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.
Refractory Period. The refractory period is the one significant difference between the sexual response cycle of males and females. The refractory period occurs during the maleâs resolution phase. It is a length of time during which a male cannot become more aroused from any kind of sexual stimulation. This period can last from a few minutes to several days, depending on the maleâs age, frequency of sexual activity, and additional factors.