Pit latrine ventilation : field investigation methodology

A methodology is described for the field investigation of the ventilation performance of ventilated improved pit (VIP) latrines, based on fieldwork done in Botswana and Zimbabwe. The methodology is based on monitoring the temperature environment if the latrine, the air flow velocity within the vent pipe, the wind speed across the top of the vent pipe and variation of atmospheric pressure inside and outside the latrine. The fieldwork indicated that the suction effect of wind across the top of the vent pipe was primarily responsible for ventilation; thermally induced updraught was of minor importance. Under low wind conditions, however, this may not be true so that there is always a need for field investigations prior to the large-scale installation of VIP latrines. Equipment needed for ventilation studies and a format for recording experimental results are included in annexes.