What Is a Cleanroom? - Paul Industries

A cleanroom is a controlled environment engineered to limit the concentration of airborne particles, along with regulated temperature, humidity, and air pressure. Air is continuously filtered through HEPA or ULPA filters and exchanged many times per hour to keep contamination below a defined limit. Cleanrooms are classified by the ISO 14644-1 standard, which ranks them from ISO 1 (cleanest) to ISO 9 based on the maximum allowable particle count per cubic meter of air.

Short definitionA particle-controlled, filtered environment classified by ISO 14644-1.

Where it’s usedPharma · biotech · cosmetic · nutraceutical · food & beverage

Key standardISO 14644-1 (airborne particle classification)

Related equipmentHEPA/ULPA filtration, sanitary process piping, HVAC pressure controls

Why it mattersContamination control protects product sterility, quality, and cGMP compliance.

How a cleanroom works

A cleanroom controls contamination by combining high-efficiency air filtration, high air-exchange rates, and directional airflow. Supply air passes through HEPA filters, which capture at least 99.97% of particles at 0.3 microns, or ULPA filters, which capture 99.999% down to 0.12 microns. The filtered air floods the room and continuously dilutes and sweeps away particles generated by people, equipment, and processes.

The number of times the entire volume of air in a room is replaced each hour is called the air change rate. Cleaner classifications require far higher rates: a less-critical ISO 8 space may use roughly 10 to 25 air changes per hour, while a critical ISO 5 zone can require several hundred. Airflow patterns also matter. Turbulent (non-unidirectional) airflow mixes and dilutes contamination and is common in lower-grade rooms, while laminar (unidirectional) airflow moves in parallel streams that sweep particles away in one direction, protecting exposed product in the most critical zones.

Rooms are also held under controlled differential pressure. A pressure cascade keeps cleaner rooms at higher pressure than adjacent, dirtier spaces, so air always flows outward from clean to less-clean and unfiltered air cannot migrate inward. Personnel enter through gowning airlocks and wear controlled garments — coveralls, hoods, gloves, and boot covers — because people are the single largest source of particles and microbial contamination.

Cleanroom classification chart (ISO 14644-1)

ISO 14644-1 defines cleanliness by the maximum number of particles of a given size permitted per cubic meter of air. The table below summarizes the most common classes used in life-science manufacturing, the maximum particles at or above 0.5 microns per cubic meter, the roughly equivalent legacy US FED-STD-209E class, and typical uses.

Common ISO 14644-1 cleanroom classes and legacy FED-STD-209E equivalents
ISO class	Max particles ≥0.5 µm per m³	~FED-STD-209E	Typical use
ISO 5	3,520	Class 100	Aseptic filling, sterile product exposure, laminar-flow zones
ISO 6	35,200	Class 1,000	Support of aseptic areas, high-precision assembly
ISO 7	352,000	Class 10,000	Background rooms around critical zones, compounding
ISO 8	3,520,000	Class 100,000	General manufacturing, packaging, material staging

Lower ISO numbers are cleaner. FED-STD-209E was the older US federal standard and was officially withdrawn in 2001 in favor of ISO 14644, but its Class 100 / 1,000 / 10,000 / 100,000 labels are still widely referenced in industry conversation. Classification measurements are also tied to the room’s operational state — as-built, at-rest, or in-operation — because occupancy and running equipment change the particle load.

Standards & references

ISO 14644: The international standard family for cleanrooms and controlled environments. Part 1 sets the airborne-particle classification (ISO 1 through ISO 9); other parts cover monitoring, testing, design, and operation.
cGMP — 21 CFR Part 211: The FDA’s current Good Manufacturing Practice regulations for finished pharmaceuticals. They require adequate control of air, environment, and contamination, making cleanroom design and monitoring a compliance requirement, not just a preference.
USP <797>: The US Pharmacopeia standard for sterile compounding. It sets environmental and engineering-control requirements — including ISO-classified air — for pharmacies and facilities preparing sterile preparations.
USP <800>: The US Pharmacopeia standard for handling hazardous drugs. It adds containment and negative-pressure requirements to protect personnel and the environment when compounding hazardous compounds.

Frequently asked questions

What is a cleanroom?

A cleanroom is an engineered space where airborne particle concentration is controlled to a measured level, usually with temperature, humidity, and pressure also held within limits. It protects sensitive processes like drug and device manufacturing from contamination. Paul Industries builds and validates cleanrooms to ISO 14644.

What defines a cleanroom versus an ordinary clean space?

A cleanroom is defined by a measured, certified airborne particle limit, its ISO class, maintained through HEPA filtration, controlled air changes, and pressurization. A merely tidy room has no such quantified, verified control. The distinction is measurement and certification, not appearance.

How does a cleanroom control airborne particles?

It supplies HEPA-filtered air at a high change rate to dilute and sweep particles away, holds positive pressure so air leaks outward, and limits what enters through gowning and airlocks. These layers work together; removing any one lets particle counts rise.

What is a HEPA filter and why does a cleanroom need one?

A HEPA filter removes at least 99.97 percent of particles at 0.3 micrometers, the hardest size to capture. Cleanrooms rely on HEPA, or the finer ULPA, filtration in the supply air to remove the particles that otherwise accumulate from people, equipment, and processes.

What does ISO class mean for a cleanroom?

ISO class, defined by ISO 14644, states the maximum airborne particles allowed per cubic meter. A lower number is cleaner: ISO 5 is very clean, ISO 8 is close to filtered office air. The class quantifies exactly how clean a given cleanroom is.

Why does a cleanroom use positive air pressure?

Positive pressure keeps the cleanroom above the pressure of surrounding spaces, so air always flows outward through cracks and doorways, blocking dirtier air from entering. A cascade of pressures between rooms protects the cleanest zone. Containment rooms invert this to trap hazards inside.

What is an air change rate in a cleanroom?

The air change rate is how many times per hour the room’s entire air volume is replaced with filtered air. Higher rates continuously flush out the particles people and equipment generate, so cleaner ISO classes require more air changes to stay in control.

Do cleanrooms control temperature and humidity as well?

Almost always, and on many projects that is the harder requirement. ISO 14644 classifies particle concentration only; it says nothing about temperature or humidity. Those come from the process: tablet compression needs controlled humidity to stop material sticking, analytical instruments need temperature stability tighter than comfort standards, and gowned operators generate heat the system must remove. A room can hold its particle class perfectly and still be unusable if humidity drifts outside what the process tolerates.

Why do people wear special garments in a cleanroom?

The human body constantly sheds skin particles and microbes. Cleanroom garments, gloves, and head and foot coverings trap these so operators do not contaminate the space. Because people are the largest contamination source, gowning is one of the most important controls.

What is the difference between a cleanroom and a laminar flow hood?

A laminar flow hood is a small bench-scale device delivering filtered unidirectional air over a limited work surface. A cleanroom is a full walk-in controlled environment. A hood protects a local area; a cleanroom controls the entire room the operators work in.

How is a cleanroom certified as clean?

Certification counts airborne particles at defined locations against the target ISO class under ISO 14644, supported by airflow, pressure, and HEPA integrity tests. A documented report proves the room meets its class. Paul Industries performs this certification as part of building the room.

What are the ISO classes of cleanrooms?

ISO 14644-1 runs from ISO 1, the cleanest, to ISO 9, roughly ordinary room air, classified by maximum permitted particle concentration at specified sizes per cubic meter. Pharmaceutical work concentrates in ISO 5 through ISO 8: ISO 5 for the critical zone in aseptic processing, ISO 7 as its background, ISO 8 for non-sterile manufacture and support areas. A class quoted without the particle size and the occupancy state is an incomplete specification.

How is a cleanroom kept clean after it is built?

By monitoring and gowning discipline rather than by the construction. Classification is reverified on a schedule, typically annually and twice yearly for ISO 5 and cleaner, with routine particle and microbial monitoring in between, filter integrity testing, and pressure differentials logged and trended. The largest variable a building cannot control is people: gowning practice and traffic discipline account for more day-to-day variation than any mechanical factor, which is why they are audited rather than assumed.

Can a cleanroom be built inside an existing building?

Yes. Cleanrooms are often installed into existing facilities using modular wall and ceiling systems that fit the available height and structure. Paul Industries assesses the space and HVAC capacity, then designs an envelope and utilities that reach the required class.

How do I find out what cleanroom I need?

Ask your quality organization which regulation or customer requirement actually applies, then design to that rather than to a number someone suggested. If nobody will ever request a classification certificate, you probably need a controlled environment rather than a cleanroom. If a certificate will be requested, the class follows the process step it protects. Getting that answer before design is the single largest cost decision on a cleanroom project, because classification drives air change rate and therefore everything downstream.

What ISO class is a cleanroom?

Cleanrooms are classified from ISO 1 (cleanest) to ISO 9 under ISO 14644-1, based on the maximum allowable airborne particles per cubic meter. In life-science manufacturing, ISO 5 through ISO 8 are the most common, with ISO 5 used for aseptic filling and ISO 8 for general production.

How is a cleanroom classified?

A cleanroom is classified by measuring the concentration of airborne particles at defined sizes, then matching that count to the limits in ISO 14644-1. The measurement is taken in a specified operational state — as-built, at-rest, or in-operation — because occupancy and running equipment affect the particle load.

What is the difference between ISO 5 and ISO 7?

ISO 5 is far cleaner than ISO 7, allowing a maximum of 3,520 particles at or above 0.5 microns per cubic meter versus 352,000 for ISO 7 — a hundredfold difference. ISO 5 typically uses unidirectional laminar airflow for aseptic product exposure, while ISO 7 often serves as the background environment supporting those critical zones.

How is a cleanroom kept clean?

Cleanrooms stay clean through continuous HEPA or ULPA air filtration, high air-change rates that dilute and remove particles, and a pressure cascade that keeps cleaner rooms positively pressurized so contaminated air cannot flow in. Strict gowning, controlled materials, and regular cleaning and monitoring further limit contamination from people and processes.

What industries use cleanrooms?

Cleanrooms are used wherever airborne contamination must be controlled, including pharmaceutical, biotech, cosmetic, nutraceutical, and food and beverage manufacturing. They are also common in medical-device production, semiconductors, and aerospace, though the required ISO class varies with the sensitivity of the process.

Need a cleanroom built or serviced?

Paul Industries designs, installs, and validates process-equipment and sanitary-piping systems for manufacturers nationwide.

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