Is ISO 5 the cleanest?

Cleanrooms are controlled environments with extremely low levels of pollutants such as dust, microbes, aerosol particles, and chemical vapors. The cleanliness of a cleanroom is categorized by its ISO rating, which ranges from ISO 1 (the cleanest) to ISO 9 (the least clean). ISO 5 is one of the higher cleanroom classifications, but is it the cleanest possible? Let’s take a closer look.

What is an ISO 5 cleanroom?

ISO 5 cleanrooms have strictly controlled air particle counts to maintain cleanliness. Specifically:

  • There must be fewer than 3,520 particles ≥ 0.5 μm per cubic meter of air
  • There must be fewer than 293 particles ≥ 5.0 μm per cubic meter of air

For reference, a human hair is about 100 μm wide. So the particles present in an ISO 5 cleanroom are tiny.

These particle counts are maintained through the use of air filtration systems including HEPA filters, specialized airlocks, sticky floor mats, cleaning protocols, and gowning procedures. Personnel wear protective coveralls, hoods, gloves, face masks, and booties while working in the cleanroom to minimize contamination.

Cleanroom ISO classifications

Here are the various ISO cleanroom classifications from cleanest to least clean:

ISO Class Maximum particles/m3 ≥ 0.1 μm Maximum particles/m3 ≥ 0.2 μm Maximum particles/m3 ≥ 0.3 μm Maximum particles/m3 ≥ 0.5 μm Maximum particles/m3 ≥ 1 μm Maximum particles/m3 ≥ 5 μm
ISO 1 10 2 1 1 0 0
ISO 2 100 24 10 4 1 0
ISO 3 1,000 237 102 35 8 0
ISO 4 10,000 2,370 1,020 352 83 0
ISO 5 100,000 23,700 10,200 3,520 293 29
ISO 6 1,000,000 237,000 102,000 35,200 2,930 293
ISO 7 352,000 83,000 2,930 293
ISO 8 3,520,000 832,000 29,300 2,930
ISO 9 35,200,000 8,320,000 293,000 29,300

As you can see, the ISO 1 standard allows virtually zero particles in the air. Each subsequent ISO class allows exponentially more particles per volume of air. This makes sense, as it becomes extremely difficult to control particle counts at very low levels.

Is ISO 1 possible?

Theoretically, ISO 1 represents the cleanest possible cleanroom standard. However, achieving and maintaining ISO 1 conditions is extraordinarily difficult in practice.

Some of the challenges with ISO 1 cleanrooms include:

  • Initial build – Constructing a cleanroom free of virtually all particles requires meticulous planning, specialized materials, and flawless execution. Even minor defects can compromise ISO 1 status.
  • Personnel – Humans naturally shed skin cells, hair, oils, and other particulates. Rigorous gowning procedures are required.
  • Maintenance – Over time, particles inevitably infiltrate. Frequent cleaning and filter changes are needed to try maintaining ISO 1 cleanliness.
  • Processes – Any materials or processes that generate particles must be strictly controlled or banned.
  • Testing – Ensuring ISO 1 standards requires expensive, highly-sensitive air particle counters.
  • Energy – High airflow and extensive filtration drives up energy costs.

While operating in true ISO 1 conditions may not be practical on an ongoing basis, some facilities can achieve ISO 1 temporarily for short durations when needed for critical processes.

Uses of ISO 5 cleanrooms

The high cleanliness and control over environmental conditions make ISO 5 cleanrooms well-suited for the following uses:

  • Microelectronics fabrication – Chips and other components can be contaminated by tiny particles. ISO 5 is commonly required for photolithography and other microelectronics processes.
  • Pharmaceutical manufacturing – Drugs and medical devices must be produced without introducing contaminants. ISO 5 or better is typical for aseptic filling and handling of sterile products.
  • Aerospace assembly – Satellites, spacecraft, and other systems are assembled in ISO 5 cleanrooms to prevent defects.
  • Healthcare facilities – Operating rooms, compounding pharmacies, and isolation rooms may maintain ISO 5 for patient protection.
  • Scientific research labs – Sensitive experiments with cell cultures, chemicals, optics, or nanomaterials often require ISO 5 or stricter cleanrooms.

The high degree of cleanliness and control makes it possible to manufacture very precise products or avoid biological/chemical contamination.

ISO 5 cleanroom design

Achieving ISO 5 standards requires careful cleanroom design. Key design elements include:

  • Air filtration – Multi-stage HEPA filters remove particles. Air supplied to the cleanroom space passes through filters rated to capture >99.999% of particles ≥0.3 μm.
  • Positive pressure – Cleanrooms are kept at a higher pressure than surrounding areas to prevent unfiltered air infiltration.
  • Air changes per hour – Frequent air exchanges, often 30-90 per hour, rapidly dilute particle concentrations.
  • Airflow control – Unidirectional laminar airflow directs clean air vertically downwards across the entire space.
  • Specialized materials – Cleanroom furniture, tools, and construction materials made of stainless steel, plastics, or easily cleaned materials.
  • Gowning procedures – Personnel must pass through airlocks and wear protective clothing covering skin and hair to limit particle shedding.
  • Automation – Robotic systems handle materials and perform processes to reduce contamination.

Careful monitoring ensures cleanliness levels are constantly maintained. Warning systems alert staff if conditions deviate from ISO 5 standards.

Building and operating an ISO 5 cleanroom

Constructing and running an ISO 5 cleanroom requires substantial investment and effort:

  • Highly specialized architectural/engineering design and construction required.
  • HEPA filtration units, HVAC systems, and controls cost hundreds of thousands or millions of dollars to install.
  • Significant energy use for ventilation and climate control.
  • Strict procedures for entry, operations, cleaning, and maintenance.
  • Rigorous contamination control training for all cleanroom staff.
  • Daily cleaning, filter changes, monitoring, and periodic re-certification audits.
  • Cost per square foot often $500-1000+

However, for organizations requiring cleanliness at the microscopic scale, the benefits outweigh the costs and challenges.

Is ISO 3 clean enough?

For some applications, ISO 3 cleanrooms provide sufficient cleanliness at lower cost. ISO 3 allows up to 10x more particles than ISO 5, but still retains sub-micron particle control. Possible benefits of ISO 3 vs ISO 5:

  • Lower construction costs – less stringent material and airflow requirements.
  • Lower energy use for HVAC systems.
  • Less staff training required on gowning and operations.
  • Reduced maintenance and re-certification costs.

ISO 3 is commonly used for medical device manufacturing, IV compounding, micromechanics, optics, and other applications with less stringent particle requirements. The cost-benefit ratio should be evaluated carefully when deciding between ISO 3 and ISO 5 cleanrooms.

Advantages of modular construction

Modular cleanrooms built using prefabricated panels offer many advantages compared to traditional cleanroom construction:

  • Faster installation – manufactured panels assembled onsite vs building from scratch.
  • Flexible layouts – modular cleanrooms reconfigured or expanded more easily.
  • Earlier occupancy – Start using cleanroom sooner, while finishing validation.
  • Improved quality control – consistency from ISO-certified factory production.
  • Lower long-term costs – Easy to upgrade filters or other components.

Modular construction is compatible with both ISO 5 and ISO 3 cleanroom classifications. Offsite pre-certification allows occupied cleanrooms to start operating faster.


ISO 5 represents an extremely high cleanroom standard, enabling microcontamination control for critical manufacturing and research applications. While achieving true ISO 1 conditions is challenging in practice, ISO 5 cleanrooms provide robust particle-free environments for processes requiring cleanliness at the microscopic scale.

Constructing and operating ISO 5 cleanrooms demands substantial investments. However, for organizations and industries relying on nanoscale contaminant control, ISO 5 provides an important tool for enabling scientific research and production of highly pure products.