Mohammed M. Khan

A sample holder for determining material properties

The determination of material properties, such as thermal conductivity, for use in fire models requires precise knowledge of all heat losses. For example, the ignition and subsequent burning of solid samples is sensitive to heat losses from the rear surface of the tested sample. The heat loss depends on the sample holder and its environment. Theoretical predictions of ignition and pyrolysis in standard flammability apparatuses show that the construction of the sample holder has a surprisingly large effect on measured properties especially for thermally thin samples. This makes flammability measurements and inferred thermal properties apparatus dependent. For example, ignition measurements of 6.4 mm (1/4″) plywood samples show a 40% reduction in the critical heat flux for ignition. The back and sides of the sample were sealed by wrapping it with aluminium foil tape. Heat losses from the sample were minimized by placing it on a sample holder having four layers of 3.2 mm (1/8″) thick insulating ceramic paper surrounded by an outer layer of aluminium tape. A detailed mathematical model is developed to fully characterize the thermal response of a sample to a prescribed heat flux in a standard flammability apparatus. The model is used to estimate the residual heat losses not eliminated by the sample holder. Model predictions accurately track the temperature response of blackened brass plates of different thicknesses exposed to several different incident heat fluxes. Brass, of course, has well known thermophysical properties; so, it also provides an excellent means for in situ calibration of the incident heat fluxes. Copyright

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.

Extinguishment of Diffusion Flames of Polymeric Materials by Halon 1301

Halon 1301 flame extinction results are discussed for the com bustion of polymethylmethacrylate (PMMA), eight composite materials, and carbon in the gas phase. Two types of combustion and flame extinction experi ments were performed: (1) in the Factory Mutual Research Corporation (FMRC) flammability apparatus (50 kW scale) for PMMA and composite materials, and (2) in the FMRC electrical arc apparatus for carbon in the gas phase. For char forming composite materials, mass transfer from the surface was low, turbulent diffusion flames were not generated, and flame extinction oc curred between 3 to 4.5% of Halon 1301, close to the value reported for the lam inar diffusion flames of polymers. For non-charring PMMA, mass transfer from the surface was high, flames were turbulent, and flame extinction was found at about 6% of Halon 1301, contrary to the accepted value of about 4% for the lam inar diffusion flames of polymers. With Halon 1301 the conditions for flame in stability and extinction for combustion efficiency less than about 0.40, with sig nificant increase in the amounts of products of incomplete combustion (such as CO and hydrocarbon), were in agreement with flame instability and extinction found for fuel-rich conditions inside well-ventilated laminar and turbulent diffusion flames, in ceiling layers of combustion products, in enclosure fires, in ventilation-controlled buoyant diffusion flames of polymers, and for flame ex tinction of heptane flames by water. Experiments in the FMRC electrical arc apparatus showed that in the gas phase combustion of carbon vapors generated in high energy arc, chemical heat release rate and combustion efficiency decreased with increase in Halon 1301. At about 7.5% of Halon 1301, conditions were close to flame extinction and at 9.0%, oxidative pyrolysis of carbon was indicated. Concentrations of Br- and F- ions, generated from the decomposition of Halon 1301, were also measured. Concentration of Br- ions was higher than the concentration of F- ions, al though there are three F atoms and only one Br atom in Halon 1301. There was brown deposit on the walls of the apparatus with extensive corrosion of rubber gaskets, electrical fan, and other components. The techniques discussed in this article appear to be attractive for the assess ment of flame extinguishability and corrosive characteristics of fire suppres sants to replace ozone layer depleting Halons.

Combustion Characteristics of Materials and Generation of Fire Products

Hazards associated with fire are characterized by the generation of calorific energy and products, per unit of time, as a result of the chemical reactions of surfaces and material vapors with oxygen from air. Thermal hazards constitute those scenarios where the release of heat is of major concern. On the other hand, nonthermal hazards are characterized by fire products (smoke, toxic, corrosive, and odorous compounds.) Generation rates of heat and fire products (and their nature) are governed by (1) fire initiation (ignition); (2) fire propagation rate beyond the ignition zone; (3) fire ventilation; (4) external heat sources; (5) presence or absence of fire suppression/extinguishing agents; and (6) materials: (a) their shapes, sizes, and arrangements; (b) their chemical natures; (c) types of additives mixed in; and (d) presence of other materials. In this handbook most of these areas have been discussed from fundamental as well as applied views. For example, the mechanisms of thermal decomposition of polymers, which govern the generation rates of material vapors, are discussed in Chap. 7, generation rate of heat (or heat release rate) from the viewpoint of thermochemistry is discussed in Chap. 5, Flaming ignition of the mixture of material vapors and air is discussed in Chap. 21, and surface flame spread in Chap. 23.

Upward Fire Growth over Thermally Thin Corrugated Paperboard

A simple analytical model is developed for fire growth of thermally-thin corrugated paperboard in a parallel panel configuration that simulates the vertical flues between stored commodities in a rack storage arrangement. It is based on a semi-empirical model for radiation-dominated flame heat transfer to panels in terms of: (1) fuel flame sootiness, (2) fire heat release rates, and (3) panel width to separation aspect ratios. The model input properties include: heat of combustion, minimum heat of gasification, yield of smoke, and critical heat flux obtained from the fire propagation apparatus. The effect of moisture on fire growth rate is incorporated in the model. The predictions of the model are compared with experimental data on the rate of chemical heat release measured for the upward fire growth of vertical corrugated paperboard samples (0.305 m × 2.4 m) placed opposite one another in a parallel panel configuration (0.153 m apart). The model predictions of exponential fire growth time constant agree reasonably well with the experimentally determined values. Because of an enhanced role of convective heat transfer for parallel panels with 0.153 m separation distance, an adjustment of radiation constant β1 was needed for reasonable prediction of fire growth time constant. For a fixed geometry, the model prediction of fire growth time constant depends on the material properties and moisture content.

Evaluation of flame spread on thin polymeric rooflight materials

An empirical flame spread parameter (dimensional), which is a function of peak chemical heat release rate and ignition behavior, obtained from bench-scale ASTM E-2058 tests, is used to correlate the flame spread behavior of eighteen thin polymeric rooflight materials in large-scale ASTM E-108 tests. Although this empirical parameter appears to correlate the extent of flame spread in large-scale tests of most rooflight materials, including melting types, the parameter fails to predict the flame spread behavior of several nonmelting materials. Data have also been analyzed using a dimensionless parameter, based on an existing concurrent flame spread model that includes the consideration of burnout for thin materials. This parameter, a flame acceleration factor (FAF), is a function of ignition time, burning duration and chemical heat release rate obtained from E-2058 tests. A correlation between FAF and the extent of flame spread measured in large-scale E-108 tests is presented. Consistent with the model prediction, flame spread remains within the flame exposure region in E-108 tests when FAF <0. Flame spread is distinctly beyond the exposure source when FAF >0. An exception is the case when there is extensive melting, a phenomenon not taken into account by the FAF model.

A New Test Method For Rating Materials As Noncombustible

Several test methods commonly employed to rate the combustibility of materials are evaluated and compared to criteria for the stability of flaming combustion in the firescience literature. These science-based criteria are then used to analyze measurements and visual observations obtained when four prototype “noncombustible” materials are tested in the Fire Propagation Apparatus (ASTM E 2058). Based on this analysis, it is proposed that observation of the presence of flame and measurement of heat release rate at an applied heat flux of 50 kW/m and an inflow oxygen concentration of 40% can be used to determine whether a material should be rated as “noncombustible.”

Development of a Standard Flammability Test for Water-Based Hydraulic Fluids

This paper is a review of the development of a standard flammability test method for hydraulic fluids since the 1970s. Over the past years, the test methodology for qualifying hydraulic fluids has been transformed from a qualitative assessment to a quantitative and model based assessment. The present standard test method deals with the calorimetric measurement of heat release rate of a highly atomized spray fire, fire point temperature measurement, and the determination of adiabatic flame temperature utilizing an existing NASA Combustion Equilibrium and Application Code. In this paper, we have emphasized on the detailed development of evaluating water-based hydraulic fluids.

Sustained Burning of Water-based Paint Sprays

Water-based paints used in automotive paint spray booths are prone to ignition and combustion might occur for these types of paints when finely dispersed in electrostatic spraying. An experimental study accompanied by equilibrium calculations of adiabatic stoichiometric flame temperature ( ad T ) has been conducted to investigate the burning behavior of water-based spray paints. Several spray fire tests have been carried out and the heat release rates of the flames have been measured. To compare the paints burning behavior, acetone has been added at various concentrations for the spray fire tests. The results have been compared against computed ad T values for the paint-acetone mixtures. Elemental compositions of the paints and their heats of combustion have been measured to compute ad T . A critical temperature ( cr ad T , ) at which combustion will not sustain itself is proposed to characterize the water-based paints. Completeness of combustion ( comb η ) of paint-acetone mixture spray fires has also been used to evaluate the burning behavior of the paints. Based on the critical temperature and completeness of combustion, two regimes of combustion have been identified.