Petroleum flash point

The flash point measures the tendency of a petroleum material to form a flammable mixture with air. It is one of the properties to be considered when evaluating the flammability of a petroleum cut. 

The flash point of a petroleum liquid is the temperature to which it must be brought so that the vapor evolved burns spontaneously in the presence of a flame. For diesel fuel, the test is conducted according to a closed cup technique (NF T 60-103). The French specifications stipulate that the flash point should be between 55°C and 120°C. That constitutes a safety criterion during storage and distribution operations. Moreover, from an official viewpoint, petroleum products are classified in several groups according to their flash points which should never be exceeded. 

Petroleum solvents are very flammable and can cause an explosion in the presence of air. For this reason, their flash points, directiy related to volatility, are always specified. 

Safety standards govern the manipulation and storage of crude oil and petroleum products with regard to their flash points which are directly linked to vapor pressure. 

Storage of Flammable Materials. The preferred storage for flammable Hquids or gases is in properly designed tanks. Floating roof tanks frequently are used in the petroleum industry for flammable cmdes and products (see Tanks and pressure vessels). The vents on cone roof tanks should either be equipped with flame arrestors or the vapor space above the contents should be inerted with a nonflammable gas or vapor, unless the flash point is weU above the maximum ambient temperature, the contents are not heated above the flash point, and the tank is not exposed to other tanks containing flammable Hquids. 

Fixed-roof atmospheric tanks require vents to prevent pressure changes which would othei wise result from temperature changes and withdrawal or addition of liquid. API Standard 2000, Venting Atmospheric and Low Pressure Storage Tanks, gives practical rules for vent design. The principles of this standard can be applied to fluids other than petroleum products. Excessive losses of volatile liquids, particularly those with flash points below 38°C (100°F), may result from the use of open vents on fixed-roof tanks. Sometimes vents are manifolded and led to a vent tank, or the vapor may be extracted by a recov-eiy system. 

In view of the above adverse effects a safety factor should be applied where flammability is assessed using flash point. For pure liquids in containers the vapor should be considered potentially flammable if the liquid temperature is upward of at least 5°C below the reported flash point. For mixtures whose composition is less certain, such as petroleum mixtures, the safety factor should be about 15°C relative to the flash point [55]. Where combinations of adverse effects are identified the safety factors should be increased accordingly. A simple but very conservative approach is to assume that all liquids having a flash point <141°F may produce a flammable atmosphere under some ambient conditions, even where no mist or froth production is involved. A more practical approach is to assume that liquids handled in air at least 5-15°C below their closed cup flash points will not present ignition risks unless... 

Regulates the use, transport or storage of petroleum spirit and - as extended by other legislation - mixtures, e.g. adhesives, thmners or lacquers containing petroleum, and non-petroleum based solvents with a flash point <73°F. 

Biodiesel does not present any special safety concerns. Pure biodiesel or biodiesel and petroleum diesel blends have a higher flash point than conventional diesel, making them safer to store and handle. Problems can occur with biodiesels in cold weather due to their high viscosity. Biodiesel has a higher degree of unsaturation in the fuel, which can make it vulnerable to oxidation during storage. 

Flammable liquid A liquid having a closed-cup flash point below 100°F (37.8°C) and having a Reid vapor pressure not exceeding 40 psia (2068.6 mm Hg) at 100°F (37.8°C), as determined by ASTM D 323, Standard Method of Test for Vapor Pressure of Petroleum Products (Reid Method). 

Methods of test for petroleum and its products. Determination of flash point. Pensky-Martens closed cup method. 

The oil used should be of a volatile type, as the more volatile oils gives the greatest sensitivity. However, the use of petroleum fractions with too low a flash point is hazardous. The choice is, therefore, usually made of a fuel oil similar to those used for diesel engines. It is common practice to add a proportion of dyestuff to the oil, partly to make adequate mixing of the explosive immediately visible, and partly to assist the user in seeing proper loading of boreholes, particularly in salt and other white materials. 

Common petroleum materials with some of the lowest flash points under normal conditions are listed... 

Kerosene or sometimes referred to as Fuel Oil 1 is a refined petroleum distillate. Kerosenes usually have flash points within the range of 37.8 °C to 54.4 °C (100 °F to 130 °F). Therefore unless heated, kerosene will usually not produce ignitable mixtures over its surface. In atmospheric burning smoke production normally occurs. It is commonly used as a fuel and a solvent. In some applications it is treated with sulfuric acid to reduce the content of aromatics, which bum with a smoky flame. 

Petroleum is typically described in terms of its physical properties (such as density and pour point) and chemical composition (such as percent composition of various petroleum hydrocarbons, asphaltenes, and sulfur). Although very complex in makeup, crude can be broken down into four basic classes of petroleum hydrocarbons. Each class is distinguished on the basis of molecular composition. In addition, properties important for characterizing the behavior of petroleum and petroleum products when spilled into waterways or onto land and/or released into the air include flash point, density (read specific gravity and/or API gravity), viscosity, emulsion formation in waterways, and adhesion to soil. 

The flash point of petroleum or a petroleum product is the temperature to which the product must be heated under specified conditions to give off sufficient vapor to form a mixture with air that can be ignited momentarily by a specified flame (ASTM D56, D92, D93). The flre point is the temperature to which the product must be heated under the prescribed conditions of the method to bum continuously when the mixture of vapor and air is ignited by a specified flame (ASTM D92). 

From the viewpoint of safety, information about the flash point is of most significance at or slightly above the maximum temperatures [30 to 60°C (86 to 140°F)] that may be encountered in storage, transportation, and use of liquid petroleum products, in either closed or open containers. In this temperature range the relative fire and explosion hazard can be estimated from the flash point. For products with flash points below 40°C (104°F), special precautions are necessary for safe handling. Flash points above 60°C (140°F) gradually lose their safety significance until they become indirect measures of some other quality. 

The flash point of a petroleum product is also used to detect contamination. A substantially lower flash point than expected for a product is a reliable indicator that a product has become contaminated with a more volatile product, such as gasoline. The flash point is also an aid in establishing the identity of a particular petroleum product. 

Ignitability-flammability. A liquid that has a flash point of less than 60°C (140°F) is considered ignitable. Some examples are benzene, hexane, heptane, benzene, pentane, petroleum ether (low boiling), toluene, and xylene(s). 

As for all petroleum products, considerations of safety in storage and transportation and, more particularly, contamination by more volatile products are required. This is usually accommodated by the Pensky-Martens flash point test (ASTM D93 IP 34). For the fuel oil, a minimum flash point of 55°C (131°F) or 66°C (150°F) is included in most specifications. 

Safety Considerations Design and location of storage tanks, vents, piping, and connections are specified by state fire marshals, underwriters codes, and local ordinances. In NFPA 30, Flammable and Combustible Liquids Code, 2003 (published by the National Fire Protection Association, Quincy, Ma.), liquid petroleum fuels are placed in Class I through Class III B based on their flash point, boiling point, and vapor pressure. 

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