The mainstream use of intumescent coatings for the design of fire safe steel structures has fostered extensive research into the development of effective intumescent coatings and the assessment of their fire performance as thermal barrier to structural elements and materials. The research community has highlighted numerous challenges related to the current design framework based on standard fire resistance furnace testing and the current methodologies have been questioned due to its over-simplifications, limitations and uncertainties. In order to overcome these challenges, numerous research studies have proposed comprehensive approaches and methodologies to investigate the effectiveness of intumescent coatings exposed to a range of heating and fire conditions. This review covers the more recent developments in the field of fire testing and analysis of the fire performance of steel elements protected with intumescent coatings. Apart from the chemical formulation, the substrate boundary conditions, the applied coating thickness, the heating conditions and the fire test method appeared to be the key governing factors. All of them should be considered for a rigorous and systematic testing and design environment that allows the explicit quantification of the effectiveness of intumescent coatings.
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In the past decades, the steel industry has experienced a rapid growth in the use of intumescent coatings for protecting load-bearing steel structures in the event of a fire. The onset of swelling is key for assuring the effectiveness of thin intumescent coatings for providing thermal insulation to the steel substrate during fire. The study presented herein investigates the onset of swelling for a commercially available thin intumescent coating applied on steel plates and exposed to a wide range of heating conditions. Experiments were performed using an array of radiant panels for controlling incident radiant heat flux at the exposed surface of coated steel samples. Within the scope of this research study, the onset of swelling was defined based on two conditions: (1) visual observation of swelling during heating or (2) time-history of the steel temperature. Research outcomes derived from this work defined a threshold for the onset of swelling in terms of steel and coating temperatures and it concluded that the onset of swelling is directly influenced by the heating conditions at the exposed surface and the original applied dry film thickness. KEYWORDS Intumescent coatings; onset of swelling; heating conditions; heat transfer modelling; fire testing; H-TRIS; fire safety. NOMENCLATURE Latin letters L Characteristic length [m] d Thickness [m] A Surface area [m 2 ] V Volume [m 3 ] A/V Section factor [m-1 ] c p Specific heat capacity [J/kgK] Δt Time increment [s] Δx Space increment [m] ΔT Temperature increment [°C, K] Accumulative thermal energy flux [J/m 2 ] h Heat transfer coefficient [W/m 2 K] Heat flux [W/m 2 ] Volumetric generated/absorbed heat flux [W/m 3 ] t Time [sec] T Temperature [°C, K] Greek letters α Absorptivity [-] / Thermal diffusivity [m 2 /s] ε Emissivity [-] ρ Reflectivity [-] / Density [kg/m 3 ] λ Thermal conductivity [W/mK] / Wavelength [μm] σ Stefan-Boltzmann Constant [5.67 • 10-8 W/m 2 K 4 ] τ Transmissivity [-] Subscript s Steel c Coating cond Conduction conv Convection rad Radiation inc Incident net Net loss Losses j Node number ∞ Ambient swell Swelling tot Total th Thermal surf Surface Superscript i Time step
A large-scale fire test was conducted on a compartment constructed from cross laminated timber (CLT). The internal faces of the compartment were lined with non-combustible board, with the exception of one wall and the ceiling where the CLT was exposed directly to the fire inside the compartment. Extinction of the fire occurred without intervention. During the fire test, measurements were made of incident radiant heat flux, gas phase temperature, and in-depth temperature in the CLT. In addition, gas flow velocities and gas phase temperatures at the opening were measured, as well as incident heat fluxes at the facade due to flames and the plume leaving the opening. The fuel load was chosen to be sufficient to attain flashover, to achieve steadystate burning conditions of the exposed CLT, but to minimize the probability of uncertain behaviors induced by the specific characteristics of the CLT. Ventilation conditions were chosen to approximate maximum temperatures within a compartment. Wood cribs were used as fuel and, following decay of the cribs, selfextinction of the exposed CLT rapidly occurred. In parallel with the large-scale test, a small scale study focusing on CLT self-extinction was conducted. This study was used: to establish the range of incident heat fluxes for which self-extinction of the CLT can occur; the duration of exposure after which steady-state burning occurred; and the duration of exposure at which debonding of the CLT could occur. The large-scale test is described, and the results from both the small and large-scale tests are compared. It is found that selfextinction occurred in the large-scale compartment within the range of critical heat fluxes obtained from the small scale tests.
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