The emission of carbon monoxide (CO), the silent killer, from coal fire is inevitable. The developed coal pillars are being extracted by opencast mining at Chirimiri due to fire. Though coal faces are quenched by spraying water under high pressure and high walls are blanketed by overburden but even then there is release of carbon monoxide at higher concentration. The paper deals with the estimation of CO concentration at various areas of the mine and its surroundings.