Vapor combustion, flammability

The surface area of a spill should be minimized for materials that are highly toxic and have a significant vapor pressure at ambient conditions, such as acrylonitrile or chlorine. This will make it easier and more practical to collect vapor from a spill or to suppress vapor release with foam. This may require a deeper nondrained dike area than normal or some other design that wilfminimize surface area, in order to contain the required volume. It is usually not desirable to cover a diked area to restric t loss of vapor if the spill consists of a flammable or combustible material. 

For combustible dusts, the explosibility limits do not have the same meaning as with flammable gases and flammable vapors, owing to the interaction between dust layers and suspended dust. This protective measure can, for example, be used when dust deposits are avoided in operating areas or in the air stream of clean air lines after filter installations WTiere in normal operation the lower explosibility limit is not reached. However, dust deposits must be anticipated with time. When these dust deposits are whirled up in the air, an explosion hazard can arise. Such a hazard can be avoided by regular cleaning. The dust can be extracted directly at its point of origin by suitable ventilation measures. 

Fire Hazards - Flash Point (deg. F) 167 OC, 85 CC Flammable Limits in Air (%) No data Fire Extinguishing Agents Foam, dry chemical, or carbon dioxide Fire Extinguishing Agents Not To Be Used Water may be ineffective Special Hazards of Combustion Products Toxic oxides of nitrogen and flammable vapors may form Behavior in Fire No data Ignition Temperature (deg. F) 900 Electrical Hazard No data Burning Rate 3.6 mm/min. 

No one realized, when a site for the furnace was decided, that flammable vapors could come out of the cooling tower. Direct contact condensers are not common, but flammable vapors can appear in many cooling towers if there are leaks on water-cooled heat exchangers. After the incident, a combustible gas detector was mounted permanently between the furnace and the tower (Figure 2-8). 

Raj, P. P. K., and H. W. Emmons. 1975. On the burning of a large flammable vapor cloud. Paper presented at the Joint Technical Meeting of the Western and Central States Section of the Combustion Institute. San Antonio, TX. 

The methods described in this chapter are meant for practical application background information is given in Chapter 4. If a quantity of fuel is accidentally released, it will mix with air, and a flammable vapor cloud may result. If the flammable vapor meets an ignition source, it will be consumed by a combustion process which, under certain conditions, may develop explosive intensity and blast. 

Confined combustion explosions (gaseous or liquid) usually occur when a flammable vapor leaks into an enclosure and mixes witJi air to form a flarmnable mix-ture, whereupon this mix+ure contacts an ignition source tliat was present before the leak occurred. This type of explosion ctm tUso occur in storage taitks or sliips where tlie vapor space above tlie stored flanunable liquid (fuel) is in tlie cxplosivity range. In tliis case, an ignition source accidentally introduced will cause an explosion. 

Scope—Articles 500 Through 505. Articles 500 through 505 cover the requirements for electrical equipment and wiring for all voltages in locations where fire or explosion hazards may exist due to flammable gas or vapors, flammable liquids, combustible dust, or ignitable fibers or flyings. 

Location and General Requirements. Locations shall be classified depending on the properties of the flammable vapors, liquids or gases or combustible dusts or fibers that may be present and the likelihood that a flammable or combustible concentration or quantity is present. Where pyrophoric materials are the only materials used or handled, these locations shall not be classified. 

Outdoor equipment of the type covered in Flammable and Combustible Liquids Code, NFPA, 30-1993 (ANSI), Section 5-3.3.2, where flammable vapor-air mixtures may exist under normal operation... 

Additional events of concern that may or may not involve flammable or combustible materials are condensed-phase explosions, uncontrolled chemical reactions, boiling liquid expanding vapor explosions (BLEVEs),... 

The key point here is to determine if flammable or combustible materials are being processed under conditions of temperature and pressure such that, if a release occurs, a significant quantity of the material may be released into the air as either a gas, vapor, mist, or aerosol. If such conditions are present, the user should assume that the potential for a vapor cloud explosion exists. Otherwise, VCE hazards can be ignored. 

Rigas, F. and Sklavounos, S., Simulation of Coyote series trials—Part II a computational approach to ignition and combustion of flammable vapor clouds, Chem. Eng. Sci., 61, 1444, 2006. 

The chemical products from complete combustion of a hydrocarbon fuel are mainly C02 and H20 (vapor). Combustion of gaseous fuel in air can occur in two different modes - one where fuel and oxygen is mixed during the combustion process, and the other where fuel and air are premixed (gas condensing boilers) and the fuel concentration must be within the flammability limits. In general the premixed situation allows the fuel to burn faster, i.e. more fuel is consumed per unit time. 

The vent must be installed on the larger outer wall to vent the combustion away from the adjoining structure. The venting constant for this flammable vapor is provided in Table 9-1 and has a value of 0.45 VkPa. Equation 9-28 is used to estimate the required vent area. The total surface area of the room (including floor and ceiling) is... 

In explosive facilities and locations where the atmosphere may contain combustible dusts, or flammable vapors or gases, ferrous metal surfaces should not be coated with aluminum paint due to the potential sparking hazard. 

Laboratories are normally classified nonhazardous locations if the quantities of flammable and combustible liquids are within the requirements of NFPA. Normally a vapor collection hood is provided when sampling and measurements are conducted with exposed liquids. The primary concern is the exhaust of vapors and the storage and removal material saturated with liquids. The exhaust hood, ducting and a radius of 1.5 meters (5 ft.) from the exhaust vent should be considered an electrically classified area. 

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. 

Testing for the presence of flammable vapors and inspection for combustible materials... 

Flammable vapors, flammable gases, combustible dusts, and ignitable fibers are hazardous materials found in many manufacturing facilities. These materials are necessary for, created by, or are unavoidable byproducts of, the manufacturing process. 

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