Fire and Materials最新文献

Understanding fire behavior during critical stages such as flashover and fully developed fire is crucial for firefighter training and safety. This empirical research investigates the influence of fuel–air ratio variations on the occurrence of flashover, the formation of fully developed fire stages, and the temperature dynamics of the upper gas layer. Wooden pallets are utilized as the fuel source in experiments conducted under controlled ventilation conditions. Five different fuel–air ratios ranging from 0.2 to 1.2 are examined, revealing significant insights. The findings of this study highlight the importance of fuel–air ratio adjustments in shaping fire behavior within controlled environments, such as firefighter training compartments. As a result, increasing the fuel-air ratio substantially extends the fully developed fire stage's duration. Moreover, the experimental findings indicate that a minimum fuel-to-air ratio of 0.545 is necessary to initiate a flashover, and fuel-air ratio escalation accelerates the flashover onset. Fuel–air ratios of 0.73 and higher caused the upper layer of gas in the chamber to reach a temperature exceeding 800°C for more than 180 s. These insights are instrumental in enhancing our understanding of fire dynamics and devising more effective firefighting strategies and safety protocols.

A series of numerical simulations and small-scale experiments have been conducted to study the smoke diffusion and maximum ceiling gas temperature in an inclined tunnel with the upper or lower portal sealed. A total of 60 simulation cases and 4 experimental tests were conducted, and different sealing conditions, heat release rates, and tunnel slopes were taken as the main variables. The results show that the sealing condition and tunnel slope have a significant impact on the smoke diffusion and flame shape. When the lower portal is sealed, smoke moves to the opening along the tunnel ceiling, and there is an obvious shear phenomenon between the smoke layer and the cold air layer. When the upper portal is sealed, the smoke layer interface in the downhill direction is almost parallel to the horizontal line, and a larger slope means a longer time taken to spill out of the tunnel. In horizontal tunnels, the maximum ceiling temperature in the tunnel with two portals opened is larger than that in the one-portal-sealed tunnel. Tunnel slope has little effect on the maximum temperature rise for the inclined tunnel with the lower portal sealed. However, in the tunnel with the upper portal sealed, the maximum temperature rise increases with the tunnel slope, and the growth is relatively linear. For inclined tunnels, a comprehensive empirical formula is finally established to estimate the maximum ceiling temperature, taking sealing condition, heat release rate, and tunnel slope into consideration.

Ship fires pose significant threats to maritime safety. This study employs advanced text mining techniques alongside the K-means algorithm to develop a risk structure for ship fires, aiming to identify key risks and fire scenarios. We collected detailed fire investigation reports from authoritative sources, creating a database of 160 incidents over the past 20 years to analyze accident patterns. To enhance traditional text mining, we extracted 260 risk descriptors using specialized dictionaries, calculating their correlations. The improved K-means algorithm, utilizing cosine distance, clustered over 1000 related word combinations, revealing 13 key risks and 42 fire scenarios. From these findings, a risk structure was established through critical importance calculations. Results indicate that damage to flammable liquid tanks or pipes and improper storage of flammable solids are critical risks, elevating fire probability by over 15%. Risks like insulation failure and electrical short circuits showed critical importance values between 0.06 and 0.07. Notably, fire scenarios involving flammable oil leaks and electrical failures are interconnected, with the combination of flammable liquid leaks and insulation failure representing the most hazardous scenario, increasing fire probability by about 30%. This study introduces a data-driven approach to identify potential risks and fire scenarios, contributing practically to risk prevention and management in maritime accidents.

This study explores the forensic potential of thermal damage traces on clothing fibers to identify arsonist. Seven common fiber materials, including cotton, linen, wool, silk, PET, nylon, and/or their blended fabrics, were picked and their thermal properties were analyzed first. A cone calorimeter, the internationally recognized standard heat resource, was applied to simulate transient high-temperature conditions similar to those in arson cases. Thermogravimetric analysis revealed that silk (270°C), wool (280°C) and cotton (280°C) entered the thermal decomposition stage first, followed by cotton–linen blends (320°C), with the synthetic fibers PET and nylon decomposed from 370°C and 400°C, respectively. Up to 450°C, all fabrics have experienced a mass loss over 50%. Macroscopic and microscopic observations (scanning electron microscopy (SEM)) showed that distinct thermal damage characteristics formed on each kind of fabrics after heating. Cotton fabric began to discolor at around 280°C, with cotton fiber presenting rupture traces due to thermal decomposition observed at 320°C. Similarly, cotton–linen fabric exhibited discoloration at around 320°C, with fiber ruptured due to thermal decomposition at 340°C. Silk fabric began to discolor at around 225°C, with carbonization traces detected by both macroscopically and SEM after heating at 310°C. Wool fabric showed discoloration and shrinkage at about 320°C, with fiber curling, cracking, wrinkling, and expansion observed microscopically. Polyester and polyester–cotton fabrics exhibited wrinkling and shrinkage at around 175°C, with fiber melting at 225°C distinguished microscopically. Nylon fabric showed wrinkling and shrinkage at around 225°C, with fiber melting observed via SEM. This analysis on thermal damage traces offers crucial forensic evidence to determine suspects' proximity to fire, aiding in arson investigations.

Engineered wood structures are widely used in modern buildings, for example, glued laminated timber, cross-laminated timber, finger-jointed solid wood, laminated veneer lumber, and so forth. These products often contain bond lines between the lamellae and/or within the lamellae. The most common types of bond lines are face bonding, finger joints, and edge bonding. The type of bond line can impact the behaviour of engineered wood in fire. At ambient temperatures, the bond line integrity is usually maintained; however, at elevated temperatures or in fire, the bond lines can lose their integrity. The new Eurocode 5 for fire design of timber structures will contain different design scenarios and parameters depending on the behaviour of adhesives at elevated temperatures. This paper aims to support the development of the new Eurocode 5. The bond line integrity was tested with 10 adhesives using two cone heater test methods and furnace tests with glulam. All specimens were made with softwood. Loaded finger-jointed specimens and unloaded face-bonded specimens were tested under the cone heater. Unloaded glued laminated timber specimens were tested in a model-scale furnace. The results are analysed and compared. Generally, a good correlation between the different types of tests was seen. The same adhesives tested in various experiments showed similar performance levels. Adhesive families may have different performances depending on various factors. To assess the adhesives and choose the appropriate calculation method, test methods for assessing the adhesives with cone heater are analysed, compared to fire test results, and proposed in this paper.

Although concrete is non-combustible, it experiences a decline in mechanical properties when exposed to high temperatures. This study investigates the impact of varying temperatures (T) and constant exposure durations (H) on the mechanical performance degradation of coral aggregate concrete. Coral seawater sea sand concrete (CSSC) was produced using equal proportions of coral aggregates, seawater, sea sand, and P•O 42.5 cement. The compressive failure characteristics of CSSC were analyzed under different T and H conditions. To characterize the mechanical properties, compressive tests were conducted on 30 sets of 150 × 150 × 150 mm cubic specimens. The resulting stress–strain curves were used to determine the influence of T and H. The results indicate that the compressive strength (f _cu ^T ) and elastic modulus (E ₀) of CSSC decrease with increasing temperature. At T = 800°C, the f _cu ^T of CSSC is reduced to 27.8% of its original value at 25°C, while the E ₀ decreases to 9.7%. Additionally, the mass loss rate (I _w ) and volume expansion rate (R _s ) increase with rising temperature. At T = 800°C, the I _w reaches 12%, and the R _s reaches 7.1%. Finally, the stress–strain constitutive model of concrete after high temperature was fitted to the experimental data.