b'FIRE SAFETYFigure 1:Effective thermal conductivity of green roof growing medium. PART 2: HEAT TRANSFER BEHAVIOUR OF GREEN ROOF SYSTEMS UNDERFIRE CONDITIONSA NUMERICAL STUDY (2019) The potential fire hazard to roof decks coveredwithvegetationhasnotyet beenfullyexplored.Thispartofthe studyanalyzedtheperformanceof green roofs in extreme heat conditions by numerical modelling of heat transfer throughtheassembly,whentheroof isexposedtoelevatedtemperatures fromtheexterior.Themainobjective wastodetermineconditionsandtimeFigure 2: Temperature profiles in the assembly.required for the roof deck to reach crit- Figure 2: Temperature profiles in the assembly. ical temperature (time to failure). Effects oftheappliedheatingload,substrate layer thickness, porosity of the substrate and the presence of gypsum board over thedeckwerealsoexamined.Itwas assumed that no moisture was present in the assembly in order to model the most severe situation.In this study, heating loads betweenServing Metro Vancouver for 122 years!50 and 200 kW/m were used, which canStrata Re-roofing Specialistsbe associated with small-scale fires andRoofing & Guttersforestfires,withtemperaturesequiv-alent to 623 C and 1,110 C, respec- 604.370.6288 tively. Growing media layer thicknesseswww.crownroofingltd.comvaried between 3 and 10 cm. SubstratesFigure 3: Temperature evolution at the deck level when a green roof is exposed to four porositybetween0.5and0.7repre-sented a more and less compacted state.different heating loads. #118-11860 HammerSmith Way, Richmond, BCV7A 5G1Two different types of roof decks were chosen: a wooden deck made of 19-mm plywoodandasteeldeck.Critical temperaturesforthesematerialswere set to 300 C and 538 C respectively, accordingtoEN1995-1-2(2003)for wood and ASTM E119 (2012) for steel. Temperatureprofilesshownin Figure2presenttheresultofaheat transfer simulation through a green roof assembly, with a 10-cm layer of substrate andaporosityof0.6installedovera wooddeck,notprotectedbygypsum boardduringexposureto50kW/m for four hours. The results show that no temperatureincreasewasobservedat the deck level after the first hour. At the end of the four-hour heating period, the deck temperature only reached 110 C, which is well below the critical valuethe point at which the deck would have caught fire. www.rcabc.orgl25'