Showing papers in "Fire and Materials in 2007"

Development of fire-retarded materials—Interpretation of cone calorimeter data

Abstract: There is little consensus within the fire science community on interpretation of cone calorimeter data, but there is a significant need to screen new flammability modified materials using the cone calorimeter. This article is the result of several discussions aiming to provide guidance in the use and interpretation of cone calorimetry for those directly involved with such measurements. This guidance is essentially empirical, and is not intended to replace the comprehensive scientific studies that already exist. The guidance discusses the fire scenario with respect to applied heat flux, length scale, temperature, ventilation, anaerobic pyrolysis and set-up represented by the cone calorimeter. The fire properties measured in the cone calorimeter are discussed, including heat release rate and its peak, the mass loss and char yield, effective heat of combustion and combustion efficiency, time to ignition and CO and smoke production together with deduced quantities such as FIGRA and MARHE. Special comments are made on the use of the cone calorimeter relating to sample thickness, textiles, foams and intumescent materials, and the distance of the cone heater from the sample surface. Finally, the relationship between cone calorimetry data and other tests is discussed. Copyright © 2007 John Wiley & Sons, Ltd.

Cone calorimeter analysis of UL-94 v-rated plastics

Abstract: Cone calorimeter analysis was conducted on 18 thermoplastics with different UL-94 vertical burn test (V) ratings. Ratings varied from V-0 to no rating (NR), and the types of thermoplastics included were polycarbonate (PC), acrylonitrile–butadiene–styrene (ABS), PC/ABS blends, high-impact polystyrene (HIPS), polypropylene (PP), and poly(vinyl chloride) (PVC). Our analysis of the cone calorimeter data found that there were correlations between UL-94 V rating and some cone calorimeter measurements (peak heat release rate (HRR) average and HRR at 60 s) and no relationship for other measurements (time to ignition and total heat release). However, no precise correlation was found due to significant differences in flame retardant mechanism and polymer fuel energy values. In this paper, we seek to explain further why a broad quantitative relationship between UL-94 V and cone calorimeter remains elusive, and also to show how the cone calorimeter can be used to understand why a material passes or fails a particular UL-94 V rating. Copyright © 2006 John Wiley & Sons, Ltd.

Thermal degradation behaviors and flame retardancy of PC/ABS with novel silicon-containing flame retardant

Abstract: A novel flame retardant (DVN) containing silicon, phosphorus, and nitrogen has been synthesized from the reaction of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), vinylmethyldimethoxy silane (VMDMS) and N-β-(aminoethyl)-γ-aminopropyle methyl dimethoxy silane (NMDMS), then incorporated into polycarbonate/acrylonitrile butadiene styrene (PC/ABS) alloy. The flame retardancy of PC/ABS/DVN is evaluated by cone calorimeter and limited oxygen index (LOI) and the thermal degradation behavior is investigated by thermogravimetric analysis under nitrogen and air. The PC/ABS/DVN sample was thermally degraded at 400°C for different amounts of time and studied by Fourier transform infrared spectroscopy to better understand the mechanism of flame retardancy. The results show that the thermal stability and flame retardancy of PC/ABS are improved by incorporation of DVN. Scanning electric microscopy results show that the outer surface of the char layer of PC/ABS/DVN after the LOI test is smooth and the internal structure is like swollen cells, which benefits the flame retardancy of PC/ABS. Copyright © 2007 John Wiley & Sons, Ltd.

Influence of gypsum board type (X or C) on real fire performance of partition assemblies

Abstract: This paper compares the responses of wall-size partition assemblies, composed of either type X or type C gypsum wallboard panels over steel studs, when each was exposed to an intense room fire. The exposures lasted from the time of ignition to beyond flashover. Heat flux gauges provided time histories of the energy incident on the partitions, while thermocouples provided data on the propagation of heat through the partitions and on the progress toward perforation. Visual and infrared cameras were used to image partition behaviour during the fire exposure. Contraction of the seams of the two types of assemblies occurred under similar thermal conditions on the unexposed surface. However, there were noticeable differences in cracking behaviour. Reduced scale experiments were performed in conjunction with the real-scale fire tests to provide insight into the contraction and cracking behaviour of the different gypsum board types. Results obtained from these experiments are discussed.

Assessing the performance of intumescent coatings using bench-scaled cone calorimeter and finite difference simulations

Abstract: A method was developed to assess the heat insulation performance of intumescent coatings. The method consists of temperature measurements using the bench-scaled experimental set-up of a cone calorimeter and finite difference simulation to calculate the effective thermal conductivity dependent on time/temperature. This simulation procedure was also adapted to the small scale test furnace, in which the standard time–temperature curve is applied to a larger sample and thus which provides results relevant for approval. Investigations on temperature and calculated effective thermal conduction were performed on intumescent coatings in both experimental set-ups using various coating thicknesses. The results correspond to each other as well as showing the limits of transferability between both fire tests. It is shown that bench-scaled cone calorimeter tests are a valuable tool for assessing and predicting the performance of intumescent coatings in larger tests relevant for approval. The correlation fails for processes at surface temperatures above 750°C, which are not reached in the cone calorimeter, but are attained in the small scale furnace set-up. Copyright © 2006 John Wiley & Sons, Ltd.

The effectiveness of magnesium carbonate-based flame retardants for poly(ethylene-co-vinyl acetate) and poly(ethylene-co-ethyl acrylate)

Abstract: In this report we outline recent work on the evaluation of magnesium carbonate-based flame retardants for polymers commonly used in halogen-free flame retardant wire and cable applications: poly(ethylene-co-vinyl acetate) (EVA) and poly(ethylene-co-ethyl acrylate) (EEA). Natural magnesium carbonate (magnesite), synthetic magnesium carbonate (hydromagnesite), and hydromagnesite/huntite blends were combined with EVA or EEA and tested for flame retardancy effectiveness with the cone calorimeter. The flammability results showed that the effectiveness of these carbonates was polymer dependent, suggesting that polymer degradation chemistry played a role in the flammability reduction mechanism. Hydromagnesites were, in general, more effective in reducing flammability, being comparable in performance to magnesium hydroxide. Finally, we report some polymer–clay (organically treated montmorillonite and magadiite) + magnesium carbonate flame retardant results which showed that the nanocomposite yielded mixed results. Specifically, the polymer–clay nanocomposite samples did not always yield the greatest reductions in peak heat release rate. Copyright © 2007 John Wiley & Sons, Ltd.

Manikin test for flame engulfment evaluation of protective clothing : Historical review and development of a new ISO standard

Abstract: The overall performance of a firefighter turnout suit can only be evaluated using both bench-scale tests and an assessment based on an instrumented manikin under defined, close to real-life conditions in a laboratory. Using manikins in rating protective clothing has already a long history which will be reflected in this paper. Efforts all over the world to reproduce a flame engulfment situation in a laboratory are currently being combined in a new draft international standard (ISO/DIS 13506.3). A round robin test showed an acceptable reproducibility for this method based on a manikin test and a gas burner system. An overview of existing measurement systems and the results of this round robin are discussed and possible improvements for the standard flame engulfment test method are proposed.

Effect of specimen size and loading conditions on spalling of concrete

Abstract: Different qualities of concrete have been fire tested using different geometries of the specimens as well as different load levels and load configurations. The main objective with the study was to examine a test methodology consisting of a full-scale test and different small scale-tests for determining the probability of spalling and the amount of spalling of fire exposed concrete structures. A reference specimen was defined as a one-sided fire exposed slab with the dimensions 1800 × 1200 mm2 giving an exposed area of 1500 × 1200 mm2. A number of concrete qualities with different probabilities for spalling, were tested using the reference specimen. These tests showed that the reference specimens worked well giving the expected test results. Small specimens were manufactured in different shapes with the same concrete as the one used in the reference tests. These small specimens were tested either at the same time as the reference specimens in the large furnace or afterwards on a small-scale furnace where the fire exposed surface was 450 × 360 mm2. The test results clearly show the increased probability and the increased amount of spalling by using external compressive loading. The results also show that by using pre-stress through bars or wires the load can be lost due to heating of the bars/wires which results in a decreased amount of spalling. The boundary of the specimen also affects the amount of spalling. The spalling around the edges was in all tests less than the spalling on the central parts of the exposed area. It could also be noted that the spalling did not pass completely through any of the specimens. The reason for this is probably that the water/vapour could migrate out from the unexposed surface of the specimen. Copyright © 2006 John Wiley & Sons, Ltd.

Flame‐retardant finishing of cotton fleece fabric: part I. The use of a hydroxy‐functional organophosphorus oligomer and dimethyloldihydroxylethyleneurea

Abstract: Cotton fleece has become a popular fashion in recent years. However, most of the 100% cotton fleece fabric is not able to meet the federal flammability standard (‘16 CFR Part 1610: Standard for the Flammability of Clothing Textiles’) without chemical treatment. In this research, we investigated the use of the combination of a hydroxy-functional organophosphorus oligomer (HFPO) as the flame-retarding agent and dimethyloldihydroxylethyleneurea (DMDHEU) as the binder to reduce the flammability of cotton fleece. We found that HFPO is effective in reducing the flammability of the cotton fleece whereas DMDHEU enhances the effectiveness of HFPO due to phosphorus–nitrogen synergism. The flammability as well as other properties of the treated cotton fleece is affected by both the concentration of HFPO and that of DMDHEU. The cotton fleece treated with HFPO/DMDHEU passes the federal flammability standard and shows high strength retention with little change in fabric whiteness and hand. We also found that the flame-retardant finishing system is durable to multiple home launderings. The combination of HFPO and DMDHEU has the potential to become a practical flame-retardant finishing system to reduce the flammability of cotton fleeces. Copyright © 2006 John Wiley & Sons, Ltd.

Detailed determination of smoke gas contents using a small-scale controlled equivalence ratio tube furnace method

Abstract: A series of tests including seven different materials and products have been conducted using a controlled equivalence ratio tube furnace test method. The main objective of the tests was to determine yields of fire-generated products at defined combustion conditions. The tube furnace test method was set up and run in close agreement with that described in BS 7990:2003. At the time of experimental work the new tube furnace method was in the process of becoming an international standard. It was thus of interest to make an assessment of the capability of the method for determining production yields of important toxic fire products from different types of materials and products. The test series included solid wood, flexible polyurethane (PUR), fire-retarded rigid PUR, a polyvinyl chloride (PVC) carpet, a high-performance data cable with fluorine-containing polymer matrix, a PVC-based cable sheathing material and fire-retarded polyethylene cable insulation material. Duplicate tests were generally conducted at both well-ventilated and vitiated combustion conditions with these materials. The smoke gases produced from the combustion were quantified for inorganic gases by FTIR technique in all tests. A more detailed analysis of the smoke gases was conducted for some of the materials. This extended analysis contained a detailed assessment of organic compounds including, e.g. volatile organic compounds, isocyanates, aldehydes and polycyclic aromatic hydrocarbons. The analysis further included measurement of the size distribution of fire-generated particles for some of the materials. The quantification of toxic inorganic gases produced by combustion at both well-ventilated and vitiated conditions was successful regarding repeatability and stability. Typical yields for the two fire stages investigated were determined for a wide range of materials and products. The detailed analysis of organic compounds further corroborated that the new tube furnace method can replicate defined combustion conditions. Copyright © 2007 John Wiley & Sons, Ltd.

Measuring chemical heat production rates of biofuels by isothermal calorimetry for hazardous evaluation modelling

Abstract: Biofuels are commonly stored in large stacks that may heat up and self-ignite from microbiological and chemical heat production This paper shows how isothermal (heat conduction) calorimetry can be used to measure heat production rates of biofuels at relatively low temperatures close to where self-heating starts to become a problem Measurements can be made to assess how the reaction rate is a function of such factors as temperature, extent of reaction, oxygen pressure, water content and the presence of catalytic compounds In the present paper, measurements on pellets made of wood and bark are presented together with an analysis of how the reaction rate of the bark pellets depends on the oxygen pressure It is also shown that 1% iron or copper ions increased the reaction rate of wood pellets by a factor of three Copyright (c) 2006 John Wiley & Sons, Ltd (Less)

Federal investigation of the evacuation of the World Trade Center on September 11, 2001

Abstract: This paper presents the findings of the NIST World Trade Center Investigation describing the occupant evacuation of WTC 1 and WTC 2 on September 11, 2001. The egress system, including stairwells and elevators, is described along with the evacuation procedures. The population in WTC 1 and WTC 2 on September 11, 2001 at 8:46 a.m. is enumerated and described, where the background of the population was relevant to the subsequent evacuation, including training, experience, mobility status, among others. The progress of the evacuation of both towers is described in a quasi-chronological manner. A decedent analysis explores where occupants were located when each tower was attacked. Multiple regression models were built to explore the sources of evacuation initiation delay (why people did not immediately start to leave the building), as well as stairwell evacuation time (how long the average occupant spent in the stairwells per floor). Issues identified as contributing to either slowing or aiding the evacuation process were explored. Egress simulations provided context for estimating how long WTC 1 and WTC 2 would have taken to evacuate with different populations, using three different models, and subject to different assumptions of damage to the building.

Performance of a non‐load‐bearing steel stud gypsum board wall assembly: Experiments and modelling

Abstract: A gypsum wall assembly was exposed to an intense real-scale compartment fire. For the wall assembly, temperatures were measured at the exposed face, within the stud cavity, and at the unexposed face during the fire exposure. Total heat flux gauges were used to measure the temporal variation of the energy incident on the walls, and cameras, both visual and infrared, were used to image the unexposed face of the wall assembly during the fire exposure. The behaviour of the wall assembly under the fire load is discussed as are current model results for a simulation of the fire test.

Survey of small‐scale flame spread test results of modern fabrics

Abstract: The flammability of apparel worn on a person has one of the highest ratios of fire fatalities per fire, and there are few statutory requirements. A series of evaluations was conducted on the flammability of 50 fabrics (both cellulosic and thermoplastic) using the (now withdrawn) NFPA 701 small-scale test. The fabrics covered a broad range of areal densities (weights) and many were not intended for apparel. A series of conclusions were reached. In particular, it is apparent that the following primary correlation exists between fabric weight and flammability: the heavier the fabric the better it behaves in a fire. Secondarily, however, the type of fabric also strongly affects this conclusion. This paper presents the results of the testing and offers an analysis.

Modelling thermal degradation of composite materials

Abstract: A one–dimensional, transient thermal degradation heat transfer model for the response of composite materials when exposed to fire is presented. The model can handle layers of different materials. Material properties are functions of temperature. The reaction can be specified using Arrhenius-type parameters or by inputting a density–temperature relationship determined by any experimental technique such as thermogravimetric analysis. The model is validated against the experimental data presented in Boyer's 1984 dissertation. Overall, the model provides excellent agreement with the experimental data. It is shown that very little difference is found between results arrived at by Arrhenius kinetics and results obtained by specifying the easier to measure density–temperature relationship. From this it is concluded that this technique is a viable alternative to Arrhenius-type models. Copyright © 2006 John Wiley & Sons, Ltd.

The effect of accelerated ageing of building wires

Abstract: The fire performance of two electric cables (building wires) designed for indoor use has been tested, both as new products and after accelerated thermooxidative ageing. The cables were aged for a maximum time of 16.5 weeks at 80°C. The cables are commercially available, and were constructed using a PVC material in one case and a non-halogenated polyolefin-based material, called Casico, in the other. The effects of ageing on the fire performance of the cables, and the chemical changes that have caused the observed fire behaviour, have been investigated and are discussed. Special attention is paid to the behaviour of the plasticizers that are used in the PVC cable, and how the fire behaviour is affected by the loss of plasticizers from the cable and by the migration of plasticizers between the parts of the cable (insulation, bedding and sheathing).

Spontaneous ignition in storage and production lines : Investigation on wood pellets and protein powders

Abstract: Three materials were tested in small-scale baskets of cubic dimensions and analyses were performed based upon the results according to the Frank-Kamenetskii (FK) method and the crossing point (CP) method. Comparison of the FK method and the CP method results was performed additionally. The activation energy E and the QA value were found. The relationship between critical ambient temperature and the storage size was determined as well as the relationship between CAT and time to maximum thermal runaway for the materials.

Reconstruction of an arson hospital fire

Abstract: An arson fire in a Swedish psychiatric detention clinic led to the death of two patients and injuries to many more. Rescue personnel were quick to go into the building on fire but had difficulties finding their way due to a very heavy smoke. The reconstruction made, indicates that a too easily ignitable mattress provided heat and radiation enough to ignite a PVC flooring material that then became the main source for fire and smoke. Analysis of soot from the fire site and measurements during the reconstruction show that the fire smoke contained large amounts of irritants that might have had an impact on the tragic outcome. In fact, comparing the toxicity of smoke gases produced during the reconstruction, based on different "toxicity indicators", suggests that irritants in the fire smoke were as dangerous as or even more dangerous than the common asphyxiate type of gases present, CO and HCN.Another suggestion from the reported work is that the importance of flooring material for enclosure fire development might be overlooked. The reconstruction clearly demonstrates that the tragic fire would not have happened if the requirements for the flooring material had been the same as for the walls and ceiling materials.

A pyrolysis model of charring materials considering the effect of ambient oxygen concentration

Abstract: In this paper, a one-dimensional integral model is developed to describe the processes involved in the transient pyrolysis of a semi-infinite charring material subjected to a constant radiant heat flux. In this model, a special factor that shows the effect on pyrolysis is considered, i.e. under the oxygen-containing atmosphere. The model tracks the char layer depth, thermal penetration depth, surface temperature and mass loss rate. Comparison with experimental results demonstrates that the predictions of the mass loss rate and temperature profile within the charring material are in good agreement with the experiment. Copyright © 2007 John Wiley & Sons, Ltd.

Prediction of fire classification for wood based products. A multivariate statistical approach based on the cone calorimeter

Abstract: Wood has long traditions as a building material, and is often used in construction elements, and as interior and exterior surfaces in the Nordic countries. In most applications, there are reaction to fire requirements to products used as surfaces, e.g. in escape routes and larger public spaces. Most wood products will therefore have to be treated with fire retardant (FR) agents to fulfil the strict requirements to properties connected to heat release and flame spread. Unfortunately, FR agents usually also increase the smoke production, as they cause a more incomplete combustion of the wood. The wood product manufacturers seek to find the optimal amount of FR additives where both heat release and smoke production in the classifying test are within the requirements given in the building regulations. This paper describes models for prediction of the European reaction to fire classes of wood products. The models are based on multivariate statistical analysis, and use test results from the cone calorimeter test as input. The presented models are, with very good precision, able to predict which Euroclass and additional smoke class a wood based product would obtain if it were to be tested in the single burning item test.

Flammability studies of sodium thiosulphate or metabisulphite impregnated wood using cone calorimeter

Abstract: Spruce wood boards impregnated with Na 2 S 2 O 3 or Na 2 S 2 O 5 were studied with the cone calorimeter. The presence of Na 2 S 2 O 3 lowered the average heat release rate in comparison to untreated material. The total amounts of CO and CO 2 production were reduced by the treatment and also the specific extinction area and mass loss rate decreased. Washing of the salt from the material with water caused partial loss of the properties. Addition of the second impregnation step using acids (HCOOH, H 3 BO 3 or H 3 PO 4 ) resulted in the fixation of the sulphur in wood, but gave not the results of single-step modification for thiosulphate. With Na 2 S 2 O 5 and without acid, the CO and time-to-ignition values were higher and average heat release rate smaller in comparison to unmodified material. Combined one step Na 2 S 2 O 5 /H 3 BO 3 treatment lowered the CO, CO 2 and specific extinction area values in comparison to the modification with Na 2 S 2 O 5 , similarly like it was observed for Na 2 S 2 O 3 /H 3 BO 3 two-step-treatment. According to time-to-ignition values, Na 2 S 2 O 5 alone at 5% addition is a better flame retardant than Na 2 S 2 O 3 at 7%, but the effect is diminished at 10% amount or presence of acids. The total smoke release curves showed decrease due to modification in both phases of the process. Introduction of water washing as well as the acid treatment further lowered the values. The best results were achieved with 15% Na 2 S 2 O 3 -2% H 3 PO0 4 -H 2 O system. According to the total smoke release curve the specimen produced more than five times smaller amount of smoke than untreated material in the first phase of the process. It seams that the concentration of Na 2 S 2 O 5 is less affecting the properties than the synergistic effect of the Na 2 S 2 O 3 or Na 2 S 2 O 5 /H 3 BO 3 system. Although the level of smoke is low, the presence of elemental sulphur causes smaller times-to-ignition than on starting material.

Fire behaviour of plastic parts in electrical appliances - Standards versus required fire safety objectives

Abstract: For most categories of consumer electrical appliances, UL and IEC standards are typically the only widely used safety standards. A number of these standards are examined to determine if they incorporate technical provisions so that complying products would thereby meet expected fire safety objectives. Specifically, the provisions are examined governing plastic parts in electrical appliances. It is found that the standards do not consistently contain provisions that would, by themselves, suffice for a designer to produce a fire-safe design. Instead, major shortcomings exist, and if an appliance were designed solely to meet the standards and without any additional fire safety considerations, it would not have a reasonable degree of safety. A typical outcome could be a product which is readily ignitable by a small external ignition source and which shows fierce burning upon being so ignited. Furthermore, an internal electrical fault in such a product would probably not be contained within the unit and, rather, would spread to its easily combustible exterior surfaces and produce a similar, fierce fire. It is urged that UL and IEC standards be upgraded so that compliance with the standards would carry a reasonable assurance that fire safety objectives have been met. The recommendations made are intended to cover all UL and IEC appliance standards, not limited to the example cases considered.

Fire losses in selected property classifications of non-residential, commercial and residential wood buildings. Part 1: hotels/motels and care homes for aged

Abstract: In an attempt to evaluate the adequacy of building code requirements for selected classifications of non-residential, commercial and residential wood buildings, researchers at Forintek Canada Corp. have examined Canadian and American fire loss statistics and compared fire losses for the selected classifications of wood buildings with those for similar buildings of non-combustible construction. They have also examined causal factors associated with fires in those structures, extent of flame and smoke spread, ability of sprinkler systems and building construction to minimize fire losses, and outcomes of fire events. Because of the volume of information that was analysed, the results are being reported through three separate papers. This, the first, presents the "big picture" with respect to fire losses in the selected classifications of non-residential, commercial and residential structures, and discusses in detail fire losses for hotel/motel properties and care homes for the aged.

Prudent practices for the design and installation of heat-producing devices near wood materials

Abstract: The conditions required to cause ignition of solid wood materials under short-term heating are examined, and it is found that the appropriate ignition temperature applicable under these conditions is 250°C. It is then shown that ignition requirements are different if long-term heating is involved and that ignition can occur at exposure temperatures much lower than the ignition temperature pertinent to short-term heating. It is shown that hot surfaces of 77 °C or higher, if located for a long duration next to a wood member are liable to lead to its ignition in a self-heating mode. Recommendation is made that prudent practices for design or installation must also involve a suitable safety factor. Copyright © 2006 John Wiley & Sons, Ltd.

An experimental study of spontaneous ignition in storages of wood pellets

Abstract: This article focuses on experimental studies of self-heating characteristics of wood pellets. Controlled experiments have been conducted in physical scales from 1 dm3 to 4 m3 with wood pellets. Basket tests have been conducted according to the "crossing-point method" to derive kinetic data on the exothermic reactions responsible for self-heating and eventually spontaneous ignition. The kinetic data was used in the planning of the large-scale experiments for predictions of approximate critical temperatures. The experiments in the 1 m3 scale were set-up basically as an enlargement of the basket tests to obtain validation experiments with controlled boundary conditions in a reasonable large scale. Several experiments were conducted and spontaneous ignition was seen in the centre of the pellet bulk at an ambient temperature of 115C. The close to real-scale experiments with 4 m3 wood pellets filled in a 6 m high silo were not strictly self heating experiments, instead a core shaped heating element was allowed to initiate the pyrolysis in the pellets. Heat and gas production and transportation from the growing pyrolysis zone were mapped with a large number of measurement points in the pellets bulk and in the top of the silo. The experimental work conducted gave kinetic data on the exothermic reactions in wood pellets, insight in self heating processes, a link between different experimental scales and knowledge regarding possibilities for detection of fires in storages of wood pellets. (Less)

Temperature effects on the mass flow rate in the SBI and similar heat-release rate test equipment

Abstract: In various medium-to-large-scale fire test equipments like the ISO room corner test (RC), and more recently, the single burning item test (SBI) the mass flow rate measurement of the combustion gases plays a key role in the determination of the heat-release rate and smoke-production rate. With the knowledge of the velocity profile and the temperature of the flow, the mass flow rate is obtained by measuring the velocity on the axis of the duct. This is done by means of a bi-directional probe based on the pitot principle. However, due to the variation of the mean temperature and the temperature gradient in any cross section of the duct, introduced by ever changing combustion gas temperatures, the velocity nor the density profile are constant in time. This paper examines the resulting uncertainty on the mass flow rate. Copyright © 2006 John Wiley & Sons, Ltd.

Predicting HCl concentrations in fire enclosures using an HCl decay model coupled to a CFD‐based fire field model

Abstract: The amount of atmospheric hydrogen chloride (HCl) within fire enclosures produced from the combustion of chloride-based materials tends to decay as the fire effluent is transported through the enclosure due to mixing with fresh air and absorption by solids. This paper describes an HCl decay model, typically used in zone models, which has been modified and applied to a computational fluid dynamics (CFD)-based fire field model. While the modified model still makes use of some empirical formulations to represent the deposition mechanisms, these have been reduced from the original three to two through the use of the CFD framework. Furthermore, the effect of HCl flow to the wall surfaces on the time to reach equilibrium between HCl in the boundary layer and on wall surfaces is addressed by the modified model. Simulation results using the modified HCl decay model are compared with data from three experiments. The model is found to be able to reproduce the experimental trends and the predicted HCl levels are in good agreement with measured values.

Pneumatic impact ignition of selected polymers in high-pressure oxygen environments

Abstract: One likely cause of polymer ignition in high-pressure oxygen systems is adiabatic-compression heating of polymers, caused by pneumatic impact. This study investigates ignition by pneumatic impact of selected polymers in high-pressure oxygen environments. Six polymers commonly used in high-pressure oxygen systems were tested in a pneumatic-impact test system at 8.3–37.9 MPa oxygen pressures. The six polymers tested were Teflon®(polytetrafluoroethylene), Neoflon®(polychlorotrifluoroethylene), PEEK (polyetheretherketone), Zytel® 42 (Nylon 6/6), Buna N (nitrile rubber), and Viton® A (copolymer of vinylidene fluoride and hexafluoropropylene). This study shows that the ignition of polymers due to pneumatic impact could be initiated by a local heterogeneous reaction between the hot oxygen and the oxidation sites of the polymer, and proposes an ignition mechanism. Ignition susceptibility of a material to the pneumatic impact can be expressed by its ignition probability. The ignition probabilities of the six polymers at the various oxygen pressures are presented. There is no good correlation between the ignition probability and the autoignition temperature. Copyright © 2006 John Wiley & Sons, Ltd.

Numerical investigation of the error on flow measurements due to exhaust gas heating and cooling in the SBI-configuration

Abstract: The possible flow measurement error due to heating or cooling of exhaust gases in the Single-Burning-Item (SBI) test is estimated from numerical experiments. It is illustrated that there is no one-to-one correspondence between the velocity profile shape and the instantaneous Reynolds number, due to the time-dependent temperature and density profile evolution in the exhaust gas pipe. A non-ambiguous relation is found between the velocity profile shape and an ‘effective’ Reynolds number, based on the turbulent viscosity. Maximum variations of the velocity correction factors, relating the mean velocity to the velocity on the pipe axis, are found to be in the order of 2% for limiting circumstances for the SBI test. The primary effect is caused by instantaneous Reynolds number variations. The effect of heating or cooling of the flow by the hot or cold pipe is noticeable, too. The statements are proved to be valid independent of the computational grid, the turbulence model and the time steps taken to obtain the numerical solutions. Copyright © 2006 John Wiley & Sons, Ltd.

An Evaluation of the Self-Heating Hazards of Cerium(IV) Nitrated Treated Towels Using Differential Scanning Calorimetry and Thermogravimetric Analysis

Abstract: This study measured the Arrhenius kinetic parameters and heat of reaction using thermogravimetric analysis (TGA) and differential scanning calorimetric (DSC) for the combustion of untreated towels and towels treated with cerium(IV) nitrate. These parameters were used to calculate the self-heating parameters, M and P (Self-heating: Evaluating and Controlling the Hazard. Her Majesty's Stationery Office: London, 1984) and the critical pile sizes of the towels at several temperatures. The results from the TGA/DSC experiments support the conclusions by Beyler et al. (Fire and Materials 2005; 30:223–240) that the cerium(IV) nitrate treatment of towels significantly enhances the ignitability of the towels but that self-heating is not a hazard for normal temperature storage scenarios other than bulk storage. It was found that the kinetic reaction data measured by TGA and DSC are only useful for predicting the specific reaction hazard for materials stored above 100°C. A comparison of the self-heating parameters measured by oven and kinetic reaction data methods for a number of materials suggests that the kinetic reaction data overestimate the critical pile size at temperatures below 100°C. In addition, it was found that the kinetic reaction data measured by TGA can be used to determine the relative self-heating hazards for modified materials. TGA testing with towels saturated with a 0.5 N solution of cerium(IV) nitrate (Ce(NO3)4) in a 2.0 N solution of nitric acid, a 2.0 N solution of sodium nitrate in 2.0 N nitric acid and simple 2.0 N nitric acid, showed that the sodium nitrate and nitric acid treated samples reacted at the same temperatures as the untreated towels, while cerium(IV) nitrate markedly reduced the reaction temperature. These tests clearly point to the importance of the cerium(IV) ion as an oxidizing agent. Thus, the TGA testing provided in a matter of days, insights that would have required months of oven testing. Copyright © 2006 John Wiley & Sons, Ltd.