Understanding Cleanrooms & Particle Count

Understanding Cleanrooms & Particle Count

October 2, 2015

At the basic level, the nature of a cleanroom is easily understandable, although it takes a bit more explanation to understand the official definition. Even someone who’s not in the industry can guess from the name that it’s a room possessing a high standard of control and cleanliness. As an introduction to the particulars a cleanroom entails, we’ll get into things like temperature control, filtration, particle count, humidity and other natural variables – as well as the levels of these variables that satisfy regulatory compliance rules.

Understanding the Nature of a Cleanroom

Contamination from external environments is one of the most important things that a cleanroom must take into account – irrespective of the work being done inside the room. With that said, the nature of the work being done inside determines the extent to which particle control is important, as well as the classification that is ultimately conferred upon the facility. First and foremost, the following figures characterize the state of a cleanroom when it is completely absent of any external contaminants. These biological elements can significantly alter the particle count; in fact, it is this sensitivity that makes a full-body coverall and other cleanroom equipment essential aspects of the working environment – to ensure that external factors don’t contribute (or contribute negligibly) to the particle count.

Clearing Up the Cleanroom Classification System

The judgment system started out as a Federal Classification; in many cases it has since been superseded by the International Organization for Standardization. The document that covers this is termed the “Cleanrooms and Associated Controlled Environments – Part1: Certification of Air Cleanliness” document, or ISO 14644-1 for airborne particulate content. The Classes range from 1 through 100,000, with Class 1 being the cleanest facility (most devoid of particles of a particular size; i.e, the “best” cleanroom). For reference, recognize that an ISO Class 1 facility has 10 particles of size 0.1 micrometers per cubic meter of air, and is also called a Class 10 facility to delineate this number of particles (this is often a point of confusion). Although there are often particles of a larger size in this same volume of air, they are ignored in the classification, because the number of such particles is significantly fewer. The ISO equivalent ranges from ISO Class 1 to ISO Class 9, with (Class) corresponding to the number of particles per cubic foot of air. Their relationship is as follows:

ISO Class 1 (Class 10)– refers to a cleanroom with less than 10 particulates of size 0.1 micrometers per cubic meter of air. This same volume is restricted to a maximum of 2 particles of size 0.2 micrometers.
ISO Class 2 (Class 100) – refers to cleanrooms that have fewer than 100 particulates of size 0.1 micrometers per cubic meter of air, and less than 24 0.2 micrometer-sized particles in the same volume.
ISO Class 3 (Class 1000) – refers to a facility with less than 1,000 0.1 micrometer-sized particles per cubic meter of air, and a maximum of 237 particles that are 0.2 micrometers in diameter.
ISO Class 4 (Class 10,000) – refers to a cleanroom with fewer than 10,000 0.1 micrometer-sized particles per cubic meter and 2,370 particles that are 0.2 micrometers in the same volume.
ISO Class 5 (Class 100,000) – designates a facility with at most 100,000 particles of size 0.1 micrometers in every cubic meter of air, and 23,700 0.2 micrometer-sized particles in the same volume.
ISO Class 6 (Class 1,000,000) – a cleanroom with up to 1 million 0.1 micrometer-sized particulates in every cubic meter of air, and 237 thousand 0.2 micrometer-sized particles in this same volume.

The remaining ISO Classes go up to ISO Class 9, and are based not on the amount of 0.1 micrometer-sized particles in every cubic millimeter of air, but larger-sized particles of diameter 0.5, 1 and 5 micrometers – designating cleanrooms with much less stringent controls. As you can see, there are overlaps in the measurements. Not only is your cleanroom judged by the particle concentration, but also by the size of the particles; you can have larger particles within a volume of air – but they must be fewer in number.

Methods of Cleanroom Control

Although cleanroom designations are made with filters already in place, they are subject to upgrades in the air flow system. Should this happen, the ISO Class designation can change to reflect the new level of particulate content per cubic meter of air. These High Efficiency Particulate Arrestors are called HEPA filters, and possess various airflow designs that can move a facility up the ladder of ISO Class designations. Even more efficient, Ultra Low Particulate Arrestors (ULPA) filters can make a cleanroom even cleaner. After you have accounted for the filters, maintenance is the next most important thing on the list. Gloves, labcoats, boot covers, hoods and other cleanroom materials comprise the bulk of the sales in the cleanroom industry; and for good reason. These must be disposed of regularly, as they pick up particulate matter from the substances being worked on inside the facility and increase the particle count inside. Taking care of these things at designated intervals ensures that your cleanroom maintains its ISO designation, and contamination is minimized within acceptable limits.