About Cleanroom

according to IEC 61340-5-1/5-2


This is the most complete information about cleanrooms on the internet.

Below you will learn:

  • What is a cleanroom?
  • Cleanroom airflow systems
  • Cleanroom classification
  • Construction of cleanrooms
  • Rules for cleanroom personnel
  • And much more…

Abtech HDW Series Modular Cleanroom

A cleanroom is a specially designed enclosed space where airborne particulates have been limited or removed by a highly sophisticated filtration system. They are used by industries that require a highly controlled and monitored environment for the production of delicate instruments or medical supplies and medicines. For a room to be classified as a cleanroom, it has to meet a precise set of international standards regarding the number of microns per cubic foot.


According to ISO 14644-1, a cleanroom is:

“… 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. 
Only particle populations having cumulative distributions based on threshold (lower limit) particle sizes ranging from 0.1 µm to 5 µm are considered for classification purposes.” 
From ISO 14644-1:2015 Cleanrooms and associated controlled environments

Part 1: Classification of air cleanliness by particle concentration. :iso:14644:-1:ed-2:v1:en


The standards regarding a cleanroom are measured in micrometers. The image on the right compares a hair follicle to a 90 µm particle of fine sand. The maximum particulate content per cubic meter for a classification ISO 1 cleanroom is 5 µm.

Duct Supply and Duct Return (from

There are three methods used to ensure that a Cleanroom can maintain its classification.

  1. Air supplied to the room is filtered by high efficiency filters, which are HEPA or ULPA, and the room is pressurized to block contaminants.
  2. The materials in construction do not emit contaminants, particles, chemicals, or gases and must be easy to clean.
  3. Workers, staff, and operators wear garments that minimize the spread of micro-particles and organisms from skin, hair, and clothing.

The primary method of ensuring that the air in a Cleanroom is at the appropriate cleanliness level is the installation of an air filtration system
that complies with the certified standards of the International Standards Organization (ISO).

Three forms of air flow systems are:

  • Duct Supply and Duct Return
  • Duct Supply and Open Return
  • Unidirectional

Here is a description of each air flow system:

BS 5295 (British Standard)

Air is ducted directly into the cleanroom and ducted directly out.
This form of cleanroom is common with manufacturers who have strict guidelines such as the pharmaceutical industry.

Duct Supply and Duct Return (from

Ducted Supply and Open Return

The ducted supply and open return air is a cost-effective and efficient method of air delivery. 
Air is ducted directly into the cleanroom and freely flows out into an open air plenum.


Duct Supply and Open Return (from

(also referred to as Laminar)

Unidirectional, or laminar, airflow systems force air in one direction. It has controlled airflow with steady air velocity from the laminar airflow hoods that direct air downward. In most Cleanrooms, the downward airflow pushes particulates out to prevent them from landing on surfaces. With a laminar system, air is pushed through filters that catch microscopic particles.

Laminar Air Flow System (from

Cleanroom Air Filters

The filtration system for a cleanroom is its most important component, since it is what keeps it clean. Cleanrooms can have single or multiple filters depending on their design and ISO classification. Most systems have filters located in the ceiling. Air travels downward from the ceiling to the floor and exits through ducts in the floor.

There are several types of air flow filters with high efficiency particulate air (HEPA) filters being the most common and widely used. High efficiency air filters have tightly packed dense material to remove contaminants, which can cause pressure drop that slows the air flow. Well-designed cleanroom filters have limited pressure drop. Below is a description of a few of the types of filters.


Pre-filter filters the air before it reaches the HEPA or ultra-low particulate air (ULPA) filters.
Their main purpose is to remove large particles and help extend the life of HEPA and ULPA filters.
A concern with pre-filters is the need to check them regularly.

Pre-Filter (from


ULPA filters are very similar to HEPA filters but are far more efficient.
They remove 99.95% of contaminants 0.12 µm in diameter.
The efficiency and quality of ULPA filters makes them more expensive.
They come in assorted sizes and supply maximum efficiency with the lowest pressure drop.

ULPA Filter(from


HEPA-filter filters out 99.99% of particles at 0.3 µm.
They are the most popular filter option and can last for many years depending on the particulate count.
HEPA filters have minimal pressure drop with maximum airflow.
The image below is of a HEPA filter with an aluminum frame designed for industrial use.


The difficulty in capturing microscopic particles is their flight path. Unlike blown dust that moves in the direction of the wind, the Brownian motion of microscopic particles causes them to travel erratically. The multiple directions of the fibers of a HEPA filter are able to capture and trap microscopic particles. The image below shows the placement of HEPA or ULPA filters in a unidirectional system.



Industrial Clean Room HEPA Air Filter (from airshowertunnel)

The fibers of a HEPA filter are randomly arranged to form a dense mat. 
As can be seen in this image.

A fibrous filter's media as seen through an electron microscope.(image credit: ECAT)

The classification of a cleanroom is determined by the amount of particulate matter (PM), a descriptor for particles and liquids in the air, it has per cubic meter.
The air we breathe has about 35 million particles in a cubic meter with an estimated size of 0.5 μm.

The most accepted classification method for cleanroom is the International Organization of Standards (ISO), an international standards setting group that has representatives
from nations around the world. ISO 14644 and ISO 14698 list the standards for cleanroom, as seen in the chart below.

ISO 14698 establishes the methodology and procedures for the elimination of biocontaminants from cleanroom.
ISO 14644 specifies the number of particulates allowed in a cubic meter of air and has macroparticle descriptions.
It was last revised in 2015 to deal exclusively with particle concentration.

Cleanroom classifications start with grade ISO 1, for extremely clean, and go to ISO 9, satisfactorily clean, which is normal room air.
The chart below details the size and number of particles allowed per cleanroom class.


ISO Cleanroom Classifications (from

The United States classification system for cleanrooms was Federal Standard 209E published by the Institute of Environmental Sciences and Technology (IEST) in 1963, which can be seen in the chart below. The IEST used a classification system that ran from Class 1, an ISO 3 class, to Class 100,000, an ISO 8 classification. Though several countries still use the IEST system, it was formally retired in 2001 as being obsolete.


International Classification Systems

Though ISO standards have been widely accepted and serve as a guide for most nations, individual countries have developed their own systems.
Below are descriptions of those systems.

(European Union Good Manufacturing Practices)

EU GMP classifications are used as a method of inspection for all phases of the production process.
Inspections are held by the participating member experts in the individual European Nations.
Their purpose is to ensure public safety.
The EU GMP worked with the United States Food and Drug Administration to establish Annex 1 as standards for cleanroom as seen in the chart below.

EU GMP Guidelines for Cleanrooms (image from european pharmaceutical review)

BS 5295
(British Standard)

BS 5295 has ten classes of standards for cleanliness as seen in the chart below. Each classification has a range of particulate counts for a more specific definition of particle size.
The BS 5295 standards were established by the British Standards Institute (BSI), which creates codes and specifications for management quality requirements.
They assist companies in meeting certification standards for other countries as well as Great Britain.

BS 5295 Classifications (from

USP 800
(United States Pharmacopeial)

USP 800 is a set of published standards for the handling of hazardous drugs (HD), which went into effect in December of 2019.
The definition of a hazardous drug was established by the National Institute for Occupational Safety and Health (NIOSH),
which states that a drug is considered hazardous if it has carcinogenicity, teratogenicity or developmental toxicity, reproductive toxicity, organ toxicity, or genotoxicity.
USP 800 is a cleanroom standard that was issued in 2017 by the USP as a revision of USP 795 and USP 797.

For Cleanrooms, USP 800 requires negative pressure, external ventilation, and air changes of 12 ACH per hour for drug storage areas.
The standards further stipulate that drugs may not be received, stored, mixed, prepared, compounded, or dispensed in positive pressure environments.

To meet the need for compliance with USP 800, ionization and polarization are used to collect particles, viruses, bacteria, volatile organic compounds, and gases.
Those systems cause contaminants to adhere to a media material and use electric fields to charge and ionize or polarize the contaminants.
For the protection of workers, ionization and polarization units polarize any ambient HD material.

Though there are many different construction methods for cleanrooms, all manufacturers have to follow the guidelines of ISO 14644-1, ISO 14698-1,
and FED STD 209E. In some cases, modular and portable cleanrooms are specially designed to assist testing facilities.
When planning Cleanroom construction, there are several factors that need to be considered, which include:

  1. Surfaces
  2. Equipment
  3. Air control system
  4. Number of personnel
  5. Lighting
  6. Doors
  7. Viewing panels
  8. Humidity control

Each of these factors are described below:


Cleanroom surfaces are smooth and impervious and will not peel, flake, corrode, create dust, or have places for microorganism to grow. They must be able to be easily cleaned and accessible. In microelectronic and semiconductor Cleanrooms, surfaces are required to be smooth and free of potential ESDs. Surface materials are shatter, dent, and crack resistant as well as crease repellent.

Floors in Cleanrooms are either epoxy resin or PVC. Resin floors are used where there is high mechanical loads since resin has high resistance and strength. The most common use of resin floors is in rooms that have water or high humidity.

PVC floors are more economical and are laid out in tiles. They are used in low little traffic areas where there aren’t heavy loads.

Epoxy Resin Flooring (from


Cleanroom equipment is manufactured from easy-to-clean materials such as stainless steel, polycarbonate, or plastic laminates. The type of equipment used in a cleanroom is anything that is not attached to the walls or floor, which includes a wide range of items from simple hand tools to showers and pass throughs.

Below are some of the types of equipment that are commonly found in a Cleanroom:

Air Control Systems:

Cleanrooms require a great deal of air and need to have the temperature and humidity controlled.
Air handling units (AHU) use 60% of a sites power.
The cleaner the room the more power that is used. To control the expense of air control units, systems are designed to recirculate the air,
which keeps the temperature and humidity stable.

Air control system is the most essential part of a cleanroom.
Cleanrooms have positive air pressure, which results in air exfiltrating into adjoining spaces with lower pressure and leaves through electrical outlets, light fixtures,
window frames, ceiling and floor interfaces, and doors. In the majority of cases, leakage is at a rate of 1% to 2%.

When planning a cleanroom, it is necessary to study how much exfiltration there is, or the amount of air that will escape the room.
In a supply, return, and exhaust system, there needs to be a 10% difference between supply and return airflow.

A common exit path is through doors. The amount of exfiltrating through a door is determined by the size of the door, pressure across the floor, and how well the door is sealed.
For a normal door, air exfiltrates at 190 cfm to 270 cfm.

In order to compensate for exfiltration, the airflow needs to be balanced where the amount exfiltrating matches the amount of infiltrating.
During the startup of a cleanroom, adjustments need to be made for exfiltration.
Turbulence, eddies, equipment, and pressure influence the air exchange rate, which is the key factor in airflow design.

The diagram below shows the exfiltration and infiltration or the air exchange rate of a unidirectional air flow system, where 1 represents the infiltration and 2 is exfiltration.
These two factors are critical for the development and construction of the air control system.

Epoxy Resin Flooring (from

Number of personnel:

The major source of cleanroom contamination is from the people who work in them
since a person sheds one billion skin cells per day that are 33 µm x 44 µm x 4 µm 10% of which carry microorganisms.
The amount of possible contamination from people makes controlling their numbers a critical consideration.

According to academic studies, only select and trained personnel should be allowed in a cleanroom.
Added to this factor is the need for adequate training in cleanroom procedures such as proper attire and protection.
Studies indicate that the higher the number of personnel, the greater the amount of contamination.




Cleanroom lighting is designed to meet specialized environmental requirements.

Unlike the air control system, lighting represents 1% of the total cost of operating a cleanroom.
Since instruments in a cleanroom are highly precise, the foot-candle, light intensity at one lumen per square foot, is very high.
Each type of cleanroom has lighting specifically designed for its purposes.

As with all cleanroom factors, the air control system takes preeminence making the planning of lighting demanding, requiring careful planning and design.

For energy efficiency, cleanrooms use LER lamps, which are easy to maintain and have a long life.

100W Low Profile Cleanroom LED Lighting (from

Other types of lighting are incandescent, high intensity, and LED.
UV lighting provides extra bacterial and contaminant control for certain types of cleanrooms.
The housing for lighting is normally steel that has its holes and openings sealed with gaskets.

In most cleanrooms, ballasts and lamp holders are easily removed to avoid disturbing cleanroom conditions.

Example of a well-lit cleanroom where a technician is testing the particle count.

Well Lit Cleanroom (image from Production Automation Corporation)

A recent development is automated lighting that uses a passive infrared sensor motion detector to avoid waste of energy,
while ensuring constant illumination for users.

In the design phase of a cleanroom, engineers determine the necessary lux level, unit of illuminance, that is necessary.
The lux level depends on the types of work to be completed.
The chart is a brief explanation of the lux level for various tasks

Lux Table (from


Cleanroom doors are responsible for keeping the room sealed from external contaminants and maintaining the controlled environment.
As with every detail of a cleanroom, the doors have to be specially designed to exacting standards.
Below are some of the details to consider when examining a cleanroom door.
The first thing to note, as with all cleanroom surfaces, doors have to be smooth and impenetrable.

  • Completely flat
  • Easy to integrate into any Cleanroom
  • Resistant to bending and shock with a thickness of 60 mm or 2.36 in.
  • Air tightness
  • Resistant to strong chemicals in cleaning products
  • Safety glazed glass
  • Resistant to ESDs
  • Swing into the room
  • High quality hardware
  • Able to be locked
  • Closed cell non-organic core
  • Seamlessly molded
  • Fire resistant

Single and Double Cleanroom Doors (from

Viewing Panels:

The purpose of viewing panels is for operators to work more efficiently and have visual contact.
They are strategically located for ease of access for supervision inspection and the elimination of the supervisor performing entry protocols.

Viewing panels must be flush to both sides of the wall, shatter proof, with a drying agent in the void between the glass panels, and fire resistant.
In ultraviolet lit rooms, they have a coating that filters the ultraviolet wavelengths.

The visual display below has examples of various types of view panels.

Viewing Panels (from

Low Humidity:

The relative humidity (RH) for a cleanroom should be between 30 to 60% at a balanced level to protect against overly moist or dry conditions.
Well balanced humidity suppresses the potential for electrostatic discharge (ESD) that could ruin products.
Humidity control is necessary as a means of preventing bacterial growth.
Two methods of humidity control are air conditioning and desiccants, a substance that induces dryness.

Air conditioning lowers the surface temperature in a cleanroom, while the desiccant process absorbs moisture in the air.
Desiccants significantly reduce dew points to five times lower than an HVAC system. Below is a diagram of a desiccant humidity filter.

Desiccant Dehumidification Filter (from

Different Levels of Cleanrooms

The level of a cleanroom is determined by its air. All cleanrooms are built the same with airtight walls, doors, windows, and very clean air.
To move from one classification to another, there has to be an increase in airflow since air removes the contaminants.
The cleaner the room, the higher rate of air exchange.

Lower levels of cleanrooms such as ISO level 9 to ISO level 6, cleanliness is based on the amount of air exchanged each hour,
while rooms at ISO levels 1 through 5, airflow is measure per second.
Equipment and furniture can block airflow and raise a cleanroom’s level of classification.

There are three different states in the determination of the level of a cleanroom: as built, at rest, and operational.
As built refers to the cleanroom’s performance without people, equipment, or furniture, its built state.
At rest is when everything has been added before performing processes.

The change in level takes a significant up or down move when it is in full operation.
It is at this state that its classification level will be determined.

The image below is of a stage three of a fully operational high bay cleanroom for NASA
with the air filters located further above the floor than is found in a transitional cleanroom.

NASA’s MMS Team Assembling Final Observatory (from

The biggest problem with Cleanrooms is people since they carry contaminants and microorganisms on their skin.
There are several steps that companies take in an attempt to control the amount of contaminants released by personnel.
The first rule is the use of specially designed clothing produced by cleanroom suppliers.

The image below is of clothing for a strictly monitored Cleanroom.

The ISO class of a Cleanroom determines the type of clothing that personnel are required to wear.
OSHA has guidelines for Cleanrooms but does not have standards for protective clothing.

Listed below are the ISO 14664 clothing requirements for Cleanrooms.

  • Hood
  • Bouffant hat
  • Coverall
  • Inner suit worn underneath coveralls
  • Boot covers
  • Goggles
  • Facemask
  • Gloves

Cleanroom Clothing (from

Cleanroom Clothing Factors:

  1. Must match the cleanroom’s risk and hazard analysis.
  2. Sturdy to avoid rips or tears
  3. Disposable
  4. Non-disposable when proper laundry is available
  5. Sized to fit worker measurements
  6. Delivered in individually vacuum sealed packaging and stored in a cleanroom environment

Disposable clothing is the most common option for Cleanroom clothing, which is disposed of in designated bins.
The image displays a “bunny suit” that is normally white and covers the whole body.
All of the labeled items are disposable.

Cleanroom Disposable Coverings (from

Rules for Cleanroom Personnel

  • Every company has their own set of rules for Cleanroom use. The list below is a general overview.
  • Entering and exiting – thoroughly wash and dry hands. Put on protective clothing. When exiting, dispose of all clothing and wash up a second time.
  • Cleaning – walls, floors, and work surfaces must be completely cleaned using SDS (Safety Data Sheet) chemicals.
  • Hygiene – personal hygiene must include a daily shower, washing of hair, brushing of teeth, and approved skin care products.
  • Clothing – personnel may be required to completely change from their street clothing prior to entering the cleanroom.
  • Work pace – personnel must move slowly at an even pace to avoid air turbulence.
  • Dropped items – items dropped or have fallen on the floor, they are not to be picked up.
  • Tools and supplies – are organized and stored in properly labeled containers and cabinets.

The definition of the types of designs for cleanrooms begins with the method of ventilation,
which can be turbulent or unidirectional with turbulent being non-directional and unidirectional or laminar having air flow in one direction.

The images below show both turbulent and unidirectional.


Beyond the types of airflow is kinds of construction, which can be modular or conventional, stick built.
Initially, all cleanrooms were stick built or permanent that is still used for large ballroom cleanrooms.
They have the advantage of being able to cover a wide area.
Stick built modular models combine the features of both types with a permanent seal at seams and joints as well as sturdy walls and air exchange units.

Below is a description of a few of the different types of cleanrooms:

Hardwall Cleanrooms

Hardwall Cleanrooms are modular cleanrooms with aluminum posts and rigid wall construction for increased air pressure.
Walls are demountable to create a completely enclosed cleanroom.
They are recommended for ISO Classes 5 to 8.

Bio-Safe Cleanrooms

Bio-Safe Cleanrooms eliminate cracks, have powder coated double walls, stainless steel panels,
and meet ISO 4 class requirements and FED STD 209E class 10 standards

Softwall Cleanrooms

Softwall Cleanrooms are a soft sided, tent like structure.
They are smaller, portable, inexpensive, and are effective at containing dust.
Their purpose is to support an already clean environment by doing spot cleaning.

Powder Containment Cleanrooms

Powder Containment Cleanrooms has a HEPA filtered clean zone with rear mounted air vents to draw air and powder away from the operator.
The recirculation system maintains continuous washing of particles from the air, which can be seen in the diagram below.

Explosion proof Cleanrooms

Explosion proof Cleanrooms are expected to be explosion proof. For industries that work with volatile chemicals,
there are specially designed explosion proof cleanrooms with thicker walls and explosion proof materials.

Fire resistant Cleanrooms

Fire resistant Cleanrooms have walls made of chemical, thermal, and fire resistant materials such as fluoropolymers.
As an extra precaution, wall materials are resistant to the effects of sunlight and radiation.

  • Cleanrooms are specially designed enclosures that are designed to eliminate contaminants and microorganisms.
  • The purity of the air in a cleanroom is determined by the number of µm particles there are in one cubic meter of air.
  • There are several classifications used to identify a cleanroom. The International Organization of Standardization (ISO) is the most widely accepted.
  • There are strict guidelines for clothing worn by workers in a cleanroom.
  • The most important component in a cleanroom is its air exchange unit.
  • Airflow in a clean room can be unidirectional or turbulent.
  • The two construction designs of cleanrooms are modular and permanent or stick.
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