20.3 Ventilated improved pit (VIP) latrine
The VIP latrine is an improvement over the simple dry pit latrine. The distinctive feature that gives the VIP latrine its name is the vent pipe installed into the pit, which is used to exhaust the foul odour from the pit and control flies (Figure 20.4). If you look back at the photos in this study session, you can see vent pipes in several of the latrines.
The principle is that a continuous flow of air comes in through the superstructure and enters the pit through the hole. This cold air will go down into the pit displacing (pushing up) the hot smelly air upward through the vent pipe. The other advantage of the vent is controlling flies. As we discussed earlier, dry pit latrines potentially serve as breeding places for flies. Newly-emerging adult flies will try to escape through the vent pipe because the pipe allows sunlight to enter into the pit and flies are photopositive (meaning they move towards light) by nature. A mesh screen tied at the top of the vent pipe will prevent flies from escaping to the outside of the latrine.
VIP latrines can have a single pit or double pit. They share the advantages of simple pit latrines with slabs described above but they also have unique advantages that improve on the limitations, namely, that flies and odours are significantly reduced. It should be noted, however, that the health risks from flies are not completely removed by ventilation.