Flammable limit

FIQURE 5-1.2. Flammability triangular diagram for methane -H oxygen -h nitrogen. 

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Flammability limits. A flammable gas will bum in air only over a limited range of composition. Below a certain concentration of the flammable gas, the lower flammability limit, the mixture is too lean to burn, i.e., lacks fuel. Above a certain concentration, the upper flammability limit, it is too rich to burn, i.e., lacks oxygen. Concentrations between these limits constitute the flammable range. 

Flammability limits are also affected by temperature. An increase in temperature usually widens the flammable range. 

The flammability limits of a hydrocarbon depend on its chemical nature and its molecular weight. Table 4.14 gives values for some common hydrocarbons. 

Targets and spirals have been observed in the CIMA/CDIMA system [13] and also in dilute flames (i.e. flames close to their lean flammability limits) in situations of enlianced heat loss [33]. In such systems, substantial fiiel is left unbumt. Spiral waves have also been implicated in the onset of cardiac arrhytlnnia [32] the nomial contractive events occurring across the atria in the mannnalian heart are, in some sense, equivalent to a wave pulse initiated from the sino-atrial node, which acts as a pacemaker. If this pulse becomes fragmented, perhaps by passing over a region of heart muscle tissue of lower excitability, then spiral structures (in 3D, these are scroll waves) or re-entrant waves may develop. These have the incorrect... 

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. 

Flammability Acrolein is very flammable its flash point is <0° C, but a toxic vapor cloud will develop before a flammable one. The flammable limits in air are 2.8% and 31.0% lower and upper explosive limits, respectively by volume. Acrolein is only partly soluble in water and will cause a floating fire, so alcohol type foam should be used in firefighting. The vapors are heavier than air and can travel along the ground and flash back from an ignition source. 

Inert Gas Dilution. Inert gas dilution involves the use of additives that produce large volumes of noncombustible gases when the polymer is decomposed. These gases dilute the oxygen supply to the flame or dilute the fuel concentration below the flammability limit. Metal hydroxides, metal carbonates, and some nitrogen-producing compounds function in this way as flame retardants (see Flame retardants, antimony and other inorganic compounds). 

In the absence of air, TEE disproportionates violently to give carbon and carbon tetrafluoride the same amount of energy is generated as in black powder explosions. This type of decomposition is initiated thermally and equipment hot spots must be avoided. The flammability limits of TEE are 14—43% it bums when mixed with air and forms explosive mixtures with air and oxygen. It can be stored in steel cylinders under controlled conditions inhibited with a suitable stabilizer. The oxygen content of the vapor phase should not exceed 10 ppm. Although TEE is nontoxic, it may be contaminated by highly toxic fluorocarbon compounds. 

Fuel Quantity of fuel per Gf" Flammability limit ia air, vol % gas Lower Higher Maximum flame speed, cm/s Spontaneous ignition temperature, °C Ignition d -jC energy, m ... 

Air is compressed to modest pressures, typically 100 to 200 kPa ( 15-30 psig) with either a centrifugal or radial compressor, and mixed with superheated vaporized butane. Static mixers are normally employed to ensure good mixing. Butane concentrations are often limited to less than 1.7 mol 1 to stay below the lower flammable limit of butane (144). Operation of the reactor at butane concentrations below the flammable limit does not eliminate the requirement for combustion venting, and consequendy most processes use mpture disks on both the inlet and exit reactor heads. A dow diagram of the Huntsman fixed-bed maleic anhydride process is shown in Figure 1. 

Compound Flash point, °C Flammability limit, vol % Lower Upper Autoignition temperature, °C... 

Safety is a critical aspect in the design of phenol plants. Oxidation of cumene to CHP occurs at conditions close to the flammable limits. Furthermore, the CHP is a potentially unstable material which can violendy decompose under certain conditions. Thus, phenol plants must be carefully designed and provided with weU-designed control and safety systems. 

Simple asphyxiant value shown is 10% of the lower flammable limit (LFL). 

The lower flammable limit (LEL) or lower explosive limit (LEL) is the minimum concentration of vapor in air below which a flame is not propagated when an ignition source is present (61—64). Below this concentration, the mixture is considered too lean to bum. The lower flammable limit and the flash point of a flammable Hquid are closely related by the Hquid s vapor pressure characteristics. 

Halothane. Halothane or Fluothane, 2-bromo-2-chloro-l,l,l-trifluoroethane [151 -67-7] is a colorless Hquid with a pleasant odor. Its lower flammability limit, 4.8% in 70% N2O/30% O2, renders it essentially nonflammable. It has a vapor pressure of 32.5 kPa (244 mm Hg) at 20 °C and is stable to soda lime. However, it is photochemicaHy reactive. 

Lower flammability limits (LFL) are expressed as vol % in dry ambient air. No entry means ASHRAE Safety Classification (2) (see Fig. 3). NR = not rated. 

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