This appendix draws upon the World LP Gas Association website, the LPGA’s Codes
of Practice, suppliers’ literature and documentation from the British Standards
What is LPG
LPG is the abbreviation used to describe liquefied petroleum gas, a group of
hydrocarbon gases typically containing three or four carbon atoms per molecule and
often referred to as C3 or C4.
The normal constituents of LPG are: propane (chemical formula C3H8), propylene
(C3H6), Butane (C4H10) and butylenes (C4H8). Commercial-quality products marketed
as butane and propane in the UK are not pure chemical hydrocarbons and contain
trace quantities of other similar gases.
In the UK, quality specifications for LPGs are defined by BS 4250 Specifications for
Commercial Propane and Commercial Butane, the typical properties of which are
given in Table 1.
TABLE 1 Limiting requirements for properties of commercial butane and propane
Gauge vapour pressure, at 40°C (measured or
calculated) (kPa), max
Total sulphur content (mg/kg), max
Mercaptan sulphur content (mg/kg), max
Hydrogen sulphide content (mg/m3), max
Ammonia content (mg/m3 in the vapour phase),
Copper corrosion, 1h at 40°C
Tendency to freeze in valves
Dienes content, mole percent max
Ethylene content, mole percent, max
Alkynes content, mole percent, max
C4 and higher hydrocarbons content, mole per cent,
C5 and higher hydrocarbons content, mole per cent
Source: BS 4250:1997.
LPG exists in gaseous form under normal atmospheric pressure and temperature.
Unlike natural gas (methane—CH4), which can only be liquefied by refrigeration, LPG
is easily liquefied by moderate compression at ambient temperat