Moisture Content, Ignitability, and Fire Risk of Vegetation in Vertical Greenery Systems

摘要

Vertical greenery systems (VGS) are getting popular as a green cladding material. However, they have not been adequately assessed in terms of fire safety. Lack of maintenance and improper irrigation systems will cause drying of plants in VGS, creating substantial fire risk. Dry plants may be easily ignited and intensify the vertical spread of fire. However, potential fire hazards of VGS are barely discussed in the existing literature. The moisture content (MC) of a plant is one of the most critical factors affecting its ignitability. This study explores ignitability and fire risk of plants under radiative heat flux at different MCs. Three commonly used plant species for VGS—namely, Hedera helix Lowe, Peperomia obtusifolia (L.) A.Dietr., and Aglaonema commutatum Schott (the cultivar Lady Valentine)—were selected for study. These plants were subjected to natural drying under ambient conditions without water supply to simulate the plants in VGS without proper irrigation. The MC of the plants was measured and cone calorimeter testing was performed at different time intervals during their drying process. Ignition, heat release, and gaseous emissions were studied under radiative heat flux. When the plants were fresh and green, no ignition was observed for all three species. Hedera helix started to ignite once MC was lower than 243 %, at a heat flux of 50 kW m−2. Peperomia obtusifolia began to ignite once MC dropped below 200%, at a heat flux of 20 kW m−2. Aglaonema commutatum ignition occurred once MC was lower than 316 %, at a heat flux of 50 kW m−2. Cone calorimeter test data were used for analyzing the three key parameters: flashover propensity, total heat release per unit area, and smoke toxicity hazard. Analysis showed that low MC creates a high risk of flash-over. Thermal risk and smoke toxicity hazard also increased at lower MC, but the risk was low for the three plants tested. These findings demonstrate the importance of maintaining healthy live plants to ensure that fire risk of VGS is minimal. This study provides good direction for assessing and understanding the fire behavior of vegetation in VGS.