Archibald Tewarson

The influence of oxygen concentration on fuel parameters for fire modeling

The influence of oxygen concentration on fuel parameters in pool fires with areas of about 0.007 m 2 and 0.07 m 2 is described for methanol, polyoxymethylene (POM), polymethyl-methacrylate (PMMA), heptane, polypropylene (PP) and polystyrene (PS). Fuel parameters include mass loss rate, combustion efficiency, convective and radiative fractions of heat of complete combustion, and yields of CO 2 , CO, and soot and low-vapor-pressure liquid products. For combustion in excess air, the combustion efficiency and the yield of CO 2 are not very sensitive to changes in m 02 and fuel areas. The fuel mass loss rate, yield of unburnt soot, flame radiative heat flux, and radiative fraction of heat of complete combustion increase and flame convective heat flux and convective fraction of heat of complete combustion decrease as m 02 is increased; for m 02 values much higher than 0.233, all the parameters approach their respective asymptotic values. There appears to be an attenuation of flame radiation by cold vapors near the surface as well as a change in the flame shape as m 02 is varied.

Ventilation-controlled combustion of polymers

Abstract Ventilation-controlled combustion in buoyant turbulent diffusion flames of polymers with CH, CHO, and CHON aliphatic and aromatic structures has been examined. Correlations have been established between equivalence ratio and combustion efficiencies (chemical, convective, and radiative), generation efficiencies of combustion products (CO, CO2, hydrocarbons, soot, and other products) and consumption efficiency of O2. Relationships resembling flammability limit diagrams have been developed between the generation efficiencies of CO and CO2, and soot and CO. With increase in the equivalence ratio, chemical and convective efficiencies of combustion, generation efficiency of CO2, and consumption efficiency of O2 decrease, whereas radiative efficiency of combustion and generation efficiencies of CO, hydrocarbons, soot, and other carbon containing products increase. These changes in the combustion properties are due to deviations from thermodynamic equilibrium and each change is correlated in terms of the equilibrium fraction of the combustion property as a function of the equivalence ratio. For similar magnitude of increase in equivalence ratio, fuels with CHO and CHON structures show rapid increase in the generation efficiencies of CO and hydrocarbons compared to the generation efficiency of soot, whereas fuels with CH structures show rapid increase in the generation efficienty of soot, compared with the generation efficiencies of CO and hydrocarbon. This is consistent with the general understanding of the formation of soot and CO. For equivalence ratio of four or greater, flames are extinguished, but nonflaming combustion continues as long as the fuel continues to be generated as a result of external heat flux exposure. Correlations have been developed as inputs to models for enclosure fires to assess thermal and nonthermal hazards due to generation of heat, soot, CO, hydrocarbons, and corrosive and toxic products and prevention and protection from such hazards.

Flammability Parameters of Materials: Ignition, Combustion, and Fire Propagation:

In this paper, flammability parameters associated with the igni tion, combustion, and fire propagation processes and their usefulness for the development of fire resistant materials are discussed. The flammability param eters discussed are: (a) Critical Heat Flux (CHF) and Thermal Response Param eter (TRP), associated with ignition, (b) Heat Release Parameter (HRP) and Fire Propagation Index (FPI), associated with combustion and fire propagation.

Polymers and Composites- An Examination of Fire Spread and Generation of Heat and Fire Products

Fiber reinforced composite (FRC) materials are used extensively because of their favorable physico-chemical properties and high strength- to-weight ratio. The use of composites in Army vehicles as a means of decreas ing weight and enhancing survivability, without reducing personnel safety, has been under study for some time. Although FRC materials are very attractive in terms of their physico-chemical properties, concern for possible fire hazard is understandable as organic polymers are one of the major constituents of the materials. A joint study thus was undertaken by the U.S. Army Materials Tech nology Laboratory (MTL) and the Factory Mutual Research Corporation (FMRC) to quantify flammability behavior of selected composite materials for the assessment of fire hazard. In the study, eight FRC materials, identified as MTL #1 to #8, were used. The FRC materials were 3 to 45 mm in thickness. The flammability behavior was examined by using the FMRC Flammability Apparatus (50 kW-Scale) and Ox ygen Index (OI) apparatus, Thermogravimetric Analysis (TGA) instrument, NBS smoke chamber (ASTM E 662), and Gas Chromatograph-Mass Spec trometer (GC-MS) instrument at MTL. This article presents results for ignition, flame spread, heat release rate, gen eration rates of products, light obscuration by smoke and flame extinction by Halon. In comparison to ordinary combustibles, such as cellulosics and most non fire retarded plastics, the eight FRC materials have higher resistance to ig nition (as indicated by the Thermal Response Parameter, TRP) and flame spread (as indicated by higher values of the Fire Propagation Index, FPI). The FPI values for the FRC materials, examined in this study, ranged from 3 to 13, indicating that for Group 1 FRC materials (FPI < 10), self-sustained flame spread beyond the ignition zone would be difficult, whereas for other Group 2 materials (FPI ≥ 10), flame spread beyond the ignition zone would be ex pected, although at a slower rate. For Group 2 materials fire protection is re quired, which could be provided by techniques such as surface coating, surface lamination using highly fire resistant FRC materials, and others. Generation of heat, smoke, toxic and corrosive products is closely related to FPI. Within the FRC materials, examined in this study, differences were found between the generation rates of heat, smoke, and other products. Results for flame extinction by Halon 1301 are also discussed. The flame ex tinction data are consistent with the design of the current suppression system for the crew compartment of Army combat vehicles. The study suggests that the FPI concept and associated parameters related to generation of heat, smoke, toxic, and corrosive products, is a useful concept for realistic flammability quantification and screening of FRC materials and for use in the hazard assessment. This, however, needs to be validated by perform ing large-scale fire tests.

Nonthermal Fire Damage

This paper deals with the general relationships between nonther mal damage and fire initiation, fire spread, generation of fire products, en vironmental conditions, and orientation and surface characteristics of targets. Data reported in the literature by various researchers have been used in the paper to discuss the relationships. Tests currently being used to assess corro sion in various laboratories and the long-range nonthermal damage research at Factory Mutual Research Corporation are reviewed.

Flame propagation in ducts

Abstract A simple heat balance has been used to analyze conditions for flame propagation in ducts. A heat flow parameter, coupled with the critical heat flux for ignition, has been used to define the ignition and extent of flame propagation for duct lining materials.

Flame propagation for polymers in cylindrical configuration and vertical orientation

Experimental results are presented for vertical flame propagation for single and multiple cylinders (electrical cables and solid pine). Experiments for single, 0.508 and 1.29 m long, cylinders were performed in our apparatuses; O 2 concentration in the range of 21 to 45% was used to enhance the flame propagation rate. Experiments for multiple cylinders were performed in our 5 MW-scale apparatus, with two (0.61 m wide and 4.9 m long) sheets of cables facing each other and separated by about 0.31 m. A new technique based on the chemical energy released during flame propagation and extent of flame propagation was used to calculate the flame propagation rate. The flame propagation rate in the 500 kW and 5 MW-scale apparatuses showed good correlation and satisfied the engineering relationships derived from the fundamental flame propagation theories. The following relationship was found for the flame propagation rate: fx1231-1 For 0.508 and 1.29 m long cylinders, the effective flame heat transfer distance was estimated to be about 0.16 m. The extent of flame propagation and propagation rate were found to be interrelated. Under our experimental condition, without additional heat flux to enhance the flame heat flux, the extent of flame propagation was estimated to be 100% of the available area for V≥5×10 −3 m/s, and for V≤1×10 −3 m/s, the estimation showed no propagation.

Flammability evaluation of clean room polymeric materials for the semiconductor industry

A new methodology, identified as the 4910 Test Protocol, has been developed to evaluate the fire propagation and smoke development behaviour of polymeric materials for use in clean rooms for the semiconductor industry. This paper reviews the scientific basis of the concepts and criteria contained in the 4910 Test Protocol. For the acceptance of polymeric materials, two criteria are used: (a) Fire Propagation Index (FPI) less than or equal to 6 (m s(-1/2))/(kWm(-1))(2/3) and (b) Smoke Development Index (SDI) less than or equal to 0.4 (gg(-1)) (ms(-1/2))/(kWm(-1))(2/3). Materials are tested in the ASTM E 2058 Fire Propagation Apparatus (previously identified as the Factory Mutual Research Flammability Apparatus). The Fire Propagation Index (FPI) is formulated from: (a) the Thermal Response Parameter (TRP), which relates the time-to-ignition to the net heat flux to the sample surface, and (b) the chemical heat release rate measured during the upward fire propagation in air having a 40% oxygen concentration to simulate flame heat transfer at large scale. The SDI is related to the smoke release rate and is obtained by multiplying the FPI value by the smoke yield. The smoke yield is defined as the ratio of the total mass of smoke released per unit mass of the vapours of the polymeric material burned. Small and large-scale fire test data have been included in the paper in support of the 4910 Test Protocol criteria. Highly halogenated and high temperature specialty polymeric materials and highly modified ordinary thermoplastics are found to satisfy the criteria.

Nonmetallic Material Flammability in Oxygen Enriched Atmospheres

Nonmetallic material flammability on Oxygen Enriched Atmo spheres (OEA) is discussed with explanations based on the latest scientific un derstanding. Flammability consists of a combination of the ignition, combustion, and fire propagation behaviors of materials. Application of the newly developed test methods and advanced-engineering polymers for OEA con ditions are discussed. The test methods use high oxygen concentration, pres sure, and external heat flux to simulate large-scale fire environments. Pressure and external heat flux effects are complementary and appear to have a stronger effect on the flammability of materials than the oxygen concentration. High oxy gen concentration in combination with external heat flux provides similar heat flux exposure to materials as normal atmosphere at high pressures. Results are presented for flame heat flux transferred back to the surface of the burning materials under high pressure (normal air) and high oxygen concentra tions (at atmospheric pressure). The use of newly developed test methods is sug gested for evaluating the probability of fires in OEA facilities such as hyperbaric chambers.

Characterization of hydraulic fluid spray combustion

The combustion intensity of hydraulic fluids and mineral oil, methanol, ethanol, and heptane, ejected vertically up ward through a pressure-jet hollow cone nozzle and stabilized by a ring burner, has been characterized in terms of heat release rates. A relationship has been established between the chemical heat release rate, fluid exit velocity, and chemical heat of combustion. Mineral oil, along with some organic esters, has the highest combustion intensity as indicated by heat release rate, followed by esters (organic and phosphates), heptane, water-in-oil emulsion, ethanol, methanol, and polyglycol-in-water. Variations in combustion intensities in hydraulic fluids are found to be due to variations in the chemical structures and additives.The efficiency of combustion is found to be sensitive to fluid exit velocity.The radiative fraction of the efficiency of combustion for phosphate esters is found to be the highest (0.38–0.40), followed by mineral oil (0.36), organic esters (0.28–0.35), water-in-oil emulsion (0.27–0.28), and polyglycol-in-water (0.12–0.25). The radiative fraction of the efficiency of combustion for ethanol and heptane spray fires is found to be less than for the pool fires. For methanol spray fire, radiative fraction of the efficiency of combustion is found to be about the same as for the pool fire.The visible flame length of hydraulic fluid spray fires varies with the chemical heat release rate to the power of 0.6 for both hollow and solid cone nozzles.