How to use this document
Copy the template below into your quality system. Replace every <<FILL: ...>> placeholder with your company, system, and process specifics, then route it through your own document control, review, and approval. The filled specimen shows one worked example; adapt the numbers and scope to your operation and verify each cited regulation or standard against the current source before you rely on it.
This is a generic, originally worded starting point. It contains no confidential, proprietary, or employer material, it is drafted with AI assistance and reviewed, it is not legal or compliance advice, and adopting it does not by itself create or prove compliance. See the Disclaimer and Terms.
This is a ready-to-use protocol for sizing a sterilizing-grade filter from small-scale flux decay data: the short-window flow-decline study, the check that the data actually fits the extrapolation model before trusting it, and the margin applied when setting the final validated filter area. It answers a different question than bacterial retention testing, whether the filter selected is large enough to complete the batch within the validated process time, not whether it removes organisms. Replace every <<FILL: ...>> placeholder and route it through your normal document control, review, and approval. A worked filled specimen follows.
1. Purpose
This protocol defines the small-scale flux decay study, the model-fit check, and the extrapolation used to set the minimum validated filter area for <<FILL: product>> at the stated worst-case process conditions, so the commercial-scale filter completes the batch within the validated maximum filtration time rather than fouling mid-run.
2. Scope
3. Responsibilities
4. Prerequisites
5. Flux decay study design
6. Model-fit check
Before extrapolating, confirm the flow-decline data from section 5 actually fits the straight-line relationship the pore-plugging model predicts. If the data does not fit within the threshold set in section 5, do not extrapolate; the fouling mechanism may not be simple pore plugging, and a different sizing approach is needed.
7. Extrapolation and scale-up
8. Acceptance criteria
9. Deviation handling
Log any deviation from the stated test fluid, pressure, or measurement window in real time. A deviation that understates the real process’s fouling severity invalidates the extrapolation for the intended claim regardless of whether the model fit passed, and requires re-execution rather than a documented exception.
10. Summary and conclusion
State plainly the minimum qualified filter area, the margin applied, and whether the commercial-scale filter actually installed in the process meets or exceeds that minimum.
11. References
PDA Technical Report No. 26, Sterilizing Filtration of Liquids.
ASTM F838, Standard Test Method for Determining Bacterial Retention of Membrane Filters Utilized for Liquid Filtration (for the paired retention study, validated separately).
Confirm the current version of each reference before issue.
12. Revision history
13. Approvals
Filled specimen
Extract for an example low-concentration antibody final filtration step. Company, product, and numbers are illustrative.
The study confirmed the pore-plugging model applied to this formulation before any capacity number was trusted, and the commercial filter area was selected with real margin above the minimum, rather than at the edge of the extrapolated capacity.
Common inspection findings this protocol prevents
- A filter area chosen from a generic manufacturer flow-rate chart with no scale-specific flux decay data behind it.
- An extrapolated capacity number accepted without first confirming the short-window data actually fits the model used to generate it.
- No stated safety margin between the extrapolated fouling point and the filter area actually installed in the commercial process.
- A sizing study run with a test fluid or pressure less severe than the real process’s worst case.
How to adapt this protocol
- Set your document number, product, and test filter model in the header.
- Confirm the model-fit threshold in section 5 before the study runs, not after seeing whether the data happens to fit.
- State your actual worst-case process parameters in section 4 explicitly; a generic or best-case test fluid understates real fouling risk.
- Set the margin in section 7 as a documented decision, not a rounding convenience, and confirm the installed commercial filter area actually meets it.
- Confirm every reference in section 11 against the current published version before issue.
