What are the ISO cleanliness levels based on?

Direct answer: ISO cleanliness levels are divided based on the number of suspended particles above a specified particle size in a unit volume of air. But if you only remember this 'basis', it is easy to use it incorrectly in actual projects.

Because grade is never an isolated number. In the same room, with different sampling points, different operating conditions, and different statistical particle sizes, the grade conclusions drawn may be different. So what really needs to be clarified is the evaluation conditions behind the grades.

Grading depends on particle concentration, not equipment parameters.

The core logic of the ISO 14644 series is very straightforward: count the cumulative number of particles per cubic meter of air at a selected particle size, and then compare it with the limit value given by the standard.

There are two keywords here: cumulative and selected particle size . The report says 'not less than 0.5μm', which means starting from 0.5μm, all particles larger than or equal to this size are added up. This caliber and step counting are not the same thing. If the instrument settings are wrong, the data will be biased.

What the air supply equipment can do is reduce the entry of particles. However, particles in the room are also affected by people, materials, machine movement, and return air paths. Therefore, the high filtration efficiency of an FFU does not mean that the area it serves can reach a certain ISO level. On-site grade must be confirmed by on-site sampling.

Determine the area boundaries and operating status first

Before evaluating the cleanliness level, three questions must be answered: which area is evaluated, what state the equipment is in, and how people and materials move around.

Regional boundaries are not drawn based on feeling. The drawings should indicate the air supply surface, return air position, partitions and openings. If you only measure one workstation, don't write the conclusion for the entire room. If the measurement is static, do not overwrite it with dynamic production data.

Running states are usually divided into empty state, static state and dynamic state. The empty state means that the equipment is installed but not producing; the static state means that the equipment is running but there are no personnel; the dynamic state means normal production. The particle concentrations in the three states may differ greatly. When comparing levels, unify the states first.

If these conditions are not clear, there is no basis for the arrangement of sampling points, and the grade numbers on the report cannot clearly indicate the scope of application.

Filter efficiency is not a substitute for field grade

It’s easy to confuse two things when purchasing: filter efficiency rating and room cleanliness rating.

Filter efficiency evaluates the product's ability to capture particles under specified test conditions, and the report is provided by the supplier. The room cleanliness level evaluates the air particle concentration in a specified area under a specified state and requires on-site testing.

The two are related, but cannot be directly converted. If the high-efficiency filter is installed in a location with insufficient air volume, sealed bypass or air flow short circuit, the on-site grade may still not meet the standard. Conversely, if the room grade meets the standard, the efficiency grade of a certain filter cannot be deduced.

Therefore, the acceptance data must be separated: the filter factory test report corresponds to the product, the on-site leak detection record corresponds to the installation seal, and the clean area particle test report corresponds to the space status. The three pieces of information answer different questions.

Return to device configuration from level target

Only after you know how the levels are divided can you have a clear direction when choosing equipment.

First clarify the protection objects and exposure paths, and then determine the particle control requirements for the target area. Then check the filtration level, actual air volume, airflow organization and sealing method. The equipment interface, maintenance space and control method must also be looked at together, and cannot be changed after installation.

Aili Industrial has manufacturing capabilities in motors, fans, control systems, sheet metal, air filters and complete machine assembly. When doing clean level projects, you can put filters, fans, structures and control conditions in the same project for verification, so that the equipment configuration and on-site evaluation boundaries are consistent.

Related products can be viewed FFU clean air supply products and HEPA and ULPA filters . When it comes to local purification at the equipment end, you can also refer to The matching method of the fan filter unit at the EFU equipment end .

Project judgment example

For a certain project, if the particle concentration measured in a small closed station is very low, it is considered that the entire factory has reached the same level. However, in other areas of the room where people move around frequently and materials are unpacked, the particle concentration is significantly higher. If the report writes local results as the whole room level, it will be misleading.

Another project only tested the static test, and checked it according to the dynamic requirements during acceptance, but the result was not up to standard. After checking back, I found that the status in the test agreement was not clearly written, and the understanding between the two parties was inconsistent.

Both cases illustrate that the level number itself is not complex, what is complex are the boundaries and conditions behind it.

Key points for selection and acceptance inspection