What is the relationship between ULPA filtration efficiency and clean room grade?

Questions like this often arise in project communication: Do I need to use U16 to achieve ISO level 3?

The presupposition of this question is that there is a conversion relationship between the two sets of indicators. Actually no. The efficiency of ULPA describes the penetration rate of the product under test conditions, and the clean room grade describes the particle concentration of the space under specified conditions. The measurement objects of the two are different, separated by a whole set of system factors such as air supply volume, air flow organization, sealing status and operation management.

Corresponding them directly will easily lead to problems in two aspects: inferring the filter element grade according to the room grade during model selection, and using the filter element report to explain the room results during acceptance.

What do the two sets of indicators say?

ULPA efficiency : The filter's ability to intercept particles under the specified test air volume, dust generation method and particle size conditions. Common grades U15, U16, and U17 correspond to different allowable penetration rates.

Cleanroom Class : The number of particles per unit volume of air under specified test conditions (static or dynamic), sampling location and method. ISO 3, ISO 5, and ISO 7 levels describe the state of the space.

One is a product indicator and the other is a space indicator. If the same ULPA is installed in different systems, the room results may be completely different; in the same clean room that meets the standard, the filter levels used may also be different.

What variables are in between?

From the filter to the room result, at least these layers must be passed in between:

Air supply volume. Particles are controlled by dilution and entrainment. If the air volume is insufficient, no matter how high the filter grade is, it will not reach the target. The number of air changes and airflow coverage must be calculated during the design process.

Airflow organization. Whether the air supply surface coverage is complete, whether the return air path is smooth, and whether there are eddies and short circuits directly determines whether the particles can be effectively taken away. The same is U16, the results may be very different between a room with reasonable airflow organization and a room with unreasonable airflow.

Sealed condition. Bypass air leakage at the end, box, and pipeline will allow unfiltered air to bypass the filter element. This type of problem is more common at the end interface. For specific troubleshooting ideas, please refer to the relevant instructions on the liquid tank seal.

Pollution load under operating conditions. If the particles brought in and out by personnel, equipment, and materials exceed the dilution capacity of the system, static compliance does not mean dynamic compliance. This is especially true in biomedical and precision manufacturing situations.

Maintenance status. After the filter element accumulates dust, the resistance increases and the air volume decreases. The performance after running for a period of time may be different from the initial state.

A problem with any one of these variables will cause the room results to deviate from expectations without changing the filter efficiency itself.

Why raising levels doesn't solve all problems

If the particles in the room are high, don’t rush to replace the filter element with a higher grade.

Assuming that the problem is air leakage from the seal, replacing it with U17 cannot stop the air coming in from the bypass. Assuming that the problem is insufficient air supply volume, increasing the filter element level will increase the resistance, and the air volume may further decrease. Assume that the problem is that the equipment produces dust, and the particles are generated in the protected area, and terminal filtration cannot help.

The order of judgment should be: first confirm the system status, and then consider whether to upgrade the filter. For specific investigation paths, please refer to the relevant instructions for investigation of substandard cleanliness. Only when system integrity and airflow conditions are met, and the process truly requires lower penetration, is it time to discuss upgrading.

The acceptance information should be written separately

It is recommended in the project document that the two types of requirements be listed separately and accepted separately:

Filter side : grade, applicable standards, rated air volume, test report and unit-by-unit number.

Room side : air volume, air flow organization, measuring point distribution, test status (static or dynamic) and cleanliness results.

In this way, when a problem occurs, it can be determined whether the product fails to meet the agreed indicators or the system operating status does not meet the design conditions. Mixed into one document, the boundaries of responsibilities are unclear and the investigation has no direction. involving For HEPA/ULPA air filter products of different grades, the testing requirements should also be clearly stated in the project documents.

Project judgment example

After a certain room was replaced with U16, particle monitoring was still high.

The recommended order of troubleshooting is: first confirm whether the air volume and airflow organization are normal, then check the end seal and bypass, and then check the dust generated by the equipment and the impact of personnel activities. If there are problems in these links, increasing the filtration level will provide limited improvement; if these links are normal, go back and evaluate whether the U16 test data meets the design requirements and whether the on-site leak detection is qualified.

Supporting The FFU fan filter unit system, the matching of the unit working point and the filter element resistance must also be checked together. Device-side applications such as The internal structure and operating status of the EFU equipment-side fan filter unit have a greater impact on the results, and verification must be carried out according to the actual working conditions of the equipment.

Selection and Acceptance Checklist

About Aili Industrial’s solution packages

The relationship between filter levels and room results is essentially a system matching problem.

Aili Industrial's manufacturing system covers filters, motors, fans, control systems and complete machine assembly, and can provide ULPA ultra-high efficiency filter and supporting air supply equipment. For clean room projects, the filter can be used with The FFU fan filter unit checks the air volume, resistance and installation conditions together; the equipment-side project can be matched with the EFU to confirm the interface and control method.

When enquiring, provide particle control targets, system air volume, installation conditions and acceptance methods, which will help determine how to combine the filter and system more appropriately. Specific performance is subject to product technical data and project acceptance results.