Smoke characteristics of coal-lined tunnel fires

Characteristics of smoke particulates generated from a coal fire in a ventilated model tunnel were investigated by laser optical transmission and by electron microscopy. Average particle diameter and mass concentration of the smoke were determined as a function of the temperature and stoichimoetry of the coal tunnel fire. Smoke particle sizes ranged from 0.2 to 0.9 μm, with larger particle sizes associated with higher smoke concentrations. These coal smoke data are relevant to several aspects of underground mine safety including the development and location of smoke detection instruments, the understanding of the fire (toxic fume) hazard, and the development of new fire protection and control techniques.     

Synergistic effects of aluminum hydroxide on improving the flame retardancy and smoke suppression properties of transparent intumescent fire-retardant coatings

A series of novel aluminum phosphate ester (APEA) flame retardants were synthesized by the salification of cyclic phosphate ester acid (PEA) with different mass ratios of aluminum hydroxide (ATH) and thoroughly characterized by Fourier transform infrared (FTIR) spectroscopy and ¹H nuclear magnetic resonance spectroscopy. The PEA and APEAs were thoroughly mixed with melamine formaldehyde resin to produce five kinds of transparent fire-retardant coatings. The synergistic effects of ATH on the thermal stability, flame retardancy, and smoke suppression properties of the coatings were investigated by different analytical instruments. The results show that the incorporation of ATH greatly decreases the weight loss, char index, flame spread rating, heat release rate, total heat release, smoke production rate, total smoke release and specific optical density in the coatings applied to plywood boards, which is ascribed to a more compact and intumescent char formed during burning, as determined from digital photographs and scanning electron microscopy images. The synergistic effects of ATH in the coatings depend on the content of ATH, and an excessive amount of ATH diminishes the synergistic effects on the flame retardancy and smoke suppression properties based on fire protection tests and cone calorimeter test. Thermo-gravimetric analysis reveals that the thermal stability and char-forming ability of the coatings gradually improve with increasing loading of ATH. FTIR analysis demonstrates that the incorporation of ATH forms a more phosphorus-rich crosslinked char and aromatic char during burning, thus effectively reducing the mass loss, heat release, and smoke production and exhibiting excellent synergistic flame retardant and smoke suppression effects in the coatings.     

Assessing smoke toxicity of burning combustibles by four expressions for fractional effective dose

Toxicity of smoke generated in a fire is difficult to measure accurately. That is because gas sensors for measuring rapidly varying concentrations of toxic gases are not yet developed. Simple expressions are searched for quick measurement in assessing smoke toxicity practically. Four equations on calculating fractional effective dose (FED) related to toxic effluents were reported in the literature, each based on different assumptions. FED value was proposed to be calculated based on peak carbon monoxide concentration and peak carbon dioxide concentration, and transient carbon monoxide, carbon dioxide, and oxygen concentrations. The four values were compared in this article using literature data on toxic gases from different materials measured by (i) cone calorimeter; (ii) full-scale burning tests; and (iii) tunnel full-scale tests. Measured carbon monoxide, carbon dioxide, and oxygen concentrations by standard equipment of oxygen consumption calorimeters were used to calculate the four FED values. It is found that the values of FED based on peak carbon monoxide and carbon dioxide concentrations (denoted as FED₂) are similar to the average values of FED calculated from the updated equation in the literature using the oxygen consumption calorimeters. Putting the values of FED₂ in fire safety design guides is then recommended.     

Specific extinction coefficient of flame generated smoke

The experimental results for the mass specific extinction coefficient (σ_s) at λ=633 nm for flame generated smoke are summarized for seven studies involving 29 fuels. The measurements are for post‐flame smoke generated by overventilated burning. From an analysis of variance for the seven studies, it was found that between‐laboratory differences were the major source of variability. The estimated mean value of σ_s is 8.7 m²/g with an expanded uncertainty (95% confidence interval) of 1.1 m²/g. A major implication of this nearly universal value is that one can infer mass concentration of smoke by making light extinction measurements. Published in 2000 by John Wiley & Sons Ltd.     

A study on fire behaviour of combustible components of two commonly used photovoltaic panels

Photovoltaic (PV) modules are installed in some modern buildings for generating renewable energy. When a building catches fire, burning PV panels can contribute to an already very hazardous environment. Two common polycrystalline silicon PV samples A and B were selected with their chemical composition analysed by the Fourier transform infrared spectroscopy with justification by X‐ray photoelectron spectroscopy results. Sample A was confirmed to be a silicate product with polyurethane adhesive, and sample B has epoxy resin and is likely to have flame retardant as claimed. Thermal analysis by heating the samples was carried out using thermogravimetric analysis and thermogravimetric analysis coupled with infrared spectroscopy. The fire behaviour was then studied by a cone calorimeter under radiative heat fluxes from 10 to 70 kWm^?2. Three key parameters representing flashover propensity, total heat release per unit area and smoke toxicity hazard were obtained from the cone calorimeter tests for ranking the thermal and smoke hazards. The thermal hazards of both PV samples are low, at least during the early stage of a fire without flame acting directly on the sample. However, vast quantities of smoke were emitted from burning PV panels under high heat fluxes. Copyright © 2016 John Wiley & Sons, Ltd.     

Size-Resolved Anhydrosugar Composition in Smoke Aerosol from Controlled Field Burning of Rice Straw

A field study was conducted to determine the effects of ambient conditions and burning practices of rice fields in Taiwan on the chemical and physical characteristics of the smoke aerosol. Rice straw was burned on an actual rice field under typical conditions and smoke particles were collected immediately downwind of the field over the full particle size spectrum. Here we present size distributions of levoglucosan, a common molecular tracer for biomass burning, as well as detailed concentration patterns of three anhydrosugars, including mannosan, and galactosan, in addition to smoke aerosol concentrations of inorganic ions and carbonaceous species. The generated smoke aerosol was characterized by a high OC/EC ratio (10) and a large fraction of potassium (K⁺) and chloride (Cl^?) ions at a Cl^?/K⁺ ratio of 2. Levoglucosan showed a distinct bimodal distribution in the smoke particles with a large fraction (up to 56%) of the total levoglucosan mass observed in very large particles (PM _{> 10} ). The prevailing ambient conditions (such as relatively high humidity), atmospheric processes (e.g., particle coagulation, hygroscopic growth, and deposition), the specific burning practices of rice fields in Taiwan (slow burning of straw spread in thin layers on the ground), as well as the inherent properties of rice straw likely influenced the particle size characteristics of the smoke tracer. Moreover, the relative abundance of the three biomass burning tracers showed a unique pattern (in good agreement with previous chamber burn measurements): levoglucosan-to-mannosan ratios were distinctly higher (with an average value of 27) than those observed for other types of biomass, such as softwood, hard wood, peat, or leaves, in previous studies. Such chemical fingerprint may be used in source apportionment studies for the assessment of contributions from the combustion of specific types of biomass.     

The effect of pyrolysis and combustion temperatures on smoke density

The small-scale smoke testing apparatus now proposed as a standard in France under the designation NF–T51–073 measures the total obscuration from a stream of smoke generated from a small sample. Although like other small-scale fire tests, it is not claimed to be of relevance to real fire situations, it is possible by varying the temperature over a wide range (200–900°C) to obtain a plot of specific optical density for various materials which broadly corresponds with general experience and certain other smoke tests. The plots show that nearly all flammable substances give a rapid rise in smoke opacity in the 350–500°C region above which there is always a steep drop sometimes to smoke densities of virtually zero. Apart from one or two synthetic materials which show a very low smoke density through-out, there is no general trend as between natural and synthetic substances. Oxygen depletion which often occurs in a real fire situation has some effect on the smoke density but it is not a major one. On the other hand, in some cases reheating the smoke can have quite a dramatic effect, due very probably to further pyrolysis and combustion.     

Characterization of the fire environments in central offices of the telecommunications industry

Eight free burning and two sprinklered fire tests were performed with electrical cable trays and live digital switch racks in a large enclosure to simulate telecommunications central office (TCO) fires started by electrical overheating. Very‐slow‐growing (non‐flaming), slower‐growing (partially flaming) and low‐intensity‐faster‐growing (flaming) fires releasing gray‐white, gray, and black smoke, respectively, were observed in the tests. Under quiescent conditions present in the unvented enclosure fire tests for cables, very‐slow‐growing fires were detected in about 1452 s, whereas the slower‐growing fires were detected in about 222 s by commercial fire detectors. Under ventilation conditions typical of TCOs, detection times were very similar for the five types of commercial TCOs fire detectors used in the tests. The average detection times for slower‐growing fires (cable fires) and low‐intensity‐faster‐growing fires (digital switch rack fires) were 242±17% and 249±11%s respectively. The TCO procedures to reduce smoke damage from fires (on fire detection, inlet ventilation flow is turned off and exhaust flow is turned on) were found to be beneficial. The extent of smoke damage decreased significantly with an increase in the exhaust flow rate. The chloride ion mass deposition suggested that equipment recovery would be possible in the smoke environment if the cable vapor concentration could be reduced below about 3 g/m³. The metal corrosion rate was found proportional to the 0.6th power of the smoke concentration, similar to that found for the corrosion of metal surfaces exposed to aqueous solutions of HCl and HNO₃ and for acid rain with no protective layer at the surface. Sprinkler water was found to wash down the smoke deposits on the surfaces with little indication of corrosion enhancement. Copyright © 2003 John Wiley & Sons, Ltd.     

Burning characteristics of building products in the light of European harmonization

Countries in the EU are in the process of changing over to a harmonized reaction‐to‐fire classification based on the Construction Products Directive (CPD, 89/106/EC) relating to construction products. It aims to remove technical barriers to trade arising from national laws and regulations, thus enabling the creation of a single European market in construction products. To scrutinize scenario‐dependent effects on burning characteristics, representative building products have been tested using alternative test methods simulating more or less identical fire stages. The test methods were the SBI test and ISO 5658‐4. Comparison of the methods also allowed evaluation with regard to the valid risk assessment of the classification system to be expected. A correlation between different test procedures may be expected as far as the main fire parameters are concerned. The quantitative generation of smoke is, however, primarily a function of the burning rate. Qualitatively smoke density depends on the decomposition conditions — temperature and ventilation — so the time during which a product is involved in the fire is essential for the assessment of smoke density. To quantify the relevant parameters, systematic investigations were made with beech using test procedures ASTM E 662 and DIN 53436/7. Copyright © 2000 John Wiley & Sons, Ltd.     

Fire and rice husk particleboard

Experimental investigations were made to assess the fire behaviour of rice husk particleboard, a potential substitute for wood particleboards. Releveant fire properties, namely non-combustibility, ignitability, fire propagation index, surface spread of flame classification, specific optical density of smoke generated, flammability and flame penetration were determined in accordance with existing standard methods. In this paper the salient results obtained are discussed.     

Quantification of smoke produced at fires. Test methods for smoke and methods of expressing smoke evolution

A limited review of the methods available for measuring smoke from burning materials has been carried out in order to define a method that could provide data for calculating smoke load. Results available in the literature have been expressed on a common basis and augmented by further experimental work carried out with a furnace similar to the National Bureau of Standards test furnace and a smoke-containment volume (13.4m³) closer to that used by the Fire Research Station test. Encouraging agreement between the data have been found for methods which allow smoke to become diluted and to accumulate. Agreement could be improved if an allowance was made for flaming being extinguished at different times in a test, dependent on thermal stress and oxygen concentration, even when a pilot light is present. To help express the results clearly, a new unit for smokiness is proposed—the obscura (ob) defined as 1 ob=1 dB light attenuation per metre of light path. The smoke-producing potential of different materials (D_o) is then expressed in units of obscura—cubic metres per gram of volatiles produced during the fire condition (ob m³ g ^?1).     

Effect of calcium carbonate filler on the fire and smoke properties of moulded polypropylene

‘Oxygen Index’, ‘Rate of Burning and Extent of Burning of Self-supporting Plastics in a Horizontal Position’ and ‘Vertical Flammability’ tests were used for examination of polypropylene copolymer HW 607M and the same copolymer filled with 40% w/w calcium carbonate. Room-scale studies were also carried out using a range of standard ignition sources. In the latter tests, measurements of the levels of smoke generated in the test chamber were monitored continuously, and intermittent measurements were made of the carbon monoxide concentrations. Small-scale testing showed that addition of the filler to the polypropylene raised the limiting oxygen index of the polymer from 17.8 to 20.3, which is only marginally lower than the oxygen concentration in ambient air (20.9); this introduces the possibility of a filled polypropylene which is not ignitable in air. However, the results of the UL94 and ASTM D635 tests did not show significant differences in flammability and rates of vertical and horizontal flame spread as between the two materials, through the unfilled polymer produced extensive burning droplets early in both tests whilst the filled polymer did not. Such droplets can spread fires to floor coverings, so that the filled plastic might be preferable in application. In our laboratory tests, the filled samples gave considerably lower smoke generation than the unfilled ones. At high heat fluxes they generated considerably less smoke than (smaller) unfilled samples containing the same mass of polymer. This suggests that the calcium carbonate has specific smoke-suppressant activity and is not merely acting as a polymer diluent. In larger-scale tests, unfilled samples were readily ignited by a domestic match, whilst the filled samples required an ignition source of 43 kJ (some six times greater than the match source) in order to light them and sustain ignition. The filled polymer did not melt on ignition and there was no lateral spread of flame from the sample. Smoke generation was considerably lower, the average optical density at maximum obscuration being 0.27, compared with 0.84 for the unfilled control. In particular, smoke suppression achieved by use of calcium carbonate at higher heat-flux levels is considerably greater than that expected for an inert diluent.     

An assessment of PVC smoke

The conventional test method for evaluating the potential of a material to produce smoke in a real fire is the NBS Smoke Density Chamber. However there are major problems with this approach. These include foremost the fact that its results do not correlate with those of real fires. Furthermore, materials that melt and drip are able to achieve a favorable, but misleading, evaluation because a significant fraction of the sample escapes the burning process. Another problem is that the test takes no account of the role the rate or extent of material burning plays in controlling the smoke density in a real fire situation. The physical problems are solved by material smoke production evaluation techniques based on measurements from the Cone Calorimeter rate of heat release apparatus, which has been developed by the National Bureau of Standards. A smoke parameter has been developed, calculated from cone calorimeter measurements, which reflects the smoke hazard of a real fire. The smoke evolution characteristics for a series of rigid thermoplastic materials have been measured using the cone calorimeter and the smoke parameter concept. The results demonstrate that due to its tendency to resist ignition and to burn very slowly, PVC would produce very little smoke in a real fire situation. Of the 15 materials tested, the expected real fire smoke performance characteristics of PVC were superior to those of all other materials except one.     

Empirical prediction of smoke production in the ISO Room Corner Fire Test by use of ISO Cone Calorimeter Fire Test data

The combustion conditions in the ISO Room Corner Fire Test make it possible to predict full scale smoke production by use of prediction models and bench scale fire test data procured by the ISO Cone Calorimeter Fire Test. The full scale smoke production is governed by the type of material burning only if the rate of heat release is less than 400–600 kW. For higher rates of heat release, the smoke production is more governed by the combustion conditions. The influence of the combustion conditions on the full scale smoke production reduces the possibilities of smoke prediction to materials causing flashover within 10 min in the ISO Room Corner Fire Test. The smoke to heat ratio S_Q (m²MJ) was used to compare smoke production between the scales. In general, the comparison revealed that the smoke yield was significantly less in full scale than in bench scale, especially for the plastics. Plastics do yield more smoke than wood based materials in both scales, but the differences in full scale are not as extreme as indicated by the bench scale smoke data. No simple correlations between the scales seem to exist. Multiple regression studies on empirical smoke prediction models show that bench scale fire parameters can be used to predict full scale fire performance. A quite accurate empirical smoke prediction model is presented for the group of materials which caused flashover within 10 min. The model predicts the full scale rate of smoke production at a rate of heat release of 400 kW. The presented results might be used to assess the fire safety hazard of visible smoke, but benchmarks of smoke hazard do not seem to exist. Thus further studies and agreement on safety levels and principles are needed for general visibility analysis concerning fire safety engineering purposes. Copyright © 1999 John Wiley & Sons, Ltd.     

Experimental investigation on fire smoke bifurcation flow in longitudinal ventilated tunnels

Investigation of smoke bifurcation flow has been receiving more attentions, however, delicate quantitative analyses on different regions of the bifurcation flow have rarely been addressed. In this study, a series of small-scale experiments were conducted to investigate smoke bifurcation flow in longitudinal ventilated tunnels. Results show that when longitudinal ventilation velocity increases to a certain value, the smoke bifurcation phenomenon emerges, and a low-temperature region forms in the center of the tunnel. Similar to the natural conditions, smoke development under relatively strong ventilation can also be subdivided into four regions. With the increase of ventilation velocity, the ceiling impact region, side wall impact region, and convergence region of two smoke streams move further downstream, indicating that the bifurcation phenomenon becomes more evident. A simple model is proposed based on theoretical analysis and experimental phenomenon to predict two characteristic lengths of smoke bifurcation flow: the offset distance of ceiling impact region and the length of low-temperature region. Both characteristic lengths increase with ventilation velocity and can be well correlated with the dimensionless ventilation velocity defined in Equation (2) ( V^′ ). The results of this work could provide references for both tunnel ventilation designers and fire science researchers.     

Numerical analysis of smoke flow under the effect of longitudinal airflow in a tunnel fire

This study investigated the influence of the longitudinal airflow on the smoke propagation in a tunnel by large-eddy simulation, which is now widely applied to study the turbulent flow. The smoke movement characteristics were studied in detail, with varying the longitudinal airflow in the tunnel. Six fire scenarios have been simulated with Fire Dynamics Simulator (FDS) and the results of the longitudinal distribution of CO concentration, temperature distribution, interface height, stratification, and the efficiency of smoke extraction in the tunnel have been analyzed to evaluate the different fire cases. FDS predicted a CO concentration distribution compared to calculated values using the Hu model. Furthermore, the predicted maximum smoke temperatures are compared to those given by the Kurioka model. A reasonably good agreement has been obtained for both models. The obtained results showed that the increase of the forced airflow velocity has for results a loss of stratification and significant decrease in the efficiency of extraction.     

Diesel exhaust particulate induces pulmonary and systemic inflammation in rats without impairing endothelial function ex vivo or in vivo

Background

There is growing evidence that particulate air pollution derived from wood stoves causes acute inflammation in the respiratory system, increases the incidence of asthma and other allergic diseases, and increases respiratory morbidity and mortality. The objective of this study was to evaluate acute respiratory effects from short-term wood smoke exposure in humans. Twenty non-smoking atopic volunteers with normal lung function and without bronchial responsiveness were monitored during three different experimental exposure sessions, aiming at particle concentrations of about 200?μg/m³, 400?μg/m³, and clean air as control exposure. A balanced cross-over design was used and participants were randomly allocated to exposure orders. Particles were generated in a wood-burning facility and added to a full-scale climate chamber where the participants were exposed for 3 hours under controlled environmental conditions. Health effects were evaluated in relation to: peak expiratory flow (PEF), forced expiratory volume in the first second (FEV₁), and forced vital capacity (FVC). Furthermore, the effects were assessed in relation to changes in nasal patency and from markers of airway inflammation: fractional exhaled nitric oxide (FENO), exhaled breath condensate (EBC) and nasal lavage (NAL) samples were collected before, and at various intervals after exposure.

Results

No statistically significant effect of wood smoke exposure was found for lung function, for FENO, for NAL or for the nasal patency. Limited signs of airway inflammation were found in EBC.

Conclusion

In conclusion, short term exposure with wood smoke at a concentration normally found in a residential area with a high density of burning wood stoves causes only mild inflammatory response.     

The Use and Application of Red-Phosphorous Pyrotechnic Composition for camouflage in the infrared region of radiation

Under laboratory conditions, there were detected burning products of pyrotechnic compositions based on red phosphorus with epoxy resin being especially trihydrogenphosphoric acid, tetrahydrogendiphosphoric acid and mixture of cyclo-triphosphoric acid, cyclo-tetraphosphoric acid and cyclo-hexaphosphoric acid. In burning products of pyrotechnic composition with magnesium added there was detected only cyclo-triphosphoric acid among cyclic derivatives. Phosphorous aerodispersions generated from smoke grenades containing these pyrotechnic compositions under field conditions could screen infrared radiation (0.82 μm, 3–5 μm, 10.6 μm wavelengths) with high efficiency. Examined pyrotechnic compositions of plasticized red phosphorus with epoxy resin proved to be suitable for smoke grenades of modern construction with both fast and slower generation of phosphorous aerodispersion.     

Polymers of vinylphosphonic acid,acrylonitrile, and methyl acrylate and their nanofibers

In this study, a small amount of vinylphosphonic acid was used to produce fire-retardant copolymers and terpolymers from acrylonitrile and methyl acrylate. The structures of copolymer and terpolymers were elucidated by ¹H-NMR and phosphorous analysis. Thermal decomposition of vinylphosphonic acid-containing copolymers and terpolymers started at lower temperatures than of poly(acrylonitrile-co-methyl acrylate). Methyl acrylate contributes to the thermal resistance of the terpolymers. Poly(acrylonitrile-co-methyl acrylate-co-vinylphosphonic acid) with a phosphorous content about 0.25% burned at a slower rate and emitted less smoke compared to poly(acrylonitrile-co-methyl acrylate). The burning tests showed that both copolymer and terpolymers containing vinylphosphonic acid behaved as a fire-retardant polymer. The phosphonate and phosphonic acid groups in the copolymer and terpolymers accelerate the cyclization of nitrile groups and inhibit the fire in the gas phase. Nanofibers were successfully produced by the electrospinning method from the copolymers and terpolymers containing vinylphosphonic acid moiety.     

PP/Al(OH)_3/Mg(OH)_2/ZB复合材料阻燃性能的研究

测试了PP/Al(OH)3/Mg(OH)2/ZB、PP/Al(OH)3/Mg(OH)2/ZB/CaCO3和PP/Al(OH)3/Mg(OH)2/ZB/CaCO3/POE复合材料的阻燃性能。结果表明:随着阻燃剂用量的增加,氧指数升高,而燃烧速率和烟密度下降,且阻燃剂的加入对延缓燃烧速率的作用效果十分显著;相同配方下试件越厚燃烧速度越慢,且随阻燃剂用量的增加,试件越厚燃烧速率下降的幅度越慢;纳米CaCO3及POE的加入可以增大氧指数,降低烟密度,有利于阻燃,但同时也会使水平燃烧速率略微增大。