Journal of Fire Sciences recent issues

Enclosure Fires, Gravity Waves, and the Backdraft Problem

Eliasson, J., Guigay, G., Karlsson, B. — 2008-09-11

The air flow to an underventilated compartment fire often depends on the flow velocities in the gravity wave of cold air that feeds the fire with oxygen. This problem has been studied in laboratory experiments and by CFD simulations. The main problem seems to be whether mixing and entrainment between the two layers of hot and cold air has a profound effect on the flow velocities. In this article, an analytical gravity wave model that can calculate the velocities in a simple gravity wave is presented. This model uses the equations of stratified flow hydraulics and the translatory wave solution of the flow equations. It is found that the velocities of the model compare very well to the velocities reported from laboratory tests and numerical simulations. Numerical simulations of stratified flow in a CFD model are discussed with respect to model construction. It is concluded that the densimetric Froude number is the main parameter for the velocity calculations and the length/height ratio is important for the friction forces.

Synergistic Effect of Lanthanum Oxide on Intumescent Flame-Retardant Polypropylene-based Formulations

Jing Wu, , Yuan Hu, , Lei Song, , Wenjie Kang, — 2008-09-11

Synergistic effects of lanthanum oxide (La₂O₃) on the flammability and thermal properties of intumescent flame-retardant polypropylene (IFR-PP) composites are investigated in the study. The limiting oxygen index (LOI), UL-94 test, and cone calorimeter results show that the flame retardancy of IFR-PP is improved significantly by the introduction of La₂O₃. The results of thermogravimetric analysis (TGA) indicate that thermal stability of IFR-PP is also enhanced. SEM pictures reveal that La₂O₃ addition improve the formation of a homogenous and compact intumescent char layer on the surface of the composites. The possible mechanism of the synergistic effects between La₂O₃ and IFR is proposed in the paper.

A Comparative Study of Effectiveness of Smoke Alarms in Two Types of Buildings

Yaping He, , Nelson, D. — 2008-09-11

Fire or smoke alarms are crucial components in building fire safety systems. The effectiveness of fire alarms is investigated in this article. A relationship between effectiveness, efficacy, and reliability is formulated. A comparative study of the effectiveness of fire alarms in two types of occupancies is conducted using the published laboratory and field study results. The current study revealed the difference between the effectiveness of the fire alarm systems in dwelling and commercial stores.

An Experimental Study of Upward Flame Spread and Interactions Over Multiple Solid Fuels

Shih, H.-Y., Wu, H.-C. — 2008-09-11

Upward flame spread and flame interactions over multiple solid fuels are experimentally studied, and the effects of flame interactions on the flame spreading rates are analyzed. Flame spreading characteristics and spreading rates are measured and compared for six different geometric arrangements of thin solids at different solid width and separation distance between solids. The flame spread rate increases as the separation distance between the parallel solids decreases because of the flow channeling effect and radiation interactions, which reaches the maximum at an intermediate separation distance and then decreases as the separation distance becomes smaller due to the flow resistance and limited thermal expansion. To compare the six types of solid geometry studied, the highest flame spread rate is enclosure type of solids, followed by -shaped solids, four parallel solids, two parallel solids, L-shaped solids, and single solid.

Combustion Behavior of Intumescent Flame Retardant Polypropylene Composites

Chuanmei Jiao, , Jun Zhang, , Feng Zhang, — 2008-09-11

The combustion behavior of polypropylene (PP) composites containing intumescent flame retardant additives, i.e., melamine pyrophosphate (MPP) and 1-oxo-4-hydroxymethyl-2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane (PEPA) was characterized by limiting oxygen index (LOI), UL 94 and the cone calorimeter. It has been found that the PP composite containing only PEPA does not show good flame retardancy even at 30% additive level. Compared with the PP/PEPA binary composite, the LOI values of the PP/PEPA/MPP ternary composites at the same additive loading are all increased, and UL 94 rating of the ternary composite (PP3) studied is raised to V-0 from no rating (PP/PEPA). The cone calorimeter results show that the heat release rate and mass loss rate of some ternary composites decrease in comparison with the binary composite.

Acoustic Pyrometry using an Off-the-Shelf Range Finding System

Hanson, T. A., Yilmaz, N., Drozda, P., Gill, W., Miller, T. J., Donaldson, A. B. — 2008-07-02

In this study, the development and validation of a non-invasive flame temperature measurement tool from an off-the-shelf ultrasonic rangefinder is discussed. Both `pulse-echo' and single-pass methods are tested. The application of this device to the measurement of bench top flame temperatures is presented.

A Possible Means of Identifying Firewise Plants

Jones, J.C. — 2008-07-02

Necessity of Testing Combustibles under Well-developed Fires

Chow, W.K. — 2008-07-02

Flashover might occur rapidly as a consequence of an arson fire in a small enclosure such as a retail shop in the Far East. Testing the products, especially those made of new synthetic materials modified with additives, in well-developed fires after flashover is necessary. This refers to both full-scale burning tests on the product and bench-scale tests under higher radiative heat fluxes. Starting a room fire test with a small fire source as in the room calorimeter and stopping it upon reaching flashover would only give the `flashover propensity.' This is good enough only for designing fire safety provisions under accidental fires. Information on the heat release rate, burning duration, smoke generation rate and the toxicity of real-scale fires cannot be determined. In this article, the necessity of testing combustibles under post-flashover conditions in fire hazard assessment is pointed out. Several arrangements in retail shops are described to support the argument. Equations in the literature on estimating the maximum heat release rates for well-developed fires in those small spaces are assessed.

Flame Retardancy of Polycarbonate upon Repeated Recycling

Statler, D., Stajduhar, E., Gupta, R. K. — 2008-07-02

In this study, two polycarbonates are put through multiple cycles of a process that involves drying the resin, extruding, and pelletizing it, drying the pellets and injection molding them into test specimens, followed by granulation. While one of the polycarbonates contain potassium diphenylsulfone sulfonate (KSS) as a flame retardant, the other polycarbonate is flame retarded with bromine. The recycling process is repeated up to eight times, and after each cycle, flammability and mechanical tests are conducted. Thermogravimetric analysis and capillary rheometry are also performed. It is found that both flame retardants maintain their effectiveness, but the notched Izod impact strength suffers upon recycling, with the polymer containing KSS displaying marginally better mechanical properties.

Flame Retardant Finishing of Cotton Fleece Fabric: Part III -- The Combination of Maleic Acid and Sodium Hypophosphite

Xialing Wu, , Yang, C. Q. — 2008-07-02

Cotton fleece does not meet the federal flammability standard (16 CFR Part 1610: `Standard for the Flammability of Clothing Textiles') without chemical treatment. In this research, the chemical reactions of maleic acid (MA) on cotton in the presence of sodium hypophosphite (NaH₂PO₂) and the use of the combination of MA and NaH₂PO₂ as a flame retardant finishing system for cotton fleece are investigated. It has been found that MA esterifies cotton cellulose at relatively low temperatures in the presence of NaH₂PO₂ as catalyst, and that MA esterified to cotton is able to further react with NaH₂PO₂ at higher temperatures (≥150°C), which bonds phosphorus to the cotton cellulose. The reactions between MA and NaH₂PO₂ on cotton also lead to the cross-linking of cotton cellulose. The treatment using the combination of MA and NaH₂PO₂ is effective in reducing the flammability of cotton fleece from `Class III' to `Class I' (16CFR1610). This is a nonformaldehyde and low cost flame retardant finishing system for cotton fleece. The treated cotton fleece still maintains `Class I' flammability after 20 home laundering cycles.

Application of Semenov Theory of Thermal Ignition to Chemical Process Safety

Jones, J.C. — 2008-05-14

The Semenov model of thermal ignition is reviewed and its applicability to chemical processing is discussed. Three such applications follow: to methyl ethyl ketone peroxide (MEKP), to an asphalt based material containing some organic peroxides, and to a cetane enhancer. Discussions herein of any independent piece of work should be seen as a `critique' rather than as a `criticism'.

A Possible Analog of the Lewis Number for Gases in a Porous Medium

Jones, J.C. — 2008-05-14

Smoke, CO, and CO2 Measurements and Evaluation using Different Fire Testing Techniques for Flame Retardant Unsaturated Polyester Resin Formulations

Nazare, S., Kandola, B.K., Horrocks, A.R. — 2008-05-14

Smoke is considered to be the main fire hazard but its production depends on major variables, principally the chemical character and the burning rate of the polymer plus the availability of oxygen and hence ventilation. The main aim of this work is to study the effect of smoke suppressants on flammability and smoke production of flame retarded unsaturated polyester resin-nanocomposites using four different testing regimes representing different fire scenarios. Samples containing zinc borate, zinc stannates, ammonium polyphosphate with and without nanoclay are analyzed for smoke generation using cone calorimetry (well-ventilated fire), a tube furnace (fully developed fire), and a smoke density chamber (under-ventilated fire). Carbon monoxide (CO) and carbon dioxide (CO₂) measurements using thermogravimetry-evolved gas analysis (TG-EGA), cone calorimetry, and tube furnace have also been analyzed and compared. Results have confirmed that the production of smoke, CO, and CO₂ depend upon smoke suppressants and fire conditions used during testing samples.

From this study it is evident that tin additives have very little influence on flammability of unsaturated polyester resin but they reduce smoke formation. The slight flame retardant action of the Res/APP/ZB sample is due to enhanced cross-linking of APP in the presence of zinc borate, whereas zinc stannates do not promote cross-linking of APP and hence show no improvement in flame retardancy. Finally, the presence of nanoclay in flame retarded resin shows significant reduction in smoke formations in both well-ventilated and under-ventilated fire condition. However, in the presence of smoke suppressants used in this study, the nanoclay is not instrumental in further suppressing smoke formation.

Flame Retardants in Commercial Use or Development for Textiles

Weil, E. D., Levchik, S. V. — 2008-05-14

Non-durable and semi-durable flame retardants based mostly on phosphate or phosphonate salts continue to be used on infrequently washed or disposable goods, and recent improvements have been made to impart better `hand' or some limited wash resistance. Backcoating with insoluble ammonium polyphosphate, usually with additives and binders to provide intumescence, has been found effective on charrable fabrics. However, the leading backcoating effective on a wider range of fabrics, including synthetics and blends, is decabromodiphenyl ether plus antimony oxide. Newer candidates in development for textile coating are polymers and copolymers of pentabromobenzyl acrylate.

The leading durable finish for cellulosic fibers, in use for about 50 years, continues to be based on tetrakis(hydroxymethyl)phosphonium salts reacted with urea and cured with gaseous ammonia. Softer versions have been recently developed using chemical or process modifications, or using selected fiber blends. Somewhat less durable phosphonic ester methylolamide finishes, not requiring gaseous curing, are used on cellulosic fabrics, especially overseas. Other competitive wash-durable phosphorus-based finishes for cellulosics and blends are in development.

Polyesters continue to be flame retarded using a phosphonate or hexabromocyclododecane in a `thermosol' process. Polyesters with built-in phosphinate structures are available as specialty fabrics. A dialkylphosphinate salt has been recently introduced as a melt spinning additive in polyester. A tribromoneopentyl phosphate melt spinning additive has been developed for polypropylene fiber.

A number of inherently flame retardant synthetic fibers recently achieving increased usage include melamine-based fiber, viscose rayon containing silicic acid, aramides, oxidized polyacrylonitrile, and polyphenylene sulfide fibers. Some of these are used in protective clothing.

The recent California and Federal mattress open-flame test standards have brought barrier fabrics into prominence. Some of these barriers use boric acid on cotton batting, others are proprietary composites and blends, both woven and nonwoven, comprising inherently flame retarded fibers combined with lower cost non-flame-retardant fibers. Upholstered furniture open-flame standards are pending.

Combustion and Thermal Behavior of Polyurethane Acrylate Modified with a Phosphorus Monomer

Xilei Chen, , Yuan Hu, , Lei Song, , Weiyi Xing, — 2008-02-19

A series of UV curable flame retardant resins were obtained by blending bis(2-acryloxyethyl) 2.6.7-trioxa-1-phosphabicyclo[2.2.2.]octane-4-methylol-1-oxide phosphate (MDMPE) in certain ratios with a commercial polyurethane acrylate (PUA). It has been found that the cured film shows good flame retardancy when the MDMPE is at 30% additive level. The cone calorimeter results show that the heat release rate decreases in comparison with the pure PUA. The thermogravimetric analysis (TGA) and real time Fourier-transform infrared spectroscopy measurements (RTFTIR) results show that the phosphate group in MDMPE first degrades to form poly(phosphoric acid) before the degradation of PUA. Then, the formed poly(phosphoric acid) effectively promotes the conversion of PUA to form char, which prevents the sample from further burning. It can be concluded that MDMPE could catalyze the degradation of PUA to form char residue, and could be used as a UV curable flame retardant which acts by a condensed phase mechanism.

Transient Ceiling Jet Temperature and Velocity Profiles in the Presence of an Upper Layer: Comparison with Predictions by LAVENT and JET Computer Fire Models

Motevalli, V., Riahi, S. — 2008-02-19

Results of a scaled experimental study are compared with the predictions produced by the LAVENT and JET computer fire models. As in most large-scale fire testing, characterization of heat release rate (HRR) and accuracy of its measurement creates a lot of uncertainty for validation of these codes. Sensitivity of LAVENT results to the assumed radiative loss of 35% is examined by varying the total HRR which corresponds to varying the convective HRR. Comparisons show that LAVENT uses the wall-jet theory at its core for prediction of the ceiling jet flow and thus does not capture the ceiling jet profile well and overpredicts the upper layer temperature during the development of the layer. The velocity is generally overpredicted since the retardation of the jet momentum by the upper layer does not seem to be modeled accurately. JET has a better user interface and slightly different parameters, but does not provide ceiling jet profiles. The major difference between JET and LAVENT include the ceiling jet temperature and velocity algorithms, the fusible link algorithms, and the use of a variable radiative fraction as a function of fire size and type.

Radiative Heat Transfer for Structural Members Exposed to Fire: An Analytical Approach

Wang, Z.-H., Tan, K.-H. — 2008-02-19

An analytical approach, as a reduced form of the more general multi-flux and discrete ordinates method for radiative transfer, is proposed in this article with clarified theoretical basis. The main assumption inherent in the proposed method is that the radiation intensities along positive and negative paths are isotropic and have constant values in each direction. A realistic nonisothermal absorbing/emitting medium with isotropic scattering is analytically treated between fire sources and structural members. General energy equations, including possible heat generation within the medium, can be adopted to solve for radiative flux and temperature distribution along the radiation path. The usage of the `optical length' can readily incorporate the compound and realistic extinction coefficient of a participating medium, including gas and particle absorption and particle scattering effects. Application of the proposed method to temperature predictions of unprotected steel members in fire yields good accuracy and reliable stability, especially for those with large section factors.

Effect of Microencapsulation and 4A Zeolite on the Properties of Intumescent Flame-retardant Natural Rubber Composites

Jincheng Wang, , Yuehui Chen, — 2008-02-19

A novel microencapsulated intumescent flame retardant (MIFR) agent containing 4A zeolite has been prepared. The morphology of MIFR agent is characterized by transmission electron microscopy (TEM). Properties such as cure and tensile characteristics, thermogravimetric analysis (TGA), and flame-retardant (FR) properties are researched and compared. The addition of this MIFR agent into natural rubber (NR) leads to an improvement in its physicomechanical and FR properties. Results demonstrate that the NR composite filled with 50 phr of MIFR-4A zeolite and 50 phr of IFR-4A zeolite show better FR and tensile properties than that of pure and 50 phr of IFR-filled NR systems.

Further Application of the Semenov Model to Evaluate the Possibility of Spontaneous Combustion in Tumble Dryers

Morrison, D.R., Ogle, R.A. — 2008-02-19

Previously, Jones applied the Semenov boundary conditions and thermal explosion theory to the problem of predicting spontaneous combustion of laundered clothing in a commercial tumble dryer. This problem is revisited here with a modification of the limiting assumptions made in the previous work. Relaxation of the limiting assumptions (i.e., considering air flow through the drum) demonstrates that the self-heating processes within the laundered load are limited by the forced convection through the tumbling clothing load. The conclusions of this paper demonstrate that inclusion of this heat loss term soundly refutes the possibility of spontaneous combustion of an uncontaminated, tumbling clothing load. The critical temperature predictions indicate that even in the case of overheating of the garment load (dryer malfunction), the garment load temperature is unlikely to exceed its critical temperature in the absence of contamination.

Addendum by Reviewer

Jones, J.C. — 2008-02-19