ISO 5 Cleanroom Requirements: Laminar Flow, Grade A/B, Testing

An ISO 5 cleanroom holds no more than 3,520 particles of 0.5 micron and larger per cubic meter, and in practice it is almost never a room. It is a zone: the space under a laminar flow hood, inside an isolator or restricted access barrier system, over a filling line, or across a small aseptic core, where unidirectional HEPA-filtered air sweeps particles away from the product before they can settle. The old name was Class 100. It is the grade of the aseptic critical zone in pharmaceutical manufacturing, the primary engineering control in sterile compounding, and the cleanest environment most process contractors ever build. The requirements are correspondingly different from those of ISO 7 and ISO 8, and this page sets them out.

The particle limits

Particle size	ISO 5 maximum per m3	ISO 7
0.1 micron and larger	100,000	not classified
0.3 micron and larger	10,200	not classified
0.5 micron and larger	3,520	352,000
1 micron and larger	832	83,200
5 micron and larger	not classified in ISO 14644-1:2015	2,930

Two things distinguish the ISO 5 row. Smaller particle sizes are classified, because at these concentrations 0.3 micron and below become relevant to semiconductor and optics work. And the 2015 revision of ISO 14644-1 dropped the 5 micron limit for ISO 5, because the expected count is too low to sample reliably; EU GMP Annex 1 nonetheless keeps a 5 micron limit of 29 per cubic meter for Grade A and B for monitoring purposes. The limit applies at every location in the stated occupancy state, and for Grade A that state is in operation.

Unidirectional airflow

ISO 7 and ISO 8 rooms dilute contamination with turbulent mixing. ISO 5 zones displace it: HEPA-filtered air enters across the entire ceiling or back wall of the zone and moves in parallel streamlines at a controlled velocity to a return below or beyond the work, so a particle released above the product is carried away rather than mixed in. EU GMP Annex 1 gives a guidance velocity of 0.36 to 0.54 meters per second at the working position; the FDA aseptic processing guidance uses 0.45 meters per second plus or minus 20 percent. Expressed as air changes this is several hundred per hour, which is why ISO 5 is confined to the zone that needs it. The concept of first air, filtered air that has touched nothing before it reaches the critical surface, governs how equipment, operators and interventions are arranged inside the zone.

ISO 5 cleanroom design: isolators, RABS and open zones

Approach	What it is	Background required
Open unidirectional zone	Laminar flow hood, ceiling module or filling line under a canopy in a conventional cleanroom	ISO 7 in operation (Grade B) for aseptic work
RABS (restricted access barrier system)	Physical barrier with glove ports around the unidirectional zone, open or closed, in a cleanroom	ISO 7 in operation (Grade B) in most designs
Isolator	Sealed, decontaminated enclosure with its own air handling, operated through gloves	ISO 8 (Grade D) or better; Annex 1 2022 expects at least Grade D and a risk-based justification

The 2022 revision of Annex 1 pushes aseptic manufacturers toward isolators and closed RABS, because separating the operator from the ISO 5 zone removes the largest particle and microbial source. The choice changes the whole facility: an isolator line needs less classified floor area and lighter gowning, and more engineering in the equipment.

How ISO 5 maps to GMP grades

Grade A is ISO 5 at rest and in operation, with a target of no microbial growth: the Annex 1 limit is “no growth” for air, settle plates, contact plates and glove prints. Grade B is ISO 5 at rest and ISO 7 in operation, with limits of 10 CFU per cubic meter of air, 5 CFU per 4-hour settle plate and 5 CFU per contact plate. So an ISO 5 specification for a pharmaceutical zone is either Grade A (the critical zone, in operation) or Grade B (the background, at rest), and the two carry very different monitoring, gowning and intervention rules. The FDA guidance uses the ISO classes directly with its own action levels.

Gowning and behavior

Operators working at an open ISO 5 zone in aseptic manufacturing wear the Grade B sterile set: sterilized coverall, hood, mask, goggles, boots and sterile gloves, changed at every entry, with aseptic gowning qualification and periodic requalification. Behavior matters as much as gowning: slow movement, no reaching over open product, interventions planned, documented and simulated in media fills. In sterile compounding, USP 797 sets the garb and hand hygiene sequence for working at the ISO 5 primary engineering control. In an isolator the gowning burden moves to the surrounding room’s grade.

Testing an ISO 5 zone

Beyond particle counts at the locations ISO 14644-1 derives from the zone area, in operation for Grade A, an ISO 5 zone is qualified by: installed HEPA filter leak testing across the full filter face; airflow velocity measured on a grid across the face of the unidirectional zone, with uniformity limits; airflow visualization by smoke studies, recorded on video, showing that air moves unidirectionally and away from the product during set-up and every intervention; recovery time where the zone is a room; and, for aseptic processes, media fills (aseptic process simulation) that prove the whole operation can produce sterile units. ISO 14644-2 sets a maximum 6-month interval for particle classification of ISO 5 and cleaner zones.

Where ISO 5 is required

Aseptic filling and closing: the Grade A zone over open product and components, under Annex 1 and the FDA aseptic guidance.
Sterile compounding: the USP 797 primary engineering control, a laminar airflow workbench, biological safety cabinet or compounding aseptic isolator.
Sterility testing: isolators or ISO 5 hoods in a classified suite.
Cell and gene therapy: open manipulations in biosafety cabinets providing ISO 5.
Semiconductor, optics and aerospace: lithography, precision assembly and contamination-sensitive work, often ISO 5 across whole bays with raised floors.

What it costs

ISO 5 is by far the most expensive grade per square foot, which is why it is confined to the smallest zone the process allows; our cleanroom cost guide gives current ranges. The decision with the largest cost effect is isolator versus open zone: the isolator costs more as equipment and saves classified floor area, air handling, gowning and monitoring for the life of the line.

How Paul Industries builds them

We build the classified suites that ISO 5 zones sit in, install and connect laminar flow modules, RABS and isolators supplied by their manufacturers, run the process piping, clean utilities and pressure controls to them, and pre-test the zone against the velocity, leak and visualization requirements above before independent certification and the media fills that follow.

Standards referenced: ISO 14644-1 · ISO 14644-2 · EU GMP Annex 1 (EudraLex Vol. 4) · USP 797 · 21 CFR 211 · FDA Process Validation guidance

Frequently asked questions

What is an ISO 5 cleanroom?

An ISO 5 cleanroom or zone holds no more than 3,520 particles of 0.5 micron and larger per cubic meter, with limits also set at 0.1, 0.2, 0.3 and 1 micron, in the specified occupancy state. It is the old Class 100, the grade of the aseptic critical zone and the sterile compounding primary engineering control, and it is normally achieved with unidirectional airflow over a defined zone rather than as a whole turbulent-flow room.

What are the ISO 5 limits at each particle size?

3,520 particles per cubic meter at 0.5 micron and larger, 832 at 1 micron, 10,200 at 0.3 micron, 23,700 at 0.2 micron and 100,000 at 0.1 micron. ISO 14644-1:2015 does not classify ISO 5 at 5 micron because the expected count is too low to sample reliably, though EU GMP Annex 1 keeps a 29 per cubic meter limit at 5 micron for Grade A and B monitoring.

Why do people still say Class 100 for ISO 5?

Because Class 100 was the name for decades. It is the Federal Standard 209E designation, 100 particles of 0.5 micron per cubic foot, which maps to ISO 5 under ISO 14644-1. FED-STD-209E was withdrawn in 2001, but Class 100 remains the phrase most people use for a laminar flow hood or an aseptic filling zone.

Why is ISO 5 a zone rather than a room?

Because the airflow that reliably achieves ISO 5 in operation is unidirectional at 0.36 to 0.54 meters per second across the whole zone, which amounts to several hundred air changes per hour. That is practical over a hood, a filling line or a small core and prohibitively expensive across a whole room, so ISO 5 is confined to the critical zone and surrounded by an ISO 7 or ISO 8 background.

Why does an ISO 5 zone need an ISO 7 background?

Because the zone is only as clean as the air drawn into it and the people around it. The classes differ by a factor of one hundred in particle concentration: ISO 7 allows 352,000 particles per cubic meter at 0.5 micron against 3,520 for ISO 5. ISO 7 is a turbulent-flow room with 30 to 60 air changes per hour; ISO 5 is a unidirectional-flow zone at several hundred equivalent air changes, with sterile gowning, smoke-visualized airflow and, in aseptic work, media fills to qualify it.

What airflow velocity does an ISO 5 zone need?

EU GMP Annex 1 gives a guidance range of 0.36 to 0.54 meters per second at the working position; the FDA aseptic processing guidance uses 0.45 meters per second plus or minus 20 percent. Velocity is measured on a grid across the face of the unidirectional zone at qualification, with uniformity limits, and the airflow pattern is confirmed by smoke studies.

What is unidirectional or laminar airflow?

Airflow in which HEPA-filtered air enters across the entire face of the zone and moves in parallel streamlines at a controlled velocity to a return, so that particles released in the zone are carried away from the product rather than mixed into the air. It is the mechanism by which ISO 5 is achieved in operation, and its integrity is proven by smoke visualization rather than by particle counts alone.

What is first air?

First air is HEPA-filtered air in a unidirectional zone that has not passed over any surface, object or hand before reaching the critical surface, such as an open container or a sterile component. Aseptic technique and equipment layout inside an ISO 5 zone are organized so that first air reaches the product and nothing interrupts it.

Is ISO 5 Grade A or Grade B?

Both, depending on the occupancy state. Grade A is ISO 5 at rest and in operation and is the critical aseptic zone, with a microbial limit of no growth. Grade B is ISO 5 at rest and ISO 7 in operation and is the background to Grade A, with limits of 10 CFU per cubic meter of air, 5 CFU per settle plate and 5 CFU per contact plate. An ISO 5 specification therefore needs the occupancy state to say which grade it means.

What is the difference between an isolator and a RABS?

An isolator is a sealed enclosure with its own HEPA air handling, decontaminated by a validated cycle (usually vaporized hydrogen peroxide) and operated entirely through glove ports, so the ISO 5 zone is physically separated from the operator and can sit in an ISO 8 room. A restricted access barrier system (RABS) puts a physical barrier with glove ports around a unidirectional zone inside a conventional cleanroom, open or closed, and generally still needs a Grade B background.

Does Annex 1 require isolators for aseptic filling?

Not in absolute terms, but the 2022 revision expects manufacturers to consider barrier technologies, isolators and closed RABS, as part of the contamination control strategy and to justify an open ISO 5 zone with operators in the Grade B room. New aseptic lines are predominantly isolator or closed RABS designs for that reason.

What are the ISO 5 cleanroom gowning requirements, and why are they different inside an isolator?

ISO 5 cleanroom gowning requirements depend on whether the operator can reach the zone. For operators working at an open ISO 5 zone in aseptic manufacturing, the Grade B sterile set: sterilized coverall, hood, mask, goggles, boots and sterile gloves, changed at each entry, with aseptic gowning qualification. In sterile compounding USP 797 sets the garb and hand hygiene sequence for the primary engineering control. Inside an isolator the operator never enters the ISO 5 zone, so gowning follows the surrounding room’s grade.

What is in an ISO 5 qualification package?

The ISO 5 cleanroom standards that apply, ISO 14644-1 for particle limits, ISO 14644-3 for the test methods and Annex 1 or the FDA aseptic guidance for the GMP expectations, and the evidence against each: particle counts at the locations ISO 14644-1 derives from the zone area, in operation for Grade A; installed HEPA filter leak testing across the full face; airflow velocity on a grid with uniformity limits; smoke visualization recorded on video showing unidirectional flow during set-up and interventions; recovery time where applicable; and, for aseptic processes, media fills. ISO 14644-2 sets particle classification at a maximum 6-month interval for ISO 5 and cleaner.

What is a media fill?

An aseptic process simulation in which sterile growth medium is processed through the whole filling operation in place of product, including planned interventions, then incubated. Contaminated units show that the ISO 5 zone, the operators and the process together cannot reliably produce sterile product. Media fills are required at qualification and periodically thereafter under Annex 1 and the FDA aseptic guidance.

What is the ISO 5 requirement in USP 797?

USP 797 requires all sterile compounding to be performed inside an ISO 5 primary engineering control, a laminar airflow workbench, biological safety cabinet, compounding aseptic isolator or compounding aseptic containment isolator, located in an ISO 7 buffer room (or, for certain isolators, a lesser-classified space as the chapter allows), with certification every 6 months.

Can an ISO 5 cleanroom be a whole room?

Yes, in semiconductor, optics and some aerospace work, where entire bays are built as ISO 5 with unidirectional downflow ceilings and perforated raised floors. In pharmaceutical and compounding work it is almost always a zone within an ISO 7 or ISO 8 room, because the air volumes needed for a full unidirectional room are only justified where the whole floor area is contamination-critical.

Why is ISO 5 specified by velocity rather than air changes?

Because in a unidirectional zone the air is not mixed, so the air change concept does not describe it. ISO 5 is specified by velocity rather than air changes, but a unidirectional zone at 0.36 to 0.54 meters per second across its face corresponds to several hundred air changes per hour, commonly quoted as 240 to 600 depending on zone height. That figure is why ISO 5 is confined to the critical zone.

What does no growth mean for a Grade A zone?

It is the microbial limit for ISO 5 in operation under Annex 1; ISO 14644 sets none. Under EU GMP Annex 1, Grade A (ISO 5 in operation) is limited to no growth in air samples, settle plates, contact plates and glove prints; Grade B (ISO 5 at rest) to 10 CFU per cubic meter of air, 5 CFU per 4-hour settle plate and 5 CFU per contact plate. The FDA aseptic guidance sets action levels of 1 CFU per cubic meter of air and 1 CFU per contact plate for the ISO 5 critical zone.

What usually goes wrong in an ISO 5 smoke study or velocity test?

Non-uniform velocity across the filter face, turbulence at the edges of the zone or around equipment shown by the smoke study, interventions that put hands or tools between the filter and the product, HEPA frame leaks, and background rooms that do not hold their own class so that particles are drawn into the zone. Most are layout and behavior problems rather than filter problems.

Isolator or open ISO 5 zone: which costs less over the life of the line?

Usually the isolator, despite the higher equipment price. ISO 5 is the most expensive grade per square foot by a wide margin, which is why it is confined to the smallest zone the process allows; our cleanroom cost guide gives current ranges by class. The largest single cost decision is isolator versus open zone: the isolator costs more as equipment but reduces classified floor area, air handling, gowning and monitoring for the life of the line.