How to confirm the level 10 cleanliness on old drawings?

When an old factory building is renovated or equipment is replaced, labels such as Level 10 and Level 100 are often turned to. Level 10 is a very demanding grade among the traditional cleanliness levels. When it appears on old drawings, it usually means that the particle control requirements in this area were stricter at that time.

But directly changing 'Level 10' to 'ISO 4' and then purchasing equipment according to this level is relatively risky. The traditional title is different from the expression of the ISO system. Old drawings often only write the grade name, without indicating the particle size, unit and test status. If these pieces of information are missing, there will be no complete basis for conversion.

Let’s first trace back to the original definition of the old drawings

When you get an old drawing marked 'Level 10', the first step is not to check the comparison table, but to check the original basis.

Design instructions . Check whether the version, test method and operating status of the cleanliness standard are indicated in the general design description of the drawing. Some old drawings will be clearly written on the description page, and some will only indicate the level name.

Acceptance records . If the acceptance report from that year is still there, it will record the particle size, sampling method and results during the test. This is the most direct evidence of what the old standards actually meant.

Process requirements . Find out what processes this area was used for back then. The sensitivity of the process to particles can help determine whether the tenth level label focuses on static or dynamic, whether it is the entire room or a local workstation.

If these materials cannot be found, at least the marked locations on the drawings, surrounding areas and the equipment layout of that year should be recorded. This information helps to infer the original design intent.

The difference in expression caliber between traditional appellation and ISO grade is in how Level 100, Level 1000, and Level 10,000 correspond to ISO levels . There is a more detailed explanation on The traceability logic of level 10 is the same, but the corresponding ISO level is higher.

Confirm particle size and units in old standards

Traditional cleanliness ratings are usually expressed in terms of the number of particles per cubic foot of air. Level 10 means that there are very few particles smaller than 0.5 μm per cubic foot.

There are two key points to confirm here.

Particle size caliber . Old standards commonly use 0.5μm as the statistical particle size. But some processes give additional attention to smaller or larger particle sizes. If the original drawing does not indicate it, it needs to be judged based on the process documents and product requirements of the year.

Unit of volume . The traditional name is cubic feet, ISO uses cubic meters. Unit conversion itself is not complicated, but if two units are mixed in old documents without being clearly marked, data interpretation may be biased.

Under the traditional 0.5μm aperture, level ten roughly corresponds to ISO 4. However, this comparison is only a reference for understanding the old title and cannot be used as the final expression of the technical document. As mentioned in What is the Difference Between Cleanliness Grade and Filtration Efficiency ? The grade evaluates the spatial particle concentration, which is two different things from the filter efficiency. It is also necessary to distinguish between these two levels when converting.

Equipment replacement cannot just use the old model

After confirming the meaning of the old standard, the device configuration needs to be rechecked.

The ten levels on the old drawings were designed based on the working conditions of that year. Now the process equipment has changed, the number of personnel has increased, and the exhaust conditions have changed. For the same ISO 4 goal, the corresponding air supply volume, filtration efficiency, and air flow organization requirements may have been different.

Filtration efficiency . The tenth stage back then may have used an older model of high-efficiency filter. Current HEPA or ULPA products may have changes in efficiency and resistance characteristics. When selecting, check the data of the specific model at the target air volume. The HEPA and ULPA filter pages have parameter descriptions for different levels of products.

Air volume static pressure . The old fan may have aged and its performance curve is different from what it was back then. After adding or replacing the filter section, the system resistance will change and the fan operating point needs to be recalculated.

Install the interface . Older FFUs may have different dimensions and mounting methods than today's standard products. The same size does not mean that the residual pressure, filter or control method is suitable for the upgraded usage conditions. The FFU clean air supply product page has interface instructions for standard products and customized solutions. For device-side replacement, please refer to EFU equipment side fan filter unit。

Aili Industrial has manufacturing capabilities in motors, fans, control systems, sheet metal, air filters and complete machine assembly. When renovating an old factory building, you can put filters, fans, structures and control conditions in the same project to check, so that the equipment configuration and the retroactive grade targets are consistent.

Scene judgment

The old drawings are labeled 'Tenth Level Operation Station', but a mechanical arm has been installed next to the operation station. The movement of the robotic arm will produce local airflow disturbances and may also bring particles. In this case, you cannot just configure the filter equipment according to the tenth level of the original drawing. You must also recheck the action shielding and workpiece protection areas, and then agree on the on-site level test conditions.

In another project, when replacing the old FFU, a new model was selected based on the original size, but the working point with a filter was not checked. After installation, it was found that the air volume was low and the air speed on the operating table was uneven. Later, the fan curve and filter element resistance were rechecked, and the operating settings were adjusted to meet the requirements.

These two situations illustrate that the confirmation of Level 10 is not just a standard conversion, but also a return to the actual working conditions on site.

Key points for selection and acceptance inspection