Experimental investigations on the influence of 'chimney-effect' on fire response of rainscreen facades in high-rise buildings

In recent years, external wall fires (or facade fires) are occurring due to mixed contribution of exterior cladding and continuous insulation in the chimney like construction of rainscreen facades. In the present work, a new experimental setup is developed and demonstrated for the initial screening of facade assembly at a lab-scale. It incorporates the real physics for investigating the fire hazards of flammable polymeric materials and the chimney effect together. Different combinations of exterior cladding (Al-45, Al-45 Class 0, Al-45 Class B) and continuous insulation (Expanded polystyrene, Polyisocyanurate and Mineral wool) with and without chimney are selected for studying their fire behaviour. The pressure differential combining with re-radiation inside the cavity led 3-6 times higher mass burning rate, flame height and temperature in tests with chimney effect to that of without for the same combination of products. With chimney, secondary fire sources are generated due to the dripping of products which further enhanced the burning and spread rate. A critical width of the chimney (13-50 mm) is established at which maximum vertical fire spread was noticed. Furthermore, the visual observations indicated that the products having thin outer Al sheets are prone to 30% early structural failure. Comparison of results with large-scale tests validated the usefulness of the current setup as an intermediate test between small and large scale for studying fire behaviour of facade materials.