What is a clean room? Clean room classifications

Types of Clean Rooms

Clean rooms can be classified based on their cleanliness level, construction, and airflow patterns. The most common classification is based on the ISO 14644-1 standard, which replaced the earlier Federal Standard 209E. This standard defines clean room classes based on the concentration of particles (0.1 micron or larger) allowed per cubic meter of air. The types include:

FED STD 209E Cleanroom Standards

FED STD 209E classified cleanrooms based on the number of particles 0.5 micrometers or larger per cubic foot of air. This standard provided a simple, straightforward way to specify the cleanliness level of a cleanroom, making it a widely used benchmark for many years.

Cleanroom Classifications

Under FED STD 209E, cleanrooms were categorized into classes based on the maximum allowable particle concentration. The primary classes included:

• Class 1: The cleanest under this standard, allowing no more than 1 particle of 0.5 micrometers or larger per cubic foot of air.
• Class 10: Allowing a maximum of 10 particles of 0.5 micrometers or larger per cubic foot of air.
• Class 100: Permitting up to 100 particles of 0.5 micrometers or larger per cubic foot of air.
• Class 1,000: Allowing up to 1,000 particles of 0.5 micrometers or larger per cubic foot of air.
• Class 10,000: Permitting up to 10,000 particles of 0.5 micrometers or larger per cubic foot of air.
• Class 100,000: The least strict under FED STD 209E, allowing up to 100,000 particles of 0.5 micrometers or larger per cubic foot of air.

These classes provided a clear and concise way to communicate the cleanliness level of a cleanroom environment, with lower class numbers indicating higher levels of cleanliness.

ISO 14644-1 Cleanroom Standards

ISO 14644-1 establishes a classification system for the air cleanliness in cleanrooms and associated controlled environments. The standard specifies classes based on the concentration of airborne particles. Unlike the previous US FED STD 209E, which measured particles per cubic foot, ISO 14644-1 uses a metric measurement, particles per cubic meter, and considers a broader range of particle sizes.

The standard identifies several classes, from ISO 1, the cleanest, to ISO 9, which reflects a level of cleanliness similar to that of an ordinary urban environment. The key factor in classifying a cleanroom under ISO 14644-1 is the maximum allowable concentrations of particles, measured in particles per cubic meter, for particles equal to or larger than the considered sizes.

Cleanroom Classifications

The ISO 14644-1 classification is determined based on the formula ��=10�×(0.1/�)2.08Cn​=10N×(0.1/D)2.08, where:

• Cn​ is the maximum allowable concentration (in particles per cubic meter) of airborne particles equal to or larger than the considered particle size,
• $N$ is the ISO class number,
• $D$ is the considered particle size in micrometers.

The most commonly referenced classes and their particle count standards include:

• ISO 1: Allows a maximum of 10 particles/m³ of size 0.1 µm or larger, with progressively fewer particles for larger sizes.
• ISO 2: Permits up to 100 particles/m³ of 0.1 µm particles.
• ISO 3 (Class 1 equivalent of FED STD 209E): Allows up to 1,000 particles/m³ of 0.1 µm particles.
• ISO 4 (Class 10 equivalent): Permits up to 10,000 particles/m³ of 0.1 µm particles.
• ISO 5 (Class 100 equivalent): Allows up to 100,000 particles/m³ of 0.1 µm particles.
• ISO 6 (Class 1,000 equivalent): Permits up to 1 million particles/m³ of 0.1 µm particles.
• ISO 7 (Class 10,000 equivalent): Allows up to 10 million particles/m³ of 0.1 µm particles.
• ISO 8 (Class 100,000 equivalent): Permits up to 100 million particles/m³ of 0.1 µm particles.
• ISO 9: Provides no maximum particle count for 0.1 µm particles but does specify limits for larger particles, essentially equating to typical urban outdoor air.

The ISO 14644-1 standard is critical for designing, monitoring, and controlling cleanroom environments to ensure they meet the necessary requirements for the specific applications they serve. Compliance with these standards is verified through initial and periodic testing to certify that a cleanroom meets the designated ISO class.

Designing a cleanroom involves a comprehensive understanding of the requirements dictated by its intended classification under standards like ISO 14644-1. Each classification has specific design implications that affect the construction, airflow, filtration, and monitoring systems of the cleanroom. Here’s an overview of key design requirements associated with different cleanroom classifications:

1. Air Filtration and Ventilation

• HEPA and ULPA Filters: High-Efficiency Particulate Air (HEPA) filters are required for most cleanrooms, capable of removing 99.97% of particles 0.3 micrometers in diameter. Ultra-Low Particulate Air (ULPA) filters, which can remove at least 99.999% of dust, pollen, mold, bacteria, and other airborne particles 0.12 micrometers in diameter, might be necessary for more stringent classifications like ISO 1 to ISO 4.
• Air Changes Per Hour (ACH): The number of air changes per hour is crucial and increases with the stringency of the cleanroom class. For example, ISO 5 (Class 100) environments might require 240 to 600 air changes per hour, whereas ISO 8 (Class 100,000) might need around 10 to 60 ACH.

2. Room Pressure

• Cleanrooms are typically designed to be positive pressure environments relative to the surrounding areas to prevent infiltration of unfiltered air. The specific pressure differential depends on the cleanroom class and the nature of the work being conducted but generally ranges from +0.02 inches of water column (in. WC) for less critical environments to +0.05 in. WC or higher for more stringent classes.

3. Temperature and Humidity Control

• Precise control over temperature and humidity is essential, not just for comfort but also to ensure the stability of materials and processes within the cleanroom. The requirements can vary significantly depending on the processes being performed but generally fall within the range of 20-22°C (68-72°F) for temperature and 45-55% for relative humidity for most applications.

4. Construction Materials

• Materials used in cleanroom construction must be non-particulating, non-shedding, and easy to clean. Common choices include stainless steel, laminated particle board, and aluminum for surfaces, and sealed or welded vinyl or epoxy for floors. Walls and ceilings should have smooth surfaces to minimize particle retention.

5. Airflow Patterns

• Laminar (Unidirectional) Airflow: Often required in the strictest cleanroom classes (ISO 1 to ISO 4), laminar airflow systems direct filtered air downward in a constant stream, with air being extracted at the floor level.
• Turbulent (Non-unidirectional) Airflow: Used in less stringent cleanrooms (ISO 5 and above), this design mixes clean filtered air with the room air by distributing air through perforated ceiling tiles or diffusers and extracting it through low wall returns.

6. Lighting and Electrics

• Cleanroom lighting should be designed to avoid shadows and minimize the generation of heat and particulates. Recessed lighting fixtures that are sealed from the cleanroom environment are commonly used. Electrical systems and outlets must also be designed to minimize particle generation and be easy to clean.

7. Monitoring and Control Systems

• Continuous monitoring of particulate levels, temperature, humidity, and pressure differentials is essential, especially in more stringent cleanrooms. This is often achieved through the integration of Building Management Systems (BMS) or Environmental Monitoring Systems (EMS) that can provide real-time data and alerts.

Designing a cleanroom is a complex process that must take into account the specific requirements of the cleanroom classification as well as the operational needs of the processes or manufacturing to be conducted within it. Collaboration between engineers, architects, and end-users is essential to ensure that the cleanroom’s design meets the necessary standards and operational requirements.

Notes:

• ULPA Filters: Ultra-Low Particulate Air filters, more efficient than HEPA, are often used in the cleanest environments (ISO 1-4).
• ACH (Air Changes Per Hour): Represents how many times the total volume of air in the room is replaced every hour. Higher classifications require more air changes to maintain cleanliness.
• Room Pressure: Positive pressure relative to surrounding areas prevents inflow of unfiltered air. More critical environments require higher differentials.
• Temperature & Humidity: Must be controlled based on the specific processes conducted within the cleanroom; more sensitive processes require more precise control.
• Construction Materials: Must be non-particulating and easy to clean; the stringency of requirements increases with cleaner classifications.
• Airflow Pattern: Laminar (unidirectional) airflow is required for the cleanest environments, while turbulent (non-unidirectional) is acceptable for lower classifications.
• Monitoring Systems: Environmental Monitoring Systems (EMS) are crucial for real-time monitoring in higher classifications; less stringent environments may require less frequent monitoring.

This table is a simplified overview, and specific requirements can vary based on the processes being performed in the cleanroom, local regulations, and industry standards. Collaboration with a cleanroom design specialist is recommended to ensure compliance with all necessary specifications.

Notes:

• ULPA/HEPA Filters: ULPA filters are used for the most stringent classes (Class 1 and Class 10), with HEPA filters being common across other classes.
• ACH (Air Changes Per Hour): Indicates the total volume of air that is replaced in the cleanroom every hour. Higher-class cleanrooms (lower class number) require more air changes to maintain the specified level of cleanliness.
• Room Pressure: Cleanrooms are typically maintained at a positive pressure relative to adjacent areas to prevent ingress of unfiltered air. Higher pressure differentials are common in more stringent cleanrooms.
• Temperature & Humidity Control: The requirements for temperature and humidity control are dependent on the specific processes taking place within the cleanroom, with more critical processes necessitating tighter control.
• Construction Materials: Materials used in construction must not contribute to contamination and should be easy to clean. Requirements become more stringent with higher cleanroom classes.
• Airflow Pattern: Laminar airflow is preferred in higher-class cleanrooms for more efficient particle removal, while turbulent airflow is acceptable in lower-class cleanrooms.
• Monitoring Systems: Environmental monitoring systems are crucial for maintaining cleanliness standards, especially in higher-class cleanrooms, allowing for real-time tracking of particulate levels and other environmental parameters.

This table serves as a general guide. The specific requirements can vary significantly depending on the cleanroom’s intended use, the sensitivity of the processes involved, and the governing regulatory standards.

Cleanroom suits, also known as bunny suits, are specialized garments designed to minimize the release of contaminants from the wearer into the cleanroom environment. These suits are an essential component of the contamination control strategy in cleanrooms, where maintaining a low level of particulate matter is crucial for the production process or research activities being conducted.

Key Features of Cleanroom Suits:

1. Material: Cleanroom suits are typically made from non-linting, non-shedding materials such as polyester or polypropylene fabric, sometimes with an integrated carbon fiber to dissipate static electricity. The fabric is chosen for its ability to trap contaminants that are naturally generated by the skin and the body.
2. Design: The suits cover the entire body, including the head and feet. They usually consist of several pieces, including a hood, coverall, boots, and gloves. The design ensures that as little skin and hair as possible is exposed, as these are significant sources of particles.
3. Closure Systems: Cleanroom suits often feature elastic or knit cuffs at wrists and ankles, and sometimes a waistband to ensure a snug fit that prevents contaminants from escaping the suit. Zippers or adhesive flaps are used to securely close the suit and often include an additional covering flap to prevent any contaminants from leaking through the zipper teeth.
4. Integrated Hoods and Boots: The hood is designed to completely cover the hair and, in some cases, the neck and shoulders, while the boots cover the shoes entirely. This comprehensive coverage is critical in maintaining the cleanliness of the cleanroom environment.
5. Gloves: Gloves are an essential part of the cleanroom suit, made from materials like nitrile or latex, and are often required to be worn at all times to prevent direct contact with cleanroom materials and surfaces.

Types of Cleanroom Suits:

• Disposable: Single-use suits are common in environments where the risk of contamination needs to be minimized as much as possible. They are discarded after use, eliminating the risk of cross-contamination from laundering.
• Reusable: These suits are made from more durable materials and are designed to be laundered in specialized facilities that ensure the suits are cleaned without introducing additional contaminants. Reusable suits are more cost-effective over time and are preferred in settings where suits need to be worn regularly.

Suit Selection:

The selection of a cleanroom suit depends on the cleanroom’s classification and the specific requirements of the tasks being performed. Higher-class cleanrooms (ISO 1-4 or Class 10-100 in the FED STD 209E standard) require more comprehensive coverage and potentially more advanced materials than lower-class cleanrooms.

Maintenance and Handling:

Proper protocols for donning and doffing cleanroom suits are crucial to prevent contamination. This includes procedures for putting on the suit in a specific order, often in a gowning room or area that serves as a buffer zone to the cleanroom. The handling, laundering, and disposal of cleanroom suits are also governed by strict protocols to maintain cleanliness standards.

Cleanroom suits are a critical component of the contamination control strategy in cleanrooms, designed to maintain the integrity of the controlled environment necessary for sensitive manufacturing processes and research.