sameer @ sgprojects.co.in has build a LPG gas detection circuit based on LM358:
LPG gas detection project’s main idea is to implement the security system for detecting leakage of liquid petroleum gas in closed environment. In this project gas leakage is identified by using MQ6 gas sensor. A simple circuit with an Op-Amp IC is powered by a step down transformer and finally the alarm produces on detecting gas.
LPG Sensor Alarm – [Link]