EoW March 2008

209 / 240

For the purposes of fire prevention and
in order to achieve objectives ensuring
people’s safety and asset protection, a
number of laws, decrees and regulations
have been introduced in order for
engineers, manufacturers, technicians and
users to execute, according to their own
responsibilities.
Electrical cables are among the structural
elements which need to satisfy fire
resistance requirements. In particular,
their behaviour has been analysed under
fire conditions and reference standards
have been established through the
development of international norms.
These standards specify the relevant test
apparatus to be used to simulate fire
conditions in order to test and analyse
reactions of the electrical cables as if they
were in their working condition.
This apparatus gives cable manufacturers
the possibility to test their product and
ensure it complies with international
standards so that it can be implemented
where such requirements are necessary.
In particular, these tests focus on no flame
spread; no fire spread; low emission of
toxic smoke and gases and fire resistance.
Test for no flame spread: The scope
is to evaluate the resistance to flame
spread by an external source for a single
cable, installed in the most unfavourable
position i.e. in vertical position. The
insulating material burns but the flame
should not spread more than 55cm from
the point the flame is applied to the single
cable. Reference standard: IEC 60332-1-1.
Test for no fire spread: The scope is to
evaluate the resistance to fire spread by
an external source for bunched cable,
installed in themost unfavourable position
(i.e. in vertical position). Different types of
tests have been planned as fire resistance
depends on a series of factors such as
the quality of the bunch non-metallic
material (thus potentially combustible),
the bunched cables configuration and the
location of ignition source(s). Reference
standard: IEC 60332-3-10.
Low emission of toxic smoke and gases:
“Smoke and gases evolved from burning
materials are responsible for more than
70% of deaths during fires,” (British
Medical Journal).
Test of smoke density: the scope is
testing that smoke evolved during the
combustion of electrical cables still
allow a good visibility in the room where
bunched cables are installed and for the
time necessary for evacuation.
Measurement of the amount of corrosive
gases: Verify that the amount of halogen
acid gases from the cable non-metallic
material does not exceed the relevant
standard values. Verify that gases evolved
during the combustion of the cables
have a level of toxicity low enough to
allow evacuation without significant
physiological damage to people.
Reference standard: IEC 60754-1 / IEC
60754-2 / IEC 61034-1.
Test of fire resistance: Scope of the test
is to evaluate the cable ability to keep
operating in the designated manner
under fire conditions for the time
necessary until fire brigade intervene.
The insulating material can be damaged
but the cable needs to keep working for
at least 90 minutes under the flame at a
temperature of 850°C. Different kinds of
tests have been planned with additional
external stresses; for example, the
mechanical shock test and one with water
spray. Reference standard: IEC 60331-11.
SIF MDC – Italy
Fax: +39 03525 8011
Email:
Website:
EuroWire – March 2008 207
Fire Safety Materials
Research and develop . . . not to get burned
Testing times from SIF ▲
HFFR compounds with superior
fire retardancy properties
The flame resistance of halogen free compounds for cable applications is commonly
measured by the highest Limiting Oxygen Index (LOI value), which is perhaps, the
most economical and precise quality control test of combustible materials.
This technique measures the minimum percentage of oxygen in the test
atmosphere that is required to marginally support combustion, and generally, a
higher LOI value gives better flame retardant performance.
Fainplast has recently developed two new HFFR compounds – HAX HF 4522 and
HAX HF 3941 – which have been specifically designed for those cable applications
requiring the ability to meet the more stringent fire test specifications.
HAX HF 4522, which passes the pressure test at 80°C has an experimental LOI
value greater than 45%. This high LOI value makes this material a good sheathing
candidate for those cables required to pass the fire test performed on cable bundles.
The second compound, HAX HF 3941, has been formulated for those applications
requiring superior thermal and flame retardant properties. Effectively, it does pass
the pressure test at 90°C (blade penetration < 50%) and exhibits a LOI value greater
than 40%, which guarantees a self-extinguishing behaviour under certain fire
conditions.
Fainplast srl – Italy Fax : +39 0736 403807
Email: Website: