How can we distinguish between simulants and hazardous substances under real conditions?

We discuss the possibility of the detection and identification of substances under real conditions. As it is well-known many harmless materials show similar spectral properties to hazardous substances. To identify a substance we are currently developing various time-dependent criteria for the estimation of the probability of a hazardous substance presence in a sample under analysis. A new type of such criteria is discussed in this paper. To explain a physical mechanism for false alarm spectral properties appearance in the signal transmitted through and reflected from a substance we make a computer simulation using 1D Maxwell's equations and density matrix formalism. A feasible approach for highly effective detection and identification of a substance is proposed.