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.
The Danish answer to the normal menstrual cycle length is 23 to 35 days long (this is from the shortest five percent to the longest 95 percent of cycles). However, cycles got shorter with increasing age so that the normal length was from 23 to 30 days by age 44 (2).