Properties of Liquefied Petroleum Gas (LPG)

Liquefied petroleum gas or liquid petroleum gas (LPG or LP gas), a mixture of propane and butane, is a flammable mixture of hydrocarbon gases used as a fuel in heating appliances, cooking equipment, and vehicles.

It is also increasingly used as an aerosol propellant and a refrigerant, replacing chlorofluorocarbons in an effort to reduce damage to the ozone layer. When specifically used as a vehicle fuel it is often referred to as auto gas.

Varieties of LPG bought and sold include mixes that are primarily propane (C3H8), primarily butane (C4H10) and, most commonly, mixes including both propane and butane. In winter, the mixes contain more propane, while in summer, they contain more butane.

Properties of Liquefied Petroleum Gas (LPG)

The properties of LPG gas are discussed below.

Liquefied Petroleum Gas (LPG)

Chemical Identity

  • Chemical Classification: Hydrocarbon Mixture
  • Synonyms: LPG, Propane, Butane, Propylene
  • Trade Name: LPG, Purofax, Bottled Gas.
  • Formula: C3H8, C4H10 (Mixture)
  • Regulated Shipping Name: Petroleum Gases, Liquefied.
  • Max. Vapour pressure @650C 16.87kg/cm2
  • Volatility: evaporation at 20C for 95% by vol. At 760mm hg  Pressure

The density of liquid (0.525 to 0.580 at 15°C)

  • Remain over water in drain etc.
  • LPG Fire cannot be extinguished with water
  • Water is used only for cooling

Density of LPG vapour (1.5 to 2.0)

  • Heavier than Air
  • Settles down in low lying area /Ground level
  • Accumulates in depression
  • Under still condition dissipation is low
  • Accumulation can give rise to potential Fire & explosion Hazards
  • Hot plate (Gas stove) shall always be at higher level compared to Cylinder

Co-efficient of volumetric expansion

  • LPG liquid expands 250 times by volume to vapour
  • At liquid full condition, any further expansion of liquid Cylinder pressure  will rise by 14 -15 kg/cm2
  • In case of fire it is essential to cool all adjacent vessels  to avoid BLEVE
  • Expansion is 100 times more than steel
  • Vapour pressure depends on temperature & has no relation to the quantity of LPG
  • Minimum allowable space 5%
Liquefied Petroleum Gas Tanker

Flammability (1.8 % – 9.5 %)

  • Small leakage can cause Fire.
  • Major leakages are with high concentrations initially, but in  contact  with air  LPG dissipates very fast and forms flammable mixture
  • Auto Ignition Temperature  (410 – 580 °C)

Latent heat (10,900 Kcal /Kg)

  • Causes formation of ice during gushing out of LPG
  • If  venting is done in uncontrolled condition,  shall lead to jamming of valves
  • Results in cold burn/ Frost bite if exposed to body


  • Colourless in both Liquid & Vapour Phase
  • Leakage cannot be detected by naked eye


  • Very Faint Smell (Odourless)
  • Leakage cannot be detected by smell. For Detection by smell a chemical is added to LPG
  • Ethyl Mercaptan – 20 ppm/odour level 2

Combustion properties

  • Oxidation of LPG vapour with air/oxygen
  • LPG requires @ 50 times its own volume of air for combustion yielding 3 to 4 times its own volumes of carbon dioxide & 10,900 kcal heat
  • Results in  loss of air after combustion
  • Limit of flammability
  • Calorific value – ideal fuel

The behaviour of LPG in a closed container

  • If no ullage, exerts a pressure of 14 to 15kg /cm2 on the container per degree rise of temperature •Vapour pressure depends on temperature & has no relation to the quantity of LPG
  • Adequate vapour must be present
  • Minimum allowable space 5%

Hazards of LPG

Health hazards

  • Non toxic
  • Asphyxiation
  • Frost bite

Fire hazards

  • Explosion
  • UVCE

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