A system and method for placement of sensors for sensing hazardous substances released from a plurality of hazard points. A processor identifies a location of a hazard point, a fence line of the plant-site, and a toxic level of concern (LOC) for the hazardous substance. The processor calculates a minimum amount of the hazardous substance (Q) for which a concentration at a centerline of a plume carrying the hazardous substance reaches the toxic LOC at the fenceline, and simulates a release of the hazardous substance in the calculated amount Q from the hazard point. The processor further calculates a pair of sensor locations where the concentration of the plume is equal to the minimum detectable concentration level of sensor based on the simulated release. The pair of sensor locations is then output by the processor.