Fire, defined

The philosophers of Greece, whose goal was to understand and describe the nature of the universe, made use of the known properties of heat, but they did not separate the concepts of heat and temperature. They knew, for example, that fire—defined as one of the four elements of the universe—would cause the expansion of air, another primal element. In the second or first century B.C., Heron of Alexandria applied this knowledge to invent a steam turbine, but he considered it only a toy. Philon of Alexandria likewise invented several devices that demonstrated the expansion property of heated air (Cohen and Drabkin, 1948 Sarton, 1959). The Greeks went no further in their investigations, although the manuscripts they left inspired the scientific thinkers of the Renaissance (Taylor, 1941). 

PRF. Defines the pulse repetition frequency (PRF), in Hz, of the probe firing. 

In this sequence the Cl also acts as a catalyst and two molecules are destroyed. It is estimated that before the Cl is finally removed from the atmosphere in 1—2 yr by precipitation, each Cl atom will have destroyed approximately 100,000 molecules (60). The estimated O -depletion potential of some common CFCs, hydrofluorocarbons, HFCs, and hydrochlorofluorocarbons, HCFCs, are presented in Table 10. The O -depletion potential is defined as the ratio of the emission rate of a compound required to produce a steady-state depletion of 1% to the amount of CFC-11 required to produce the 1% depletion. The halons, bromochlorofluorocarbons or bromofluorocarbons that are widely used in fire extinguishers, are also ozone-depleting compounds. Although halon emissions, and thus the atmospheric concentrations, are much lower than the most common CFCs, halons are of concern because they are from three to ten times more destmctive to O, than the CFCs. 

Smoke, Flash, and Fire Points. These thermal properties may be determined under standard test conditions (57). The smoke poiat is defined as the temperature at which smoke begias to evolve continuously from the sample. Flash poiat is the temperature at which a flash is observed whea a test flame is appHed. The fire poiat is defiaed as the temperature at which the fire coatiaues to bum. These values are profouadly affected by minor coastitueats ia the oil, such as fatty acids, moao- and diglycerides, and residual solvents. These factors are of commercial importance where fats or oils are used at high temperatures such as ia lubricants or edible frying fats. 

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. 

Equipment Tests. Procedures for rigorous, detailed efficiency determination are available (ASME Test Codes) but are rarely used. For the objective of defining conservation potentials, relatively simple measurements are adequate. For fired heaters, stack temperature and excess O2 ia stack should be measured for turbiaes, pressures (ia and out) and temperatures (ia and out) are needed. 

In fossil fuel-fired boilers there are two regions defined by the mode of heat transfer. Fuel is burned in the furnace or radiant section of the boiler. The walls of this section of the boiler are constmcted of vertical, or near vertical, tubes in which water is boiled. Heat is transferred radiatively from the fire to the waterwaH of the boiler. When the hot gas leaves the radiant section of the boiler, it goes to the convective section. In the convective section, heat is transferred to tubes in the gas path. Superheating and reheating are in the convective section of the boiler. The economizer, which can be considered as a gas-heated feedwater heater, is the last element in the convective zone of the boiler. 

In the fire codes, the atmospheric boiling point is an important physical property used to classify the degree of hazardousness of a Hquid. If a mixture of Hquids is heated, it starts to bod at some temperature but continues to rise ia temperature over a boiling temperature range. Because the mixture does not have a definite boiling poiat, the NFPA fire codes define a comparable value of boiling poiat for the purposes of classifying Hquids. For petroleum mixture, it is based on the 10% poiat of a distillation performed ia accordance with ASTM D86, Standard Method of Test for Distillation of Petroleum Products. 

The combustion chamber of a modem steam generator is a large water-cooled chamber in which fuel is burned. Firing densities are important to ensure that the chamber wall metal temperatures do not exceed the limits of failure of the tubes. Firing densities are expressed in two ways volumetric combustion intensities and area firing intensities. The volumetric combustion intensity is defined by equation 23,... 

Flammability. Dimer and trimer acids, as well as monomer acids derived from dimer acid processing, are neither flammable nor combustible as defined by the Department of Transportation (DOT) and do not represent a fire ha2ard ... 

Flammability—Flash Point The closed-cup flash point determination produces the most important data to determine the potential for fire. The flash point is the lowest temperature at which the vapors can be ignited under conditions defined by the test apparatus and method. 

Combustible Eiquid A term used to classify certain liquids that will burn on the basis of flash points. The National Fire Protection Association (NFPA) defines a combustible liquid as having a flash point of 100°F (37.8°C) or higher. See also, Flammable Liquid. Class II liquids have flash points at or above 100°F, but below 140°F. Class III liquids are subdivided into two subclasses. 

DANGEROUS SUBSTANCES (uk) Defined substances which may be hazardous to the fire services in an emergency. (Dangerous Substances (Notification and Marking of Sites) Regulations 1990.)... 

Low-excess-air firing (LEA) is a simple, yet effective technique. Excess air is defined as the amount of air in excess of what is theoretically needed to achieve 100% combustion. Before fuel prices rose, it was not uncommon to see furnaces operating with 50 to 100% excess air. Currently, it is possible to achieve full combustion for coal-fired units with less than 15-30% excess air. Studies have shown that reducing excess air ft-om an average of 20% to an average of 14% can reduce emissions of NO, by an average of 19%. 

Point Source a source of pollution that is well defined, such as the smokestack of a coal-fired power plant or smelter. 

Burning Rate - Defined as the rate (in millimeters per minute) at which a pool of liquid decreases as the liquid bums. Details of measurements are provided by D. S. Burgess, A. Strasser, and J. Grumer, Diffusive Burning of Liquid Fuels in Open Trays, Fire Research Abstracts and Reviews, 3, 177 (1961). 

Flammability Range - Defined as the difference between the UEL and LEL. This difference is an indication of how wide the flammability limits of a chemical are. The wider this range, the more hazardous the chemical may be considered from a fire standpoint. 

Ignition Temperature - This is defined as the minimum temperature at which a chemical substance will ignite without a spark or flame being present. Along with the values of flash point and flammability range, it provides and indication of the relative fire potential for the chemical. 

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