Cleanroom Terminology: Air Change Rates

Cleanroom Terminology: Air Change Rates

Air Changes per Hour are important factors in determining the design and evaluating the performance of a cleanroom. The air changes per hour, airflow pattern, and exchange efficiency all have significant implications on cleanroom performance and cost, which in turn determines the return on investment for a cleanroom.

What are air changes per hour, and how are they accounted for in cleanroom design? We’ll break down the answers to these questions and more.

What are Air Changes Per Hour?

As defined by ISO 146144-4 standards, air changes per hour refers to the number of times per hour the air in a cleanroom is replaced with clean, filtered, and treated air. It’s calculated by dividing the volume of air sent into the cleanroom as a unit of time by the total volume of the cleanroom. 

Air Changes Per Hour or Air Change Velocity

Cleanrooms, by definition, require air changes in order to meet air quality requirements for particle count and more. As the environment gets more clean with lower ISO classes, more and more air changes are needed to reach stringent classification standards

ISO standards express air changes per hour differently for cleanrooms with unidirectional and non-unidirectional airflow. 

Non-Unidirectional Airflow = Air Changes Per Hour

Non-unidirectional, or mixed flow, refers to the airflow pattern in a cleanroom. Typically, cleanrooms that fall within ISO Classes 5 and above use this type of airflow. It is sufficient for removing the designated number and size of particles at a regular rate per their classification standard. 

For cleanrooms that comply with ISO Classes 4-9, hourly air changes per hour are sufficient to express how many times the air in the cleanroom is completely refreshed. Applications like pharmaceutical, packaging and manufacturing, biosciences and health typically fall in this classification range and comply with air changes per hour as described. 

Unidirectional Airflow = Airflow Velocity

As cleanroom classifications become more stringent, the air changes per hour must increase to remove particles and keep the air cleaner. Cleanrooms with unidirectional airflow, typically Class 5 and below, have the strictest cleanroom classifications. To maintain air quality, the air changes per hour is so rapid it is expressed instead as airflow velocity, either in meters per second or feet per minute. 

These cleanroom environments must remain extremely clean, so the constant flow of contaminant-free air, either vertically or horizontally, is vital to keep particles from settling on surfaces and maintain classification standards. 

Cleanroom applications such as microelectronics, sensor manufacturing, and other sensitive processes must be performed in such environments with strict air quality control and consistent removal of contamination.

Air Changes Per Hour and Cleanroom Classifications

air changes per hour are an essential component of cleanroom classification standards. They make it possible to reach the particle count and size restrictions each class sets. Let’s take a look how air changes per hour and classification are related.

ISO 14644-1 Cleanroom Standards


Maximum Allowed Particles (per m3)

Air Changes Per Hour

Airflow Velocity (ft/min)

Ceiling Coverage

≥0.2 µm

≥0.3 µm

≥0.5 µm

≥1 µm

≥5 µm


















































































As you can see from the chart above, classes are organized by three major factors: particle size and count, air changes per hour or airflow velocity, and percentage of ceiling coverage. Once the air changes per hour rises above 200, it is better expressed as airflow velocity in feet per minute. 

What’s My Air Changes Per Hour?

The best air changes per hour for your cleanroom is the one that allows you to reach the required cleanliness required by your cleanroom classification. The level of activity and actions that introduce contaminants in your specific cleanroom may affect the amount of particles generated, and thus the air changes per hour required to remove them.

Your cleanroom’s air changes per hour describes conditions when the room is in operation, but you may lower the air changes per hour when the cleanroom is not in use to save energy and operation costs.  

Designing Cleanrooms to Meet Air Changes Per Hour

Your cleanroom is designed to meet your cleanroom classification. All the systems that support air quality and cleanliness work together to achieve consistency.

To design a cleanroom that meets your classification with adequate air changes per hour, the cleanroom must contain enough fan filter units and a uniform airflow pattern. A greater percentage ceiling coverage of fan filter units is required to reach necessary air changes. 

Although the percentage of ceiling coverage for fan filter units isn’t a metric directly referenced by ISO standards, it helps estimate construction costs. What’s most important is that the cleanroom has the systems it needs to thoroughly and consistently change the air to reach its cleanliness requirements. 

Upgrading Cleanroom Classifications and Air Changes Per Hour

If you need to upgrade your cleanroom to meet stricter classification standards or adapt your facility to handle a more sensitive project, an important step is to increase or adjust the filtration and air changes per hour to remove more particles of a smaller size from the air. 

When moving from ISO Class 7 to ISO Class 6, for example, you’ll need to increase your air changes from 60-90 ACH to 150-240 ACH to filter all but 35,200 particles at 0.5 microns per cubic meter. Consider that, to support this shift, you may need to upgrade your HVAC system.

Meet Your Classification With Cleanroom Professionals

Think you need to update your cleanroom’s air changes per hour? The cleanroom design experts at Angstrom Technology can help! We can evaluate your space and systems to ensure they’re working effectively, and help you upgrade them to change air more efficiently. To learn more, give us a call or reach out online.

What’s the Deal With Segmented Cleanrooms?

What’s the Deal With Segmented Cleanrooms?

An important part of cleanroom design is the choosing the best layout to suit your unique application. If your cleanroom has the challenge of needing to meet changing requirements or different levels of cleanliness, air changes, or pressure for different stages of work or to contain hazardous substances, it can be complicated to fit all of your cleanroom needs in one design. 

The solution to this problem is to segment your cleanroom design. Segmented cleanrooms are commonly used in medical applications that require separate spaces for different products or processes to ensure the safety of employees and their work.  Let’s explore segmented cleanrooms and their uses, and how their attributes can go beyond necessity in medical cleanrooms.


What Are Segmented Cleanrooms?

Segmented cleanrooms embrace different requirements and cleanroom classifications within a single cleanroom design. To do this, separate spaces are created within the cleanroom and modified to match the necessary requirements. Depending on the needs of the facility, this could mean a cascading pressure system utilizing a negative pressure room and higher pressure ante room; separate areas that meet different classifications, such as for manufacturing vs. packaging, treatment vs. isolation and quarantine, etc.; or any other separate-but-linked purposes your application requires.

Even when segmenting your cleanroom design isn’t required by your industry-specific standards or cleanroom classification, segmentation can offer added benefits like energy efficiency and cost savings. Rather than running the entire cleanroom at the lowest possible classification, a segmented cleanroom makes use of its systems where they’re most needed. This saves energy from powering FFUs and the cleanroom HVAC system, and lessens the strain on expensive HEPA filters. Also, there may be areas in the cleanroom where specialized products, like ESD-safe or classification-compliant materials, can be limited. By restricting use of those extra materials and energy costs to the segment where they’re being used, you’ll save money in your cleanroom design, build, and daily operational costs.


What Medical Applications Benefit from Segmented Cleanrooms?

Segmented cleanrooms are useful in medical applications where different requirements are necessary, particularly in medical device cleanrooms, pharmaceutical cleanrooms, and medical research cleanrooms.

Medical Device Cleanrooms

Medical device cleanrooms are governed by different requirements depending on the stage of production;  for example, between manufacturing and packaging. Most medical device manufacturing cleanrooms are required to comply with ISO 14644-1 Class 5-7, while medical device packaging is regulated by Class 7-8 standards. Also, while both phases are confronted with risks due to electrostatic discharge, it is most important to control static in the packaging phase, requiring more safeguards to dispel or conduct charges away from devices using ESD-safe equipment and materials. 

A segmented medical device cleanroom design could accommodate all of these requirements, by separating classifications within the same facility. Rather than running the entire space at the lowest possible classification, a segmented cleanroom would save significant energy costs, and be able to more efficiently prioritize operations according to each phase of medical device assembly.

Pharmaceutical Cleanrooms

Many pharmaceutical cleanrooms are designed using cascading pressure rooms with different pressure levels. In this system, each segment has a higher or lower pressure and a specific use to help protect contaminants from leaving one space and transferring to another where they could reduce the effectiveness of compounds, nullify test results, or even endanger human or animal life.

For example, the compounding area in a pharmaceutical cleanroom has different classification requirements and even a different pressure than the ante room attached to it. The purpose of the ante room is to allow the pressure difference to exist, and create a step down for employees to prepare before entering or after exiting the stringent segment. Segmented cleanrooms allow a single pharmaceutical cleanroom to house separate classifications in order to work with hazardous compounds safely and efficiently.

Medical Research Cleanrooms

Medical research cleanrooms may require an adjacent space for biosafe procedures or to house a negative pressure room. If the work involves sensitive or hazardous substances, a more rigorous classification and pressure will be required to isolate the work from external contamination or restrict contaminants from exiting the cleanroom. Segmented cleanrooms are used to allow these processes to occur within the same facility. An intuitive cleanroom design helps researchers focus on their work and feel safe within their environment. 

Interested in a unique cleanroom layout for your application? Get in touch with Angstrom Technology! Whether you want to create a segmented pharmaceutical cleanroom or upgrade your cleanroom classification, our experts can help you design, build, and install the ideal cleanroom for you. Reach out to us online today for a free quote.

Cleanroom Terminology: Garments

Cleanroom Terminology: Garments

Every part of your cleanroom’s design should work for you, from its protective flooring and wall panels to the fume hoods and HEPA filters. Each element serves a purpose to change the air, reduce risk, or limit contamination. What about garments? What are they, and how do they serve you and your cleanroom’s work? Here is everything you need to know about cleanroom garments.


What Are Cleanroom Garments?

Cleanroom garments are pieces of clothing worn in a cleanroom to limit human contamination. They are essentially filters for people, blocking contaminates and shedding particles from entering the cleanroom environment as much as possible. Cleanroom garments are necessary in almost all class standards, though garment and material specifications may differ. 


What Are Cleanroom Garments Used for?

In your cleanroom, you can control almost every contaminating factor through isolation, careful cleaning procedures, and thorough sterilization — except humans. People are the most contaminating element of cleanroom environments, and the hardest to keep clean. From dead skin cells to hair, textile fibers and dust, and microbes from body oils, saliva, and other bacteria — even when practicing meticulous personal hygiene, humans are sloppily packaged messes. The average person sheds 10 million particles of skin alone in a single day. The more we move and talk, the more particles and microbes we shed, putting sensitive work at risk. While we have almost complete control over the rest of the environment, we’ll never be able to entirely eliminate human contamination of cleanrooms. 

Cleanroom garments are the best solution to this problem. They cover people up, limiting particle shedding as much as humanly possible. They significantly reduce our risk of ruining the cleanliness of our workspaces, and are absolutely essential to meet rigorous class standards.

Cleanroom garments have another important purpose. Not only do they block our contaminates from hurting our products, but they are protective for the wearer as well. In cases where the work could be caustic or hazardous, cleanroom garments can protect delicate skin, eyes, and respiratory systems from dangerous substances.


What’s Included? Common Cleanroom Garments

Cleanroom garments are essential for life-as-usual within almost all cleanrooms. They should be non-particle shedding, easy to put on, comfortable to wear for long periods of time, and be able to withstand the process of sterilization. Different cleanroom garments will be required depending on your class type. Your class will also specify the materials that can be worn. Some typical cleanroom garment items include: a coat and pants or coverall to cover the body; head gear like a mask, hood or both; goggles; shoe covers or boots; and, of course, gloves. 


Coat and Pants, or Coverall

The coat and pants or combination coverall must be made of an appropriate fabric type for your cleanroom class standard, either woven, spun-bonded, or laminated fabric. They will have as few seams as possible and fit a bit large but not baggy. All clothing must have adjustable closures at the openings, with no pockets.


Head Gear 

Cleanroom head gear will cover all hair completely to prevent any loose hairs from shedding into your cleanroom environment. Beard covers are available, too. If extreme control or protection is required, a hood with its own ventilation and filtering may be necessary.


Face Masks 

Cleanroom-specific face masks are either surgical-style with elastic or fabric straps, or a veil that is attached to the rest of the suit.



If your cleanroom requires the use of goggles, they are used to prevent shedding of particles from the eyes or eyebrows, and also act as protection against sparks or splashing substances. 


Shoe Covers

Shoe covers are usually used when entering a gowning room. Before entering the cleanroom, more sterile footwear is donned to further limit possible contamination. Some low class standards might allow just shoe covers to be worn over appropriate footwear within the cleanroom.



Boots are typically used as a cleanroom garment to cover pant legs and are secured with straps to fasten over footwear. They have rubber or plastic soles for advanced protection against static electricity.



Barrier gloves are the most common piece of cleanroom garments, and can be made from a variety of materials, depending on your cleanroom’s needs: Latex will fit well but may be allergenic; nitrile gloves are tear and chemical-resistant; vinyl is a low-cost glove material option but it can tear easily. All gloves must be powder free. They are pulled over the wrists to cover the sleeve of the garment. For extra protection, gloves can be layered.


Cleanroom garments will vary for different applications including pharmaceutical or laboratory applications, manufacturing cleanrooms, or grow rooms. Combined with good personal hygiene, slow and deliberate movement, and proper training, garments are effective defenses against cleanroom contamination by people. 

Your class standards will be the ultimate guide for what cleanroom garments your application requires. If you have questions about your cleanroom classifications or standards, talk to the experts at Angstrom Technology! We can help you design and install a cleanroom that adheres to any classification your application requires. Visit us online to reach out.

Cleanroom Terminology: BioSafety Hoods & Cabinets

Cleanroom Terminology: BioSafety Hoods & Cabinets

Anyone in quality assurance or testing who works in or has to design a cleanroom knows how confusing the terminology around cleanrooms can be. To demystify some of the cleanroom design processes, here is an explanation of two potentially confusing terms: biosafety hoods and biosafety cabinets.

What is a biosafety hood?

A biosafety hood is generally known as a fume hood. The purpose of a fume hood is to isolate fumes from materials that may be hazardous and filter those fumes out of your cleanroom space. An exhaust fan at the top of the cleanroom building pulls air, fumes, and airborne contaminants out of the fume hood and exhausts outside of the building.

What is biosafety cabinetry?

Biosafety cabinetry works very similarly to biosafety fume hoods. Biosafety cabinetry uses laminar airflow to filter airborne fumes and contaminants away from the cabinet area, which like a fume hood can be used as a work surface or storage area.

What are the classifications?

There are three classes of biological safety cabinets, Class I, Class II, and Class III. The classification determines the level of protection. Class I protects the user and the surrounding environment, but does not protect the sample. Class II and Class III protect the user, sample, and surrounding environment. Class II is divided into four subcategories, A1, A2, B1, and B2, based on exhaust system and minimum airflow. Class III is the highest level of protection and control. Class III cabinets are also known as “glove boxes” and are completely gas-tight with a double-door autoclave or dunk tank. 






Class I




Class II




Class III





Special considerations

If your cleanroom requires work with dangerous, hazardous, or toxic substances with airborne contaminants or fumes, your cleanroom likely requires some kind of biosafety cabinetry or hood. The level of protection necessary for your specific application, whether your application requires Class I, Class II, or Class III cabinetry, will depend on the specific operations and substances used in your cleanroom. 


Looking for a cleanroom that incorporates biosafety cabinetry? Angstrom Technology can design a cleanroom to accommodate any kind of cabinetry or other equipment necessary for your application.

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