Antimicrobial Log Reduction & Durable Dose

The formula

This is the expression the tool evaluates. Every term is named underneath, with the unit it must be supplied in.

How the result is derived

Step by step, from the values you type to the figure on screen.

1. The 6 inputs are read from the form on every keystroke: Inoculum Recovered at Zero Contact, Recovered After Contact, Specified Log Reduction, Active Applied, Retention After Wash Cycle and Threshold Active for Efficacy.
2. Each value is checked against the accepted range in the input table below. A value outside its range stops the calculation rather than producing a misleading figure — the results blank out and a message appears.
3. The validated values are substituted into the expression above, which resolves Log Reduction together with every supporting figure in one pass — no value is carried over from a previous entry.
4. The supporting outputs — Percentage Reduction, Organisms Surviving, Margin over Specification, Count the Target Allows, Percentage the Target Equals, Active After Washing, Margin over Threshold, Loading a Durable Claim Needs and Shortfall in Loading — come from the same pass, so they always describe the same case as the headline figure.
5. Results are rounded for display only. The full-precision value is used throughout the chain, so reading a rounded intermediate figure back into the tool by hand can shift the last digit.

What each input means

Where to read each value on the floor, the unit it must be in, and the range the tool accepts.

What the tool returns

The headline figure and every supporting value it is built from.

Worked example

The tool loads with this case already solved — the Log Reduction shown above is its answer. Change one value and the difference from this baseline is the sensitivity of the result to that variable.

How to use it

1. Work through the input groups in order — Test Result and Dose & Durability. The defaults are a realistic case, so you can change one value at a time and watch what moves.
2. There is no calculate button. Every figure recalculates as you type or drag, which is what makes this usable for a what-if sweep rather than a single answer.
3. Read Log Reduction in the dark results panel — that is the headline figure, expressed in log.
4. Check the supporting rows underneath (Percentage Reduction, Organisms Surviving, Margin over Specification, Count the Target Allows, Percentage the Target Equals, Active After Washing, Margin over Threshold, Loading a Durable Claim Needs and Shortfall in Loading) before acting on the headline — they are where an implausible input usually shows itself first.
5. Reset to defaults returns every field to the reference case, which is the quickest way to check whether a surprising result came from the tool or from an input you had changed earlier.

Where this is used

• Process planning — establishing Log Reduction before a trial is booked, so machine time and material in Finishing, Coating, Lamination & Functional Performance are committed against a calculated figure rather than an estimate.
• Costing and quotation — Log Reduction is an input to the cost sheet, and quoting from a worked number rather than a remembered one is what keeps a margin intact.
• Troubleshooting — when the floor result drifts from plan, entering the measured values (starting with Inoculum Recovered at Zero Contact) shows how much of the gap in Log Reduction each variable explains.
• Teaching and study — the accepted ranges bracket normal Finishing, Coating, Lamination & Functional Performance practice, so moving one variable at a time shows the shape of the relationship rather than a single answer.

Assumptions and limits

• AATCC 100 and ISO 20743 differ in inoculum, contact time and neutralisation, so a log reduction from one is not directly comparable with the other and neither transfers to JIS L 1902 without care; quote the method with the number. The zero-contact count must come from the treated specimen at time zero rather than from an untreated control, because a finish that inhibits growth without killing will otherwise be credited with a kill it did not perform - and a specimen where the organism simply failed to survive the contact period on the untreated fabric produces a large apparent reduction from a test that proved nothing. Log reduction is a ratio and carries no information about absolute risk: three log from a large inoculum leaves more organisms than two log from a small one. The dose model treats efficacy as a threshold, which is a simplification of a dose-response curve that is steep but not vertical; near the threshold small dose differences move the log reduction substantially, and that region is exactly where a marginal formulation sits. Nothing here addresses regulatory approval of the active, which in most markets is a separate and harder gate than efficacy, or the question of whether an antimicrobial finish delivers any hygiene benefit in use as opposed to on a specimen.
• Every input is bounded to the range normal practice occupies (Inoculum Recovered at Zero Contact 100 to 100000000 CFU, Recovered After Contact 1 to 100000000 CFU and Specified Log Reduction 0.5 to 8 log, and so on for the rest). Those bounds are guard rails against typing errors, not a claim that the formula fails one unit outside them.
• The calculation is deterministic: the same inputs always give the same result. It carries no allowance for machine condition, operator skill, ambient conditions or lot-to-lot material variation unless an input above explicitly represents one.
• Nothing is sent anywhere. The maths runs in your browser, so the numbers you type never leave the page.

Questions people ask