The term fire-retardant as applied to organic (i.e., containing carbon) materials, is intended to refer to reduced fire hazard, as all will burn under certain circumstances. The tests used specified in building codes, such as NFPA 701, are more correctly flame resistance tests, which test a fabric's ability to resist ignition with the flame size and duration in the test conditions. The result is a comparative test, which provides a IFR Stage Curtain Fabric measure of the material's resistance to propagating combustion caused by small scale ignition sources. These tests do not predict the burning characteristics of full scale hazards. In many cases, if exposed to a sufficiently large and sustained exposure fire, the fire-retardant fabrics will burn vigorously. Polyester is inherently flame retardant, and therefore doesn't flare up when applied to various tests. Any amount of heat delivered within a long enough time IFR Blackout Curtain Fabric interval will have no impact on the fabrics' integrity while a limited amount of heat delivered within short enough time interval may ignite or melt the fabric. A simple method for evaluating the threshold incident energy for ignition or melting of fabrics as a function of convective and radiant heat flux has been developed.