Flammability Measurements Research Articles

Studies on the temperature dependence of extinction oxygen index values for cellulosic fabrics. I. Cotton

AbstractThe concept of extinguishability as a measure of textile flammability is reviewed. Definition and determination of extinction oxygen index enables a parameter to be defined from which the effects of ignition time and fabric structure may be removed. This so‐called extinction oxygen index (EOI) and the derived value at zero ignition time [EOI]0 more exactly define the burning/nonburning fabric boundary than does the more widely used limiting oxygen index (LOI). This first paper reports the determination of EOI and [EOI]0 values for a series of cotton fabrics in the temperature range 20–200°C. The influence of the various fabric parameters of area density, air permeability, sample thickness, bulk density, and moisture content was investigated. The advantages of using the EOI rather than the LOI concept as a measure of textile flammability is indicated in the discussion of the results of this study with reference to previous work concerned with LOI data for cotton. In particular, the significance that environmental temperature has on EOI and related parameters reported here and previously reported LOI data is discussed in terms of various published models which define the burning/extinction threshold.

Char formation from polyolefins. Correlations with low-temperature oxygen uptake and with flammability in the presence of metal halogen systems

The oxidative degradation and combustion of polypropylene were investigated by simultaneous thermal analysis (STA) and by flammability measurements. STA shows that, while halogen compounds and metal oxides invariably increase char formation from the polymeric substrate, metal chelates can act both as inhibitors and as promoters of carbonisation. In general, however, there appears to be a direct correlation between the effect of an additive on oxygen uptake and that on char formation. Pro-oxidants which catalyse char formation are effective condensed-phase flame retardants, as a result of their producing fewer volatile species from the polymer.

Aging effects on fire‐retardant additives in polymers

AbstractExtensive thermal aging experiments have been conducted on (i) ethylene‐propylene rubber (EPR) formulations containing various commercial halogenated‐hydrocarbon fire‐retardant additives together with Sb2O3, and (ii) on chlorosulfonated polyethylene (CSPE) formulations with and without added Sb2O3. Significant losses of both chlorine and antimony are found on aging, dependent upon the ability of the particular halocarbon to undergo intramolecular dehydrohalogenation. The stoichiometry indicates antimony volatilization as SbCl3. Arrhenius treatment of the data for the EPR formulation which undergoes the most rapid loss gives an overall activation energy of 34 kcal/mol for antimony volatilization and indicates that fire‐retardant loss should become appreciable only at temperatures significantly above ambient (i.e., 70°C). Oxygen index flammability measurements showed moderately increased flammability for certain aged EPR samples, but showed significantly decreased flammability for aged CSPE which was correlated with the loss of other volatile components from the formulation.

Thermal analysis and flammability of polymers Effect of halogen-metal additive systems

Thermal analyses have been carried out on systems containing a thermoplastic polymer (ABS or HDPE), a halogenated hydrocarbon (decabromobiphenyl or a chlorinated wax) and one or two metal-containing compounds. The results were compared with flammability measurements on the same systems, as determined by limiting oxygen index. Thermal analyses of the additives on their own has shown the extent to which the metal compounds are volatilised as their metal halides, thus indicating their possible similarity to the mechanism of flame-retardant action of antimony oxide. Such results are shown to be misleading in terms of providing an indication of flame-retardant efficiency. However it is possible to obtain meaningful correlations between the information obtained from thermal analysis of complete systems, i.e. including the polymeric substrate, and comprehensive studies (e.g. by triangular diagrams) of the flammability.

Seasonal Variations in Fuel and Fuel Consumption by Fires in a Bluestem Prairie

Plots in an ungrazed, re—established grassland near Omaha, Nebraska, USA, dominated by little bluestem (Andropogon scoparius), were burned at 3—wk intervals from March through November 1976. The amount of vegetative biomass consumed during burning, a measure of flammability, was high throughout the study period, varying from >99% in April to 84% in mid—June. Areas burned in March were able to carry a second fire in October of the same year. High flammability throughout the growing season, in conjunction with current fire and climatic records, suggests that widespread, late—summer fires were probably common in presettlement, ungrazed, bluestem prairies.

Improved fire resistance test method for belt materials

A moderately scaled apparatus was developed for determining the fire resistance characteristics of mice conveyor belts and similar type materials. The test method overcomes the limitations of existing laboratory-scale methods and provides a measure of both ignitability and flammability in quantitative terms. Data are presented for nine belt materials, and fire resistance ratings are proposed in terms of the flame spread rate, heat release rate, and critical ignitor heat flux.

A General Correlation of the Flammability of Natural and Synthetic Polymers

The concept that flammability is fundamentally related to the potential thermal energy available per unit of volume of material emerged from attempts to correlate the effect of composition variables on the flammability of neoprene vulcanizates as measured by the oxygen index (O.I.) test. The origins of this test clearly show that it is a highly specific measure of flammability—the tendency of a composition to continue to burn once ignited—and that it is thermodynamically related to the heat of combustion of materials. This relationship is developed to a linear correlation which includes a wide variety of synthetic and natural materials and permits reasonable prediction of O.I. values from elemental analysis. Polymeric materials containing carbon and oxygen in atom ratios of less than 6 to 1 are more flammable than predicted. The effect of atmospheric temperature on O.I. can be predicted in relation to the O.I. value at normal temperature. This effect is shown to be independent of the composition of the material being tested. These two correlations permit the construction of a simple general map of flammability against which experimental data can be compared and judgments made with respect to the significant variables involved. There appears to be a significant relation between O.I. data, as viewed from these correlations, and the data of other flammability tests.

The combustion of flexible polyurethane foams: Mechanisms and evaluation of flame retardance

Studies have been made of the combustion of flexible foamed polyurethanes and of the effect there-on of a wide range of halogen- and phosphorus-containing compounds, with particular reference to the chemical reactions occurring during “ageing” of the foams. Flammability measurements show that ageing improves the fire resistance of foams containing the two most effective flame-retardant additives (tris (2,3-dibromopropyl) phosphate and tris (2-chloroethyl) phosphate) when these are present in more than a critical concentration. Thermal degradation studies indicate that at least a part of these additives is incorporated into the polyurethane structure. The relative effectiveness of all the compounds investigated is discussed in the light of known mechanisms of flame retardance.

A general correlation of the flammability of natural and synthetic polymers

The concept that flammability is fundamentally related to the potential thermal energy available per unit of volume of material emerged from attempts to correlate the effect of composition variables on the flammability of neoprene vulcanizates as measured by the oxygen index (O.I.) test. The origins of this test clearly show that it is a highly specific measure of flammability—the tendency of a composition to continue to burn once ignited—and that it is thermodynamically related to the heat of combustion of materials. This relationship is developed to a linear correlation which includes a wide variety of synthetic and natural materials and permits reasonable prediction of O.I. values from elemental analysis. Polymeric materials containing carbon and oxygen in atom ratios of less than 6 to 1 are more flammable than predicted. The effect of atmospheric temperature on O.I. can be predicted in relation to the O.I. value at normal temperature. This effect is shown to be independent of the composition of the material being tested. These two correlations permit the construction of a simple general map of flammability against which experimental data can be compared and judgments made with respect to the significant variables involved. There appears to be a significant relation between O.I. data, as viewed from these correlations, and the data of other flammability tests.

Pyrolysis–gas chromatographic analysis of poly(vinyl chloride). II. In situ absorption of HCl during pyrolysis and combustion of PVC

AbstractA pyrolysis–gas chromatographic technique for measuring the amount of hydrogen chloride released during the high temperature pyrolysis of poly(vinyl chloride) resins, plastisols, copolymers and compounds containing inert fillers has been developed. The technique, which is also applicable to the analysis of chlorinated polyethylene and chlorinated poly(vinyl chloride), is based on the use of a standard precursor of HCl, poly(vinyl chloride) homopolymer. The analysis has been successfully used to measure the degree of in situ absorption of HCl during pyrolysis by certain basic fillers [K2CO3, CaCO3, CaO, MgO, Al(OH)3, Na2CO3, Al2O3 and LiOH] dispersed in a poly(vinyl chloride)–o‐dioctyl phthalate matrix. Combustion of a number of combustion residues (chloride determination) revealed that the amount of HCl absorbed by the basic filler was independent of the method of degradation (pyrolysis or combustion). Flammability measurements of those matrices having the same composition indicate that in situ absorption of HCl during combustion has little effect on the overall flammability of these materials.

Energy release rates in fire retardant evaluation

Rate of spread and other indirect measurements of fire intensity are often used as measures of flammability when fire-retardant chemicals are evaluated under laboratory conditions. The authors describe a system for obtaining the energy release rate directly and show its importance and relation to retardant effectiveness.

Flammability of epoxy resins

AbstractFlammability determinations have been made for epoxy resin formulations. The oxygen index, defined as the volume fraction of oxygen in an oxygen/nitrogen atmosphere that is required just to sustain steady candlelike burning of a stick of the material, has been used as the measure of flammability. The formulations selected for study were those for which the chemical composition of the ingredients was known at least approximately and for which uniform cast slabs (1/8 in. thick) could be readily prepared. They covered a range of compositions of commercial interest. The results have been interpreted in terms of a proposed model for candlelike burning. Effects due to resin composition, cure conditions, fillers, and flame‐retardant additives are discussed.