Itisknownthatthereisalagtimeforsmokeplumeinducedbyfirestransportingfromafireorigintothelocationofinterestunderneathanunconfinedandflatceiling.Thislagbehaviorofsmokeplumealsoexistsforafireunderaslopedceiling,andisfundamentaltoestimatetheactivationtimeofafiredetectororotherfireextinguishingsystem.Thisstudyfocusesonthelagtimeofsmokeplumeunderaslopedceiling.Basedontheweak-plumetheoryatearly-firephaseandpreviousstudiesconcerningthefireplumecharacteristicsunderaslopedceiling,acalculationmethodonlagtimeoffireplumetransportingispresentedintheory.Meanwhile,twodimensionlessequationspredictingthelagtimeoffireplumeforsteadyfireandunsteadyfireareproposedrespectively.Furthermore,thecriticaltimecalculationequationisalsoproposedtodeterminetheapplicabilityofquasi-steadyassumptionforatime-dependentfire.
