Fire
Retardant Cables
The fire properties of cables are of great importance from a fire
safety perspective. To ensure that cable performs up to the mark on fire safety
standards is critical to both manufacturers and end users.
Cables are used for transmission of electricity. Hence, efficient
transmission of electricity is the basic value proposition that we offer to the
customer. However, mere transmission is not enough. Safety and especially human
safety is of prime importance. Cables, therefore, have to be shock proof as
well as short circuit proof.
Fires have been a major cause of losses of both human life as well
as property, and hence, safety from fire is one of the major areas of focus for
us. 90 percent of the fires are electrical fires, mainly caused by a Defective
Electric Circuit (DEC). DEC can be caused by overloading, short circuit, faulty
installation, or due to poor quality of products used, which again could be
poor quality of raw materials, or poor quality of manufacture, or both. The
sufferer is mainly the common man, who has to bear the brunt of mistakes or
cost cutting measures of someone else. We are acutely conscious of this fact
and we have been the first Company in India who offered FR (Flame Retardant)
cables as a standard feature on all our XLPE cables.
Since, cost becomes a major factor in almost all purchase
decisions, especially for Industrial products, we constantly look to
manufacture products that are less prone to catch and propagate fires without
adding to costs. Hence, Research & Develop-ment is a constantly ongoing
process for making safe cables without added costs.
There are different types of safety norms used for cables as per
applications, all are important from safety, technical & commercial point
of view. Few of those are:
- For standard installation conditions – cables with standard flame retardancy are used.
- For installations in non-hazardous industries and open conditions–Cables with improved oxygen index are used, popularly known as ‘FR’ cables.
For installations with human surroundings and chemical or
refineries, or hazardous plants etc – Cables with improved oxygen index and low
smoke properties are used, popularly known as ‘FRLS’ cables.
- Further, cables with ‘Low smoke & Zero halogen (LSZH)’ are used in Hospitals, Railways and metros, high rise buildings, shopping malls, theaters, airports, i.e. basically areas of high population in closed circumstances.
- Fire survival cables are mandatory to use where circuit integrity is of prime importance in case of fire.Those are used mainly along with fire alarm systems, elevators, lighting systems at Metro railways, airports, high rises, mines, etc.
Fire retarding properties in cable are of great importance. To
make it simpler to understand, will take example of ‘Fire triangle’. It has got
three sides ‘Oxygen (Air), Fuel (Flammable material) & Heat (Source of
fire)’. If anyone of the component is missing, flame or fire will not propagate
itself nor will it spread.
For making the cable safe from fire, we improve the properties of
cable jacket and try and ensure self-extinguishing compounds, which even if
there is external fire, they will not propagate the flames.
Technically it is narrated as below:
- Outer jacket of the cables are of flame retardant material only, which doesn’t allow fire propagation. It is measured as per IS 10810 Part 53 or IEC 60332 Part 1.
- In the atmosphere normal Oxygen percentage is 21 percent, we improve the cables Oxygen index to a level of 30 to 35 percent. Means in the standard atmospheric condition till the percentage of oxygen reaches 30 to 35 percent; cable will not act as fuel. It is measured as per IS 10810 Part 58 or ASTM D 2863.
- This condition can be also looked from different angle i.e. if source of fire (heat) is more than at 21 percent also cable can act as fuel. For such condition temperature index is measured, which is maintained in the range of 250 to 350 °C. Therefore till such high temperatures cables don’t act as fuel. It is measured as per IS 10810 Part 64 or ASTM D 2863.
It is reported that 80 percent deaths which occurs due to fire are
not caused by burns; they are actually caused by the inhalation of these toxic
gases. We can therefore realize that smoke generated from these conventional
polymers under fire is the most important issue that a cable manufacturer has
to consider. Considering this issue FR, FRLS, LSZH & FS cables have evolved.
Fire Survival cables which maintain circuit integrity for minimum
3 hrs up to 950 deg Celsius under fire, water and shock conditions to ensure
transmission of signals and communication.
PE vs PVC usages in cable insulation for fire safety?
PVC (Polyvinyl chloride) is a flame retardant material; it has
this plus point over PE (Polyethylene). However, it is applicable for outer
jacket only. As mentioned above depending on application one has to choose
material for outer sheath.
As far as insulation is concerned, PE or XLPE (cross-linked
polyethylene) has got more advantage over PVC. PE is not used in insulation of
energy cables, and is only used in lower voltages of telecommunication cables.
XLPE is used in insulation world over, and it does not propagate
flame, nor does it emit smoke or toxic gases and world over; XLPE is insulation
and PVC or LSZH is used in sheathing, which is a safe proposition from the
point of flame resistance.
There are developments going on to improve the property of Polyethylene
to make it flame retardant, and we will see better standards implemented, which
is now imperative especially after the few large fires where lots of valuable
human lives have been lost.
What standards and certifications are the most prevalent in India,
and globally to ensure fire properties of cables? Are your products able to
meet those standards’ requirements?
Indian standards for cables e.g. IS 1554 (for PVC insulated
Cables), IS 7098 (for XLPE insulated cables, or IS- 694 for wires and
flexibles) covers the requirements for cables for safety against fire.On the
cable or wire outer jacket additional properties against fire are mentioned by
marking word ‘FR’ or ‘FRLS’. By this user understands the cable type.
Internationally also, similar practices are followed and there are
tests to monitor the performance of the cable under fire condition.
a) Smoke emission from cable during fire is monitored as under:
- For ‘FRLS’ cables during fire, visibility maintained is at least 40% or smoke density of 60% maximum. It is measured as per IS 10810 Part 63 or ASTM D 2843.
- For ‘LSZH’ cables during fire, visibility maintained is at least 80% or smoke density of 20%. It is measured as per IS 10810 Part 63 or ASTM D 2843.
b) Halogen Acid gas emission from cable during fire is monitored.
- For ‘FRLS’ cables during fire, maximum halogen gas emitted should be 20% by weight. It is measured as per IS 10810 Part 59 or IEC 60754 Part 1.
- For ‘LSZH’ cables during fire, maximum halogen gas emitted should be 0.5% by weight. It is measured as per IS 10810 Part 59 or IEC 60754 Part 1.
c) Flame retardant tests for cables installed in group
- Condition of fire for group of cable is simulated & extend of fire propagation is measured. It is measured as per IS 10810 part 62 or IEC 60332-3.
Depending on the specifications and end usage chosen, we have capabilities to manufacture and test all these products in house.
For fire safe cables, a combination of Standards are being
followed:
• Test for Oxygen Index – ASTM D 2863
• Test for Temperature Index – ASTM D 2863
• Test for Smoke Density – ASTM D 2843
• Test for Acid Gas evolution- IEC 60754
• Flammability Tests – Category A, B, C as per IEC 60332-3
• 3 m Cube Test – IEC 61034/BS 7622
• Fire Resistance Test – BS 7846 & BS 6387
STANDARDS FOR FIRE RESISTANT CABLES:
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BS
|
British
Standard Institution
|
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BS
5266-1
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Emergency
lighting. Code of practice for the emergency lighting of premises
|
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BS
5839-1
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Fire
detection and fire alarm systems for buildings. Code of practice for system
design, installation, commissioning and maintenance
|
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BS
5839-6
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Fire
detection and fire alarm systems for buildings. Code of practice for the
design, installation and maintenance of fire detection and fire alarm systems
in dwellings
|
|
BS
5839-8
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Fire
detection and fire alarm systems for buildings. Code of practice for the
design, installation, commissioning and maintenance of voice alarm systems
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BS
5839-9
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Fire
detection and alarm systems for buildings. Code of practice for the design,
installation, commissioning and maintenance of emergency voice communication
systems
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BS
6387
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Specification
for performance requirements for cables required to maintain circuit
integrity under fire conditions
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BS
7211
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Electric
cables. Thermosetting insulated, non-armoured cables for voltages up to and
including 450/750 V, for electric power, lighting and internal wiring, and
having low emission of smoke and corrosive gases when affected by fire
|
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BS
7346-6
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Components
for smoke and heat control systems. Specifications for cable systems
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BS
7629-1
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Electric
cables. Specification for 300/500 V fire resistant screened cables having low
emission of smoke and corrosive gases when affected by fire. Multicore and
multipair cables
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BS
7846
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Electric
cables. Thermosetting insulated, armoured, fire-resistant cables of rated
voltage 600/1000 V, having low emission of smoke and corrosive gases when
affected by fire. Specification
|
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BS
8434-2
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Methods
of test for assessment of the fire integrity of electric cables. Test for
unprotected small cables for use in emergency circuits.
BS EN 50200 with a 930° flame and with water spray |
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BS
8491
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Method
for assessment of fire integrity of large diameter power cables for use as
components for smoke and heat control systems and certain other active fire
safety systems
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BS
8519
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Selection
and installation of fire-resistant power and control cable systems for life
safety and fire-fighting applications. Code of practice.
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CEI
|
Comitato
Elettrotecnico Italiano
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CEI
20-11 / EN 50363
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Insulating,
sheathing and covering materials for low voltage energy cables
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CEI
20-36/2-1
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Tests
for electric cables under fire conditions - Circuit integrity - Part 21:
Procedures and requirements - Cables of rated voltage up to and including
0,6/1,0 kV
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CEI
20-45
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Fire
resistant elastomeric insulated cables, halogen free (LSOH) with rated
voltage Uo/U 0.6/1 kV
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DIN
|
Deutsches
Institut fur Normung
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DIN
4102
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Fire
behaviour of building materials and building components - Part 12: Circuit
integrity maintenance of electric cable systems; requirements and testing
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EN
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European
Norm
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EN
50200
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Methods
of test for resistance to fire of unprotected small cables for use in
emergency circuit
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EN
50266
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Test
for vertical flame spread of vertically-mounted bunched wires and cables
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EN
50267/2-1
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Method
of determination of amount of halogen acid gas evolved during combustion of
polymeric materials taken from cables
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EN
50267/2-2
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Determination
of degree of acidity (corrosivity) of gases by measuring PH and conductivity
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EN
50288-7
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Sectional
specification for instrumentation and control cables
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EN
50362
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Method
of test for resistance to fire of larger unprotected power and control cables
for use in emergency circuits
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EN
50363
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Insulating,
sheathing and covering materials for low voltage energy cables
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EN
60228
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Conductors
of insulated cables
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EN
60332-1
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Test
for vertical flame propagation for a single insulated wire or cable
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EN
60332-2
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Test
for vertical flame propagation for a single small insulated wire or cable
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EN
60332-3
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Test
for vertical flame spread of vertically-mounted bunched wires or cables
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EN
61034
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Measurement
of smoke density of cables burning under defined conditions
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IEC
|
International
Electrotechnical Commission
|
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IEC
60228
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Conductors
of insulated cables - Guide to the dimensional limits of circular connectors
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IEC
60331
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Test
for electrical cables under fire conditions. Circuit integrity.
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IEC
60332-1
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Tests
on electric and optical fibre cables under fire conditions -Test for vertical
flame propagation for a single insulated wire or cable
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IEC
60332-3
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Test
on electric cables under fire conditions - Test for vertical flame spread of
vertically-mounted bunched wires or cables
|
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IEC
60502-1
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Power
cables with extruded insulation and their accessories for rated voltages from
1 kV (Um = 1,2 kV) up to 30 kV (Um = 36 kV) - Part 1: Cables for rated
voltages of 1 kV (Um = 1,2 kV) and 3 kV (Um = 3,6 kV)IEC 60754-1Method for
determination of amount of halogen acid gas evolved during combustion of
polymeric materials taken from cables
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IEC
60754-2
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Determination
of degree of acidity (corrosivity) of gases by measuring pH and conducivity
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IEC
60793-1
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Optical
fibres
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IEC
60794-1
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Optical
fibre cables
|
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IEC
61034-2
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Measurement
of smoke density of electric cables burning under defined conditions (LT)
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NBN
|
Norme
Belge
|
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NBN
C 30-004
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Fire
resistance of electical cables - Classification and test methods
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NBN
713-020
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Fire
resistance of building materials
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NF
|
Norme
Française
|
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NF-C-32-070
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Insulated
cables and flexible cords for installations - Classification tests on cables
and cords with respect to their behaviour to fire
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SS
|
Singapore
Standard
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SS
299 part 1
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Fire
resistant cables - Performance requirements for cables required to maintain
circuit integrity under fire conditions
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VDE
|
Verband
der Elektrotechnik Elektronik Informationstechnik
|
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VDE
0815
|
Wiring
cables for telecommunication and data processing systems part 814 - Testing
of cables, wires and flexible cords Continuance of insulation effect under
fire conditions
part 814 - Testing of cables, wires and flexible cords Continuance of insulation effect under fire conditions |
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VDE
0482
|
part
267 - Common test methods for cables under fire conditions - Test on gases
evolved during combustion of materials from cables
part 1034 - Measurement of smoke density of cables burning under defined conditions |