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[[Image:LPG cylinders.JPG|thumb]]
'''Liquefied petroleum gas'''  (also called '''LPG''', '''GPL''', '''LP Gas''', or '''liquid propane gas''') is a [[flammable]] mixture of [[hydrocarbon]] gases used as a [[fuel]] in heating appliances and vehicles. It is increasingly used as an [[aerosol propellant]] and a [[refrigerant]], replacing [[chlorofluorocarbon]]s in an effort to reduce damage to the [[ozone layer]]. When specifically used as a vehicle fuel it is often referred to as ''[[autogas]]''.

Varieties of LPG bought and sold include mixes that are primarily [[propane]] ({{chem|C|3|H|8}}), primarily [[butane]] ({{chem|C|4|H|10}}) and, most commonly, mixes including both propane and butane, depending on the season&nbsp;&mdash; in winter more propane, in summer more butane{{citation needed|date=November 2011}}. [[Propylene]] and [[butylenes]] 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]]. In the United States, [[thiophene]] or [[thiol|amyl mercaptan]] are also approved odorants.

LPG is synthesised by refining petroleum or "wet" [[natural gas]], and is usually derived from [[fossil fuel]] sources, being manufactured during the refining of [[crude oil]], or extracted from oil or [[natural gas|gas]] streams as they emerge from the ground. It was first produced in 1910 by [[Walter O. Snelling|Dr. Walter Snelling]], and the first commercial products appeared in 1912. It currently provides about 3% of the energy consumed, and burns cleanly with no soot and very few sulfur emissions, posing no ground or water pollution hazards. LPG has a typical specific [[calorific value]] of 46.1&nbsp;MJ/kg compared with 42.5&nbsp;MJ/kg for fuel-oil and 43.5&nbsp;MJ/kg for premium grade petrol (gasoline).<ref>{{Cite book|title=Automotive Handbook |year=1996 |publisher=[[Robert Bosch GmbH]] |location=Stuttgart |isbn=0837603331 |editor=Horst Bauer |edition=4th|pages=238–239}}</ref> However, its energy density per volume unit of 26 MJ/l is lower than either that of petrol or fuel-oil.{{Citation needed|date=November 2010}}

LPG evaporates quickly at normal temperatures and pressures and is supplied in pressurised [[steel]] cylinders. They are typically filled to between 80% and 85% of their capacity to allow for [[thermal expansion]] of the contained liquid. The ratio between the volumes of the vaporized gas and the liquefied gas varies depending on composition, pressure, and temperature, but is typically around 250:1. The pressure at which LPG becomes liquid, called its [[vapor pressure|vapour pressure]], likewise varies depending on composition and temperature; for example, it is approximately {{convert|220|kPa|bar}} for pure butane at {{convert|20|°C|°F}}, and approximately {{convert|2.2|MPa|bar}} (319 psi) for pure propane at {{convert|55|°C|°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.

Large amounts of LPG can be stored in bulk cylinders and these can be buried underground.

==Uses==
=== Rural heating ===
[[File:LP gas cilinder.jpg|thumb|200px|right| Cylinders with LP gas in [[Nepal]] ]]
Predominantly in Europe and rural parts of the United States, LPG can provide an alternative to electricity and heating oil (kerosene). LPG is most often used where there is no access to piped natural gas.

LPG can be used as a power source for [[combined heat and power]] technologies (CHP). CHP is the process of generating both electrical power and useful heat from a single fuel source. This technology has allowed LPG to be used not just as fuel for heating and cooking, but also for de-centralised generation of electricity.

LPG can be stored in a variety of ways. LPG, as with other fossil fuels, can be combined with renewable power sources to provide greater reliability while still achieving some reduction in CO<sub>2</sub> emissions.

===Motor fuel===
[[Image:lpg-connector.jpg|thumb|LPG filling connector on a car]]
{{Main|Autogas}}

When LPG is used to fuel [[internal combustion engines]], it is often referred to as [[autogas]] or auto propane. In some countries, it has been used since the 1940s as a petrol alternative for spark ignition engines. Two recent studies have examined LPG-fuel-oil fuel mixes and found that smoke emissions and fuel consumption are reduced but [[hydrocarbon]] emissions are increased.<ref name="Zhang">{{Cite journal|doi=10.1243/095440705X6470 |title=A study on an electronically controlled liquefied petroleum gas-diesel dual-fuel automobile |year=2005 |last1=Zhang |first1=Chunhua |last2=Bian |first2=Yaozhang |last3=Si |first3=Lizeng |last4=Liao |first4=Junzhi |last5=Odbileg |first5=N |journal=Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering |volume=219|issue=2 |pages=207}}</ref><ref name="Qi">{{Cite journal|doi=10.1016/j.enconman.2006.06.013 |title=Combustion and exhaust emission characteristics of a compression ignition engine using liquefied petroleum gas–fuel-oil blended fuel |year=2007 |last1=Qi |first1=D |last2=Bian |first2=Y |last3=Ma |first3=Z |last4=Zhang |first4=C |last5=Liu |first5=S |journal=Energy Conversion and Management |volume=48|issue=2 |pages=500}}</ref> The studies were split on CO emissions, with one finding significant increases,<ref name="Zhang"/> and the other finding slight increases at low engine load but a considerable decrease at high engine load.<ref name="Qi"/> Its advantage is that it is non-toxic, non-corrosive and free of [[tetra-ethyl lead]] or any additives, and has a high [[octane rating]] (102-108 RON depending on local specifications). It burns more cleanly than petrol or fuel-oil and is especially free of the [[particulate]]s from the latter.

LPG has a lower energy density than either petrol or fuel-oil, so the equivalent [[fuel consumption]] is higher. Many governments impose less tax on LPG than on petrol or fuel-oil, which helps offset the greater consumption of LPG than of petrol or fuel-oil. However, in many European countries this tax break is often compensated by a much higher annual road tax on cars using LPG than on cars using petrol or fuel-oil. Propane is the third most widely used motor fuel in the world. 2008 estimates are that over 13 million vehicles are fuelled by propane gas worldwide. Over 20 million tonnes (over 7 billion US gallons) are used annually as a vehicle fuel.

Not all automobile engines are suitable for use with LPG as a fuel. LPG provides less upper cylinder lubrication than petrol or diesel, as a consequence LPG fueled engines are more prone to wearing valves if not suitably modified. 

Vehicles for use in and out of buildings such as [[forklifts]] are often run on LPG as it is cleaner when operatinh within the building. But due to fumes given off and the buring of oxygen they should not be operted within a fully closed up space, factories and warehouse with large loading doors being common places for there use. In closed warehouses & coldstores electric trucks are usually used due to he ventilation issue. 

Many modern common rail diesel engines respond well to LPG use as a supplementary fuel. This is where LPG is used as fuel as well as diesel. Systems are now available that integrate with OEM engine management systems.

===Refrigeration===
LPG is instrumental in providing [[off-the-grid]] refrigeration, usually by means of a [[gas absorption refrigerator]].

Blended of pure, dry "isopropane" (refrigerant designator '''R-290a''' ) and [[isobutane]] (R-600a) have negligible [[ozone depletion potential]] and very low [[global warming potential]] and can serve as a functional replacement for [[Chlorofluorocarbon|R-12]], [[Chlorodifluoromethane|R-22]], [[1,1,1,2-Tetrafluoroethane|R-134a]],and other [[chlorofluorocarbon]] or [[hydrofluorocarbon]] [[refrigerant]]s in conventional stationary refrigeration and air conditioning systems.<ref>{{Cite web|url=http://ec.europa.eu/environment/ozone/pdf/hcfc_technical_meeting_summary.pdf |title=European Commission on retrofit refrigerants for stationary applications |format=PDF |date= |accessdate=2009-07-30|archiveurl=http://web.archive.org/web/20080719195805/http://ec.europa.eu/environment/ozone/pdf/hcfc_technical_meeting_summary.pdf|archivedate=2008-07-19}}</ref>

Such substitution is widely prohibited or discouraged in motor vehicle air conditioning systems, on the grounds that using [[Flammability|flammable]] hydrocarbons in systems originally designed to carry non-flammable refrigerant presents a significant risk of fire or explosion.<ref>{{Cite web|url=http://www.epa.gov/ozone/snap/refrigerants/hc12alng.html |title=U.S. EPA hydrocarbon-refrigerants FAQ |publisher=[[United States Environmental Protection Agency]] |date= |accessdate=2009-07-30}}</ref><ref>[http://web.archive.org/web/20070216103634/http://www.vasa.org.au/pdf/memberlibrary/hydrocarbons/hc_white_paper.pdf Compendium of hydrocarbon-refrigerant policy statements, October 2006]{{Dead link|date=July 2009}}</ref><ref>{{Cite web|url=http://www.autoacforum.com/MACS/HCwarning.pdf |title=MACS bulletin: hydrocarbon refrigerant usage in vehicles |format=PDF |date= |accessdate=2009-07-30}}</ref><ref>{{Cite web|url=http://www.sae.org/news/releases/05hydrocarbon_warning.htm |title=Society of Automotive Engineers hydrocarbon refrigerant bulletin |publisher=Sae.org |date=2005-04-27 |accessdate=2009-07-30}}</ref><ref>{{Cite web|url=http://www.shadetreemechanic.com/cc_hydrocarbon_refrigerants.htm |title=Shade Tree Mechanic on hydrocarbon refrigerants |publisher=Electromechanics.com |date=2005-04-27 |accessdate=2009-07-30}}</ref><ref>{{Cite web|url=http://www.labour.gov.sk.ca/Default.aspx?DN=2fb5ac24-d90e-4408-bf40-559793bd8e96 |title=Saskatchewan Labor bulletin on hydrocarbon refrigerants in vehicles |publisher=Labour.gov.sk.ca |date=1996-01-01 |accessdate=2009-07-30}}</ref><ref>[http://www.vasa.org.au/content/refriggas/index.php#Bookmark%202 VASA on refrigerant legality & advisability]{{Dead link|date=July 2009}}</ref><ref>{{Cite web|url=http://www.energy.qld.gov.au/zone_files/petroleum_pdf/safety_alert025.pdf |title=Flammable Refrigerant Alert |format=PDF |date= |accessdate=2009-07-30|archiveurl=http://web.archive.org/web/20081217150006/http://www.energy.qld.gov.au/zone_files/petroleum_pdf/safety_alert025.pdf|archivedate=2008-12-17}}</ref>

Vendors and advocates of hydrocarbon refrigerants argue against such bans on the grounds that there have been very few such incidents relative to the number of vehicle air conditioning systems filled with hydrocarbons.<ref>{{Cite web|url=http://www.parliament.nsw.gov.au/prod/parlment/HansArt.nsf/V3Key/LA19971016015 |title=New South Wales (Australia) Parliamentary record, 16 October 1997 |publisher=Parliament.nsw.gov.au |date=1997-10-16 |accessdate=2009-07-30}}</ref><ref>{{Cite web|url=http://www.parliament.nsw.gov.au/prod/parlment/hansart.nsf/V3Key/LC20000629051 |title=New South Wales (Australia) Parliamentary record, 29 June 2000 |publisher=Parliament.nsw.gov.au |date= |accessdate=2009-07-30}}</ref> One particular test was conducted by a professor at the [[University of New South Wales]] that unintentionally tested the worst case scenario of a sudden and complete refrigerant loss into the passenger compartment followed by subsequent ignition. He and several others in the car sustained minor burns to their face, ears, and hands, and several observers received lacerations from the burst glass of the front passenger window. No one was seriously injured.<ref>[http://web.archive.org/web/20060823205258/http://www.vasa.org.au/pdf/memberlibrary/hydrocarbons/maclaine-cross.pdf VASA news report on hydrocarbon refrigerant demonstrations]{{Dead link|date=July 2009}}</ref>

===Cooking===
[[Image:LPG Truck.jpg|thumb|upright|Truck carrying LPG cylinders to residential consumers in Singapore]]
According to the 2001 Census of [[India]], 17.5% of Indian households or 33.6 million Indian households used LPG as cooking fuel in 2001, which is supplied to to their homes by Indian Oil which is known as Indane.<ref>{{Cite web|url=http://www.censusindia.gov.in/ |title=Indian Census |publisher=Censusindia.gov.in |date= |accessdate=2009-07-30}}</ref> 76.64% of such households were from urban India making up 48% of urban Indian households as compared to a usage of 5.7% only in [[rural]] 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 area|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.

==Security of supply==
Because of the natural gas and the oil-refining industry, Europe is almost self-sufficient in LPG. Europe's security of supply is further safeguarded by:
* a wide range of sources, both inside and outside Europe;
* a flexible supply chain via water, rail and road with numerous routes and entry points into Europe;

As of early 2008, world reserves of natural gas&nbsp;&mdash; from which most LPG is derived&nbsp;&mdash; stood at 6,342.411 trillion cubic feet. Added to the LPG derived from cracking crude oil, this amounts to a major energy source that is virtually untapped and has massive potential. Production continues to grow at an average annual rate of 2.2%, virtually assuring that there is no risk of demand outstripping supply for the foreseeable future.

{{Citation needed|date=June 2010}}

==Comparison with natural gas==
LPG is composed primarily of propane and butane, while natural gas is composed of the lighter methane and ethane.
LPG, vaporised and at atmospheric pressure, has a higher [[calorific value]] (94&nbsp;MJ/m<sup>3</sup> equivalent to 26.1kWh/m³) than [[natural gas]] ([[methane]]) (38&nbsp;MJ/m<sup>3</sup> equivalent to 10.6&nbsp;kWh/m<sup>3</sup>), which means that LPG cannot 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.

==Environmental Effects==
Commercially available LPG is currently derived from fossil fuels. Burning LPG releases {{chem|CO|2}}, an important greenhouse gas, contributing to [[global warming]]. LPG does, however, release less {{chem|CO|2}} per unit of energy than that of coal or oil. It emits 81% of the {{chem|CO|2}} per [[kWh]] produced by oil, 70% of that of coal, and less than 50% of that emitted by coal-generated electricity distributed via the grid.{{Citation needed|date=August 2009}} Being a mix of propane and butane, LPG emits less carbon per [[joule]] than butane but more carbon per joule than propane.

LPG can be considered to burn more 'cleanly' than heavier molecule [[hydrocarbons]], in that it releases very few [[particulates]] when burnt.

==Fire risk and mitigation==
{{Ref improve section|date=September 2009}}
{{Undue|section|date=September 2009}}
[[Image:Gaskessel gr.jpg|thumb|upright|A spherical gas container typically found in [[Refinery|refineries]]]]
Since LPG turns gaseous under ambient temperature and pressure, it must be stored in special pressure vessels. If the containers are cylindrical and horizontal, they are referred to as "cigars" or "bullets", whereas circular ones are "spheres".

LPG containers that are subjected to fire of sufficient duration and intensity can undergo a boiling liquid expanding vapour explosion ([[BLEVE]]). Due to the destructive nature of LPG explosions, the substance is classified as a [[dangerous goods|dangerous good]].<ref>[http://www.desktoplawyer.co.uk/dt/browse/law/index.cfm?fs=lga&sid=75858&aid=35391 The Dangerous Substances and Explosive Atmospheres Regulations]. Retrieved on 27 June 2007.</ref> This is typically a concern for large refineries and petrochemical plants that maintain very large containers. The remedy is to equip such containers with a measure to provide a [[fire-resistance rating]]. Large, spherical LPG containers may have up to a 15&nbsp;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 container 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 container 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 containers. 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 containers from potential sources of fire. In the case of rail transport, for instance, LPG containers 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 can occur to the primers, which can result 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 [[plasters]]. The rest are amply protected by soil. Speciality 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 it is difficult to detect mechanical damage to the outer waterproofing of the vessel through [[soil]]. A small stone scraping back and forth across the [[epoxy]]-painted hull can jeopardise 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 [[plasters]] 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 [[passive fire protection]] products, is subject to stringent [[Listing and approval use and compliance]]. The problem with this is though, that exterior structures of this nature are not subject to the [[building code]] or the fire code, meaning that one still sees the majority of LPG containers without any fireproofing at all, as there are often no local regulations, let alone any [[Authority Having Jurisdiction]], apart from an [[insurance]] [[inspector]], to force owners to use the proper mitigation methods. Insurance companies are also in a competitive quandary, where such items are concerned, as they compete not only on the basis of rates, but also on the strictness of the demands by their inspectors. LPG vessel [[Fire test|fireproofing tests]] are varied. The only realistic exposure offered is done at the [[Braunschweig]] test facility of [http://www.bam.de/ "BAM"] Berlin. BAM's procedure is to expose a small LPG container to the hydrocarbon test curve and to quantify the results. [[North America]]n methods are based on [http://ulstandardsinfonet.ul.com/scopes/1709.html UL1709]. While UL1709 uses the correct time/temperature curve for testing, it is limited to testing steel columns (not even beams), whereas BAM actually exposes a real LPG container that has been fireproofed. No matter the fireproofing method one uses, it is very important to pay close attention to [[listing and approval use and compliance]] 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 [http://www.dibt.de/ 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.

In June 2009, a freight train carrying LPG [[2009 Viareggio train accident|derailed in the rail station of Viareggio, Italy]]. 29 people were killed and over 30 people were injured.

==See also==
* [[Blau gas]] - ? brand
* [[Calor Gas]] - UK Gas brand
* [[Compressed natural gas]] (CNG)
* [[Endothermic]]
* [[Filling Carousel]]
* [[Fireproofing]]
* [[Fire-resistance rating]]
* [[Gasoline gallon equivalent]]
* [[Hybrid vehicle]]s and [[Hybrid electric vehicle]]s
* [[Intumescent]] (fire proof)
* [[Industrial gas]]
* [[Liquefied natural gas]] (LNG)
* [[Natural gas]]
* [[Passive fire protection]]
* [[Product certification]]
* [[Underwriters Laboratories]]
* [[World LP Gas Association]]
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* [[Listing and approval use and compliance]]
* [[List of CO2 emitted per million Btu of energy from various fuels]] -->

==References==
{{Reflist|2}}

==External links==
{{Portal|Energy}}
* [http://www.worldlpgas.com WLPGA] World LP Gas Association
* [http://www.propanecouncil.org PERC] Propane Education & Research Council
* [http://www.npga.org/i4a/pages/index.cfm?pageid=1 NPGA] National Propane Gas Association, USA
* [http://www.propane101.com Propane 101] Explaining propane and LP Gas fundamentals

{{Fuel Transport}}

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[[Category:Petroleum production]]