Fire Behavior and Safety Assessment of Transformer Oils and Alternative Insulating Fluids: A Review of Cone Calorimeter and Pool Fire Studies

Experimental study on the combustion characteristics of carbonate solvents under different thermal radiation by cone calorimeter

Temperate forests of Central Europe are exposed to increasing fire risk. However, little is known about combustion properties of leaf litter, which plays an important role in the spread of surface fires. We used cone calorimetry to compare combustion properties of leaf litter samples from seven common tree species of Central European forests by reconstructing a litter layer of original depth in sample holders with a size of 10 cm × 10 cm. In addition to mono-specific leaf litter beds, combustion experiments included mixtures of different litter types, mixtures of litter and bryophytes and one mixture of litter and fine woody debris, totalling to 13 different setups (i.e. litter types). Recorded combustion properties included ignitability, flaming duration and heat release. Differences in combustion properties were analysed using analyses of variance followed by pairwise post-hoc tests. Combustion properties mainly differed between different litter types (broadleaf, pine needle, short needle). Highest total and peak heat release were observed for Scots pine (Pinus sylvestris), while peak heat release rates showed only minor differences for litter of the remaining species. Broadleaf litter was characterized by highest ignitability. For short-needle litter, we observed long flaming duration and incomplete combustion, resulting in the lowest total heat release on a sample mass basis. For litter mixtures of pine and broadleaf litter, we observed lower peak heat release rates in comparison to mono-specific pine litter. Mosses reduced peak heat release rates and increased the proportion of unburned biomass. However, the magnitude of this effect differed between bryophyte species included in the mixtures. The addition of fine woody debris strongly increased total heat release, highlighting the importance of fine woody fuels for fire behaviour. The results of this study provide valuable baseline information on combustion behaviour of leaf litter from Central European forests. Due to the limitations of laboratory combustion experiments to reproduce conditions of real forest fires, there is a need for future field studies investigating fire behaviour under natural conditions.

Combined effect of palygorskite and melamine polyphosphate on flame retardancy properties of polyamide 11 nanocomposites

Plywood samples treated with ammonium polyphosphate (APP) and 4A zeolite were prepared to investigate the effect of zeolite on wood’s burning behavior using a cone calorimeter under a heat flux of 35 kW/m2. Results showed that APP decreased the heat release rate (HRR), total heat release (THR), and mass loss rate (MLR) of treated plywood. However, APP significantly increased the total smoke release (TSR) and carbon monoxide (CO) yield. The addition of 4A zeolite reduced the HRR, peak HRR, and THR of the plywood treated with only APP. The second HRR peak in a typical plywood curve diminished with the addition of as little as 2% 4A zeolite. The average specific extinction area (ASEA) and CO yield decreased significantly with the presence of zeolite in the APP. The ignition time did not change significantly and the TSR increased when zeolite was present. Thus, a suitable amount of 4A zeolite works synergistically with APP in promoting flame retardancy in flame retardant plywood.

A novel coating of hyperbranched poly(urethane-phosphine oxide) for poly(methyl methacrylate) with high fire safety, excellent adhesion and transparency

Cone calorimeter is widely used to study fire behaviour of materials employing small size samples. This equipment allows obtaining parameters such as time to ignition (TTI), heat of combustion, mass loss rate (MLR), or heat release rate (HRR) under different heat fluxes. Some studies have considered a linear fitting between MLR and HRR peaks and the incident heat flux. In accordance with this hypothesis, the computer model Fire Dynamics Simulator (FDS) has included a simple model to extrapolate burning rate data collected from a cone calorimeter test to the heat feedback occurring during a simulation. Nevertheless, deviation in the prediction of the HRR peaks at 75 kW m−2 of approximately 39.3% and of 37.1% for the first and second peak, respectively, were found. Therefore, this work presents a correlation between the incident heat flux and the global HRR per unit area curve, testing up to five different cables and several heat fluxes. To do so, some modifications of the FDS correlation are performed to consider the effect of the flame heat flux in the decomposition of the cables. Once experimental data are acquired, a computational analysis is carried out using FDS to achieve the flame heat flux in the samples. Additionally, this flame heat flux has also been obtained from the literature. As a conclusion, the addition of the flame heat flux to the cone calorimeter incident heat flux provides better predictions than the linear fitting methodology defined in the FDS Guide. Furthermore, this correction is checked with: (1) the example included in FDS guide, decreasing the HRR peaks errors from around 38% to around 25%; and (2) to seven different cables from the literature, decreasing the HRR peaks relative errors, as average, from 14.2 to 9.5% approximately.

In the north-eastern United States, invasive plants alter forest fuels, but their combustion characteristics are largely unknown. We assessed unground samples of foliage and twigs in the cone calorimeter for 21 non-invasive, native species, paired with 21 invasive species (18 non-native). Variables included sustained ignition, peak heat release rate, total heat release, and especially average effective heat of combustion, which is independent of initial sample mass. Heat of combustion was overall slightly lower for invasive species than for counterpart non-invasive species, and was significantly lower for Norway maple, black locust, and glossy buckthorn than for three non-invasive trees. It was low for invasive Japanese stiltgrass, sheep sorrel, and glossy buckthorn, and for non-invasive whitegrass, interrupted fern, grape, sphagnum moss, and three-lobed bazzania. Heat of combustion was high for invasive roundleaf greenbrier (native), scotchbroom, tree-of-heaven, Japanese honeysuckle, Japanese barberry, swallow-wort, and garlic mustard, and for non-invasive plants of fire-prone ecosystems: black huckleberry, pitch pine, bear oak, northern bayberry, and reindeer lichen. Heat content of twigs and foliage interrelates with other factors that affect fire behaviour, yet the cone calorimeter results enabled comparison of combustion properties among many species. These data have potential application as improved inputs for fire behaviour modelling.

At present, little information is available in the scientific literature related to the durability (weathering resistance) of fire-retarded wood and natural fiber-reinforced thermoplastics. In this work, thermoplastic profiles for façade applications based on high-density polyethylene, wheat straw particles, and fire-retardants were extruded and their reaction-to-fire performance before and after artificial weathering evaluated. Profile geometries were either solid or hollow-core profiles, and fire-retardants (FR) were added either in the co-extruded layer or in the bulk. Various FR for inclusion in the co-extruded layer were screened based on UL-94 tests. For profile extrusion, two types of FR were chosen: a coated intumescent combination based on ammonium polyphosphate (APP) and an APP coated with melamine and without formaldehyde. Before weathering, the peak heat release rate (pHRR) and the total heat release (THR), which were determined using cone calorimeter measurements, were reduced by up to 64% and 67% due to the FR. However, even before weathering, pHRR of the profiles was relatively high, with best (lowest) values between 230 and 250 kW/m2 under the test conditions. After 28 days of artificial weathering, changes in reaction-to-fire performance and color were evaluated. Use of the APP in the co-extruded layer worsened color change compared to the formulation without APP but the pHRR was not significantly changed. The influence of weathering on the fire behavior was small compared to the difference between fire-retarded and non-fire-retarded materials. Results from the cone calorimeter were analyzed with regard to ETAG 028, which provides requirements related to the durability of fire performance of building products. In many formulations, increase in THR was less than 20% compared to before weathering, which would place some of the profiles in class C or better (EN 13501-1). However, due to the high pHRR, at best, class D was obtained under the conditions of this study. In addition to cone calorimeter measurements, results from the single flame source test, limiting oxygen index determination and thermogravimetric analysis, are shown and discussed. Strength properties, water uptake and swelling of the profiles, thermal conductivity, and energy dispersive X-ray data are also presented.

Heat release rate of a typical furniture foam sofa was assessed with a cone calorimeter. The sofa arrangement included two layers of fabric, cotton and foam. Individual component materials and combination of them were tested. A high radiative heat flux of 50 kW m 2 was used to consume all materials in the tests. The sustained ignition time, peak heat release rate and total heat release rate were deduced from the heat release rate curves. These data are useful for classifying the materials by calculating two parameters describing the possibility to flashover. The superposition of heat release rate curves and total heat released (THR) were studied. It is observed that adding the heat release rate curves for component materials would not give the heat release rate curve of a furniture arrangement with different combinations of materials. However, the THR for the components can be added to give the THR of the arrangement.

Effect of lithium salts LiPF6 and LiBF4 on combustion properties of electrolyte with EC/PC/EMC under different pressures

Fire parameters, behaviour, and comparative thermal hazard of food grains based on the cone calorimeter tests

The flammability of living vegetation is influenced by a variety of factors, including moisture content, physical structure and chemical composition. The relative flammability of ornamental vegetation is of interest to homeowners seeking to make their homes ‘fire safe’. The relative importance of the factors influencing fire behaviour characteristics, such as flammability, is unknown. In the present study, oxygen consumption calorimetry was used to obtain selected combustion characteristics of ornamental vegetation. Peak heat release rate, mass loss rate, time to ignition and effective heat of combustion of 100 × 100-mm samples of foliage and small branches were measured using a bench-scale cone calorimeter. Green and oven-dry samples of 10 species were collected and tested seasonally for a period of 1 year. Similar measurements were made on whole shrubs in an intermediate-scale calorimeter. The range of cone calorimeter peak heat release rates for green and oven-dry samples was 1–176 and 49–331 kW m−2, respectively. Moisture content significantly reduced heat release rates and increased time to ignition. Peak heat release rates for Olea europea and Adenostoma fasciculatum were consistently highest over the year of testing; Aloe sp. consistently had the lowest heat release rate. The correlation of peak heat release rates measured by the cone calorimeter and an intermediate-scale calorimeter was statistically significant yet low (0.51). The use of the cone calorimeter as a tool to establish the relative flammability rating for landscape vegetation requires additional investigation.

In this article, the flame retardant poly(aminopropyl/phenyl)silsesquioxane (PA) was incorporated into thiol-ene (TE), to obtain a flame-retardant thiol-ene (FRTE) composite. The cone calorimeter (CONE) measurement results showed that, compared with neat TE, the peak of heat release rate (PHRR) and total heat release (THR) of FRTE have decreased by almost 23.7% and 14.5%, respectively. Thermogravimetric analysis (TGA) results further confirmed that the flame retardant PA could induce the initial thermal degradation of TE, and increased the amounts of residual char. Moreover, the activation energies of FRTE were calculated through the Kissinger and Flynn–Wall–Ozawa methods. Compared with the neat TE, the activation energies of FRTE were raised by the addition of PA. It indicated that the flame retardant PA promoted cross-linking reactions of TE, to form a compact char layer and retarded further the thermal degradation of the polymer matrix.

Aluminum hypophosphite (AP) was used to prepare flame-retarded thermoplastic polyurethane (FR-TPU) composites, and their flame retardancy, thermal degradation and mechanical properties were investigated by limiting oxygen index (LOI), vertical burning test (UL-94), thermogravimetric analysis (TGA), cone calorimeter (CC) test, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and tensile test. TPU containing 30 wt% of AP could reach a V-0 rating in the UL-94 test, and its LOI value was 30.2. TGA tests revealed that AP enhanced the formation of residual chars at high temperatures, and slightly affected the thermal stability of TPU at high temperatures. The combustion tests indicated that AP affected the burning behavior of TPU. The peak of heat release rate (PHRR), total heat release (THR) and mass loss rate (MLR) greatly reduced due to the incorporation of AP. The tensile test results showed that both the tensile strength and the elongation at break slightly decreased with the addition of AP. The digital photos and SEM micrographs vitrified that AP facilitated the formation of more compact intumescent char layer. Based on these results mentioned above, the flame-retarding mechanism of AP was discussed. Both the self-charring during the decomposing process of AP and its facilitation to the charring of TPU led to the great improvement in the flame retardancy of TPU.

Fly-ash, a kind of large solid waste in energy industry, has brought about serious environmental problems and safety consequences. No efficient way has been found yet to deal with it worldwide. The focus of contemporary research are mainly placed on the reuse of aluminum and iron, but with a low utilization rate less than 30%. Having destroyed the ecological balance, fly-ash has become a challenge drawing the attention of people in the solid waste industry. In this paper, a smoke-suppressant and flame-retardant layered double hydroxide (LDH) featuring Mg-Al-Fe ternary was successfully synthesized by fly-ash after coprecipitation. XRD results presented LDHs successful synthesis. Then, exploration on the flame retarding properties of LDHs in composites composed by ethylene vinyl acetate (hereinafter referred to as EVA)/LDHs was carried out by UL-94, limiting oxygen index (LOI), cone calorimeter (CCT), smoke density (SDT), and thermogravimetry-Fourier transform infrared spectrometry (TG-IR) tests. UL testing results showed that most of the samples had a vertical combustion rating of V-0. LOI results showed the highest LOI value of ELDH-1, amounting to as high as 28.5 ± 0.1 while CCT results showed that the rate of heat releasing, mass loss, and smoke production of composite materials were decreased significantly compared with corresponding data of pure EVA. The ELDH-1 sample displayed the lowest peaks of heat release rate (pHRR) value of 178.4 ± 12.8 Kw·m−2 and the lowest total heat release (THR) value of 114.5 ± 0.35 KJ·m−2. Then, SDT indicated that under respective ignition and non-ignition conditions, all composite materials present a good smoke suppression performance. Additionally, digital photographs after CCT demonstrated that EVA/LDHs composites could enhance the formation of compact charred layers, and prevent their splitting, which effectively prevent the underlying materials from burning. Finally, TG-IR findings showed that compared with pure EVA, EVA/LDHs composites also achieved a higher-level thermal stability.