ISO 4-9 Cleanrooms

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About ISO

The primary authority on clean room classification standards is the International Organization for Standardization (ISO), which is the global representation of national standard bodies. The ISO is a non-governmental group with its headquarters in Geneva.

ISO implies equal representation by member nations and is made up of more than 160 countries, with each represented by its standard body. The United Kingdom Accreditation Service (UKAS) is the standard body representing the UK.

To decide on best practices, ISO’s member subject experts come together to form a committee. After two sessions comprising a draft standard and a draft vote, a FDIS (Final Draft International Standard) is then created. If the FDIS is approved from the central secretariat, it is then published as an official international standard.

Modular Cleanroom Benefits

  • Modular Construction
  • Quick Assembly Time
  • Versatility
  • Reconfiguration
  • Airflow Control
  • Inexpensive Modifications

ISO and Cleanrooms

Cleanrooms are built to meet cleanliness classification levels, dependent on the industry in question. It’s important to match industry type to a specific cleanroom model. This is because different industries work with different levels of air purity.

Manufacturing and assembling electronic components within the electronic industry depends critically on cleanrooms.  Biotech and Pharmaceutical companies deploy ISO Class 5 to ISO Class 8 to avoid particulate contamination. Medical companies work with ISO Class 7 and ISO Class 8 to avoid surface contamination. Food industries ultimately depend on secure cleanroom environments for food safety.

Cleanroom industry requirements fall under ISO 14644-5:2004 – an ISO category that lists the basic requirements for cleanroom operations.

Cleanroom Design, Build & Validation

  • Budgeting and planning
  • Engineering, design & layout
  • Airflow and filtration design
  • Construction and Installation
  • Full Certification of our product
  • Industry-specific equipment installation
  • Validation

How To Determine A Cleanroom Classification

Cleanrooms are classified based on the level of air cleanliness. Cleanroom classes cover the range of ISO 1 to ISO 9.  An ISO 1 is the cleanest, whereas an ISO 9 is the dirtiest status for cleanroom standards.

Analysis shows there are about 500,000 to 1 million particles per cubic feet of air. To measure contaminants found in the cleanroom, the standard deployed is a micron or micrometer (μm) Micron measurement represents the cleanroom standard size for contaminants.

A micron is equivalent to one-millionth of a metre. A micron is smaller than a living cell and can only be seen by a powerful microscope. A dust particle is about 60 microns, while the size of a bacterium is roughly 2 to 10 microns.

Cleanrooms are broken into categories based on contaminant size and quantity per air volume. Cleanroom classifications each have a concentration limit for contaminants; ISO classifications are measured in cubic metres (m3 of air). There are three criteria determining cleanroom classification:

  • Particle size to be filtered from the cleanroom
  • Source of contamination within the cleanroom
  • Amount of air needed to circulate the contaminant out of the cleanroom

Particle size within a Cleanroom

A cleanroom is categorised based on the level of air cleanliness within its space. This categorisation is measured on particle size and quantity per air volume (number of air contaminants per cubic metre). It must be determined whether a specific size of the contaminant particle or various particle sizes need to be filtered from the cleanroom.

If there is a request for less than 100 particles per square foot in a cleanroom, the ISO classification will be an ISO 5 (or Class 100). The former Federal Standard 209 featured class numbers which are still being used. It is abbreviated to FS 209. Find below ISO classifications and equivalent FS 209 class numbers.

  • ISO 3 represents class 1
  • ISO 4 represents class 10
  • ISO 5 represents class 100
  • ISO 6 represents class 1,000
  • ISO 7 represents class 10,000
  • ISO 8 represents class 100,000

ISO classes are represented in cubic metres of air, while cubic feet are the unit calculation for FS 209.

Source of Contamination

There are three sources of cleanroom contamination:

Contamination brought into the Cleanrooms by workers: personnel still bring small amounts of contaminants into the cleanroom. Cosmetics are not encouraged in the cleanroom, as they can be responsible for contaminant particles of silicon or sodium. There should be strict enforcement of cleaning procedures – especially for the ISO 7 cleanroom classification. An ISO Class 5 is designed not to tolerate more than 3,520 particles equal or larger than 0.5 microns per cubic metre of air. Notebooks and pens specially made for cleanrooms should be used only to reduce contaminants.

Industry type work Process: contamination caused by the ongoing industry work process (manufacturing, health or pharmaceutical) also affects airflow.

Cleanroom operational layout is important: the placement of systems and equipment can affect airflow, with poor positioning of filtration systems leading to a build-up of contaminants, which in turn can bring about poor ISO classification; for instance, ISO classification depreciation from an ISO 7 to ISO 8 and an ISO 8 to an ISO 9.

ISO Class 9 as a Controlled Environment

An earlier goal of the ISO standard was the creation of ISO Class 9 to be a controlled and environmental technique method. Features of a controlled environment include the ability to exert pressure, alternate temperature and increase air filtration methods within a cleanroom. There is control in particle level, temperature and humidity re-allotment within the cleanroom. The particle level change happens due to HEPA filtration methods.

There is however no control on the particle size.

Amount of air to work with

  • It takes twice the amount of air to move back to a former ISO classification level: for instance, it would take twice the amount of air to move from an ISO 8 classification back to an ISO 7 if there was an earlier depreciation from an ISO 7 to ISO 8 classification.
  • Choose a manageable cleanroom space: choosing a large cleanroom size that isn’t necessary means more air/work for that volume of space.

ISO Classification and hourly air change

HEPA filters help circulates the air needed to reduce cleanroom contaminants. Depending on the ISO class, there are required averages for the number of air changes per hour. The number of air changes per hour refers to the volume of filtered air in a single hour divided by the cleanroom volume.

  • ISO class 1, ISO class 2 and ISO class 3 will require 500 to 750 air changes per hour
  • An ISO class 5 will require 240 to 360 air changes per hour in a unidirectional flow
  • An ISO class 6 will require 90 to 180 air changes per hour
  • ISO class 7 will require 30 to 60 air changes per hour
  • ISO 8 will require 10 to 25 air changes per hour

Cleanroom state and ISO Level

There are three states a cleanroom can be in before ISO level readings should be taken. These cleanroom states are:

  • Cleanroom just being built: the (under construction) empty cleanroom should be tested for air particles and readings taken. These readings would serve as a benchmark.
  • Cleanroom at rest: adding equipment without workers present introduces a certain level of contamination. The cleanroom should have a particle assessment carried out.
  • Cleanroom in operation: introducing workers also means introducing an extra amount of contamination. A cleanroom in operation might be rated an ISO 7, while a cleanroom at rest could be rated an ISO 6. The cleanroom is tested in an operational state. Values can be analysed to see how many workers introduce more contaminants, as well as measure the air flow performance against the number of occupants and equipment. There should be a complimentary interplay between good air flow and cleanroom designs to reduce clogging.

ISO classifications and FFM ceiling space allocations

There is a direct relationship between ISO classification and Fan Filter Modules (FFMs) housed in cleanroom ceilings. Additional FFMs improve ISO classifications.

An ISO Class 8 has roughly 5 to 15% of its ceiling space made up of FFMs. Introduce additional FFMs that have 15 to 25% ceiling space for an improvement to an ISO 7 Class. Introduce more FFMs with a 25-40% ceiling space allocation and an ISO Class 6 is created.


FFM allotment for ISO classes include:

ISO Class 1

Electronic and life science industries utilise ISO Class 1. Industrial processes make use of ultra-fine particles and nanotechnology. FFM ceiling coverage in an ISO class 1 is 80 to 100%.

ISO Class 2

A ceiling FFM space coverage of 80 to 100% is required.

ISO Class 3

ISO Class 3 requires FFM space coverage of 60 to 100%.

ISO Class 4

A ceiling FFM coverage of 50 to 90% is required.

ISO Class 5

A room FFM ceiling coverage of 35 to 70% is required.

ISO Class 6

An FFM ceiling coverage of 25 to 40% is required for an ISO Class 6.

ISO Class 7

A ceiling FFM of 15 to 25% is required for an ISO Class 7.

ISO Class 8

An FFM ceiling coverage of 5 to 15% required for ISO Class 8


For more information

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phillip.godden
Phillip Godden

Phillip Godden is the Founder & Chief/Executive Officer at Total Clean Air.

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