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Log reduction is a measure of how thoroughly a decontamination process reduces the concentration of a contaminant. 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.
Z-value is a term used in microbial thermal death time calculations. It is the number of degrees the temperature has to be increased to achieve a tenfold (i.e. 1 log 10 ) reduction in the D-value . The D-value of an organism is the time required in a given medium, at a given temperature, for a ten-fold reduction in the number of organisms.
From this perspective, D-values can be understood as roughly analogous to half lives of radioactive substances, however a half life involves a reduction of 50% rather than 90%. The half life is actually roughly 30% (log 10 2 ≈ 30.103%) of the D-value, so if D = 10 minutes, the number of living microorganisms will be halved in about 3 minutes.
Marcus's method is a structural analysis used in the design of reinforced concrete slabs.The method was developed by Henri Marcus and described in 1938 in Die Theorie elastischer Gewebe und ihre Anwendung auf die Berechnung biegsamer Platten. [1]
What is often called a "log reduction" (technically a reduction by one order of magnitude) represents a 90% reduction in microbial population. Thus a process that achieves a "6-log reduction" (10 −6 ) will theoretically reduce an initial population of one million organisms to very close to zero.
[4]: 146 Another health effect associated with structural dampness is the presence of bacteria in an indoor environment. Bacteria require water to grow and multiply and certain species can cause disease in humans, thus the intrusion of water into an indoor environment can place the health of occupants at risk from bacterial infections.
The steel shuttering pinches the top surface of a concrete slab due to the weight of the next slab being constructed. Concrete slabs, block walls and pipelines are susceptible to cracking during ground settlement, seismic tremors or other sources of vibration, and also from expansion and contraction during adverse temperature changes.
Similarly, at larger depths, silt and sand particles may crush and cause a reduction in pore spaces, reducing the biological activity. Bacterial activity is also impacted by challenges such as predation, competition, pH, temperature, and nutrient availability. [55] These factors can contribute to the population decline of bacteria.