Smoke, flash and fire points

These parameters are related to the free fatty acid content of oils because fatty acids have higher vapor pressure than the triacylglycerols. Smoke point is the temperature at which smoke is first seen. Flash point is the temperature at which the volatiles are produced in amounts that ignite but do not support a flame. Fire point is the temperature at which the volatiles are produced in a quantity that 

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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. 

When a fat or oil is heated, thermal instability may cause decomposition, and depending on the temperature reached, subsequent combustion of volatile gaseous decomposition products (Mehlenbacher, 1960). The thermal stability of fats and oils is thus essentially a chemical characteristic. However, stability is characterized by measuring certain critical temperatures, the smoke, flash and fire points, at which certain heat-induced changes become apparent. It is appropriate, therefore, to include here methods for measuring these critical points. 

Measurement of smoke, flash and fire points is carried out subjectively by observing the surface of an oil sample while the sample is being heated. (The critical temperatures are higher than the upper limit of the melting point range of a fat.) The smoke point is the temperature at which the sample begins to give off a continuous stream of bluish smoke, observable... 

Standard methods for the determination of the critical temperatures are published by the AOCS (AOCS Official Methods Cc 9a 48 (smoke, flash and fire points by an open cup method), and Cc 9b-55 and Cc 9c 95 (flash point by open cup methods), Firestone, 1998) and by the British Standards Institution (BS 684 Section 1.8 1976 (smoke point), BSI, 1976b and BS 684-1.17 1998/ISO 15267 1998 (flashpoint by a closed cup method), BSI, 1998b). 

Smoke, Flash, and Fire Point—Cleveland Open Cup Method (Cc 9a-48) determines the temperatures at which fats and oils smoke, flash, or burn. Smoke point determinations sometimes are used to follow degradation of frying oils with use. 

Other physical properties such as the smoke, flash, and fire points of oils and fats are measures of their thermal stability when heated. The smoke point is important for the oils and fats used for deep-frying. The flash point and fire points are a measure of residual solvent in crude and refined oils and are also a safety requirement. 

Smoke, flash and fire points Oxidative state °C... 

Figure 1. Relationship between free fatty acid content and smoke, flash, and fire points of cottonseed and peanut oils.----------, Refined cottonseed oii --------, peanut oil.

Flash and Fire Point. Flash point is the temperature at which the volatile products are evolved at such a rate that they are capable of being ignited but not supporting combustion. At the fire point, the accumulated breakdown products are capable of supporting a flame on their own. A crude cottonseed oil with a fatty acid content of 1.8% was found to have a flash point of 560°F or 293.3°C. Solvent-extracted oils can have a low flash point because of a solvent residue. A flash point analysis would identify this crude oil deficiency to prevent an accidental fire or explosion in an atmosphere that was not explosion proof. Crude vegetable oil shipments received with a flash point below 250°F are rejectable by most trading rules. Figure 1 shows the relationship between free fatty acid content, smoke, flash, and fire points of processed cottonseed and peanut oils. 

The smoke, flash, and fire points of soybean oil have been determined by the Cleveland Cup method and show considerable variation. Dickhart (117) reported a smoke point of 138°C while Detwiler and Markley (76) reported 241-250°C. 

Fatty acids are much more volatile than glycerides therefore, smoke, flash, and fire points of oils depend principally... 

Fatty acids are much more volatile than glycerides therefore, smoke, flash, and fire points of oils depend principally on the content of free fatty acids, and decrease if hydrolytic degradation is extended during frying. The smoke point of cottonseed, corn, or peanut oils, e.g., decreases from about 232°C at a free fatty acid content of 0.01% to 93°C at a free fatty acid content of 100%i. The unsaturation of oil has hardly any effect on its smoke, flash, and fire points. 

Smoke Point, Fiash Point, and Fire Point The smoke point, flash point, and fire point of an oil are relevant parameters in deep-fat frying processes. The fatty acid composition of the oil is not relevant (unless the oil has short-chain fatty acids, as is the case of butter or coconut oil). The most important effect is generally that of free fatty acids (FFA) in the oil. The following values have been reported for fully refined sunflower oil (with 0.10% free fatty acids) smoke point = 209°C flash point = 316°C fire point = 341°C (5). 

The smoke, fire, and Hash points of a fatty material are measures of its thermal stability when heated in contact with air. The smoke point is the temperature at which smoking is first detected in a laboratory apparatus protected from drafts. The flash point is the temperature at which the volatile products are evolved at a rate sufficient to be ignited, but not to support combustion. The fire point is the temperature at which the volatile products support continued combustion. 

Ignition Temperature, Flash Point, Fire Point, and Smoke Point... 

Four important tests which are used to characterize an engine fuel are the spontaneous ignition temperature (SIT), flash point, fire point, and smoke point. These tests are standardized, and specialized fuels have specific requirements as defined by these tests. The SIT is dependent on the composition of the fuel and the conditions of the walls of the cylinder. Diesel fuels require low SIT with short delay times of the order of 1-2 ms. The SIT of heptane (CN = 60) is 330°C, whereas benzene with CN = —10 has a SIT of 420°C. 

Fire Hazards - Flash Point (deg. F) 95 CC Flammable Limits in Air (%).- 0.8 (LEL) Fire Extinguishing Agents Foam, dry chemical, or carbon dioxide Fire Extinguishing Agents Not to be Used Water may be ineffective Special Hazards cf Combustion Products Not pertinent Behavior in Fire Forms heavy black smoke and soot Ignition Temperature (deg. F) 488 Electrical Hazard Not pertinent Burning Rate 2.4 mm/min. 

Other important properties include Hash point, volatility, viscosity, specific gravity, cloud point, pour point, and smoke point. Most of these properties are related directly to the boiling range of the kerosene and are not independently variable. The flash point, an index of fire hazard, measures the readiness of a fuel to ignite when exposed to a flame. It is usually mandated by law or government regulation to be 120° or 130° F (48° or 72° C), Volatility, as measured... 

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