Download FD 01 - Behaviour of plastics in fire

FPASA BULLETIN FD 01
BEHAVIOUR OF PLASTICS IN FIRE
The widespread use of plastics indicates that it is likely to be involved, in one form or another, in
almost every fire that occurs. Their burning characteristics vary considerably depending on
composition and the following information is intended as a general guide to the behaviour in fire of
the more common varieties.
Main material classes
Thermoplastics
Provided the heat is not such as to decompose the material, this class can be remoulded. Scrap
thermoplastic material can thus be re-used without difficulty within certain limits.
Thermosetting plastics
After initial moulding these materials cannot be softened for remoulding. This is because the
moulding completes a chemical reaction which gives an irreversible structural rigidity.
Plastics in most common use
1.
Phenolic resins (thermosetting)
Phenolic resins are made principally from phenol or cresol, but furfuryl and resorcinol are
also used. All of the chemicals react with formaldehyde under certain conditions to yield a
range of resinous materials. These resins may be used without further treatment or in a
solvent such as alcohol or acetone to give varnishes, adhesives and impregnating media.
More commonly they are ground and blended with fillers, pigments and other additives to
give moulding powders, or used for bonding paper or cloth in the manufacture of laminated
sheet.
2.
Amino plastics (thermoplastics and thermosetting)
This class of plastics includes urea-formaldehyde (thermosetting), aniline-formaldehyde
(thermoplastic), and melamine-formaldehyde (thermosetting) resins.
Urea-formaldehyde resins are glass-like materials made by the interaction of urea and
formaldehyde. They are used to prepare thermosetting moulding powders, adhesives and
impregnating media and for the manufacture of laminated sheet.
The fire properties of the urea-formaldehyde resins are, in general, the same as those of
phenolic resins. Some coating materials in the class have sufficient resistance to heat to be
suitable as stoving enamels, while others have flame-retardant properties.
Aniline formaldehyde resins are mainly used for casting wood and for the manufacture of
laminated sheet.
Melamine formaldehyde resins are used in moulding powders, for impregnating wood, as
adhesives and in textile finishing.
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3.
Cellulose plastics (thermoplastics)
Cellulose nitrate in the form of celluloid was the original plastic material and was used in
photographic film, moulded articles, cellulose lacquers and gun cotton. Once cellulose
nitrate is ignited it is difficult to stop the ensuing decomposition. Flaming can be stopped by
copious amounts of water but the decomposition continues and unless the cellulose nitrate is
submerged in water or the cooling is continued, re-ignition is likely to occur. Cellulose
acetate has replaced the nitrate in may applications and is now the leading cellulose plastic
with extensive use as a moulding material and in the manufacture of film and fibre.
Ethyl cellulose is similar to, but more stable than cellulose acetate.
4.
Vinyl plastics (thermoplastics)
Ethenoid plastics form a class which includes both rigid and rubber-like products. They are
formed by the polymerisation of vinyl compounds and include polyvinyl chloride, polyvinyl
acetate, polyvinyl alcohol, polyvinyl acetyls, polystyrene, polymethyl-methacrylate, other
acrylic resins and their esters, polythene and various copolymers. The fire properties of
plastics within this class vary between those exhibited by polyvinyl chloride and polymethylmethacrylate.
5.
Polyamide plastics (thermoplastics)
Nylon is the generic name of this class of materials, which are made, for example, by the
reaction between aliphatic dicarboxylic acids and aliphatic diamines. They have found
extensive application in the manufacture of synthetic fibres, bristles and filaments.
On application of flame, fibres of these materials fuse and retreat from the flame rather than
ignite.
6.
Polyester resins (thermoplastics and thermosetting)
Some polyesters are known as alkyd resins. They are produced by the interaction of
polyhydric alcohols and polybasic acids. They are used for coatings for metals and fabrics
and for bonding glass fabric in the manufacture of low-pressure mouldings and laminated
sheet, with limited applications in moulding and casting. Some polyester resins are
copolymerised with styrene or methyl-methacrylate.
7.
Casein and other protein plastics (thermoplastics and thermosetting)
These materials are derived from a wide variety of natural sources, such as milk or soya
beans, by the reaction of formaldehyde with the casein. They are used to a decreasing
extent in the preparation of extruded products, sheet and moulding.
8.
Epoxide resins
Epoxy resins are commonly made by the reaction of epichlorohydrin and certain phenols.
Their principal applications are as adhesives, casting and coatings. Combinations of
polyamide and epoxide resins are coming into use as flame- and heat- resistant and anticorrosion varnishes and coatings.
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Material
Burning
characteristics
Burning
rate
Material
Burning
characteristics
Burning
rate
Amino
Aniline
Formaldehyde
Difficult to ignite
Burns with yellow
flame
Black smoke and
odour
Of aniline and
formaldehyde
Difficult to ignite
Odour fish-like
Very slow
Polystyrene
Not difficult to ignite
Burns with dark
yellow flame, black
smoke
Slow
Very slow
Polytetrafluoroethylene
Urea
Formaldehyde
Difficult to ignite
Burns with blue/
green-edged
Odour of
Formaldehyde
or fish-like.
Very slow
Polythene
(Polyethylene)
Cellulose
Cellulose
acetate
Not difficult to ignite
Burns with dark yellow
flame.
Odour of acetic acid
Slow burning
to very low
depending
on grade.
Polyvinyl
acetal
Cellulose
triacetate
Difficult to ignite.
Burns with yellow flame.
Odour of acetic acid.
Not difficult to ignite.
Drips. Burns with dark
yellow flame with black
smoke. Odour of butyric
acid (rancid butter).
Low
Polyvinyl
butyral
Extremely flammable,
readily ignited. Burns
with bright yellow
flame.
May decompose
explosively
started. Cannot be
stopped
by water.
Very high
Non-combustible.
Decomposes slowly
at 400oC.
Not difficult to ignite.
Burns with blue
flame with yellow
top.
Odour of paraffin
was.
Molten material is
clear.
Not difficult to ignite
Burns with purple
mottled flame.
Odour of acetic
acid.
Not difficult to ignite.
Odour of butyric
acid (rancid butter).
Very difficult to
ignite.
Burns with
yellow/green
flame.
Odour acrid.
Not difficult to ignite.
Burns with yellow
flame.
Ethyl
cellulose
Not difficult to ignite.
Burns with blue-edged
Yellow flame.
Slow
Phenolic
Phenol
formaldehyde
Epoxide
Epoxide
Difficult to ignite.
Burns with yellow/
green flame.
Odour slightly
sweet.
Not difficult to ignite.
Burns with blue/white
flame. Floral odour.
Moderate
to slow
Polyamide
Nylon
Moderate to
slow
Protein
Casein
Melamine
Formaldehyde
Cellulose
Acetate
butyrate
Cellulose
nitrate and
celluloid
Ethenoid
Polymethyl
methacrylate
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Polyvinyl
chloride
Polyvinyl
formal
Polyvinylidene
chloride
Very difficult to
ignite.
Burns with
yellow/green
flame.
Odour acrid.
Self-extinguishing.
Difficult to ignite.
Burns with yellow
flame.
Odour phenol.
Difficult to ignite.
Burns with bluish
flame.
Odour of burning
Vegetation
Not difficult to ignite.
Burns slowly with
yellow flame.
Odour of burnt milk
Slow with drips
Slow
Slow
Very low
Low to very
low
Very low
Slow
Published by:
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(Incorporated Association not for Gain)
(Reg. No. 73/00022/08)
P O Box 15467
Impala Park
1472
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