
• Temperature transmitters
• Digital temperature sensors
• Data loggers

RTDs are widely used where stable and accurate temperature measurement is required.

RH Sensors

Common technologies include:

• Capacitive RH sensors
• Temperature/RH transmitters
• Electronic data loggers

The sensor should be selected according to:

• Accuracy
• Range
• Stability
• Response time
• Calibration capability
• Environmental compatibility

Pressure Sensors

Common instruments include:

• Magnehelic gauges
• Differential pressure transmitters
• Electronic pressure sensors
• Digital manometers

Electronic transmitters are commonly integrated with BMS/EMS systems.

33. Sensor Location

Sensor location should be based on qualification and risk assessment.

Consider:

• Room geometry
• Product location
• Personnel height
• Supply air
• Return air
• Heat-generating equipment
• Doors
• Equipment
• Hot/cold spots
• Mapping results

Avoid automatically installing sensors:

• Directly under supply diffusers
• Immediately beside doors
• Near heat sources
• In abnormal airflow locations

Pressure sensors should have clearly defined reference points.

Incorrect reference-point selection can generate misleading pressure readings.

34. BMS vs EMS

BMS

Building Management System generally manages facility and engineering systems such as:

• HVAC
• Temperature
• Pressure
• AHU operation
• Alarms
• Equipment status

EMS

Environmental Monitoring System is typically focused on monitored environmental conditions and their associated records, alarms, trends and data review.

Depending on facility architecture, BMS and EMS may interact or share data.

35. BMS, EMS, SCADA and PLC Comparison

The actual architecture varies between facilities.

36. Data Integrity

Automated environmental monitoring systems create GMP data that should be managed appropriately.

Important considerations include:

• Unique user access
• Audit trails where applicable
• Time synchronization
• Data backup
• Electronic records
• Electronic signatures where applicable
• Alarm records
• Trend records
• Data review
• Retention
• Access control

ALCOA+ principles should be applied where applicable.

Manual transcription creates additional risks such as:

• Transcription errors
• Missing records
• Incorrect timestamps
• Data manipulation
• Delayed recording

37. Calibration

Temperature, RH and pressure instruments should be calibrated according to an approved program.

A calibration program should define:

• Frequency
• Reference standards
• Traceability
• Acceptance criteria
• Calibration method
• As-found results
• As-left results
• Out-of-tolerance assessment

38. Calibration vs Verification vs Qualification

These activities should not be used interchangeably.

39. HVAC Qualification

Typical HVAC qualification activities may include:

• URS
• DQ
• FAT
• SAT
• IQ
• OQ
• PQ

Depending on the system, qualification/testing may cover:

• Temperature
• RH
• Airflow quantity
• Air changes
• Room pressure
• Airflow patterns
• HEPA filter integrity
• Particle classification
• Recovery
• Alarm operation
• Control-system functionality

WHO HVAC guidance identifies parameters such as temperature, RH, supply/return/exhaust quantities, room air-change rates, room pressures, airflow patterns and warning/alarm systems among parameters that may require qualification.

40. Airflow Visualization / Smoke Study

Airflow visualization can help demonstrate:

• Direction of airflow
• Potential turbulence
• Airflow reversal
• Contamination risk
• Impact of doors
• Critical-area protection

In sterile facilities, airflow visualization is an important element of contamination-control verification.

It should be designed and executed using an approved protocol and appropriate acceptance criteria.

41. Recovery Testing

Recovery testing assesses how quickly an area returns to an established cleanliness condition after a defined disturbance, where applicable.

Recovery testing may be considered during cleanroom qualification.

It should not be confused with temperature/RH recovery.

42. Routine Monitoring

Monitoring can be:

• Continuous
• Periodic
• Manual
• Automated

The frequency should be based on:

Risk + Product Sensitivity + Process Requirements + Facility History + Regulatory Expectations + Qualification Data

Monitoring should include:

• Actual values
• Trends
• Alarms
• Excursions
• Sensor status
• Calibration status

43. Alarm Management

Environmental monitoring alarms may include:

Temperature

• High
• Low

RH

• High
• Low

PD

• High
• Low
• Pressure reversal

Alarm systems should define:

• Warning limits
• Action limits
• Alarm delay
• Deadband/hysteresis where appropriate
• Acknowledgement
• Escalation
• Response
• Documentation

Alarm limits should not be arbitrarily selected.

44. Warning Limit vs Action Limit

Warning Limit

Indicates movement toward an undesirable condition.

It provides an opportunity for preventive intervention.

Action Limit

Indicates a condition requiring formal action according to the applicable procedure.

The relationship among:

Design Condition → Normal Operating Range → Alert/Warning Limit → Action Limit

should be clearly defined.

45. Temperature Excursion

A temperature excursion should trigger a structured response.

Step 1: Confirm the reading

Check:

• Sensor status
• Calibration
• Duplicate/independent measurement where appropriate

Step 2: Determine duration

Identify:

• Start time
• End time
• Maximum/minimum value
• Total exposure

Step 3: Identify affected materials

Determine:

• Raw materials
• In-process materials
• Finished products
• Packaging materials

Step 4: Assess impact

Consider:

• Stability
• Product specification
• Process sensitivity
• Storage requirements
• Exposure duration

Step 5: Investigate root cause

Check:

• AHU
• Cooling/heating
• Sensor
• BMS
• Power
• Door opening
• Maintenance
• Seasonal conditions

Step 6: CAPA

Implement corrective/preventive action based on the root cause.

46. RH Excursion

Potential impacts include:

• Moisture uptake
• Powder flow problems
• Tablet defects
• Capsule shell issues
• Microbial risk
• Product degradation

Investigation should consider both:

Magnitude + Duration

A short excursion slightly outside an operational range may not have the same product impact as a prolonged major excursion.

47. Pressure Differential Excursion

Potential causes include:

• AHU failure
• Exhaust failure
• Fan failure
• VFD problem
• Damper position
• Filter blockage
• Door opening
• Door seal failure
• HVAC balancing issue
• Power failure
• Sensor failure

The investigation should determine whether the intended airflow direction was compromised.

48. Pressure Reversal

Pressure reversal is potentially more significant than a simple numerical excursion.

For example:

If Room A is intended to be cleaner than Room B and air should flow from A → B, but the pressure relationship reverses, air may potentially move from B → A.

The investigation should therefore assess:

• Duration
• Airflow direction
• Door status
• Personnel/material movement
• Process activity
• Environmental monitoring results
• Potential contamination pathway

49. Excursion Investigation Flow

Alarm

↓

Verify reading

↓

Check sensor/calibration

↓

Check BMS/EMS

↓

Determine duration

↓

Identify affected area

↓

Identify affected product/material

↓

Assess process/product impact

↓

Assess contamination/microbial risk where applicable

↓

Root Cause Analysis

↓

CAPA

↓

QA disposition

50. Root Cause Analysis

Common tools include:

5 Why

Useful for relatively straightforward failures.

Fishbone

Categories may include:

• Man
• Machine
• Method
• Material
• Measurement
• Environment

FMEA

Useful for prospective risk assessment.

Fault Tree Analysis

Useful for complex system failures.

51. Common HVAC Root Causes

Possible causes include:

• Cooling coil failure
• Heating coil failure
• Humidifier failure
• Dehumidification failure
• Fan failure
• VFD failure
• Damper failure
• Filter blockage
• Sensor drift
• Calibration failure
• Incorrect setpoint
• BMS communication failure
• EMS communication failure
• Power interruption
• Excessive door opening
• Poor room sealing
• Exhaust imbalance
• Seasonal environmental changes

52. Impact Assessment

When an excursion occurs, QA should consider:

Material

Was the raw material exposed?

Product

Was the product exposed?

Duration

How long did the condition exist?

Magnitude

How far outside the defined range was it?

Process

Was manufacturing active?

Stability

Could the excursion affect product stability?

Microbiology

Could environmental conditions affect microbial risk?

Contamination

Could pressure reversal create contamination/cross-contamination risk?

Historical Data

Have similar excursions occurred previously?

53. Common GMP Mistakes

Top 20 mistakes

1. Treating generic values as universal GMP requirements.
2. Using arbitrary temperature setpoints.
3. Using arbitrary RH limits.
4. Using arbitrary pressure-differential limits.
5. Poor sensor placement.
6. Inadequate calibration.
7. Ignoring seasonal variation.
8. Failure to perform mapping.
9. Poor alarm management.
10. Failure to investigate excursions properly.
11. Ignoring door-opening effects.
12. Ignoring pressure cascade.
13. Confusing pressure with airflow.
14. Ignoring HVAC balancing.
15. Excessive manual data transcription.
16. Poor trend analysis.
17. Weak BMS/EMS data controls.
18. Inadequate change control.
19. Inadequate HVAC qualification.
20. Failure to reassess the system after HVAC modification.

54. Practical Case Study 1: High RH During Compression

Situation

A tablet compression area experiences sustained high RH.

Observation

Operators report:

• Increased sticking
• Picking
• Poor powder flow

Investigation

Review:

• RH trend
• Temperature trend
• HVAC performance
• Formulation
• Lubrication
• Compression parameters
• Tooling condition

Possible Root Cause

Dehumidification performance deteriorated, resulting in an environmental condition outside the established operating range.

Corrective Action

Restore HVAC performance and evaluate affected batches/materials.

CAPA

• Preventive maintenance improvement
• Alarm review
• Dehumidification monitoring
• Trend review

55. Practical Case Study 2: Low RH and Static Electricity

Situation

A powder dispensing area experiences unusually low RH.

Observation

Operators report:

• Static charge
• Powder adherence
• Handling difficulties

Investigation

Check:

• RH sensor
• Calibration
• HVAC
• Material properties
• Equipment grounding
• Process conditions

Conclusion

Low RH may contribute to electrostatic behavior, but the investigation should not assume RH is the sole cause.

56. Practical Case Study 3: Pressure Differential Loss

Situation

A clean manufacturing room loses pressure differential against the corridor.

Immediate Actions

• Verify pressure reading.
• Check door status.
• Check AHU.
• Check exhaust.
• Check fan/VFD.
• Check dampers.
• Check sensor.
• Assess whether airflow direction was compromised.

QA Assessment

Evaluate:

• Duration
• Production status
• Material exposure
• Environmental monitoring
• Potential contamination pathway

57. Practical Case Study 4: Warehouse Temperature Excursion

Situation

A warehouse temperature exceeds its approved storage condition.

Investigation

Review:

• Mapping data
• Monitoring data
• Duration
• HVAC operation
• Door openings
• Power interruption
• Product stability data

QA Decision

Product disposition should be based on scientifically justified impact assessment rather than simply assuming that every excursion automatically requires rejection.

58. Practical Case Study 5: Simultaneous Temperature, RH and PD Excursion

Situation

An AHU fails.

Consequences

Potentially:

Temperature ↑

RH changes

Pressure differential ↓

Investigation

Review:

• AHU failure
• Fan status
• HVAC interlocks
• BMS alarms
• EMS data
• Door opening
• Product exposure
• Environmental monitoring

This demonstrates why temperature, RH and PD should be considered as an interconnected system.

59. GMP Audit Checklist

60. Troubleshooting Guide

61. SOP Framework

SOP Title

Monitoring and Control of Temperature, Relative Humidity and Pressure Differential

1. Purpose

To define the procedure for monitoring and controlling temperature, RH and pressure differential in GMP-controlled areas.

2. Scope

Applicable to designated manufacturing, storage, packaging and support areas.

3. Responsibilities

Define responsibilities of:

• Production
• QA
• Engineering
• Validation
• Microbiology where applicable
• Warehouse

4. Definitions

Include:

• Temperature
• RH
• PD
• Warning limit
• Action limit
• Excursion
• BMS
• EMS

5. Equipment

List:

• Temperature sensors
• RH sensors
• PD gauges/transmitters
• Data loggers
• BMS
• EMS

6. Procedure

Define:

• Monitoring
• Review
• Recording
• Alarm handling
• Excursion handling

7. Calibration

Define calibration requirements.

8. Excursion

Define escalation and investigation requirements.

9. Documentation

Define records to be maintained.

10. Training

Personnel should be trained before performing activities.

62. Interview Questions and Answers

Q1. Why are temperature and RH important in pharmaceutical manufacturing?

Because they can affect product stability, process performance, material properties, microbial risk and equipment operation.

Q2. Is there one universal GMP temperature requirement?

No. Requirements are generally established based on product, process, facility, regulatory and risk considerations.

Q3. What is pressure differential?

It is the difference in air pressure between two spaces and is used to help establish intended airflow direction.

Q4. Why is positive pressure used?

Generally to reduce ingress from less-clean surrounding areas into cleaner areas.

Q5. Why is negative pressure used?

Generally for containment applications where preventing contaminants from escaping is a priority.

Q6. What is pressure cascade?

A planned sequence of pressure relationships between interconnected areas.

Q7. What happens if PD reverses?

Potentially, air can flow in an unintended direction. The impact depends on the areas involved, duration, door status, process activity and contamination risk.

Q8. What is temperature mapping?

A documented study used to determine temperature distribution within a defined area over time.

Q9. What is RH mapping?

A study used to evaluate spatial and temporal humidity distribution.

Q10. Why is sensor location important?

Because a sensor installed near a supply diffuser, door or heat source may not represent the environmental condition relevant to the product/process.

Q11. What is the difference between BMS and EMS?

BMS generally manages building/HVAC systems, while EMS focuses on environmental monitoring and associated data. Actual architecture varies by facility.

Q12. What is calibration?

Calibration establishes the relationship between an instrument’s indication and a reference standard.

Q13. What is HVAC qualification?

Demonstration that the HVAC system can perform according to predefined requirements.

Q14. What is a smoke study?

Airflow visualization used to demonstrate airflow patterns and potential contamination pathways.

Q15. What is the first action during an environmental excursion?

Verify the reading and assess the situation while initiating the approved response procedure.

Q16. Should every temperature excursion result in batch rejection?

No. Product disposition should be based on a documented scientific impact assessment.

Q17. What causes high RH?

Possible causes include:

• Dehumidification failure
• High outdoor moisture load
• Cooling-coil performance issues
• Incorrect HVAC control
• Door opening
• Sensor issues

Q18. What causes low PD?

Possible causes include:

• Supply fan failure
• Exhaust imbalance
• Damper problem
• Door opening
• HVAC control failure
• Filter blockage

Q19. What is ALCOA+?

A set of principles used to support trustworthy, complete and reliable GMP data.

Q20. What is the most important principle for environmental limits?

The limits should be scientifically justified, risk-based, product/process appropriate and supported by qualification and regulatory expectations.

63. Temperature vs RH vs PD

64. BMS vs EMS

The specific architecture and regulatory controls should be assessed for the actual computerized system.

65. Calibration vs Qualification

66. Product Protection vs Personnel Protection

Product Protection

Often supported by:

Cleaner area → Higher pressure → Air flows outward

Personnel/Containment Protection

May require:

Containment area → Lower pressure → Air flows inward

Neither approach should be selected automatically. The correct strategy comes from the contamination-control and containment assessment.

67. Practical Decision Tree

Temperature/RH/PD Excursion Detected

↓

Verify reading

↓

Check sensor/calibration

↓

Check BMS/EMS

↓

Determine duration

↓

Determine affected area

↓

Identify affected materials/products

↓

Assess product/process/microbial/contamination impact

↓

Initiate deviation

↓

Perform RCA

↓

Implement CAPA

↓

QA disposition

68. Practical Numerical Example: Pressure Differential

Suppose:

Room A = +15 Pa relative to corridor

Corridor = +5 Pa relative to adjacent area

Then Room A has a 10 Pa pressure difference relative to the corridor.

The important point is not merely the number.

The facility should demonstrate that:

• The pressure relationship is stable.
• The intended airflow direction is maintained.
• Doors can function correctly.
• There is no unacceptable turbulence.
• The system remains within qualified conditions.

69. Practical Numerical Example: Temperature Conversion

To convert Celsius to Fahrenheit:

°F = (°C × 9/5) + 32

For example:

25°C = 77°F

For pharmaceutical environmental control, however, the important question is not simply whether the temperature is expressed in °C or °F, but whether it remains within the scientifically justified approved range.

70. Practical RH Concept

Suppose air at a given temperature can hold 20 units of water vapor at saturation.

If it actually contains 10 units:

RH = 10 / 20 × 100 = 50%

If temperature changes, the saturation capacity changes, so RH may change even if the actual moisture content has not changed.

This explains why temperature and RH should be evaluated together.

71. Regulatory Framework

Important references include:

US FDA GMP

21 CFR 211.46 requires adequate control over air pressure, microorganisms, dust, humidity and temperature when appropriate to manufacturing, processing, packing or holding operations.

WHO GMP

WHO GMP emphasizes controlled manufacturing environments and risk-based GMP principles.

WHO HVAC Guidance

WHO HVAC guidance covers design, qualification and maintenance and specifically addresses temperature, RH, pressure differential, airflow and related HVAC parameters.

ISO 14644

ISO 14644-4:2022 addresses cleanroom design, construction and start-up and provides a framework for cleanroom performance rather than imposing a single universal environmental recipe.

EU GMP

EU GMP requirements should be interpreted together with applicable annexes, particularly Annex 1 for sterile manufacturing and Annex 11 when computerized systems are relevant.

72. Regulatory Requirement vs Industry Practice

Always classify numerical values correctly.

This distinction is essential during GMP audits.

73. Key Principle for Setting Environmental Limits

A scientifically sound approach is:

URS

↓

Product Requirements

↓

Process Requirements

↓

Quality Risk Assessment

↓

HVAC Design

↓

Engineering Specification

↓

Qualification

↓

Operating Range

↓

Warning/Alert Limits

↓

Action Limits

↓

Routine Monitoring

↓

Trend Review

This is much more defensible than simply selecting “20–25°C / 40–60% RH” because it is commonly used in the industry.

74. Top 10 Practical Questions an Auditor May Ask

1. How were your temperature limits established?
2. How were your RH limits established?
3. How were your pressure-differential limits established?
4. Where is your scientific justification?
5. Show me your mapping report.
6. Why is this sensor located here?
7. What happens if pressure differential is lost?
8. How do you investigate an RH excursion?
9. How do you ensure environmental data integrity?
10. How do you demonstrate continued HVAC performance?

A strong GMP system should be able to answer all ten using controlled documentation and objective evidence.

75. Recommended Environmental Control Strategy

An effective pharmaceutical facility should establish an integrated strategy covering:

1. Design

HVAC and facility design.

2. Risk Assessment

Identify environmental risks.

3. Qualification

Demonstrate system capability.

4. Calibration

Ensure reliable measurement.

5. Monitoring

Collect reliable environmental data.

6. Trending

Identify deterioration and seasonal patterns.

7. Alarm Management

Respond promptly to abnormal conditions.

8. Excursion Management

Assess impact scientifically.

9. CAPA

Prevent recurrence.

10. Periodic Review

Confirm continued suitability.

76. Frequently Asked Questions

What is the importance of temperature in pharmaceutical manufacturing?

Temperature can affect product stability, process performance, microbial risk, material behavior and equipment operation.

What is RH in pharmaceutical manufacturing?

RH is the percentage of moisture present in air relative to the maximum moisture the air can hold at that temperature.

Why is RH important in tablet manufacturing?

RH can affect moisture-sensitive formulations, powder flow, static electricity, sticking, picking and other process characteristics.

What is pressure differential in a cleanroom?

It is the pressure difference between adjacent spaces used to help establish intended airflow direction.

Why are pharmaceutical cleanrooms maintained under positive pressure?

Positive pressure can reduce ingress of air from less-clean adjacent spaces into cleaner spaces.

When is negative pressure required?

Negative pressure may be appropriate when containment of hazardous or potent materials is required.

What is a typical cleanroom pressure differential?

A commonly referenced cleanroom design range is approximately 5–20 Pa between adjacent spaces of different cleanliness levels, but this should not be treated as a universal GMP mandate.

What temperature is normally maintained in pharmaceutical manufacturing?

There is no single universal GMP temperature. The approved range should be based on product, process, facility and risk.

What RH is normally maintained in pharma manufacturing?

There is no universal GMP RH value for all pharmaceutical operations.

Is there one universal GMP temperature requirement?

No.

Is there one universal GMP RH requirement?

No.

Is there one universal GMP pressure differential requirement?

No.

How is temperature mapping performed?

By strategically placing calibrated data loggers throughout the area and evaluating temperature distribution over a defined period under representative/worst-case conditions.

How frequently should temperature and RH be monitored?

The frequency should be risk-based and established by the approved monitoring program.

What happens during a pressure differential excursion?

The reading should be verified, the cause investigated and potential contamination/containment impact assessed.

What is the difference between BMS and EMS?

BMS generally manages building/HVAC systems, while EMS is generally focused on environmental monitoring and associated records.

How are temperature and RH sensors calibrated?

They are compared against traceable reference standards using an approved calibration procedure.

What is the relationship between RH and product stability?

Moisture-sensitive products may experience physical or chemical changes when exposed to unsuitable humidity conditions.

How does pressure differential prevent cross-contamination?

It helps establish airflow from cleaner/product-protected areas toward less-clean areas or, in containment applications, inward toward the containment zone.

What should be done during HVAC failure?

Initiate the approved response, verify environmental conditions, assess affected materials/products, investigate the failure and document the impact through the pharmaceutical quality system.

77. Conclusion

Temperature, Relative Humidity and Pressure Differential are not merely three numbers displayed on an HVAC dashboard.

They are interconnected environmental controls supporting:

Product Quality

Process Performance

Contamination Control

Containment

Cleanroom Performance

GMP Compliance

A robust pharmaceutical environmental-control program should therefore be:

• Scientifically justified
• Risk-based
• Product-specific
• Process-specific
• Facility-specific
• Qualified
• Calibrated
• Monitored
• Alarmed
• Trended
• Investigated
• Controlled through the pharmaceutical quality system

The most important principle is that there is no universal temperature, RH or pressure-differential number that can simply be copied from one pharmaceutical facility to another.

The appropriate operating ranges should be established using:

URS + Product Requirements + Process Requirements + Quality Risk Assessment + HVAC Design + Qualification + Regulatory Requirements + Historical Data

For non-sterile pharmaceutical manufacturing, WHO’s HVAC guidance itself emphasizes that HVAC parameters and design should be approached scientifically and that the guidance is not intended to prescribe one fixed set of design parameters.

For US-regulated manufacturing, 21 CFR 211.46 establishes the requirement for adequate environmental control where appropriate to the manufacturing, processing, packing or holding operation.

Ultimately:

Good environmental control is not about maintaining a number. It is about demonstrating that the pharmaceutical facility consistently maintains an environment suitable for the product, process, personnel, contamination-control strategy and intended GMP outcome.