A

Action Limit

An action limit is an established relevant measure (e.g. microbial, or airborne particle limits) that, when exceeded, should trigger appropriate investigation and corrective action based on the investigation.

Airborne Particles and related definitions

A particle is defined as a minute piece of matter with defined physical boundaries.

Particle size is the diameter of a sphere that produces a response, by a given particle-sizing instrument, that is equivalent to the response produced by the particle being measured.

The particle concentration is the number of individual particles per unit volume of air, typically 1m³

Particle size distribution is the cumulative distribution of particle concentration as a function of particle size.

A macroparticle is a particle with an equivalent diameter greater than 5µ/

Airborne Particle Counts

Airborne particle counts are an air sampling method, used to determine if a cleanroom is meeting the required particle concentration limits within its ISO 14644-1:2015 class parameters. Airborne article counts are performed during the initial classification of a cleanroom, during periodic revalidation (ISO) or requalification (GMP) of a cleanroom and may also be required as operational process monitoring for GMP cleanrooms.

Air Changes per Hour

Air changes per hour or the air change rate (ACR) is the amount of times a cleanroom can completely replace its air volume within an hour. The higher the air changes per hour, the more effective it will be at removing contamination, therefore achieving a higher classification.

Air Conditioning

Air conditioning to regulate temperature and humidity control should be considered as part of the full cleanroom HVAC (Heating, Ventilation and Air Conditioning) solution.

All controlled air needs to be appropriately blended in the ducting before introduction into the cleanroom through HEPA or ULPA filters, to ensure any temperature and humidity requirements are met.

Air Handling Unit (AHU)

An airlock is the main system that conditions, filters, and circulates air throughout the cleanroom.

Airlock

An airlock is an enclosed space with interlocked doors, constructed to maintain air pressure control between adjoining rooms (generally with different air cleanliness standards). The intent of an airlock is to preclude ingress of particle matter and microorganism contamination from a lesser controlled area.

There are three different types of airlocks, which can vary based on the level of cleanliness required. These are:

• Personnel airlocks: To allow people to enter or exit the cleanroom environment, typically known as change rooms.
• Material airlocks: For moving materials or equipment.
• Pass-through airlocks: These are smaller compartments for passing tools or materials between rooms, typically known as pass through hatches.

By controlling the transition, cleanroom airlocks play a crucial role in maintaining the integrity of the cleanroom environment.

Air Shower

An air shower is a specialised chamber designed to reduce contaminants from people or objects before entering a cleanroom or controlled environment. The air shower removes particles from an operative or an object using high-velocity air jets

Alert Level

An alert level is an established relevant measure, (e.g. airborne particle levels or microbial counts), giving early warning of potential drift from normal operating conditions and validated state, which does not necessarily give grounds for corrective action but triggers appropriate scrutiny and follow-up to address the potential problem. Alert levels are established based on routine and qualification trend data and are periodically reviewed. The alert level can be based on a number of parameters including adverse trends, individual excursions above a set limit and repeat events.

As-built Cleanroom

An ISO 14644-1:2015 occupancy state where the cleanroom or clean zone is complete with all services connected and functioning but with no equipment, furniture, materials or personnel present.

Aseptic Preparation/Processing

In EU GMP, aseptic preparation/processing is the handling of sterile product, containers and/or devices in a controlled environment in which the air supply, materials and personnel are regulated to prevent microbial, endotoxin/pyrogen and particle contamination.

ATEX – ATmosphères EXplosibles

ATEX is the EU directive for equipment used in potentially explosive atmospheres (sometimes relevant for solvent-based Cleanrooms).

At-Rest Cleanroom

An EU GMP state, where the definition of at-rest state is the condition whereby the installation of all the utilities is complete including any functioning HVAC, with the main manufacturing equipment installed as specified but not operating and without personnel present in the room.

 

B

Barrier

A barrier is a physical partition that affords aseptic processing area (usually grade A) protection by separating it from the background environment. Such systems frequently use, in part or totally, the Barrier Technologies known as RABS or isolators.

Bio-Decontamination

Bio-decontamination is a process that eliminates viable bioburden via use of sporicidal chemical agents.

Bioburden

A bioburden is the total number of microorganisms associated with a specific item such as personnel, manufacturing environments (air and surfaces), equipment, product packaging, raw materials (including water), in-process materials, or finished products.

Biocide

A biocide is defined in the European legislation as a chemical substance or micro-organism intended to destroy, deter, render harmless, or exert a controlling effect on any harmful organism by chemical or biological means.

Biocides are used to protect humans, animals, materials or articles against harmful organisms such as bacteria, by the action of the active substances contained in the biocidal product. They are widely used in high grade pharmaceutical cleanrooms to disinfect equipment such as isolators and laminar flow cabinets, as well as surfaces. They are also widely used to disinfect product and equipment entering the clean room by transfer.

Biological Indicator (BI)

A biological indicator is the population of microorganisms inoculated onto a suitable medium, (e.g. solution, container or closure), and placed within a steriliser or load or room locations to determine the sterilisation or disinfection cycle efficacy of a physical or chemical process. The challenge microorganism is selected and validated based upon its resistance to the given process. Incoming lot D-value, microbiological count and purity define the quality of the BI.

BMS – Building Management System

A centralised control system that monitors and automates services in a Cleanroom facility, including HVAC, lighting, power, access control and fire systems. It can provide real-time data, alarms, and energy management for the facility and integrate into a site wide system.

Breakout Panel

A breakout panel is required to satisfy Health and Safety regulations and provide a convenient and quick escape route from the cleanroom in the event of an emergency. Breakout panels should be clearly marked and need to be able to be removed in seconds to allow exit.

 

C

CFM – Cubic Feet per Minute

CFM is the abbreviation for cubic feet per minute (ft³/min). When used in the context of a particle counter’s flow rate, it is a measurement of the velocity at which air flows into the sample probe. For example, a flow rate of 0.1 CFM means the particle counter will sample 0.1 cubic feet of air per minute.

Change Area

A change area or gowning area is a room in which operatives can don their cleanroom garments prior to entering the main cleanroom zone. It is good practice for all cleanrooms to include a change area as it helps operatives adhere to gowning procedures. A change area should contain sufficient space for changing, storage for clothing and bins for the disposal of packaging.

Often a change area operates at a lower classification and pressure than the main area, so the pressure cascade is maintained.

In GMP facilities: A change area or personnel airlock (PAL) is an enclosed space with interlocked doors, constructed to maintain air pressure control between adjoining rooms, (generally with different air cleanliness standards). The intent of an airlock is to preclude ingress of particle matter and microorganism contamination from a lesser controlled area.

Clean Area

An area with defined particle and microbiological cleanliness standards usually containing a number of joined cleanrooms.

Cleaning

Cleaning is a process for removing contamination e.g. product residues or disinfectant residues.

Cleanroom

A cleanroom is defined by ISO 14644-1:2015 as

“a room within which the number concentration of airborne particles is controlled and classified, and which is designed, constructed and operated in a manner to control the introduction, generation and retention of particles inside the room.”

And by EU GMP Annex 1 (2022) as

“a room designed, maintained, and controlled to prevent particle and microbial contamination of drug products. Such a room is assigned and reproducibly meets an appropriate air cleanliness level.”

Cleanroom Classification

A method of assessing level of cleanliness against a specification for a cleanroom or clean zone. method of assessing level of cleanliness against a specification for a cleanroom or clean zone. Levels should be expressed in terms of an ISO Class (1 to 9) or EU GMP Grade (A to D), which represents maximum allowable concentrations of particles in a unit volume of air.

Cleanroom Qualification

Cleanroom qualification is an EU GMP term and is a method of assessing the level of compliance of a classified cleanroom or clean air equipment with its intended use.

Closed System

In an EU GMP cleanroom, a closed system is a system in which the product is not exposed to the surrounding environment. For example, this can be achieved by the use of bulk product holders, (such as tanks or bags), that are connected to each other by pipes or tubes as a system, and where used for sterile products, the full system is sterilised after the connections are made. Examples of a closed system can be (but are not limited to) large scale reusable systems, such as those seen in active substance manufacturing, or disposable bag and manifold systems, such as those seen in the manufacture of biological products. Closed systems are not opened until the conclusion of an operation. The use of the term “closed systems” in this definition does not refer to systems such as RABS or isolator systems.

CFD – Computational Fluid Dynamics

CFD is a modelling tool used to predict airflow and particle movement inside Cleanrooms.

CFU – Colony Forming Unit

A colony forming unit is a microbiological term that describes a single detectable colony that originates from one or more microorganisms. Colony forming units are typically expressed as CFU per ml for liquid samples, CFU per m³ for air samples and CFU per sample for samples captured on solid medium such as settle or contact plates. Settle plate samples are typically measured over a 4 hour exposure period.

CNC – Controlled Non Classified area

The International Society for Pharmaceutical Engineering (ISPE) defines a controlled non-classified area as an area where HVAC systems are specifically designed to reduce airborne contaminants below the level of the ambient environment and both temperature and relative humidity are controlled more tightly than in the ambient environment.

Coving

Coving is a curved or rounded transition between two or more surfaces in a cleanroom, for example between flooring and walls or walls and ceiling. Coving reduces the risk of contamination build-up and creates smooth and easy to clean surfaces.

Critical Surfaces and Critical Zones

In EU GMP cleanrooms, critical surfaces are surfaces that may come directly into contact with, or directly affect, a sterile product or its containers or closures. Critical surfaces are rendered sterile prior to the start of the manufacturing operation, and sterility is maintained throughout processing. Critical zones are locations within the aseptic processing area in which product and critical surfaces are exposed to the environment.

 

D

Decontamination

A process that eliminates viable bioburden, (the number of bacteria living on a surface that has not been sterilised), via use of chemical agents.

Design Qualification (DQ)

Design Qualification (often referred to in the sequence of Design Qualification, Installation Qualification, Operational Qualification and Performance Qualification) is the process where the compliance of the design with the User Requirement Specification (URS) and any regulatory requirements, e.g. EU GMP, are verified, demonstrated and documented.

Dew Point (dp) vs Relative Humidity (RH)

Dew point is the temperature that a volume of air reaches when it becomes saturated with water vapour, causing dew to form. It is used as a standard parameter to determine humidity control in an environment like a dry room. Whereas relative humidity (RH) indicates the present state of humidity, relative to a maximum humidity given the same temperature. RH is often expressed as a percentage.

Disinfection

The process by which surface bioburden is reduced to a safe level or eliminated. Some disinfection agents are effective only against vegetative microbes, while others possess additional capability to effectively kill bacterial and fungal spores.

Disinfection can be achieved by the application of a biocide/sporicidal to achieve log reduction of microorganisms.

Door Interlock

Door interlocks prevent potential contamination between two clean rooms which may happen when two doors are accidentally opened at the same time. Interlocked doors support good cleanroom entry and exit practices by only allowing one door to open at a time, preserving integrity of the higher grade cleanroom.

DOP Testing – Dispersed Oil Particulate testing also known as Installed Filter System Leakage Test

This test is performed to confirm that installed filter systems with integral efficiency of 99.95% or higher at most penetrating particle size (MPPS) are properly installed by verifying the absence of bypass leakage in the installation, and that the filters are free of defects (small holes and other damage in the filter medium, frame, seal and leaks in the filter bank framework). A leak detected in excess of 0.01% of the upstream mass concentration is deemed to exceed the maximum allowable penetration.

 

E

EMA – European Medicines Agency

European regulator that enforces GMP for medicines.

EMS – Environmental Monitoring System

A dedicated system for continuous real-time monitoring of critical Cleanroom parameters such as airborne particles, pressure differentials, temperature and humidity. It can generate audit-ready records and instant alarms to ensure ongoing compliance.

ESD – Electrostatic Discharge

ESD is the rapid, spontaneous transfer of electrostatic charge between two objects at different electrical potentials, typically occurring when they come close together or into contact. This sudden flow of current can produce a visible spark and is commonly associated with static electricity buildup. In cleanrooms, static dissipative materials are common when electrostatic discharge is a process risk.

EU GMP Annex 1 – Manufacture of Sterile Medicinal Products

The primary regulatory document defining Cleanroom grades (A–D) for pharmaceutical production.

 

F

Fast Action Doors

Fast action doors (also known as rapid roller doors) in cleanroom environments are specialised, fast-acting fabric or flexible high-performance doors that provide large, efficient openings for material and personnel transfer while minimising air exchange and contamination risks.

FDA – U.S. Food and Drug Administration

U.S. regulator equivalent to MHRA/EMA for drugs and medical devices.

FFU – Fan Filter Unit

Self-contained HEPA/ULPA filter with integrated fan. An alternative to contamination control via central AHU and terminal HEPA/ULPA filtration without an integrated fan.

Flooring

The main types of cleanroom flooring finishes are vinyl which is most commonly welded from a sheet, and epoxy resin coating.

 

G

GDP – Good Documentation Practice

GDP refers to the standardised set of procedures and protocols in regulated industries, to ensure that all documentation is accurate, complete, clear, legible, contemporaneous, original, and attributable. It ensures that records reliably reflect what was actually done, allow full traceability, support data integrity, and meet regulatory requirements.

GMP – Good Manufacturing Practice

GMP is the set of regulations governing pharmaceutical production; EU GMP and U.S. cGMP.

Gowning procedure

A gowning procedure is the systematic, step-by-step process of donning specialised protective garments and accessories to minimise the introduction of particulate, microbial, or other contaminants from personnel into a cleanroom environment. This procedure typically follows a precise sequence (often from the top-down) and is performed in designated gowning areas to maintain cleanliness levels appropriate to the cleanroom classification.

 

H

HEPA – High Efficiency Particulate Air

A HEPA is a filter that removes particles from air passing through it and due to its high performance is a typical type used to create a cleanroom environment.

HMI – Human-Machine Interface

Touch panels or screens inside the Cleanroom for controlling equipment.

Humidity Control

Humidity Control in cleanroom environments refers to the precise regulation of relative humidity (RH) levels within a controlled space, to maintain optimal conditions for product quality, process stability, personnel comfort, and contamination prevention.

The process involves using HVAC, as well as often humidifiers, de-humidifiers and monitoring systems to achieve and verify the specified relative humidity percentage tolerance range.

HVAC – Heating, Ventilation and Air Conditioning

The overall environmental control system for a Cleanroom facility.

 

I

Installation Qualification

Installation Qualification (often referred to in the sequence of Design Qualification, Installation Qualification, Operational Qualification and Performance Qualification) is the process where the compliance of the installation of a cleanroom with the User Requirement Specification (URS) and any regulatory requirements, e.g. EU GMP, are verified, demonstrated and documented.

ISO 14644-1

International standard defining Cleanroom classification by airborne particle concentration (ISO 1 to ISO 9).

Isolator

An Isolator is a decontaminated, enclosed barrier system that supplies and maintains Grade A (ISO Class 5) or better air quality in its interior while providing continuous, uncompromised physical isolation of the internal process zone from the surrounding environment (including cleanroom air and operators).

There are two major types:

• Closed isolator systems: exclude external contamination by performing all material transfers via aseptic connections to auxiliary equipment rather than direct openings to the environment. The system remains fully sealed during operations.
• Open isolator systems: permit continuous or semi-continuous material ingress/egress through one or more engineered openings. These openings are protected by design features such as continuous overpressure, unidirectional airflow, or other barriers to prevent ingress of external contaminants into the isolator.

 

L

LAF – Laminar Air Flow

Unidirectional airflow, usually vertical, at 0.3–0.5 m/s (also called laminar flow).

LED Lighting

Refers to specialised light-emitting diode (LED) fixtures. These fixtures provide energy efficient, bright, uniform illumination while strictly minimising particle generation, contamination risks, and environmental disruptions. Fixtures can be selected at a range of lux (illuminance) levels depending on the user’s process.

LFL – Laminar Flow Hood / Cabinet

Localised clean zone. Often a bench top with hood with fan filtration above.

Lux Levels

Lux is a unit of illuminance, measuring the amount of luminous flux per unit area incident on a surface. In cleanroom terms, lux is the standard metric for specifying required lighting levels to ensure adequate visibility for tasks such as visual inspection, documentation, and safe operations without creating glare or shadows.

 

M

Magnehelic Gauge

A Magnehelic gauge is a widely used analogue differential pressure gauge that measures and visually indicates differential pressures between two areas, such as between a cleanroom and an adjacent area, room and corridor.

M&E – Mechanical & Electrical

UK/Commonwealth term for the coordinated design and installation of all mechanical (HVAC, plumbing, etc.) and electrical systems in a cleanroom project.

MEP – Mechanical, Electrical and Plumbing

An alternative acronym to M&E; covers HVAC, power, lighting, fire suppression, process piping, and controls essential to cleanroom operation.

MHRA – Medicines and Healthcare products Regulatory Agency

UK regulator responsible for GMP inspections and licensing.

Micron

A micron is a unit of length equal to one millionth of a metre, commonly used to measure particle sizes and filter ratings in cleanroom and contamination control contexts.

Modular Cleanroom

A Modular cleanroom is made up of prefabricated materials, using typically standardised, factory-made modular components – primarily non-shedding wall panels (e.g., ‘sandwich’ panels with cores like honeycomb, specialist foam or rockwool and skinned finishes.

This design type enables greater architectural flexibility, faster assembly and disassembly compared to a ‘traditional build’. It also allows for relocation, reconfiguration, or future expansion with reduced disruption, while maintaining required cleanliness levels and compliance with standards like ISO 14644, EU GMP Annex 1.

 

O

Operator

An operator is a trained person who performs tasks, operations, or monitoring inside a controlled cleanroom environment while following strict gowning, hygiene, behavioural, and procedural protocols to minimise contamination and maintain required cleanliness levels.

Operational Qualification

Operational Qualification (often referred to in the sequence of Design Qualification, Installation Qualification, Operational Qualification and Performance Qualification) is the process where the compliance of the Operation of a cleanroom with the User Requirement Specification (URS) and any regulatory requirements, e.g. EU GMP, are verified, demonstrated and documented.

 

P

Panel System

A panel system in cleanroom construction refers to a prefabricated modular wall and ceiling system made of non-shedding ‘sandwich panels’. These are typically made up of cores of foam, honeycomb, or rockwool and smooth, cleanable surfaces such as uPVC, epoxy powder coating, laminates, vinyl or stainless steel that are joined with sealed, flush connections to form airtight, durable, and easily assembled cleanroom enclosures.

Pass Through Hatch

A Pass-through hatch (also called a transfer hatch or airlock hatch) is a sealed, dual-door transfer device installed in cleanroom walls to allow safe, controlled passage of materials between areas of different cleanliness levels without direct personnel movement or air exchange that could compromise contamination control.

It typically features interlocking doors (preventing both from opening simultaneously), and often with HEPA filtration in higher class cleanrooms or GMP facilities.

Performance Qualification

Performance Qualification (often referred to in the sequence of Design Qualification, Installation Qualification, Operational Qualification and Performance Qualification) is the process where the compliance of the Performance of a cleanroom with the User Requirement Specification (URS) and any regulatory requirements, e.g. EU GMP, are verified, demonstrated and documented.

Pressure Cascade

A pressure cascade in cleanroom environments is a controlled system of progressively decreasing (or increasing) air pressure differentials between adjacent areas, designed to prevent cross-contamination by ensuring that air flows from cleaner to less clean zones (positive pressure cascade) or from contaminated to cleaner zones (negative pressure cascade, typically seen in biosafety or hazardous material areas). This is achieved through a balanced HVAC supply and exhaust airflow.

Pressure Differential

Pressure differential is the controlled difference in air pressure between two adjacent spaces or zones, typically measured in Pascals (Pa), used to direct airflow and prevent cross-contamination.

 

Q

Qualification

Qualification in cleanroom context is producing documented evidence that provides assurance that equipment or facilities will perform to the required specification detailed in the user requirement specification (URS) and the design qualification (DQ).

 

R

Rapid Roller Doors

Rapid roller doors (also known as fast action doors) in cleanroom environments are specialised, fast-acting fabric or flexible high-performance doors that provide large, efficient openings for material and personnel transfer while minimising air exchange and contamination risks.

RABS – Restricted Access Barrier System

Physical barrier with glove ports and HEPA airflow; used as an extra risk mitigator within typically GMP cleanrooms.

 

S

Single Leaf Swing Door

A single leaf swing door in cleanroom environments is a hinged door with one solid panel (leaf) that swings open on side-mounted hinges, providing a simple, reliable access point while maintaining an airtight seal when closed via gaskets, magnetic seals, or compression latches to support required pressure differentials and contamination control.

Sterile Product

A sterile product is a pharmaceutical, medical device, or biopharmaceutical item that is free from viable microorganisms and meets strict sterility assurance levels, achieved through validated sterilisation processes like terminal sterilisation or aseptic manufacturing techniques, as required by standards such as EU GMP Annex 1.

 

T

Temperature Control

Temperature control refers to the precise regulation of air temperatures within stated specification tolerances, achieved using HVAC systems.

Terminal Sterilisation

Terminal sterilisation is a validated process applied to a finished product in its final sealed container to eliminate all viable microorganisms, achieving a high sterility assurance level, commonly using methods such as moist heat, dry heat, gamma irradiation, electron beam, or ethylene oxide, as required by standards like EU GMP Annex 1.

 

U

ULPA – Ultra-Low Penetration Air

Filter removing ≥99.999 % of particles ≥0.12 µm; typically used in ISO 3–ISO 5 areas. An equivalent but higher performing filter than a HEPA.

UPS – Uninterruptible Power Supply

Battery-backed or generator-supported power system that keeps critical cleanroom systems (HVAC, FFUs, monitoring, etc.) running during mains failure to maintain operation.

UDF – Unidirectional Flow (same as laminar flow)

Same as laminar flow – Unidirectional airflow is usually vertical, at 0.3–0.5 m/s.

URS – User Requirement Specification

A formal document that comprehensively defines exactly what the end user needs the cleanroom to do: classification, size, environmental conditions, material types, regulatory standards, equipment interfaces and more. The URS is the foundation for design, costing, and validation.

 

V

Validation

Validation in the cleanroom context is the documented, systematic process of demonstrating (through testing, monitoring, and objective evidence) that a cleanroom facility, equipment, systems (for example HVAC, HEPA filtration, pressure cascades), processes, or procedures consistently achieve and maintain the required cleanliness, environmental control, and performance levels specified by standards such as ISO 14644 or EU GMP Annex 1.

VHP – Vapour-Phase Hydrogen Peroxide

Common gaseous bio-decontamination method for cleanrooms and isolators.

VOCs – Volatile Organic Compounds

Gaseous chemical contaminants (solvents, alcohols, siloxanes, etc.) released from materials, cleaning agents, or processes that can adsorb onto sensitive surfaces and cause product defects.

 

W

WFI – Water For Injection

Water for Injection (WFI) is highly purified, sterile water of injectable quality used typically in pharmaceutical manufacturing within cleanroom environments for the preparation of parenteral (injectable) drugs, reconstitution of powders, final rinsing of equipment, and as a diluent or solvent in aseptic processing.