PURPOSE: To prevent the occurrence of a fire by providing an oil absorbing wall cutting the flow of a liquid on a liquid flowing passage, detecting an accumulated inflammable liquid and/or an absorbed inflammable liquid in this wall, and activating an automatic fire extinguisher based on the detected result.
CONSTITUTION: An absorbing member 21 absorbing only oil is fixed on a floor face Al so as to cut off a liquid flowing passage A, and an absorbing sheet 22 absorbing all liquids including oil is fitted to the absorbing member 21 to form an oil absorbing wall 2. When an inflammable liquid flows in from the liquid inflow side of the oil absorbing wall 2 and the absorbing member 21 and the absorbing sheet 22 absorb this inflammable liquid, the electric resistance value of the oil absorbing wall 2 is increased as the absorption quantity of the inflammable liquid is increased. When the absorbed inflammable liquid quantity becomes the preset quantity or above, a resistance meter 3 generates a detection signal and sends it to an automatic fire extinguisher 1. The automatic fire extinguisher 1 activates a warning mechanism or a chemical radiating mechanism according to the received detection signal.