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Liquefied petroleum gas (also called '''LPG''', '''LP Gas''', or '''autogas''') is a mixture of Hydrocarbon Gas es used as a Fuel in heating appliances and vehicles, and increasingly replacing Chlorofluorocarbon s as an aerosol propellant and a refrigerant to reduce damage to the Ozone Layer . Varieties of LPG bought and sold include mixes that are primarily Propane , mixes that are primarily Butane , and the more common, mixes including both Propane (60%) and Butane (40%), depending on the season—in winter more propane, in summer more butane. Propylene and Butylene s are usually also present in small concentration. A powerful odorant, Ethanethiol , is added so that leaks can be detected easily. The international standard is EN 589 . LPG is manufactured during the refining of Crude Oil , or extracted from oil or Gas streams as they emerge from the ground. At normal temperatures and pressures, LPG will evaporate. Because of this, LPG is supplied in pressurised , likewise varies depending on composition and temperature; for example, it is approximately 220 Kilopascal s (2.2 Bar ) for pure butane at 20 °C (68 °F), and approximately 2.2 Megapascal s (22 bar) for pure propane at 55 °C (131 °F). LPG is heavier than air, and thus will flow along floors and tend to settle in low spots, such as basements. This can cause ignition or suffocation hazards if not dealt with. PRODUCTION LPG is synthesised by Refining Petroleum or 'wet' Natural Gas ; it was first produced in 1910 by Dr. Walter Snelling, and the first commercial products appeared in 1912. It currently provides about 3% of the energy consumed. USAGE IN VEHICLES See Also: Autogas When LPG is used to fuel Internal Combustion Engines , it is often referred to as autogas. In some countries, it has been used since the 1940s as an alternative fuel for spark ignition engines. More recently, it has also been used in diesel engines. REFRIGERATION AND AIR CONDITIONING In highly purified form, various blends of the LPG constituents propane and iso-butane are used to make hydrocarbon refrigerants, which are increasingly being used in refrigeration and Air Conditioning systems including domestic Refrigerator s, building air conditioners and vehicle air conditioning. This is partly because of concerns about the Greenhouse effect of the widely used HFC 134a . Hydrocarbons are more energy efficient, run at the same or lower pressure and are generally cheaper than HFC 134a. LPG AS COOKING FUEL According to the 2001 Census of Indian households. LPG is subsidised by the government. Increase in LPG prices has been a politically sensitive matter in India as it potentially affects the Urban Middle Class voting pattern. LPG was once a popular cooking fuel in Hong Kong ; however, the continued expansion of Town Gas to buildings has reduced LPG usage to less than 24% of residential units. LPG is the most common cooking fuel in Brazil ian urban areas, being used in virtually all households. Poor families receive a government grant ("Vale Gás") used exclusively for the acquisition of LPG. LPG AND SNG LPG has a higher Calorific Value (94 MJ/m³ equivalent to 26.1kWh) than natural gas ( Methane ) (38 MJ/m³ equivalent to 10.6kWh), which means that LPG can not simply be substituted for natural gas. In order to allow the use of the same burner controls and to provide for similar combustion characteristics, LPG can be mixed with air to produce a synthetic natural gas (SNG) that can be easily substituted. LPG/air mixing ratios average 60/40, though this is widely variable based on the gases making up the LPG. The method for determining the mixing ratios is by calculating the Wobbe Index of the mix. Gases having the same Wobbe index are held to be interchangeable. LPG-based SNG is used in emergency backup systems for many public, industrial, and military installations, and many utilities use LPG Peak Shaving plants in times of high demand to make up shortages in natural gas supplied to their distributions systems. LPG-SNG installations are also used during initial gas system introductions, when the distribution infrastructure is in place before gas supplies can be connected. Developing markets in India and China (among others) use LPG-SNG systems to build up customer bases prior to expanding existing natural gas systems. FIRE RISK AND MITIGATION ]] LPG containers that are subjected to fire of sufficient duration and intensity can undergo a boiling liquid expanding vapour explosion (. If the containers are cylindrical and horizontal, they are referred to as "cigars", whereas circular ones are "spheres". Large, spherical LPG containers may have up to a 15 cm steel wall thickness. Ordinarily, they are equipped with an approved pressure relief Valve on the top, in the centre. One of the main dangers is that accidental spills of Hydrocarbon s may ignite and heat an LPG container, which increases its temperature and pressure, following the basic Gas Laws . The relief valve on the top is designed to vent off excess pressure in order to prevent the rupture of the tank itself. Given a fire of sufficient duration and intensity, the pressure being generated by the boiling and expanding gas can exceed the ability of the valve to vent the excess. When that occurs, an overexposed tank may rupture violently, launching pieces at high velocity, while the released products can ignite as well, potentially causing catastrophic damage to anything nearby, including other tanks. In the case of "cigars", a midway rupture may send two "rockets" going off each way, with plenty of fuel in each to propel each segment at high speed until the fuel is spent. Mitigation measures include separating LPG tanks from potential sources of fire. In the case of rail transport, for instance, LPG tanks can be staggered, so that other goods are put in between them. This is not always done, but it does represent a low-cost remedy to the problem. LPG rail cars are easy to spot from the relief valves on top, typically with railings all around. In the case of new LPG containers, one may simply ''bury'' them, only leaving valves and armatures exposed, for easy maintenance. Great care must be taken there though, as mechanical damage has been known to occur to the primers, which has resulted in hazardous corrosion of the containers. For the buried container, only the exposed parts need to be treated with approved Fireproofing materials, such as Intumescent and or Endothermic coatings, or even fireproofing Plaster s. The rest are amply protected by soil. Specialty removable covers exist for easy access to the dials and components that must be accessed for proper maintenance and operation of the equipment. LPG containers are subject to significant motion due to expansion, contraction, filling and emptying – even with very thick steel walls. This operational motion makes the burial option less attractive in the long run because one cannot tell mechanical damage to the outer waterproofing through Soil . A simple pebble scraping back and forth across the Epoxy -painted hull can remove the waterproofing and be the cause for Corrosion . Whilst one may calculate and justify on paper the use of inorganic plasters to cover entire spheres, it can be difficult to keep Plaster s operable for extended periods of time. Major errors have also been made in the past in this field, as the presumption was that the steel substrate would be adequately protected from rusting through the use of alkaline plasters. The alkalinity in such plasters is due to the presence of cement stone. This alkalinity, however, does not typically have a permanent character, which means that waterproofing with high quality Epoxy primers is very important. Also, exterior waterproofing of the plaster is required by some fireproofing plaster vendors, as reduced alkalinity in exposed plasters can have a deleterious effect on the cement stone, which binds the plaster in the first place. By contrast, the intumescent and endothermic coatings are usually epoxy based to begin with, meaning that corrosion of the substrate is no problem whatsoever. Fireproofing, not unlike all and to be sure that the product one chooses has undergone Product Certification , whereby the original test included the environmental exposures that the product will be exposed to during operations. Particularly with organic products, such as the endothermic and intumescent ones, one must closely review the ageing criteria and be able to quantify how long the product is expected to be operable for. This is where UL1709 "shines". Anything that can withstand the full battery of environmental exposures prior to the actual fire test, is a very tough product indeed. The idea is to rule out conditions that may render the product inoperable before it is ever exposed to a fire. By using products that have received the appropriate environmental tests FIRST, and the fire expose afterwards, using the very same test sample with all the applicable exposures, one can then demonstrate Due Diligence , but not otherwise. Likewise, the DIBt ageing qualifications for intumescents have proven to be very reliable. With close attention to the bounding and coverage of ageing and environmental exposures, it is absolutely possible to buy a lot of time for firefighting measures to relieve the LPG containers of the energy exposure from accidental fires and thus reduce the likelihood of a BLEVE to the maximum possible extent. SEE ALSO
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