CLEANROOM DESIGN STANDARDS GUIDE

What Are Cleanroom Design Standards?

Cleanroom design standards translate process, product, personnel, and contamination-control needs into requirements for the facility and its building systems. ISO 14644 defines internationally recognized cleanroom classification, design, testing, monitoring, and operational frameworks. A cleanroom is a room in which airborne particle concentration is controlled and classified, while other relevant contaminants and environmental parameters may also be controlled as needed.

Cleanrooms and related controlled environments support applications in pharmaceuticals, biotechnology, sterile compounding, medical devices, electronics, aerospace, food and beverage, and research. The appropriate design depends on the process risk, required cleanliness, occupancy state, applicable regulations, and the facility's user requirements. Understanding those inputs early helps prevent a room from being designed to a particle class while missing the controls needed for its actual use.

ISO Cleanroom Standards

The ISO 14644 family provides the primary international framework for cleanrooms and associated controlled environments. ISO 14644-1 classifies air cleanliness by airborne particle concentration, while ISO 14644-4:2022 addresses the process for design, construction, and start-up. The classification selected for a room should come from its intended use and contamination-control requirements, not from a universal industry-to-class assignment. The particle concentration limits below are based on ISO 14644-1.

• ISO Class 1: This is the most stringent ISO classification. The maximum concentration at 0.1 micrometer is 10 particles per cubic meter.
• ISO Class 2: The maximum concentrations include 100 particles at or above 0.1 micrometer and 10 particles at or above 0.3 micrometer per cubic meter.
• ISO Class 3: The maximum concentrations include 102 particles at or above 0.3 micrometer and 35 particles at or above 0.5 micrometer per cubic meter.
• ISO Class 4: The maximum concentrations include 1,020 particles at or above 0.3 micrometer and 352 particles at or above 0.5 micrometer per cubic meter.
• ISO Class 5: The maximum concentrations include 3,520 particles at or above 0.5 micrometer and 832 particles at or above 1.0 micrometer per cubic meter. ISO Class 5 conditions are commonly used for critical work zones in aseptic processing and sterile compounding, subject to the applicable regulatory framework.
• ISO Class 6: The maximum concentrations include 35,200 particles at or above 0.5 micrometer and 293 particles at or above 5.0 micrometers per cubic meter.
• ISO Class 7: The maximum concentrations include 352,000 particles at or above 0.5 micrometer and 2,930 particles at or above 5.0 micrometers per cubic meter. This classification is used for a range of controlled background and production spaces, depending on the process.
• ISO Class 8: The maximum concentrations include 3,520,000 particles at or above 0.5 micrometer and 29,300 particles at or above 5.0 micrometers per cubic meter. ISO Class 8 may be used for support, gowning, preparation, or production spaces when supported by the facility's risk assessment and process requirements.
• ISO Class 9: The maximum concentrations include 35,200,000 particles at or above 0.5 micrometer and 293,000 particles at or above 5.0 micrometers per cubic meter. Although its concentration limit approximates ordinary room air, ISO Class 9 is still a defined ISO classification when formally specified and demonstrated.

Other Regulatory & Industry Standards

ISO classification is only one layer of cleanroom design. The applicable regulatory and technical framework depends on the product, process, market, and jurisdiction. Common references include:

• FDA: U.S. Food & Drug Administration regulations and guidance establish current good manufacturing practice expectations for drugs, biologics, and medical devices. The specific facility and environmental controls depend on the regulated activity; FDA does not assign one universal cleanroom design to every product category.
• GMP: Good manufacturing practice requirements are established through regulations and guidance in each jurisdiction. For U.S. drug manufacturing, FDA enforces CGMP regulations; EU medicinal products are governed by EU GMP, including Annex 1 for sterile products.
• USP: United States Pharmacopeia chapters establish compounding standards, including USP <797> for compounded sterile preparations, USP <795> for nonsterile preparations, and USP <800> for handling hazardous drugs. Adoption and enforcement may also depend on federal or state requirements.
• ANSI-accredited standards: Standards developed through American National Standards Institute accredited organizations may apply to specific equipment or applications. Examples include NSF/ANSI 49 for biosafety cabinets and ANSI/ASHRAE standards for ventilation and environmental control.
• ASHRAE: The American Society of Heating, Refrigerating and Air-Conditioning Engineers develops HVAC and ventilation standards and guidance that may inform system design. These references complement the cleanroom’s user requirements and applicable regulations; they do not determine the ISO particle classification.
• IEST: Institute of Environmental Sciences and Technology Recommended Practices provide additional technical guidance for cleanroom design and performance testing. Relevant documents include IEST-RP-CC012 for cleanroom design considerations, IEST-RP-CC006 for cleanroom testing, and IEST-RP-CC034 for installed HEPA and ULPA filter leak testing. These documents are commonly used alongside ISO 14644 and applicable regulatory or industry requirements.

Architecture & Structural Requirements

Cleanroom architecture should support contamination control, cleaning, maintenance, operations, and pressure integrity. Exact construction requirements should be defined through the user requirement specification, risk assessment, process needs, and applicable regulatory framework. Common design considerations include:

• Materials & Finishes: Materials should be low-shedding, durable, cleanable, and compatible with the chemicals and processes used in the room. Resistance to moisture or microbial growth may be important where cleaning methods or process risks warrant it.
  • Walls: Common systems include modular panels, coated gypsum, aluminum, stainless steel, or other sealed finishes selected for the required durability and cleanability.
  • Ceilings: Ceiling systems should limit particle generation and support cleaning, access, filtration, lighting, and pressure integrity appropriate to the application.
  • Flooring: Welded sheet vinyl, epoxy, polyurethane, and other seamless or sealed systems are commonly selected for durability, cleanability, and chemical compatibility.
  • Surfaces: Exposed surfaces should minimize ledges, crevices, and difficult-to-clean joints where contamination could accumulate.
• Seams & Junctions: Joints and penetrations should be sealed and detailed to support cleaning and pressure control. The required degree of seamless construction depends on the cleanliness level, process, cleaning method, and regulatory expectations.
  • Coved Corners: Coved floor-to-wall transitions and other radiused junctions can improve cleanability. They are common in higher-control environments but are not a universal requirement for every ISO-classified room.
  • Flush Fixtures: Recessed or flush-mounted lights, windows, and service panels can reduce ledges and simplify cleaning. Their use should be based on the room's cleanability and maintenance requirements.
  • Sealants: Joints and penetrations should use durable, low-shedding sealants compatible with the surrounding materials, cleaning agents, and environmental conditions.
• Airflow Paths: Supply air, return locations, room layout, equipment, personnel, and pressure relationships should work together to remove or dilute contamination and protect critical areas. Airflow visualization and other qualification tests can help confirm that the installed system performs as intended. Common airflow approaches include:
  • Non-Unidirectional Airflow: Often used in ISO Class 6-8 rooms, mixed airflow dilutes contaminants with filtered supply air and removes them through returns. Performance depends on air distribution, heat loads, obstructions, occupancy, and contaminant generation.
  • Unidirectional Airflow: Commonly used to protect critical zones, including many ISO Class 5 applications, this approach uses airflow moving in a single direction in a uniform manner. Velocity and uniformity should be established for the specific process and system design rather than assumed from one universal range.

HVAC & Air Handling Standards

Cleanroom HVAC systems must provide enough filtered air, airflow distribution, temperature and humidity control, and pressure control to meet the room's defined requirements. Positive pressure is common when protecting a cleaner area, while negative pressure may be required when containing hazardous materials.

• HEPA Filters: High-efficiency particulate air filters are widely used in cleanrooms. Filter classification and performance should be specified under the applicable filter standard; the familiar 99.97% at 0.3 micrometer description is a general convention and does not fully describe every modern HEPA classification or its most penetrating particle size.
• ULPA Filters: Ultra-low penetration air filters provide higher efficiency and may be selected for very stringent contamination-control applications. The required efficiency and test method should be specified rather than inferred solely from the ISO room class.
• Air Change Rates: Air changes per hour (ACH) express the volume of supply air relative to room volume. ISO 14644-1 does not assign a required ACH range to each class. Designers establish airflow quantity using factors such as cleanliness target, contaminant generation, airflow pattern, recovery needs, heat load, occupancy, and applicable regulations.

Environmental Controls

Cleanroom environmental conditions should support the process, personnel, equipment, contamination-control strategy, and applicable requirements. Common parameters include:

• Temperature: Temperature limits should be selected for product and process needs, equipment performance, gowning, and operator comfort. There is no universal ISO operating range for every cleanroom.
• Relative Humidity: Humidity limits may be driven by microbial control, electrostatic discharge, material stability, corrosion, condensation, or personnel comfort. The appropriate range is application specific.
• Pressure: Pressure relationships are established to control contaminant movement. Positive pressure commonly protects cleaner spaces, while negative pressure supports containment. Setpoints and alert/action limits should reflect the facility layout, door operation, process risk, and applicable requirements.
• Air Changes: The required airflow rate should be justified through design analysis and confirmed during qualification. Historical ranges can support early planning, but ISO classification is demonstrated by particle concentration, not by ACH alone.

These parameters are interdependent. A defensible design documents the intended operating state, acceptance criteria, monitoring strategy, alarm response, and how the system will maintain control as conditions change.

Validation & Testing Standards

Cleanroom qualification and certification verifies selected aspects of the installed facility against predefined requirements. ISO 14644-1 addresses airborne particle classification, while ISO 14644-3 describes test methods for cleanrooms and associated controlled environments. Depending on the application, the qualification package may also include HEPA filter integrity, airflow volume or velocity, pressure differentials, room recovery, temperature, humidity, airflow visualization, and microbiological monitoring.

Testing should be tied to approved acceptance criteria and the room's intended occupancy state. In regulated projects, commissioning and qualification may include design qualification (DQ), installation qualification (IQ), operational qualification (OQ), and performance qualification (PQ), but the lifecycle and terminology should follow the facility's quality system and project scope. TSS supports cleanroom testing and certification, controlled-environment qualification, calibration, and microbiological environmental monitoring.

Common Mistakes & Design Pitfalls

Common design failures include unclear user requirements, poor coordination between the process and HVAC design, obstructed supply or return paths, unsuitable materials, inadequate pressure control, insufficient access for testing and maintenance, and acceptance criteria that are not defined until after construction. Operational factors such as equipment placement, personnel flow, gowning, cleaning, and monitoring should be considered during design because they can materially affect performance after start-up.

Early design reviews and commissioning help identify these issues while changes are still practical. Testing at start-up then provides objective evidence of whether the installed cleanroom meets its defined requirements.

Let Us Help You

TSS can support cleanroom projects through design review, commissioning and qualification testing, certification, calibration, and environmental monitoring. Contact us to discuss the applicable standards, acceptance criteria, and testing strategy for your facility.