Filtration is the process of removing particles from a moving fluid by passage through small openings. In most filtering operations of environmental significance the mechanism is less that of physical straining than of compaction and adsorption onto surfaces of the filter medium (Pfafflin et al. 2008). Filtration of air in an insect rearing facility to remove microbial contaminants and insect diseases, e.g. bacteria, fungi and viruses, and particles, e.g. moth body scales, and hazardous or irritating chemicals that are health hazards to workers. Filters may be coarse, fine (see HEPA) or designed to remove particular chemicals or materials from the air (Dyck 2010, Oborny 1998). See ‘sanitation’.