Tips for Environmental Health Staff in Malawi: Common errors when constructing Ventilated Improved Pit-latrines (VIP)

This tip has therefore been written as a reminder or refresher on the basic operational principles of VIPs with an intention of improving the quality of VIPs thereby making them more user friendly than they are constructed now.

VIP latrine was researched in Zimbabwe. The main aims of the designs were to come up with a pit latrine that reduce offensive odor while making sure that fly breeding is being controlled. These properties were additions to other properties of improved latrines that include having easy to clean surface with a slope to allow self cleansing (drainage), provision of foot rests and proper positioning of the squat hole and foot rests to prevent users messing on the surface of the slab.

Reduction of offensive odor
VIPs are intended to reduce offensive odor of latrines by means of convectional air currents. As biochemical processes are occurring on faeco matter facilitated by microorganisms in the pit, heat is generated as one of the by-product thereby raising the temperature of air in the pit which is very offensive. As the temperature of air rises, its weight becomes lighter than the air in the latrine room. The vent pipe gives room for escaping of warm air as the heavier cool air from the latrine room, through the squat hole, presses on the warm air in the pit which is lighter and is forced out. For this to work well, positioning of the latrine is also crucial. The latrine should be located to the leeward side of the premise facing the windward direction at a reasonable distance. The door of the latrine should not completely close the entrance to allow more air entering into the latrine room.
 

Common errors on this part are:

1. No due consideration is given in positioning of the latrine in most cases
2. Squat holes are fitted with covers. This then chokes the air current

Control of fly breeding
VIPs are designed to kill all the flies that enter or breed in the pit as they want to fly out of the latrine pit. The roof of the latrine provides a shade in the latrine room and pit while the vent pipe provides a spotlight in the pit. Flies get attracted and follow the light rays from the vent pipe so that they can get out. As flies try to get out through the vent pipe, they get trapped by a wire mesh fitted at the upper end of the vent pipe. The vent pipe should be painted black or made of any material that absorbs a lot of heat for killing trapped flies. The superstructure should be constructed in a way that it will promote darkness in the latrine room.
 

Common errors

1. Mesh holes at the upper end not small enough to trap flies. The mesh is provided as a decorating material
2.  Vent pipes are usually white in color

Other properties
The floor should be cemented and preferably provided with foot rests to prevent transmission of hook worms. The outer edge of the floor should be higher than the squat hole edge of the floor to facilitate draining of fluids into the pit. Positioning of the foot rest should be properly done in such a way that when somebody is squatting to defecate, the anal end should directly point at the centre of the squat hole. This ensures cleanliness and is properly done by a foot rest marker or mould.
Workmanship should be excellent to provide a fine and smooth finish. This facilitates cleanliness and makes the latrine more appealing to use.
 

Common errors

1. The floor do not have proper gradient making draining of fluids poor
2. Foot rests are positioned anyhow
3. Workmanship is mostly poor

I hope this is a good refresher. Your tips are also welcome to be posted on the page so that common errors in the Environmental Health practice could be minimized.