1 For surface waters, between 20 and 40 mm (upstream the strainer)  For municipal wastewater: for raw water, from 15 to 30 mm (but upstream from a straining and/ or lamellae settling process, fine screening is necessary); for sludge (if necessary), 10 mm or less.
Other studies. According to some studies, 18-year-old males have a refractory period of about 15 minutes, while those in their 70s take about 20 hours, with the average for all men being about a half-hour. Although rarer, some males exhibit no refractory period or a refractory period lasting less than 10 seconds.
Report Abuse. Refractory material is one that retains and maintains its strength at high temperatures without softening or deformation in shape. The most important chemical composition of refractory is the oxides of aluminum, silicon and magnesium. Another oxide usually used in refractory is the oxide of calcium.eport Abuse. Refractory material is one that retains and maintains its strength at high temperatures without softening or deformation in shape. The most important chemical composition of refractory is the oxides of aluminum, silicon and magnesium. Another oxide usually used in refractory is the oxide of calcium.