Glossary of Cleanroom Terminolgy

Class 1 – 100,000 Cleanrooms

The cleanroom classes are defined as the number of allowable airborne particles found in a specific size micron (or larger) per volume of air. So for instance, a Class 1,000 (ISO 6) cleanroom allows only 35,200 particles of size 0.5 microns or larger in a cubic foot of air.

View the chart below for more information.

  • Class 100,000 (ISO 8 / M 6.5) Basic Clean 15% 15%
  • Class 10,000 (ISO 7 / M 5.5) 30% 30%
  • Class 1,000 (ISO 6 / M4.5) 45% 45%
  • Class 100 (ISO 5 / M 3.5) 60% 60%
  • Class 10 (ISO 4 / M 2.5) 80% 80%
  • Class 1 (ISO 3 / M 1.5) Extremely Clean 100% 100%


A room, enclosure, or any other environment where contaminants are controlled within specified limits. Air is directed through the room to control the airborne particle levels and in some cases temperature and humidity. The level of contamination control separates one class of cleanrooms from another.


High Efficiency Particulate Air. HEPA Filters are used to remove 99.9% of particles as small as .3 microns.

Laminar Flow – Laminar Flow is unidirectional airflow. In a cleanroom, it is filtered air flowing vertically or horizontally with uniform velocity in a single direction. Filtered air flows through your cleanroom and back to an air return, to be re-filtered and returned to the room. Laminar flow is a major part of keeping your cleanroom contaminant free.

Air Shower

An air shower is a hallway or room leading to the entrance of a cleanroom. In an air shower, high velocity air blows off particles that could contaminate a cleanroom. Sometimes, air showers are combined with static removal equipment or HEPA filters to make the them more effective in the removal of hair and other contaminants.

Air Lock

An air lock is a room attached to a cleanroom that acts as a buffer zone between the cleanroom and outside space. Air locks have interlocking doors that keep the cleanroom pressurized and particle free during the transfer of objects or personnel and are commonly used for gowning.

Air Plenum

The space between an inner and outer wall or between the cleanroom ceiling, and roof deck. Air is supplied into the ceiling plenum and then flows through a HEPA or ULPA filter into the cleanroom and is returned through the double wall plenum back to the filters to be recirculated.

Backward Compatible

All Angstrom Technology cleanrooms are backward compatible, meaning they can be repaired or expanded with new materials that match the aesthetics and performance of the original. No purchase is ever outdated or wasted because you can improve, expand, improve cleanliness, increase classification, and upgrade discrete zones at any time.

Bio Safety Hood Classification

Class 1

The Class I Biosafety cabinet is a ventilated cabinet with in inward airflow and outlet HEPA filters. It was previously referred to as the CDC Hood and served a valuable function in its time by protecting personnel and environment. Since it offers no product protection, it has been essentially obsolete for the past several decades. 

Class 2

(Types A and B) are Laminar Flow Biological Safety Cabinets that protect personnel, product and environment. They provide inward airflow to protect personnel, downflow HEPA filtered air to the rok area to protect the product and exhaust HEPA filtered air to protect the environment from particulate and aerosol hazards.

Class 3

Class 3 Bio Safety is defined as a ventilated glovebox. This is a gas-tight chamber operated through sealed gloves which provide a complete barrier between the worker and hazardous material. The glovebox is maintained under negative pressure with HEPA filtered supply air and double HEPA filtered exhaust air.

Ceiling Grid System

The prefabricated framework of interlocking bars that hold lights, filters and other ceiling components in a cleanroom is a grid system. A sealant may be used to prevent airflow around filters and lights.


Special cleanroom apparel that is made of synthetic fiber, such as nylon, Tyvek or Dacron that are lint-free and limit contamination from personnel.

Flooring System

Different types of flooring are used in cleanrooms, depending on the class and level of cleanliness needed. Flooring material can be made of material that controls static, it can be perforated for laminar flow, sticky for trapping dust, or seam sealed for contamination control.

Federal Standard

Standard 209E are the Federal Government’s basic design and performance requirements for cleanrooms. It describes methods for class verification, cleanliness monitoring and other maintenance issues.


A micron is a millionth of a meter. To compare, a human hair is about 100 microns wide.


Replaceable filters that remove large contaminants from the air before it’s cycled through HEPA or ULPA filters for final purification.


Particulate is contamination in the air, or contamination generated from a process.


A pass-thru is a chamber for passing items between the cleanroom and outside room. The higher pressure in the cleanroom forces particles out when the inner door opens. Less traffic in and out of a cleanroom means fewer chances for contaminants to enter.

Sticky Mat

A sticky mat is a special mat located at the entrance to a cleanroom that is covered with an adhesive coating that removes dirt and other particles from shoes.


The speed at which a room cleans itself and returns to normal is known as recovery.

Talk Through

A talk-thru is a special, covered opening in the cleanroom wall that allows people outside to talk to those inside without entering the room and causing contamination. Standard membrane and electronic talk-thrus are common.

Testing & Certification

In order to be assured your cleanroom meets prescribed standards, testing and certification of the room itself, as well as major components is recommended. HEPA and ULPA filters, laminar flow equipment, ionization equipment, safety cabinets and HVAC equipment, and others, are recommended for testing annually.


Sealant is used to seal filters, lights and other cleanroom components to prevent the spread of contaminants. Silicone, plastic and gel sealants are commonly used.

ULPA Filters

Ultra Low Penetration Air. ULPA Filters are used to remove 99.9% of particles as small as .1 microns.

As Built

A term used to describe a functioning cleanroom with no furniture, process equipment, or personnel. When inspected, it is considered ‘as built’. This level is tested in new rooms only and is very easy to pass.

At Rest

A term used to describe a fully operational room with furniture, process and support equipment in place but not operating with personnel. When inspected, it is considered ‘at rest’. This is the most commonly tested condition and is also easy to pass because no particles are being generated within the room by personnel.


When the cleanroom is fully furnished and staffed, it is considered operational. This is the most difficult inspection level to pass because it includes personnel, the dirtiest component of an operational cleanroom. People can shed hundreds of thousands of particulate per hour.