Temperature autoignition

Hilado and Clark report difficult-to-find autoignition temperatures while eliminating apparent discrepancies in literature values. Table 1 shows their compilation. 

Material Lowest Reported AIT in Glass Lowest Reported AIT if Other Than Glass or Unspecified Material Lowest Reported AIT in Glass Lowest Reported AIT if Other Than Glass or Unspecified  

1 Straight-Chain Paraffins 1.2 Single-Branched Paraffins  

Propylcyclopentane 269 516 15 4.4 Four-Ring and Five-Ring Cycloparaffins  

1 -Methyl-2-ethylbenzene 1 -Methyl-3-ethylbenzene 1 -Methyl-4-ethylbenzene 

1 -Methyl-4-isopropylbenzene (p-cymene) Diisopropylbenzene Styrene (vinylbenzene) (cinnamene) a-Methylstyrene 

Lowest Reported AIT if Other Than Glass or Unspecified 

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Autoignition temperature. The autoignition temperature of a material is the temperature at which it will ignite spontaneously in air without any external source of ignition. 

Combustion of a flammable gas-air mixture occurs if the composition of the mixture lies in the flammable range and if there is a source of ignition. Alternatively, combustion of the mixture occurs without a source of ignition if the mixture is heated up to its autoignition temperature. 

The autoignition temperature is the minimum temperature required for self-sustained combustion in the absence of an external ignition source. The value depends on specified test conditions. Tht flammable (explosive) limits specify the range of concentration of the vapor in air (in percent by volume) for which a flame can propagate. Below the lower flammable limit, the gas mixture is too lean to burn above the flammable limit, the mixture is too rich. Additional compounds can be found in National Fire Protection Association, National Fire Protection Handbook, 14th ed., 1991. 

Substance Autoignition temperature, °C Flammable (explosive) limits, percent by volume of fuel (25°C, 760 mm) ... 

Flash points and autoignition temperatures are given in Table 11. The vapor can travel along the ground to an ignition source. In the event of fire, foam, carbon dioxide, and dry chemical are preferred extinguishers. The lower and upper explosion limits are 1% and 7%. 

Table 11. Flash Points and Autoignition Temperatures of the Cg Aromatic Compounds...

Syltherm XLT is a polydimethylsiloxane intended for Hquid-phase systems which operate at low temperatures. Syltherm 800 is a modified dimethylsiloxane polymer intended for Hquid-phase systems. The recommended maximum fluid temperature is greater than the autoignition temperature. 

Some of the tests and criterion used to define fire resistance may be found in the Hterature (9). Additionally, the compression—ignition and hot manifold tests as defined in MIL-H-19457 and MIL-H-5606, respectively the Wick test as defined by Federal Standards 791, Method 352 flash point and fire point as defined in ASTM D92 autoignition temperature as defined in ASTM D2155 and linear flame propagation rate are defined in ASTM D5306 are used. 

Properties of the principal hydrocarbons found in commercial hexane are shown in Table 9. The flash point of / -hexane is —21.7 °C and the autoignition temperature is 225°C. The explosive limits of hexane vapor in air are 1.1—7.5%. Above 2°C the equiUbrium mixture of hexane and air above the Hquid is too rich to fall within these limits (42). 

Undesirable combustible gases and vapors can be destroyed by heating to the autoignition temperature in the presence of sufficient oxygen to ensure complete oxidation to CO2 and H2O. Gas incinerators are appHed to streams that are high energy, eg, pentane, or are too dilute to support combustion by themselves. The gas composition is limited typicaUy to 25% or less of the lower explosive limit. Gases that are sufficiendy concentrated to support... 

Direct-Flame Incinerators. In direct-flame incineration, the waste gases are heated in a fuel-fired refractory-lined chamber to the autoignition temperature where oxidation occurs with or without a visible flame. A fuel flame aids mixing and ignition. Excess oxygen is required, because incomplete oxidation produces aldehydes, organic acids, carbon monoxide, carbon soot, and other undesirable materials. 

Diketene is a flammable Hquid with a flash point of 33°C and an autoignition temperature of 275°C. It decomposes rapidly above 98°C with slow decomposition occurring even at RT. The vapors are denser than air (relative density 2.9, air air = 1). The explosive limits in air are 2—11.7 vol % (135). In case of fire, water mist, light and stabilized foam, as well as powder of the potassium or ammonium sulfate-type should be used. Do not use basic extinguisher powders and do not add water to a closed container. 

Compound Molecular weight Mp, °C Viscosity, mPa(=cP) Flash point, °C Autoignition temperature, °C... 

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