Effects of substrate thermal conditions on the swelling of thin intumescent coatings

The experimental study presented herein investigates the influence of the substrate thermal conditions on the behaviour of thin intumescent coatings. Steel plates coated with a commercially available solvent-based thin intumescent coating were exposed to a constant incident radiant heat flux of 50 kW/m2 in accordance with the heat-transfer rate inducing system (H-TRIS) test method. The influence of different substrate thermal conditions was investigated using sample holders capable of controlling the thermal boundary conditions at the unexposed surface of tested steel plates and comparing them to coated timber samples. Experimental results evidence that the substrate thermal conditions govern the swelling of intumescent coatings, thus their effectiveness in protecting load-bearing structural elements. The substrate temperature controls the swelling of intumescent coatings because it defines the temperature experienced by the reacting virgin coating located close to the coating-substrate interface. The physical and thermal properties of the substrate control the capacity of the system to concentrate/dissipate heat in proximity of the coating-substrate interface. In this way, the substrate thermal conditions govern the temperature evolution of the reacting intumescent coating, consequently the swelling process. Accordingly, high swelling rates were recorded for highly insulating conditions (timber substrate), while low swelling rates for poorly insulating conditions (water-cooled heat sink)

Understanding flame extinction in timber under external heating using high-activation energy asymptotics

The present study analyses the flame extinction of timber under different levels of external heating and oxygen contents in the surrounding atmosphere. An existing theoretical framework conceived initially for the analysis of a counter-flow diffusion flame established above the surface of a condensed fuel is extended for charring materials to deliver a fundamental understanding of the self-extinction of timber. This study shows that the energy balance at the burning surface is influenced primarily by the magnitude of external heating conditions, which directly influences the evolution of bulk properties such as flame temperature, location, and stagnation plane position. Variations in the oxygen content had a lesser influence over these bulk properties. For all investigated conditions, the limits of the strain rate range where a flame can be sustained were shown to vary substantially, and critical Damköhler number (Da) analyses were conducted. Blow-off at high strain rates (low Da) occurs for all investigated conditions. The value of this critical Da decreases when increasing either the magnitude of the external heating or the oxygen content as flame temperature increases. Quenching at low strain rates (high Da) is only found for sufficiently low magnitudes of external heating. There, the associated critical Da increases when increasing either the external heating or the oxygen content. Above a certain degree of external heating, the flame can be theoretically sustained even at infinitely-low strain rates. By comparing these results to experimental data, the experimental critical Da at quenching was found to behave like the theoretical results but with a lower sensitivity to variations in the parameters studied. To account for this discrepancy, a fuel dilution parameter is introduced to incorporate the complex dependencies of timber decomposition and surface reactions not captured by the theoretical framework

Influence of heating conditions and initial thickness on the effectiveness of thin intumescent coatings

The study presented herein shows an experimental methodology aimed at analysing the effectiveness of intumescent coatings through detailed characterisation of their thermo-physical response for a range of heating conditions and applied initial dry film thickness (DFT). Steel plates coated with a commercial solvent-based thin intumescent coating were exposed to well-defined and highly-repeatable heating conditions in accordance with the H-TRIS test method. Experimental results emphasise that the swelling process and the resulting swelled thickness govern the thermo-physical response of intumescent coatings, thus their effectiveness. During swelling, the coated steel asymptotically tends to the temperature range 300–350 °C, regardless of the heating condition or DFT. Thermo-gravimetric analysis demonstrates that the coating undergoes the swelling reaction at this temperature range. Once the swelling process is completed, the steel temperature increases above 350 °C. The steel temperature acts as an indicator of the swelling process, as the reaction occurs near the steel-coating interface. The intumescent coating swells and insulates the steel substrate by displacing the already-swelled coating towards the direction of the heat source. Aiming at predicting the swelling of intumescent coatings, empirical correlations are derived: the swelling rate is governed by the heating conditions and the maximum swelled thickness is governed by the initial DFT

Effective Organizational Practices for Middle and High School Grades

At the request of the Accountability Review Council, Research for Action identified effective organizational practices used by better performing schools serving substantial numbers of low income middle and high school students in the School District of Philadelphia. These practices are organized into three spheres: Conditions for Teaching, Student-Centered School Community, and Instructional Program. For each sphere, the report offers broad strategies and specific practices to enact the strategies. Nuanced school case studies show how the practices can work synergistically and coherently in schools to help students succeed

Making A Difference: Year Two Report of the Pennsylvania High School Coaching Initiative

This report examines the implementation of the second year of three for the Pennsylvania High School Coaching Initiative (PAHSCI). Funded by the Annenberg Foundation, this initiative focuses on literacy and math coaches providing support to teachers from across the major subject areas to create literacy-rich classrooms in which students actively engage in learning tasks that deepen their content knowledge and strengthen their abilities to think critically and communicate well. This report presents findings from the first two years of research. It includes survey research as well as in-depth qualitative research in participating schools and districts and provides recommendations for PAHSCI stakeholders as they refine the program and for other education reformers as they consider the benefits of instructional coaching as a strategy for improving high schools and student achievement

Study on the effectiveness of fire suppression deluge systems in tunnels

The required water flow for adequate deluge system operation during a tunnel fire is currently only prescribed by a few regulatory authorities. Car fires are commonly used as references when addressing water-based suppression; nevertheless, limited public information exists on the amount of water required for correctly suppressing a car fire and the thresholds by which the suppression systems fails to be effective. This paper aims at delivering key experimental outcomes to fill this gap in car tunnel fire suppression. The effectiveness of deluge sprinkler systems was investigated by performing a series of full-scale car fire experiments. These experiments were performed by symmetrically positioning a single car under a single sprinkler nozzle, with activation happening (i.e. the sprinkler going off) at a certain time from ignition (which defines the size of the fire), and carefully gauging the burning behaviour of the car fire. A single car was used as it was deemed as the minimum unit for a fire. Temperatures inside, around, and above the car were measured and infrared camera footage was used to gauge flame heights during the experiment. Results from this study yielded two forms of car fire suppression by a deluge system: gradual and instantaneous. A correlation between heat release rate and required water flow for the deluge system is also presented. Outcomes herein show that a water flow per unit area of 6.6 mm/min is the minimum water flow required to effectively reduce the temperature in the immediate vicinity of a car fire of different sizes

Overcoming risk assessment limitations for potential fires in a multi-occupancy building

Decision-making under risk has been a key issue in systems with a potential for major losses such as chemical process industries (Bhopal - 1984, Toulouse - 2001) or high occupancy buildings (World Trade Center - 2001, Grenfell Tower - 2017). For the past decades, engineering disciplines have supported risk management decision-making through the implementation of risk assessments using quantitative approaches. The popularity of this approach relates to the quantitative definition of risk given by Kaplan in 1981, who decomposed risk into a set of scenarios, probability of occurrence and consequences. Recently, research on quantitative risk assessments (QRA) has reported key limitations on identifying the set of scenarios and estimating their probability of occurrence. These limitations may lead to uncertainties of up to three orders of magnitude that affect the QRA’s ability of delivering reliable information to stakeholders. This research uses an alternative definition of risk and applies it to a case study of a multi-occupancy building in the event of a fire. The proposed approach quantifies the maximum damage potential (MDP) of the system when all the active safety measures are allowed to fail, even those with low failure frequencies. The system’s MDP is compared to its maximum allowable damage (MAD), which is previously defined by the stakeholders. This approach allows defining design modifications and operational rules aiding the development of the building’s fire safety strategy. Finally, a comparison between the obtained results and a typical QRA is used to comment on the suitability of the proposed approach when evaluating risk in complex systems

Bond Behavior of CFRP-to-Steel Bonded Joints at Mild Temperatures: Experimental Study

The performance of steel structures strengthened with externally bonded fiber-reinforced polymer (FRP) rely heavily on the interfacial shear stress transfer mechanism of the FRP-to-steel bonded interface. Much is known about the behavior of FRP-to-steel bonded joints under mechanical loading, but little is known about the performance of this type of bonded joints at elevated temperatures. Almost all adhesives typically used in FRP-to-steel applications experience a change in their mechanical behavior at temperatures <70°C. Therefore, gaining a sound understanding of the behavior of FRP-to-steel bonded joints at elevated temperatures is necessary. This paper presents a series of tests where carbon FRP (CFRP)-to-steel bonded joints are subjected to elevated temperatures. The outcomes of this paper showed that, at elevated temperatures, the dominant failure mode of the CFRP-to-steel bonded joints is the cohesion failure within the adhesive. The bond strength was found to increase with the temperature until the heat deflection temperature (HDT). The bond–slip behavior of the interface was found to undergo significant changes with increasing temperature. Specifically, the initial elastic stiffness and the peak shear stress were found to decrease as the temperature increases. The fracture energy was found to increase at temperatures below the HDT but then decrease drastically when the temperatures exceed the HDT

Towards a better understanding of fire performance assessment of façade systems: Current situation and a proposed new assessment framework

This manuscript presents tools and data that serve to enable an evaluation of the risk associated with vertical fire spread on buildings. A highly detailed context to cladding fires is described to unveil the complexity and magnitude of the problem and to identify gaps of information. An engineering framework is then developed which delivers required information that fills some of those gaps and that needs to be used towards achieving quantified fire performance. The data itself has been published as a publicly available database, entitled the Cladding Materials Library (www.claddingmaterialslibrary.com.au). This data can be used to support building fire risk assessments or as the basis for more in-depth research into façade fires. This paper presents the context of the data together with the competency framework necessary for upskilling building professionals to have the capacity to implement the engineering framework