Log reduction is a measure of how thoroughly a
decontamination process
Decontamination (sometimes abbreviated as decon, dcon, or decontam) is the process of removing contaminants on an object or area, including chemicals, micro-organisms or radioactive substances. This may be achieved by chemical reaction, disinfect ...
reduces the
concentration
In chemistry, concentration is the abundance of a constituent divided by the total volume of a mixture. Several types of mathematical description can be distinguished: '' mass concentration'', ''molar concentration'', '' number concentration'', ...
of a
contaminant
Contamination is the presence of a constituent, impurity, or some other undesirable element that spoils, corrupts, infects, makes unfit, or makes inferior a material, physical body, natural environment, workplace, etc.
Types of contamination
Wi ...
.
It is defined as the
common logarithm of the ratio of the levels of contamination before and after the process, so an increment of 1 corresponds to a reduction in concentration by a factor of 10.
In general, an -log reduction means that the concentration of remaining contaminants is only times that of the original. So for example, a 0-log reduction is no reduction at all, while a 1-log reduction corresponds to a reduction of 90 percent from the original concentration, and a 2-log reduction corresponds to a reduction of 99 percent from the original concentration.
Mathematical definition
Let and be the numerical values of the concentrations of a given contaminant, respectively before and after treatment, following a defined process.
It is irrelevant in what units these concentrations are given, provided that both use the same units.
Then an and -log reduction is achieved, where
:
.
For the purpose of presentation, the value of is rounded down to a desired precision, usually to a whole number.
;Example:
Let the concentration of some contaminant be 580 ppm before and 0.725 ppm after treatment. Then
:
Rounded down, is 2, so a 2-log reduction is achieved.
Conversely, an -log reduction means that a reduction by a factor of has been achieved.
Log reduction and percentage reduction
Reduction is often expressed as a
percentage. The closer it is to 100%, the better.
Letting and be as before, a reduction by % is achieved, where
:
;Example:
Let, as in the earlier example, the concentration of some contaminant be 580 ppm before and 0.725 ppm after treatment. Then
:
So this is (better than) a 99% reduction, but not yet quite a 99.9% reduction.
The following table summarizes the most common cases.
:
In general, if is a whole number, an -log reduction corresponds to a percentage reduction with leading digits "9" in the percentage (provided that it is at least 10%).
See also
*
Decimal reduction time
References
{{reflist
Dimensionless numbers
Logarithmic scales of measurement
Units of measurement
Units of chemical measurement