Fire Performance
A short burn is a high critical flux. The better the carpet, the bigger the number — which is the opposite of what the burn length looks like.
— W/cm²
Flux at the point where flame propagation stopped
The exponential is a fit to the standard flux profile, not the standard itself — E648 specifies a calibrated flux-versus-distance table for each apparatus and the reported result must be read from that table, so refit A and B against your own calibration before trusting a margin close to a threshold. A classification also rests on the full specified specimen set with its mounting and conditioning, not on one burn. Fire classification is regulated life-safety work: this predicts a test result, it does not substitute for one.
Carpet Flammability Radiant Panel Critical Flux Predictor — free, with the formula and a worked example, at Textile School.