Flammability Designation

Class IA - Liquids with flash points below 73°F and boiling points below 100 F. An example of a Class lA flammable liquid is n-pentane (NFPA Diamond 4). 

Class IB - Liquids with flash points below 73 F and boiling points at or above 100°F. Examples of Class IB flammable liquids are benzene, gasoline, and acetone (NFPA Diamond 3). 

Class II - Liquids with flash points at or above 1(X)°F but below 140°F. Examples of Class II flammable liquids are kerosene and camphor oil (NFPA Diamond 2). 

These designations serve as useful guides in storage, transport, and spill response. However, they do have limitations. Since these designations are somewhat arbitrary, it is useful to understand the basic concepts of flammability. 

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A number of equipment selection guides have been published. Pratt and Hanson [Chap. 16 in Handbook of Solvent Extraction, Lo, Baird, and Hanson, eds. (Wiley, 1983 Krieger, 1991)] provide a detailed comparison chart for 20 equipment types considering 14 characteristics. Pratt and Stevens [Chap. 8 in Science and Practice of Liquid-Liquid Extraction, vol. 1, Thornton, ed. (Oxford, 1992)] modified the Pratt and Hanson selection guide to include solvent volatility and flammability design parameters. Stichlmair [Chem. Ing. Tech., 52(3) pp. 253-255 (1980)] and Holmes, Karr, and Cusack (AIChE... 

Storage tanks should have temperature monitoring with alarms to detect the onset of reactions. The design should comply with all appHcable industry, federal, and local codes for a class IB flammable Hquid. The storage temperature should be below 37.8°C. Storage should be under an atmosphere of dry nitrogen and should vent vapors from the tank to a scmbber or flare. 

Hazards. The solvent should be nontoxic and nonhazardous adequate design must take into account flammability and explosivity characteristics of the solvent. 

DMF can be purchased ia steel dmms (DOT 17E, UNlAl, 410 lbs net = 186 kg), tank tmcks, and railcars. On Oct. 1, 1993, new regulations in the United States were estabUshed for DMF under HM-181 the official shipping name is /V, /V- dim ethyl form am i de (shipping designation UN 2265, Packing Group III, Flammable Liquid). Formerly, it was classified as a Combustible Liquid in bulk quantities, but as "Not Regulated" in dmms (49 CFR). International overseas shipments have an IMCO classification of 3.3. 

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. 

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. 

Waste facihties should be designed to prevent explosions in sewer systems and typically are comprised of suitable traps, vents, clean-outs, collecting chambers, etc. Flammable gas detectors are installed in sewers to warn of ha2ardous concentrations, and inert gas blanketing of closed process sumps generally is advisable. 

Fire and Explosion Prevention. Prevention of fire and explosion takes place in the design of chemical plants. Such prevention involves the study of material characteristics, such as those in Table 1, and processing conditions to determine appropriate ha2ard avoidance methods. Engineering techniques are available for preventing fires and explosions. Containment of flammable and combustible materials and control of processes which could develop high pressures are also important aspects of fire and explosion prevention. 

Calcium carbide is classed as a ha2ardous chemical under Department of Transportation regulations. Domestic shipments are mainly in steel tote bins varying in capacity from 2.5—4.5 t. A small amount continues to be shipped in industrial wide mouth steel dmms of 270 kg capacity. Containers must be marked "Flammable soHd, dangerous when wet" and have the United Nations designation UN 1402. 

Thermal Properties. Thermal properties include heat-deflection temperature (HDT), specific heat, continuous use temperature, thermal conductivity, coefficient of thermal expansion, and flammability ratings. Heat-deflection temperature is a measure of the minimum temperature that results in a specified deformation of a plastic beam under loads of 1.82 or 0.46 N/mm (264 or 67 psi, respectively). Eor an unreinforced plastic, this is typically ca 20°C below the glass-transition temperature, T, at which the molecular mobility is altered. Sometimes confused with HDT is the UL Thermal Index, which Underwriters Laboratories estabflshed as a safe continuous operation temperature for apparatus made of plastics (37). Typically, UL temperature indexes are significantly lower than HDTs. Specific heat and thermal conductivity relate to insulating properties. The coefficient of thermal expansion is an important component of mold shrinkage and must be considered when designing composite stmctures. 

Most storage containers for ciyogens are designed for a 10 percent ullage volume. The latter permits reasonable vaporization of the contents due to heat leak without incurring too rapid a buildup of the pressure in the container. This, in turn, permits closure of the container for short periods of time to either avoid partial loss of the contents or to transport flammable or hazardous ciyogens safely from one location to another. 

Understanding how sudden pressure releases can occur is important. They can happen, for example, from ruptured high-pressure tanks, runaway reactions, flammable vapor clouds, or pressure developed from external fire. The proper design of pressure rehef systems can reduce the possibility of losses from unintended overpressure. 

For many years the usual procedure in plant design was to identify the hazards, by one of the systematic techniques described later or by waiting until an accident occurred, and then add on protec tive equipment to control future accidents or protect people from their consequences. This protective equipment is often complex and expensive and requires regular testing and maintenance. It often interferes with the smooth operation of the plant and is sometimes bypassed. Gradually the industry came to resize that, whenever possible, one should design user-friendly plants which can withstand human error and equipment failure without serious effects on safety (and output and emciency). When we handle flammable, explosive, toxic, or corrosive materials we can tolerate only very low failure rates, of people and equipment—rates which it may be impossible or impracticable to achieve consistently for long periods of time. 

The F EI measures realistic maximum loss potential under adverse operating conditions. It is based on quantifiable data. It is designed for flammable, combustible, and reactive materials that are stored, handled, or processed. It does not address frequency (risk) except indirectly, nor does it address specific hazards to people except indirectly. 

NFPA 30 and API Standard 2000 provide gmdance for design of overpressure protec tion involving storage tanks that operate at or near atmospheric pressure. In particular, NFPA 30 focuses on flammability issues, while API 2000 addresses both pressure and vacuum requirements. The ASME code (Sections I and TII) and API RP 520 are the primaiy references for pressure rehef device sizing requirements. 

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