In purchasing HEPA/ULPA filters, procurement managers often face a dilemma: stringent quality requirements versus severe cost pressures. The EN 1822 standard itself provides a crucial option that can influence price—”full scan testing” versus “partial scan testing.” Understanding the differences and risk boundaries between these two is essential for every professional procurement officer.
Why does “partial testing” exist?
According to the EN 1822 standard, for filters with large areas (typically exceeding 0.5㎡ or specific dimensions), “partial scan testing” is permitted as an alternative. The underlying logic is to infer the integrity of the entire filter by scanning specific areas of the filter media and frame (such as frame seams, the center and edges of the filter media).
- Core Advantages:Significantly reduces costs and testing time. Full scan testing is time-consuming and incurs high equipment and labor costs, which directly impacts the final selling price of the filter. Localized testing offers an economically viable certification path for such large filters.
- Application Prerequisites: The effectiveness of this method rests on the premise that the filter manufacturer possesses highly consistent and stable production processes and quality control. It assumes that testing at key points can represent the overall quality level of the filter media.
Three Limitations of Partial Testing
However, purchasers must be keenly aware of the limitations of localized testing, which constitute the “risk boundary” of its use.
- 1. Risk of Missed Detections: Localized testing cannot cover 100% of the filter area. This means that isolated, tiny pinholes or defects existing in non-scanned areas may be missed. For environments seeking “absolute safety,” this is a theoretical risk that cannot be ignored.
- 2. Absolute Dependence on Production Processes: The reliability of localized testing is strongly correlated with the manufacturer’s production quality control capabilities. If the raw materials (filter media) themselves have unpredictable sporadic defects, or if there are fluctuations in the frame bonding process, localized testing cannot provide the comprehensive, “ironclad” assurance that full scanning offers.
- 3. Mismatch between Risk and Level: The higher the efficiency level of a filter (e.g., U15 and above), the lower its tolerance for a single leak. A minor defect that is insignificant on a low-efficiency filter can become the culprit causing the entire cleanroom to be downgraded on an ultra-high efficiency filter.
Decision Guidelines: Choosing Between Local Testing and Full-Scan Testing?
As a purchaser, you can develop a clear procurement strategy based on the risk level of the end-use scenario.
Scenarios where “local testing” of filters is acceptable:
Final stage protection for large air conditioning systems: As a backup filtration unit in environments with ISO Class 7 (Class 10,000) cleanliness and below.
Recirculating air handling units in non-critical areas: Such as in some industrial environments or auxiliary functional areas where individual particles are not sensitive.
Non-core projects with extremely limited budgets and manageable risks.
Scenarios where “full scan testing for each filter” must be insisted upon:
Terminal air supply in high-level cleanrooms: Such as biopharmaceutical aseptic workshops and microelectronic chip production lines with ISO Class 5 (Class 100) and above. Any undetected leak can lead to product contamination or batch scrapping, with potentially huge costs.
This includes any biosafety cabinets or clean benches used in aseptic operations, cell culture, or pathogen research.
It also affects critical process equipment, such as FFU/U units installed directly above filling lines or lithography machines.
Frankfurt-based filtration expert Trenntech explicitly recommends in its technical guidelines: “For all critical areas directly impacting core process quality, we insist on providing filters that undergo full-scan testing on a per-unit basis. This is not only a standard requirement but also a commitment to product quality for our customers.” The core task for the purchaser is to act as a risk assessor and manager, clearly defining quality red lines based on application scenario risks, the cost of quality failure, and the company’s risk tolerance. A wise decision that can withstand the test of time must be made on the balance between cost and quality.