Fire and Materials最新文献

Linear low-density polyethylene (LLDPE) combined with the piperazine pyrophosphate (PAPP) and melamine cyanurate (MCA) was adopted to prepare the flame retardant LLDPE composite by melt blending. The research results showed that the PAPP/MCA mixture with a mass ratio of 4:1 presented the optimal flame retardant effect. With the 25 wt% addition amount, the LLDPE composite passed the UL-94 V-0 level (1.6 mm), and the limiting oxygen index (LOI) reached 29.4%. The peak of heat release rate (PHRR) decreased by 78.9% from 877.5 to 185.0 kW/m², which is attributed to the good synergistic effect between PAPP and MCA, forming the stable and compact char layer. Besides, the thermal behaviors were characterized through thermogravimetric (TG) analysis, and the synergistic mechanism was investigated by scanning electron microscopy (SEM), TG analysis-infrared spectrometry (TG-IR), and x-ray photoelectron spectroscopy (XPS). The results indicate that the good synergistic flame retardant effect can enhance the flame retardancy of LLDPE materials, and with the addition of MCA and PAPP, a flame retardant LLDPE composite with good thermal stability and mechanical properties can be prepared with no molten droplets on combustion, which provides a feasible solution for the application of high-performance halogen-free flame retardant LLDPE materials.

Standard methods for fire resistance testing require large-scale assemblies and are typically conducted on specialized furnaces at considerable cost. This research focused on developing a scaling methodology for a reduced-scale fire resistance test that reduces the size of the test article while maintaining the same thermal and structural response exhibited in the large-scale test. The developed scaling methodology incorporates uniform geometric scaling, Fourier number time scaling, and furnace boundary condition matching. The scaling laws were experimentally validated with fire exposure tests on gypsum wallboard samples at three scales (full-scale, 1/2-scale, and 1/6-scale). In the tests, samples were exposed to a full-scale equivalent of 60-min of ASTM E119 fire curve exposure on a reduced-scale horizontal furnace, and the temperature rise through the thickness profile was measured. Models were created to calculate the modified fire curves for the smaller-scale tests. Experimental results show that on the exposed surface, the 1/2-scale absolute temperature was within 1.7% of full-scale, while the 1/6-scale temperature was within 2.5%. While the time-dependent properties of burning and cracking caused visual differences in these gypsum tests, modeling and temperature measurements demonstrated that the test results were thermally similar. The good similarity of temperatures is achievable in fire exposure tests of non-combustible gypsum wallboard down to 1/6-scale.

Polyurethane is widely used in building facades as a good energy-saving and environment-friendly organic material, and the U-shaped structure is a common facade form as it could improve indoor lighting and ventilation. Through numerical simulation and theoretical analysis, this study found the flame spread rate of polyurethane foam over a U-shaped facade was affected by the structural dimensions due to three main factors: lateral air entrainment restriction, bottom air entrainment restriction, and flame fusion between the back wall flame and side wall flame. The average flame spread rate was negative linearly correlated with the back wall width and positive exponentially correlated with the side wall length. This was due to that the side walls caused lateral air entrainment restriction, reduced the heat loss, enhanced the thermal feedback, generated an upward induced airflow close to the back wall, elongated the flame, and also caused the flame fusion between side walls and the back wall, thus accelerated the flame spread process compared to the flat structures.

To address the global requirement for a phosphorus-free fire-extinguishing agent, this study elucidated the ability of calcium acetate to extinguish cup-burner flames. The inhibition efficiency of calcium acetate powder (<50 μm) was compared with that of silica-uncoated ammonium dihydrogen phosphate (<50 μm), a chemical contained in agents used in typical ABC fire extinguishers. Calcium oxide and calcium carbonate powders were also used to investigate the suppression mechanisms of calcium acetate. The cup-burner experiments demonstrated that (i) calcium acetate, calcium hydroxide, and ammonium dihydrogen phosphate could extinguish cup-burner flames; (ii) calcium carbonate could not extinguish cup-burner flames; and (iii) the fire-suppression ability of calcium acetate was higher than that of ammonium dihydrogen phosphate, which was in turn higher than that of calcium hydroxide. Thermogravimetric analysis (TG) and X-ray diffraction measurements revealed that, although the calcium-compound powders decomposed and produced calcium oxide during flame extinction, significant differences existed among the fire inhibition efficiencies of the calcium compounds. TG and particle-size measurements proved that the high fire-suppression ability of calcium acetate resulted from the high ability of calcium acetate to generate inert gases during its decomposition, which diluted the oxygen concentration, thereby extinguishing the fires.

Structures are conventionally designed to maintain load-bearing capacity during the heating phase of a fire. However, in structures with moderate or high thermal inertia, the thermal field which results in the lowest structural resistance is likely to occur after the heating phase. This is of particular interest for timber connections because the strength and elastic modulus of timber reduces until the formation of char while steel plates and fasteners, which transfer forces between elements, conduct heat through the connection. It is unclear how thermal fields develop in timber connections during the cooling phase of fires and what influence different cooling rates have. Experiments on identical timber beam-column subassemblies exposed to the same heating duration but two different cooling phases are presented. The results show that exposed steel components conduct heat into the connection, which propagates a thermal wave through the elements. Although the thermal waves had similar speeds, the specimen absorbed more thermal energy during the longer cooling phase, resulting in higher temperatures. Since the strength and elastic modulus of timber decrease at temperatures below 100°C, these results provide evidence that the structural resistance of a timber connection decreases in the cooling or post-cooling phases and that a longer cooling phase is more severe than a shorter one. Further investigation into thermal exposure during the cooling phase of realistic compartment fires and the response of a wide variety of timber connections is required to quantify the reduced performance and support the development of appropriate design methods.

Rigid polyurethane foam (RPUF) has many excellent properties, but its flammability has been a challenge for the application of RPUF compounds. In this research, piperazine pyrophosphate (PAPP) and expandable graphite (EG) were added to the RPUF matrix to improve the fire performance of RPUF. Thermogravimetric analysis (TGA) revealed that PAPP and EG contributed to the early decomposition of the FR-RPUF matrix, and the char residue of RPUF-3 reached 37.1 wt% when the PAPP: EG ratio was 1:1. The flame-retardant test indicated that the FR-RPUF composites reached the V-0 level, and the limiting oxygen index (LOI) value of RPUF-4 was 28.8%. In addition, cone calorimeter tests showed that the addition of flame retardants reduced the peak heat release rate (PHRR) and total heat release (THR), further improving the fire performance of the compounds. The analysis of the char residue confirmed the formation of a denser char residue and significant improvement in the graphitization degree due to the PAPP/EG synergistic effect, indicating that the char residue could effectively isolate oxygen and heat and act as a flame retardant in the condensed phase.

The cover image is based on the Research Article Effect of immersion time on the combustion characteristics of oil-impregnated transformer insulating paperboard by Jiaqing Zhang et al., https://doi.org/10.1002/fam.3097.

This study presents the results of a set of large-scale fire tests performed on horizontal polyurethane foam slabs. Slab thickness, ignition location, and environment (free burn or corner wall) were varied over 23 individual tests. In a continuation of a previous study by the authors, four different slab thicknesses, five different ignition locations, and three environmental modification combinations were tested to examine the potential effects these parameters may have on the test outcomes. Wall configurations were composed of either gypsum plaster board or particle board wall linings and enclosed two sides of the foam slabs. The results obtained were heat release rate, peak HRR, total heat release, and effective heat of combustion, smoke production rate, total smoke production, specific extinction area and soot yield along with flame spread rate calculations obtained using a specifically designed sample tray. These were then analysed to quantify the effects of the test input parameter changes. Results highlight the influence of test input parameter changes on almost all the chosen fire metrics analysed. Slab thickness showed relatively straight forward linear changes to global metrics such as total heat release and total smoke production, while effective heat of combustion showed no change. The smoke production parameters of specific extinction area and soot yield showed minor trends towards higher values with increased slab thickness. Flame spread rates also showed an increased velocity with thicker slabs. Changes to the environment surrounding the foam slabs, from a free-burning scenario to a corner wall configuration that obstructed two sides of the foam slab generally resulted in faster growth of HRR and higher peak values when compared to the free-burn tests. This outcome was most obvious for the wall tests using combustible materials, where growth rates were comparative to an ultra-fast t^2 fire, and peak HRR value rose to over triple that of the free-burn test results. Flame spread rates were highly impacted by the addition of a corner wall, spread rates increased, and the overall pattern of spread rates across the face of the slabs changed entirely. The influence on smoke production values was minor, and for other smoke metrics, the scenario changes showed little influence. However, the values obtained for soot yields were approximately an order of magnitude lower than those given in standard reference books, such as the SFPE handbook for flexible polyurethane foam. This was an interesting additional finding as soot yield values are often directly used in CFD models to simulate smoke spread and determine life safety criteria in fire safety engineering (FSE).

This study provides an analysis on the fire safety of passengers and the fire protection of coaches and buses. A brief review of major bus fire incidents, an overview of current regulations in Europe, and their limitations are presented. The study finds that the current small-scale fire test methods described in UN ECE Reg No. 118 need to be replaced by test methods that can assess the reaction to fire of materials when exposed to ignition sources of varying sizes. To address these shortcomings, the study proposed an expert recommendation to update the material fire safety requirements and testing for buses. Additional measures are proposed, derived from objectives and strategies applied in other transport sectors, and can be tested through existing European and international standards, which are widely used by several industries. These measures aim to extend the time with tenable conditions for a safe evacuation in case of fire, reduce the degree of damage to buses, reduce the risk for fast and excessive thermal exposure on modern energy carriers needed for a more sustainable transport sector.