PROPERTIES OF LPG
To provide an over view of the properties
and hazards of LPG. .
What is LPG
Liquefied Petroleum Gas (LPG) is a product
of the Oil and Gas Industry.
LPG =
40% Butane
+
60%Propane
It is a mixture of two gases – 60% propane
and 40% butane for commercial LPG. The
higher grade propane mix is approximately
90% propane and 10% butane.
At room temperature LPG is a gas, but it
can easily be compressed to a liquid which
is easier to store and transport.
Physical Properties
It is important to know the physical
properties of LPG because this will help you
to handle the fuel safely and correctly.
Typical Properties of LPG
Butane
Propane
0
-42
Relative density (SG) at 15 C
0.57-0.58
0.50-0.51
Litres per tonne at 15 C
1723-1760
1965-2019
Relative density gas to air at
15  C & 1 atmosphere
1.9-2.1
1.4-1.5
Ratio gas to liquid volume at
15  C & 1 atmosphere
233
274
1.8%-8.5%
2.4%-9.5%
Boiling Point in C at
atmospheric pressure
Limits of flammability % by
volume of gas/air mixture
Density
LPG liquid is only about half as dense as
water. This means that as a liquid it will
float on water.
LPG vapour is denser than air. This means
that it will sink to the ground and accumulate
in low spots.
LPG liquid floats on water
Compressing and Releasing LPG
LPG is compressed so that it forms a liquid
that can be easily stored and transported.
When compressed, about 250 litres of gas
will become just one litre of liquid.
If it is released from its pressure vessel, or
when it leaks, a very small quantity of LPG
liquid will become a very large volume of
vapour/air mixture.
250ltr
1 Litre of LPG becomes 250 litres of gas
As LPG gets warmer it expands, but it
expands more than water or other petroleum
products.
LPG absorbs heat when it changes from a
liquid to a gas.
It will absorb heat from:
 The air
 From whatever it touches
When LPG leaks you can often detect the
leak by the white cloud where the gas is
escaping. The cloud is caused by LPG
taking heat out of the air and causing
moisture to condense or even freeze.
If escaping LPG liquid touches you it may
cause severe frostbite.
The pipes or tanks from where the LPG is
escaping will also get very cold. Moisture in
the air will condense into water on the tank
and may turn to ice.
You must wear personal protective
equipment when handling LPG or when
dealing with a leak or a bleed down
operation.
Always wear protective clothing
The minimum requirements are eye
protection (goggles or safety glasses with
eye shields) and impervious gloves (leather
not fabric).
Viscosity
LPG has a very low viscosity which means it
moves very easily. LPG may leak from
systems that can otherwise hold water or
other petroleum products.
Because LPG vapour is heavier than air,
when it does leak it will sink to the ground
and accumulate in any low spots.
The Smell
In its natural form LPG has no smell.
However, most commercial LPG is given a
smell so that leaks can be easily detected.
The smell is described as being like rotten
cabbages with a touch of garlic.
Enough smell is added so that leaking LPG
can be detected before it forms a flammable
gas/air mixture.
Some LPG which is used as lighter fuel or
as an aerosol propellant is unodorised.
Breathing LPG
LPG is not poisonous but it is an asphyxiant.
If you breathe in the vapour, this will
displace the oxygen your body needs and
you will suffocate.
Breathing LPG in small doses can produce
nausea and cause headaches.
Breathing LPG is bad for your health
Igniting LPG
A mixture of air and LPG can be ignited if
the amount of LPG in the air is between
about 2% and 10%
The mixture of air and LPG must be heated
to above 380 C before it will ignite
spontaneously.
Limits of Flammability
2.4
Propane
0% LPG
100% Air
Butane
0% LPG
100% Air
LPG
0% LPG
100% Air
Petrol
0% Petrol
9.5
100%LPG
0% Air
1.8
8.5
100%LPG
0% Air
2%
10%
100%LPG
0% Air
1%
6%
100%
Petrol
0% Air
100% Air
5%
Natural Gas
0% LPG
100% Air
Acetylene
0% Acet
100% Air
15%
100% Gas
0% Air
3%
95%
100% Acet
0% Air
Lean
Rich
Flame Temperature
The maximum flame temperature for LPG is
2,000C.
The maximum flame temperature is 1,930C
for propane and 1,900C for butane.
Butane
Propane
Ignition Temperature in C
475
466
Maximum burning velocity
meters per second
0.38
0.45
Maximum flame temperature in
C
1,900
1,930
Maximum ignition energy in
millijoules
0.25
0.25
Ignition Energy
The ignition energy needed to start
combustion of hydrocarbon vapours is very
low. It is usually less than one millijoule.
This energy is significantly less than that
from any visible flame, most electrical
sparks and electrostatic discharges down to
the lowest level detectable by human
contact.
Any electrical apparatus larger than a digital wrist-watch has the potential to generate
enough energy to ignite LPG vapour. This is why we need suitable, well maintained
equipment for use in hazardous atmospheres where flammable gases may be
present.