Fire Safety Journal最新文献

Zwitterionic siloxane-sulfobetaine (siloxaneSB) surfactants are developed to replace per- and poly-fluoroalkyl substances (PFAS) used currently in aqueous firefighting foams because PFAS pose significant threats to environment and human health. SiloxaneSB surfactant's head and tail structures are varied gradually, one step at a time, to vary hydrophilicity of the head and hydrophobicity, and oleophobicity of the tail. Identical methods and conditions are used across all the surfactants to correlate surfactant structure to interfacial and foam properties, and fire suppression. The results suggest that the amphiphilic balance of the siloxane surfactant have dramatic effects on CMC, interfacial tension, foam expansion ratio, foam degradation, heptane vapor permeation through a foam layer, and fire suppression but little effect on bubble size, coarsening, and liquid drainage. They show synergism between siloxaneSB and alkylpolyglycoside in gasoline fire suppression while trisiloxane-polyoxyethylene exhibited synergism in heptane fire suppression. A 28 ft² gasoline pool-fire suppression results were consistent with the bench-scale findings for tetrasiloxaneSB and trisiloxane-polyoxyethylene formulations. Small changes to surfactant molecular structure can dramatically improve its amphiphilic balance, synergisms, fuel-foam interactions resulting in improved effectiveness of fluorine-free foams but depend very much on the fuel, unlike the fluorocarbon surfactants.

Densified wood (DW) is a novel engineering material with excellent mechanical properties. It forms a thermally insulating and hardly-cracked char layer during pyrolysis and combustion. However, the scientific fundamentals regarding how wood structural characteristics (e.g. density) affect its charring behavior remain unknown, which is important for the fire safety of wood. In this work, the charring shrinkage and cracking of NW and DW with various densities (ρ) under heating exposures (Q_r) are investigated and analyzed. Partial crack closure was observed due to the oxidation. As wood ρ increases or Q_r decreases, the number of cracks (N_c) decreases and cracking time (t_c) is delayed because both the surface temperature (T_surf) and altered thermal stress concentrations on the wood surface are reduced. DW presents an earlier mass loss peak and lower peak value due to the delignification. DW presents high fluctuations in T_surf due to the combing effect of thermal inertia and radial rebound. As wood ρ increases, char shrinkage depth at t_c decreases and shrinkage gradient at t_c increases first and then decreases. An empirical correlation is proposed and well-predicts the N_c based on ρ and Q_r. It can be potentially implemented in the combustion model to improve prediction accuracy.

Dead needle debris accumulates in pine forest floors and poses wildfire hazards. This manuscript reports on laboratory-scale research, where gravity-fed liquid nitrogen (LN₂) jets were used to suppress and extinguish pine needle fires. Minimum quantities of LN₂ needed for fire extinction were determined, and similar quantities of gravity-fed water jets or water sprays were also used to illustrate differences in the underlying extinction mechanisms. LN₂ snuffed the fires instantaneously, as its massive flash-vaporization and volumetric expansion displaced the surrounding air and starved the fires for oxygen. Concomitant cooling of the flame zone and the fuel bed also occurred by the vaporizing cryogen. To the contrary, water suppressed the fire by wetting and cooling accessible fuel surfaces. However, fuel bed surfaces which were not wetted continued to pyrolyze and smolder, and eventually reignited. In these experiments, a portion of the volatile LN₂ jet vaporized in transit, a portion vaporized while traversing the hot gases of the flame, a portion vaporized in the pine needle pile, and some reached the ground and was absorbed therein. Application of LN₂ to fires in confined spaces was most effective for fire extinction. Application of the cryogen to hot spots facilitated flash vaporization for maximum volumetric expansion.

This paper presents experimental and numerical studies to investigate the mechanical behaviour of bolted lap joints at elevated temperatures. The load-deformation curves, failure modes, and resistance values of the specimens were obtained from experimental studies. A solid finite element model generated using ABAQUS software was validated and verified by the experimental results and analytical models to investigate the different failure modes and predict the fire resistance of bolted lap joints at elevated temperatures, respectively. Then, the component-based finite element model (CBFEM) was prepared to analyse the fire behaviour of bolted lap joints as an alternative to design specifications for structural fire engineers. The CBFEM was verified by the validated solid model and analytical models in terms of load-deformation curve, fire resistance, and failure modes. Parametric studies were performed to investigate the influence of several parameters on the fire response of bolted lap joints. The study shows that the CBFEM may be used to design bolted lap joints at elevated temperatures and the 5 % limit strain for plates proposed in EN 1993-1-5 can be applicable for predicting the fire resistance of steel connections.

Experiments were conducted on the detection of fires when using different operation modes of an indoor supply and exhaust ventilation system. The operating conditions of the supply and exhaust ventilation system were identified that exclude the formation of hazardous concentrations of products of thermal decomposition, gasification and combustion of class A materials (wood, cardboard and linoleum). The changes in the concentrations of the gas-air mixture components (CO, O₂, CO₂) were recorded in different operation modes of the supply and exhaust ventilation system and for different mechanisms of thermal decomposition and flame combustion initiation. The performance characteristics of the supply and exhaust ventilation system were determined that are necessary and sufficient for efficient operation of fire detection, containment and suppression systems.

Urban fires are a prevalent type of fire that requires prompt and effective responses. Determining the appropriate number of firefighters at the alarm time is crucial, but it mostly relies on the experience of decision-makers. Due to the fuzziness and limitations of human knowledge, there is often a deviation between the number of firefighters dispatched relying on personal subjective experience and the realistic demand. This paper proposed a historical data-based method for predicting the demand number of firefighters in urban fire. Initially, the National Fire Incident Reporting System (NFIRS) data and Global Historical Climatology Network Daily (GHCN-D) weather data were combined to create a fused dataset. The dataset was subjected to anomaly detection and feature selection, then the processed data was used to predict the number of firefighters using artificial neural network (ANN). In this process, the Genetic Algorithm (GA) was applied to optimize ANN structure. Finally, comparative experiments were conducted to evaluate the performance of the proposed method, which demonstrated superior accuracy in comparison to common regression models and traditional ANN. This advancement brings the number of dispatched firefighters closer to the actual demand and contributes to ensuring an adequate allocation of firefighters for urban fires. Consequently, decision-makers can make more informed decisions regarding the number of firefighters to dispatch, leading to more effective responses to urban fires.

Many fire services have expanded their fire prevention focus to include other community-based risks, such as water safety, road safety, and youth engagement. However, to date, little research focus has been directed to examining the economic and social value of these wider prevention activities and whether they represent a wise resource investment. Further work is also needed to establish the reliability of existing fire prevention economic models. The following study adopts a cost-benefit analysis approach to economically evaluate the range of prevention activities delivered by one fire service in England (Merseyside), which focus on accidental dwelling fires, road, water, and arson-related incidents, and promoting youth engagement. Data was accessed from open sources and a systematic search of existing economic models and fire service records. Cost-benefit ratios demonstrated that the economic value provided by prevention investment was five and 21 times the investment for accidental and deliberate fires. Social value provided by youth engagement activities ranged from two to 13 times the investment for the Beacon Project and Fire Cadets. Findings pose important implications for informing fire sector discussions regarding the resourcing of prevention to address community risks, and for improving data collection to robustly model the economic and social value of activities.

The char layer plays a critical role in the fire behaviour of engineered timber. Several chemical and physical processes can reduce char layer thickness and integrity. A series of experiments studied 12 cross-laminated timber (CLT) columns (130 × 790 × 125 mm WxHxD) exposed to combined thermal (20 kW/m² or 50 kW/m²) and mechanical loading (39 kN, eccentric). Char loss from the surface lamella was observed and the impact of this on the thermal response of the timber studied. In all cases, unprotected CLT exhibited fall-off of charred pieces. Cracking, shrinkage and movement of char contributed significantly to the exposure of underlying timber sections to external heating. There was no direct correlation between char fall-off and the measured glue line temperature in this configuration. To enable comparison between CLT with and without char fall-off, a thin layer of glass fibre-reinforced polymer was added to the exposed surface of six samples which prevented all char fall-off. Retention of the char layer significantly decreased temperatures beneath the char layer, loss of section and burning duration compared to samples with char fall-off.

Pressure treated wood (PTW) and wood-plastic composite (Trex®) were exposed to glowing firebrand piles in a bench-scale wind tunnel. The air flow velocity was 0.9–2.7 m s⁻¹, the firebrand coverage densities were 0.06 and 0.16 g cm⁻², and the pile footprint was 5 × 10 cm² with either the 10-cm or 5-cm sides perpendicular to the incident air flow. Several types of flaming ignition events were observed including flames attached to the substrate surface in front of the pile (preleading zone ignition), and flames attached to the pile that sometimes spread onto the substrate downstream of the pile (downstream ignition). The most frequent and long-lasting flaming combustion occurred in experiments performed at 2.4–2.7 m s⁻¹ using 0.16 g cm⁻² firebrand coverage density piles with 10-cm sides perpendicular to the air flow. Trex® was less prone to preleading zone ignition but was more prone to downstream ignition. Unlike Trex®, PTW exhibited a propensity for sustained smoldering for a wide range of air flows.

Experimental research findings are reported on the characteristics of physicochemical processes at different stages of fire development and suppression. Fires involving solid materials like wood, cardboard and linoleum were investigated. The minimum necessary and sufficient volumes of firefighting liquid (water with different additives, e.g., a foaming agent, bentonite, bischofite, etc.) and their spraying times were identified. Differences in spraying characteristics (droplet velocities, sizes and concentration) were recorded. A relationship between the spraying characteristics of fire extinguishing agents and efficiency of fire suppression was established. Correlations were identified between the operational characteristics of fire detectors during fire suppression involving several fire extinguishing agents. The most efficient compositions in terms of fire suppression time and extinguishing agent consumption were found for typical indoor combustible materials. Mathematical equations were derived to predict the key characteristics of fire suppression.