CLASS 3 - FLAMMABLE LIQUIDS
This class makes up more than 50%
of all the dangerous substances
moved by road in the UK each year
Flammable liquids can be divided
broadly into two categories:
• Liquid fuels, mostly (but not all) petroleum derived,
e.g. petrol, kerosene, diesel, gas oil
• Solvent and raw material applications,
e.g. methanol, ethanol, acetone, toluene
NDGTC
FLAMMABILITY
 It’s not the liquid, but its vapour that burns
 Evaporation causes great increase in volume from two to four hundred-fold
 Volatility - the readiness with which a liquid
evaporates
 Higher volatility means
greater fire hazard
 Evaporation can only happen
on exposure to the atmosphere
 So effective containment prevents vapour
formation and so prevents fires
NDGTC
PRECAUTIONS TO AVOID SPILLAGE
Tankers/tank containers
• Ensure all hose connections are
properly and securely made
• Securely close all valves, manlids, etc.
after loading/unloading
• Ensure tank/compartments are not overfilled
• Drain hoses and ensure end-caps fitted
• Strictly observe all site procedures
Packaged goods
• Refuse leaking or badly damaged receptacles
• Check that all receptacles are safely loaded and
securely stowed
• Report any leaks (however small) that develop
during the journey
NDGTC
SEGREGATION
Flammable Liquid + Oxidiser = Potential explosion
Thus it is vital that these two danger labels are kept
well apart during handling and transport
NDGTC
OTHER HAZARDS
– Some flammable liquids are also toxic
and/or corrosive
– Some flammables produce acidic
or toxic gases when they burn
– Some toxic flammables are also skin absorptive
– Skin contact can give rise to allergies & dermatitis
– Vapours can cause strong eye irritation
– Inhalation of certain vapours can lead to poisoning,
narcosis, or damage to lungs,
brain tissue, etc.
See ‘Tremcard’ for details
NDGTC
OTHER FLAMMABLE VAPOUR DANGERS
• Since flammable vapours are heavier (denser) than
air, accumulations in confined spaces can lead to
suffocation danger
• Flammable vapours are all colourless,
so leaks will not be normally be visible
• Most have a perceptible smell, so this
could warn of leaks
• Because of their density, vapours can flow some
distance from the leak, particularly where confined or
channelled by drains, ditches, etc. and cause a fire
hazard elsewhere
NDGTC
FLASH POINT
 The ease with which a flammable liquid
catches fire is referred to as its flammability
 The commonest measure of flammability
is the flash point
 Defined as the lowest temperature of a liquid
at which it gives off just sufficient vapour
to form an ignitable mixture with air
 Thus, the vapour from a liquid below
its flashpoint is insufficient to ignite
 The vapour from a liquid at or
above its flashpoint can be ignited
 Low flashpoint indicates high flammability
 The flashpoint is the chief determinant of
whether or not a flammable liquid is regulated
 Under CDG, ADR & IMDG, liquids with flashpoint
60 C. or less are in class 3
(Diesel extended to 100 C)
NDGTC
AUTO IGNITION TEMPERATURE
• Even with a vapour-air mixture in the right proportions,
an adequate temperature will be needed to ignite it
• This could be an external ignition source, or the
mixture could self-ignite if it became hot enough
• This temperature is called the auto-ignition temperature
• Some examples:
• Acetone
540 deg.C
• Petrol
300 deg.C
• Diesel
250 deg.C
• Carbon disulphide
100 deg.C
• Note the particularly low value of carbon disulphide
which could even be ignited by contact with hot water
pipes, vehicle exhausts, etc.
NDGTC
FLAMMABLE RANGE
• Flammability depends not only on vapour and air
mixing, but also on how much of each is present
• A flammable atmosphere is a vapour-air mixture
within the correct proportions to burn
• The top end of the range is called the upper explosive
limit (UEL) and the bottom the lower explosive limit (LEL)
• Outside these limits, the mixture will not burn
• Some examples:
• Petrol
1% ---- 6%
• Acetone
3% ---- 13%
• Methanol
7% ---- 37%
• Thus, an explosive mixture could build up in a
notionally empty tank or receptacle where air and
residual vapour have mixed
NDGTC
VOLUME RATIOS
• Remember that when a liquid evaporates
there is always a huge increase in volume,
for petrol roughly 250 times.
• So this 40,000 litre petrol tank
is capable of producing
40,000 x 250 litres of petrol
vapour (i.e. 10 million litres)
which when mixed with air
at the lower end of the flammability range, say 2%
gives about 500,000,000 litres of highly flammable
atmosphere
NDGTC
MISCIBILITY
# Tremcards will describe flammable liquids as being
miscible or immiscible with water
# Meaning will, or will not mix with water
e.g. Miscible - methanol, acetone
Immiscible - petrol, benzene
# This is important to the emergency services when
dealing with a fire
• Water will not deal with an immiscible liquid fire
and may well make it worse by spreading it
• Water will deal with a miscible liquid fire, but
large quantities may be needed, and jets should
be avoided
NDGTC
FIRE AND FLAMMABLE LIQUIDS
Remembering the fire triangle, when vapour and air
are present in the right proportions, all that is necessary
is a source of ignition. Examples to be avoided:
Smoking, matches, lighters, portable stoves
Static electricity - make sure of earthing
Lightning - loading/unloading should cease
Current sparks - mobile phones, CBs
Vehicle defects - hot tyres, bearings, brakes
Vehicle accidents - drive carefully
The oxygen side of the fire triangle is always present,
so vapours must be contained and sources
of ignition must be kept away
NDGTC
PERSONAL PROTECTIVE EQUIPMENT
# Goggles and gloves should be regarded as the
absolute minimum
# Respirators may be needed where vapours pose a
breathing danger
# Tanker drivers tend to need higher levels
of protection because of their greater
potential exposure
# Always read the Tremcard (or similar)
and as a final note Some substances with flashpoints higher than
60C. may be carried as class 3 if transported
at temperatures above their flashpoint
e.g. Liquid tar at 150 deg.C
NDGTC