Evolution of Cable Fire Safety Standards in Australia

INTRODUCTION

Fire safety standards for electrical cables have evolved over the past few decades to the
extent that they are now well established along with cable materials and designs that meet
these standards. Australian Standards have largely followed international standards such as
the IEC, with many now adopting the entire content of the IEC standards.

Separately to this evolution Australia had also developed their own unique standard for fire
resistant cables which more closely aligns with the requirements of the building industry.

The purpose of this paper is to (i) review the evolution of the fire safety standards in
Australia, recapping the purpose of each, (ii) review how cables are constructed that meet
these standards, and (iii) finally look at how the Australian industry went on their own to
develop a standard for fire resistance.

BACKGROUND

Cables designed for safety systems, are commonly referred to as “Fire Rated” cables. The
key elements of Fire Rated cables are as follows:-

• Flame retardant – do not propagate fire

• Low smoke – reduces obstruction to evacuation of buildings during fire
• Zero halogen – does not create toxic fumes and corrosive by-products during fire
• Maintains circuits integrity – keeps electrical equipment going during fire

We will now explore each of these key elements in a bit more detail.

FLAME RETARDANT CABLES

Flame retardant cables do not propagate fire, ie they use materials which are difficult to
ignite and are self-extinguishing, they also retard the spread of fire. That is to say that if a fire
starts within the cable, say due to an internal fault, the cable will not spread the fire to other
areas of a building, factory etc.

Flame retardant cables are commonly used in in buildings, plants, enclosed infrastructure
and ships. Another key aspect of flame retardant cables is that they avoid adding fuel to a
fire. It may not be necessary to use flame retardant insulation materials, but it is most
important that flame retardant materials are incorporated in the cable sheathing. When
developing flame retardant cable it is important to assess the combination of insulation,
sheathing materials and the other combustible components of a cable, eg fillers and bedding
layers to make an overall assessment of the performance of the cable.

Standards exist that were developed a number of decades ago that detail test methods to
establish the flame retardant properties of materials and cables. Some of the widely used
standards are summaries briefly below.

Oxygen Index Test – AS/NZS 2122.2

This is a material test which determines the percentage of oxygen in air that supports
combustion of a material. Since air contains 21% oxygen it stand to reason that any material
when test to this standard that registers an oxygen index greater than 21% will be difficult to
burn and the higher the number the more difficult it is to burn the material. PVC for example
has an oxygen index around 23 making standard building cables flame retardant while fire
rated cables, which aim to achieve a high degree of flame retardant properties usually
contain materials having an oxygen index at least 28-30, while materials in the mid 30s are
not uncommon. (XLPE is a common material used in electrical cables, and has an oxygen
index around 18%, which therefore indicates, that by itself, it has very poor resistance to
combustion and will burn readily in open air when exposed to flame.)

Single Cable Vertical Flame Propagation Test – AS/NZS 1660.5.6

While the oxygen index test gives a good measure of the flame retardant properties of a
material, it may not give a good indication of the flame retardant properties of a complete
cable. This is due to the complex makeup of cables, and the variety of materials used, ie
insulation, fillers to make cable round, bedding layers, armour and outer sheath. Al of these
cable materials will have an influence on the overall flame retardant properties of a cable.
For this reason complete cable flame propagation tests have been developed and the first to
check is the single vertical flame propagation test details in AS/NZS 1660.5.6.

Here a 600 mm length of cable is subject to flame applied by

a “Bunsen Burner” type flame source as per the figure at right.
The flame application time varies in line with the cable
diameter and the pass criteria is such that the cable must not
burn up to 50 mm from the top support of the cable, and any
falling particles that fall away from the burning cable must not
ignite the paper laid under the cable sample.

All cables complying with AS/NZS 5000.1 and AS/NZS 5000.2

must comply with this standard, which includes all TPS
cables, single insulated building wire, XLPE/PVC SDIs,
orange circular PVC/PVC cables for example.

This test standard evolved from the European standards such

as the IEC and the current version (2005) adopts the entire
content of the equivalent IEC 60332-1 standard. There are
other standards around the world that have similar test
methods, such as the UL 1581 in the USA, but Australia has
largely followed European standards and practices.

(IEC stands for “International Electrotechnical Commission” and is an organisation that

develops standards for European industry, and therefore has contribution from the majority
of European nations, and are also widely used around the world and are recognised for their
high level of technical competence.)

Multiple (Bunched) Cable Vertical Flame Propagation Test – AS/NZS 1660.5.1

This standard goes further than the single cable flame propagation test by testing cables in
bunches, which increases the amount of combustible material, which increases the amount
of fuel to be burnt. This is more onerous than the single cable test, and in general will require
materials with higher oxygen index to pass, typically above 28. Again careful selection of all
cable materials is necessary to achieve a pass in this test. (It is not necessary to use an
insulation material of high oxygen index as the sheath material has the greatest influence on
passing this test.)

There are four levels or categories associated with this test, ie Cat A, B, C and D, which
relate to the volume of combustible material in a cable. Cat A being the most onerous (7
litres/metre of test sample), while Cat D is the least onerous (0.5 litres/metre of test sample.)
Therefore depending on the category to be tested and the size
of cable either a single large cable might be needed or a lot of
small cables.

In this test 3.5 m lengths of cable are mounted on cable ladder

tray vertically in a test chamber with a standard ribbon burner
applied to the base of the cable assembly. (See image at right.)
The cables are clamped to the ladder by steel or copper wire.
The flame is applied 500 mm from the bottom of the cable
samples. (Flame application time is 40 minutes for Cat A and B
and 20 minutes for Cat C and D.)

A pass is achieved if flames do not propagate more than 2.5 m

from position of burner.

Similar to the single vertical cable test, the bunched cable test
standards evolved from the European standards and the current
version (2005) adopts the entire content of the equivalent IEC
60332-3 standard.

LOW SMOKE ZERO HALOGEN (LSZH) CABLES

Now we look at the second and third key element of fire rated cables that being Low Smoke
and Zero Halogen. What exactly does this mean?

Cables with these properties are made from materials that DO NOT contain
halogens. (Halogens comprise the group of chemical elements that includes
Fluorine, Chlorine, Bromine, Iodine etc.) Materials containing these elements tend
to give off lots of smoke and the combustion by-products, or residue, tend to be
acidic and very corrosive. Therefore PVC (Poly Vinyl Chloride) is NOT used in Fire
Rated cables, while materials such as XLPE or HFI-90-TP, some rubber materials
not containing Chlorine such as EPR, and specially developed thermoplastic
sheathing materials, such as HFS-90-TP or HFFR.

Cables that are categorised as LSZH are those that emit a low level of smoke,
toxic fumes and corrosive gases.

These cables are used in confined areas with large amount of cables within close
proximity to human traffic and/or presence of sensitive electronic equipment. They
avoid people getting blinded by the smoke, avoid harmful effects on humans due to
inhalation of toxic fumes, and avoid corrosion of sensitive electronic equipment.
Smoke Density - AS/NZS 1660.5.2

Testing of cables for smoke emission during fire is

done to AS/NZS 1660.5.2 and is done in a 3 metre
cube smoke chamber. Cable samples 1 metre
long, (the number of cables being determined in
accordance with their diameter), are supported
within the chamber over a tray of alcohol based
fluid, which serves as the flame source. (See
image at right.)

After ignition of the alcohol based flame source

the smoke given off during combustion of the
sample/s is determined by measuring the amount
of light transmitted from one side of the chamber
to the other using a specified light source (100 W,
2000 lm – 3000 lm), and light detector (photocell).

For a “Low Smoke” cable a pass is achieved if more than 60 % of light is transmitted through
the chamber. (AS/NZS 4507 pass criteria is 50% - 70% depending on cable diameter.)

Again the Australian Standard for determining smoke density is based on the European
standards, namely IEC 61034 and the current version (2006) adopts the entire content of the
equivalent IEC 61034 standard, including both Part 1 and 2 of the IEC standard within the
one AS/NZS 1660.5.2.

Acidity and Corrosiveness of Smoke Emissions – AS/NZS 1660.5.3 & AS/NZS 1660.5.4

The first part of this series of test determines the amount of halogen acid gas evolved during
combustion of a material. (Note that this test is done on cable materials as opposed to
complete cable samples.)

The basic principle of these tests is to burn a small quantity of material in an enclosed
environment which is fed with air at one end such that the smoke emissions can be collected
by bubbling the smoke/air mixture through a number of water containers. The sample of
water can then be checked to determine various properties such as:-

• Volume of hydrochloric acid in the water (AS/NZS 1660.5.3)

o Halogen free cables will return a zero result under this test
• Acidity (pH) level of water (AS/NZS 1660.5.4)
o A pass is achieved if the pH is > 3.5
• Conductivity of water (AS/NZS 1660.5.4)
o A pass is achieved if conductivity is < 10 µS/mm
The test apparatus is depicted in
the image at right.

Again the Australian Standards for

determining the acidity and
corrosiveness of cable materials
has followed European practice and
standards, namely the IEC 60754
series and the current versions
AS/NZS 1660.5.3 (1998) and
AS/NZS 1660.5.4 (1998), while not
yet adopting the entire content of
the equivalent IEC 60754 standard,
Part 1 and 2, they do align with
these standards.

CIRCUIT INTEGRITY

This is the final key element and perhaps the most important and complex element of fire
rated cables and the one where differing test methods exist for determining this property of
cables. The properties of cables which afford circuit integrity, or also known as “Fire
Resistance” in the cable industry are listed below.

• Keeps electrical equipment going during fire

• Used in buildings, plants, enclosed infrastructure, ships and sites where the cable is
expected to continue to function for essential services/mission critical applications
whilst under fire.
• Fire Safety in Buildings
• Fire Alarm and Security cabling
• Emergency Exit signs and facilities
• Power and control for Fire Fighting equipment eg Water Pumps

(Note: It is implied that a Fire Resistant cable should be Flame retardant and Low Smoke
Zero Halogen as well, but it is not necessarily the case. (It should also be realised that
although this statement may be true it may be difficult to achieve fire resistance with cables
containing halogenated materials because the acidic and conductive nature of the
combustion by-products of these materials are likely to cause a failure when performing the
circuit integrity test.))

There are two fundamental test methods and standards available throughout the world for
determining the circuit integrity properties of cables, those that employ a ribbon type burner
and those that are performed in an enclosed furnace system. The main difference is that the
ribbon burner test methods do not apply the same amount of heat as the furnace test
method. Therefore cables that can pass ribbon burner test may not pass the furnace test. (It
is the furnace test that has been adopted by the Australian Building Industry for testing the
fire resistance of building materials, which will be covered later in this article.)
Ribbon Burner Standards – AS/NZS 1660.5.5 & IEC 60331

Similar to the other fire safety standards for cables the AS/NZS 1660.5.5 circuit integrity test
standard has followed European practice and is based on IEC 60331, which was developed
and first published in 1970. Therefore this test method has quite an established track record,
with its evolution being the introduction of higher temperatures, the inclusion of shock (or
mechanical impact) and an optional water spray.

The test set-up for fire alone is depicted in

the image at top right, while the test setup
for fire with shock is depicted at bottom
right. The latest version of
AS/NZS 1660.5.5 (2005) adopts the entire
contents of IEC 60331 and there are a
number of sections/parts to the
AS/NZS 1660.5.5 and IEC 60331
standards that align as listed below.

AS/NZS IEC Test

1660.5.5 60331
Section 2 Part 11 Apparatus - Fire
alone at a flame
temperature of
750 oC
Section 3 Part 12 Apparatus - Fire
with shock at a
temperature of
830 oC
Section 4 Part 21 Procedures and
requirements –
Cables of rated
voltages up to and
including 0.6/1 kV
Section 5 Part 23 Procedures and
requirements –
Electric data cables
Section 6 Part 25 Procedures and
requirements –
Optical fibre cables
Section 7 Part 31 Procedures and
requirements – Fire
with shock - Cables
of rated voltages up
to and including
0.6/1 kV

As depicted in the images at right, for fire alone a cable sample of approximately 1200 mm
long is clamped at its ends and support in the centre by two metal rings spaced
approximately 300 mm apart. The burner is of a “specific” type fuelled by propane gas and
has a length of 500 mm. The standards define the test setup in more detail concerning
control of fuel flow, positioning of the burner, etc. The cable ends are exposed so that
continuity can be measured by powering with a suitable three phase or single phase supply
which is loaded with an indicating device, such as a lamp that draws a load current of
0.25 A. In-line fuses are also installed in the circuit so that short circuits between conductors
can also be detected.

A pass is achieved if both the lamp/s remain alight and no fuse fails, during the
recommended flame application time, usually 90 minutes. (Temperature control is performed
by means of an initial verification stage by varying the gas flow rates and measuring the
flame temperature with thermocouples positioned appropriately in the location that will be
occupied by the cable sample.)

The test method for fire with shock involves mounting the cable sample to a metallic frame
as depicted in the image on previous page, the cable being installed with a 180 degree bend
at the cable manufacturer’s minimum bend radius. A metal bar is employed as a shock
producing device that strikes the frame every 5 minutes throughout the duration of the test.
In this test the flame applications is usually 120 minutes and the pass criteria is the same as
for fire alone.

Ribbon Burner Standards - BS 6387

There are certainly many other international standards that exist that deal with circuit
integrity testing of cables, German VDE, French NFC, most of which adopt similar ribbon
test methods as the IEC 60331 standard. The British Standard BS 6387 is one such
example of a widely accepted international
standard. This standard also describes a ribbon
burner test with the test apparatus being similar to
IEC 60331. For fire alone this is known as Cat A, B
or C, which relate to the test temperature, of
650 oC, 750 oC or 950 oC respectively. There is a
difference in the test for fire with shock in that the
cable sample is mounted on a fire rated board (see
image at right), rather than the frame as shown in
the image on the previous page. Shock is achieved
by a metal bar striking the board at regular
intervals, ie 30 seconds.

Note the two 90 degree bends in the cable sample which are done at the cable
manufacturer’s minimum bend radius. Fire with shock use the same test temperatures as fire
alone, but use the letters X, Y, or Z
respectively.

An optional water test can be performed where

the sample is sprayed with water from a
sprinkler system (similar to the type used in
building fire sprinkler systems), see image at
right.
Further details of the test durations, sample setup, sprinkler application time, etc, can be
obtained from the relevant standards.

The details provided in this article are simply to give the reader an insight into the principles
of the various test methods that exist around the world.

Furnace Standards – AS/NZS 3013

As an alternative to the ribbon burner test that I have described in the previous pages,
Australia has also developed and adopted a more onerous furnace test based on that used
for the testing of building materials.

The key features of the AS/NZS 3013 test method, not only include the use of a furnace, but
include the following elements:-

• Test method includes both testing under fire conditions and mechanical (impact and
cuting) testing
• Test method can be used to test cables, busways, cable supports (trays) and fixing
(saddles, ties etc)
• Fire test on cables require cable to be mounted on designated cable tray
• Test temperature is continuously monitored and controlled throughout the fire test
and follows the time/temperature curve of AS 1530.4
• Fire test method includes an option water spray test at the end to simulate practical
fire extinguishing methods
• Purpose is to develop a circuit integrity classification for the wiring system, ie not just
cable

The point above regarding the classification of the wiring system is important as this allows
users and installers a simplified means to describe the rating of the wiring system required
by a particular installation. The wiring system “WS” classification system of AS/NZS 3013 is
described below. (eg WS52W being the most common for cables.)

First numeral indicates time for which cables or busways are able to maintain circuit integrity.

• 1 = 15 minutes
• 2 = 30 minutes
• 3 = 60 minutes
• 4 = 90 minutes
• 5 = 120 minutes (2 hours commonly requested)

Second numeral represents degree of mechanical impact and cutting force that wiring
system element can withstand without failure

• 1 = Light (2.5 Joule Impact & 0.3 kN Cutting)

• 2 = Moderate (15 Joule Impact & 1.0 kN Cutting) (2 is common for cables)
• 3 = Heavy (50 Joule Impact & 5.0 kN Cutting)
• 4 = Very Heavy (500 Joule Impact & 5.0 kN Cutting)
• 5 = Extremely Heavy (5000 Joule Impact & 5.0 kN Cutting)

Supplementary letter “W” represents additional water spray test.

The picture below shows the furnace (fire chamber) after completion of the two hour fire test,
where the chamber roof is removed, complete with cable tray and cable in readiness for the
water spray test. Circuit integrity of the test component is monitored through the fire test by
means of a multiphase or single phase supply applied to each conductor of the cable under
test connected to a 60 W lamp. In addition in line fuses are used to detect conductor to
conductor contact, with additional indicating lamps connected across each fuse as a visible
sign of the fuse opening.

A pass is achieved if the lamp/s remain alight and no fuse fails, for the during of the fire test,
usually 120 minutes for most fire rated cable used in Australia.

The photo at right shows

the same fire chamber roof
during application of the
water spray test, which is
performed as prescribed in
the standard for a period of
180 s. The standard
prescribes such elements
as elapsed time after fire
test to start water spray test,
environment where the
water spray test is to be
performed, water flow rate,
etc. Throughout the water
spray test the circuit
integrity of the cable system
is monitored is monitored in the same way as for the fire test.
The next two photos show a typical test configuration for cable and cable tray prior to fire
testing and then post fire testing. Note the bends in the cable, which is similar to the
requirements of the IEC 60331 and the BS 6387, where two 90 degree bends must be
placed in the cable at the cable manufacturers minimum bend radius.

The principle behind the development of fire test method described in AS/NZS 3013,
and the manner in which the cable sample is setup, is to ensure that the test method
as much as is possible closely matches the method in which a cable system is likely
to be installed in practice.

In addition, as eluded to at the start of this section on AS/NZS 3013, the fire test is
performed according to a controlled time/temperature curve which is also used by the
building industry for the testing of building materials, ie walls, floors, roofs, columns, beams,
door assemblies, ducts, critical services, etc. The time/temperature curve is detailed in
AS/NZS 1530.4, see graph below, and therefore there is a direct link between the building
standards as defined by the ABCB (Australian Building Code Board) National Construction
Code (NCC) and AS/NZS 3013, where AS/NZS 3013 is referenced with the NCC.
Some key pints to note about the time/temperature curve defined in AS/NZS 1530.4.

• The curve itself was based on the characteristics of a cellulose fire, cellulose being a
material common to building products, eg wood.
• Although AS/NZS 3013 caters for testing of wiring system components up to two
hours, the curve itself extends to six hours. However only cable with copper
conductors will pass the two hour test since the melting point of copper is just above
the two hour test temperature (melting point of copper = 1085 oC)
• The temperature attained after two hours is over 1000 oC, which exceeds the test
temperature of all of the IEC and BS standards.

The second part of the AS/NZS 3013 WS rating system rating is the mechanical rating. The
test method adopted for checking the mechanical integrity of a cable involves an impact and
a cutting test.

The impact test

involves dropping a
defined mass a
prescribed distance
onto a cable sample
using a defined shaped
impact head. See
image of test setup at
right.

The drop height and

weight to be dropped is
selected in accordance
with the mechanical
category level (1 – 5),
the test piece must be
conditioned at its rated
operating temperature
eg 110 oC, and within
60 seconds the sample is subjected to three such impacts, within a 300 second time period.
Circuit integrity monitoring is similar to that used for the fire test, except that it is reconfigured
to use an ELV voltage of between 18 volts and 30 volts for safety reasons.

A pass is achieved if the cable continues to carry the test current, and conductor has NOT
made contact with another conductor, a screen, an armour or other earthed metal layer, or
the impact test load assembly.

The cutting test involves applying a constant force to a defined shaped steel wedge onto a
cable sample using a compression testing machine capable of measuring the load force .
See image below. The force to be applied is selected according to the mechanical category
level (1-5) and again the test piece is conditioned according to its rated operating
temperature. The cutting test is performed at four locations with the test piece rotated 90
degrees about its axis after testing at each location.
The contact monitoring system is depicted in the above sketch and consists of a voltage
source providing a supply of nominal 9 volts dc and an indicating device such as a lamp or
audible buzzer. A pass is achieved if the sample of cable has survived the level of cutting
force, ie the wedge has not made contact with the conductor as indicated by the contact
monitoring system.

AS/NZS 3013 was first published in 1990, the current version being 2005. The most notable
development in the latest version being the change to allow testing of individual components
to be combined to construct a wiring system.

A good example of this was the change in the standard that sees the cable being tested on
cable tray as opposed to being tested by itself where the cable was clipped to the underside
of the furnace roof.

Circuit Integrity – Supplementary Note

It can be concluded from the above discussion, regarding test methods to establish the
circuit integrity performance of cables, that the pass criteria is based only on continuity of the
power supply voltage and current. This includes the testing of data cables as described in
AS/NZS 1660.5.5 Section 5 and in IEC 30331 Part 23, where similar currents and voltages
are applied through the test as for power cables.

This test method has gained acceptance in the industry for power cables that enables
comparative results to be obtained, and this is where the major development in standards
and test methods has occurred over the past few decades. However these established test
methods may not be so relevant for determining the change in signal transfer quality in fire
rated data and signal cables.

To fill this gap there is currently work being undertaken to establish a suitable procedure and
test criteria for data, signal and including coaxial cables in the “EN” range of standards. For
example under the umbrella of EN 50289, which documents the test methods for
communications cable, sub part 4-16 (ie EN 50289-4-16) documents the criteria for
determining the circuit integrity of control and communications cables when using the fire
test methods of the relevant EN fire test standards, ie EN 50200 burner standard, and
EN 50577 furnace standard.

Draft standard EN 50289-4-16 details pass criteria for different cable types (twisted pair and
coaxial), and differing signal frequency ranges (<100kHz, 100 kHz – 100 MHz, and 100 MHz
– 1000 MHz) where depending on the operating frequency limits for the cable, differing
criteria is applied, ie continuity, capacitance attenuation, return loss, and near end cross-talk.
CONSTRUCTION OF FIRE RATED CABLES

In a discussion on the construction of fire rated cables there are two fundamental
components of their construction.

i. That component that allows the cable to continue to function during a fire (circuit
integrity). This is usually determined by the material that is wrapped around or
encloses the conductor.
ii. That component that fulfils all the other features of a fire rated cable, ie flame
propagation, low smoke and halogen free. This is determined by the materials used
for the insulation and sheath of the cable.

It is fair to say that in over one hundred years of cable development, only three designs exist
that cater for component (i).

MIMS (Mineral Insulated Metal Sheathed) Cables

These cables employ copper conductors enclosed in a Magnesium

Oxide (mineral) insulation which is capable of surviving extreme
temperatures well over 1000 oC. A copper sheath encloses the
conductors and insulation, which may be further protected by an outer
plastic sheath to improve corrosion performance of the copper sheath.

This design was invented in 1896 and is still in use today albeit with
issues in handling, terminating and availability. The main advantages
of the design were its inherent fire survival characteristics which were
not realised until many decades after its invention. In addition the
MIMS cable has good mechanical properties and has inherent electromagnetic noise
reduction characteristics due to the copper sheath.

Mica/Glass Tape

The development of mica/glass taped conductors began around the same time as the
development of standards for circuit integrity, which was in the early 1970s. Special fire
resistant conductor barrier tapes containing mica and glass protect the conductor during fire,
after all of the insulation and sheathing material have burnt away.

Mica is a naturally occurring mineral and has an extremely high melting point typically over
1000 oC.

Mica tapes used in the electrical cable

industry usually comprise mica paper
bonded to an electrical grade glass cloth
backing tape. The number of tapes to be
applied to a conductor will depend on the fire
test standard that the cable is designed to
meet. Mica taped cables that pass the
IEC 60331 standard may not pass the AS/NZS 3013 furnace test.
The main disadvantages to the use of Mica in cables are associated with OH&S issues as
the mica can flake and crumble into very small fragments during cable stripping and the
extra time involved in stripping the mica and cleaning the conductor.

Insulation and sheathing materials can be selected from a large range, provided they meet
the requirements of being flame retardant, low smoke and halogen free. Common materials
used in fire rated cables are XLPE or rubber (eg HFFR – Halogen Free Flame Retardant) for
insulation and HFS (Halogen Free sheath) or again rubber based materials (eg HFFR).

Whichever materials are used it is important to ensure that they are aligned with the
maximum operating temperature of the cable, ie the combination X-HF-110/HFS-110-TP
insulation/sheath for a 110 oC rated cable. (It is also of interest to note that the temperature
of the insulation and sheathing material does not relate to the circuit integrity performance of
the cable.)

Ceramifiable® Materials

This is the newest development in cable material for fire safety, being those materials that
“ceramify” or turn into a hard ceramic like material during a fire. They are a special
proprietary compound developed by Olex and the CSIRO in 2004 which do not rely on a
flame barrier tape to afford protection of the conductor during fire. The cable therefore
comprises only two layers, the Ceramifying insulation and the sheath.

The special Ceramifying insulation complies with

an AS/NZS 3808 material type such as R-E-110,
HFI-90-TP, depending on the individual product
type and would typically include a halogen free,
flame retardant HFS-90-TP sheath.

Apart from the obvious advantages of simplicity of

design (two layers), ease of stripping and the
avoidance of the OH&S issues associated with the
Mica tape design, a little known advantage of the Ceramifiable® design is the reduction in
calorific content in the cable.

For example XLPE as used in Mica taped cables, has a low oxygen index and will readily
combust in air if subject to fire. Therefore these designs require a good (high oxygen index)
flame retardant sheath material to ensure they meet the required flame propagation tests.
The insulation material of the Ceramifiable® design has a much higher oxygen index in
comparison to XLPE and exhibits lower heat release levels during combustion. In other
words the Ceramifiable® design has a lower propensity to keep a fire going. (In fact XLPE
has equivalent energy content to that of petrol, for the same weight, whereas the
Ceramifiable® has less than half.)

LINKING CABLE FIRE SAFETY STANDARDS AND THE BUILDING INDUSTRY

I had briefly mentioned the link between the time/temperature defined in AS/NZS 1530.4 and
the building standards in the previous section on the AS/NZS 3013 furnace standard for
circuit integrity. This will be expanded a little further in this final section of this article.
(A review of the ABCB National Construction Code shows that all of the key elements of a
fire rated cable are included. Flame propagation and smoke emission of building materials
are detailed within the NCC which references AS/NZS 1530.3. This standard determines the
“Spread-of-Flame Index” and “Smoke-Development Index” of building materials. However
only the test for fire resistance of building materials as defined in AS/NZS 1530.4 is shared
with the cable test standard AS/NZS 3013.)

Building materials, such as walls, floors, roofs, columns, beams, door assemblies, ducts,
critical services, etc, as required by the NCC must be tested to the requirements of
AS/NZS 1530.4. Furthermore The NCC defines a similar fire resistance category system as
AS/NZS 3013. The NCC defines an “FRL” of a material, where FRL stands for Fire
Resistance Level in a format xx/yy/zz, where the letters represent the time in minutes to
failure of the test, ie:-

• xx = Structural adequacy (eg as applied to load bearing elements, beams and

columns
• yy = Integrity (eg maintains barrier to prevent flames or hot gases passing through)
• zz = Insulation (minimises temperature rise of the exposed face of building element)

Some typical examples of the FRL system as defined in the NCC, emergency lift shafts are
required to have an FRL of 120/120/120 when tested in accordance with AS/NZS 1530.4.
And main switchboards supplying emergency equipment are required to have an FRL of
120/120/120.

SUMMARY

The overall message intended by this article is that although the characteristics of fire and
the way that materials behave during a fire are complex, much research and development
has gone into preparing standards that enable scientific and repeatable test methods to be
documented within these standards to allow cables to be tested to determine their
performance during a fire. And many of these standards have been in use for many
decades.

Secondly the development of fire rated cables has come a long way in the past few decades
such that cable manufacturers are well placed today with the knowledge of materials and
cable designs that ensure that these fire safety standards can be met. Nonetheless users
and installation contractors must remain diligent in ensuring that the cable manufacturer has
the necessary test reports to support any claims for the performance during fire of their fire
rated cables and the standards that they meet.

(When conducting fire tests on fire rated cables it is not necessary to conduct the test on
every cable size, nor for every order. In the case of AS/NZS 3013, the standard dictates the
cable (conductor) size that is to be tested, which is deemed to qualify a range of sizes as
detailed in the standard. In the case of other standards, such as the IEC, qualification
guidelines are not included and the process of determining a qualification criteria is usually
left to negotiation between the supplier and customer. Some fundamental principles are
usually adopted, such that the cable size tested will qualify other cable sizes provided that
they employ the same materials and are of essentially the same design, the only difference
being the conductor size.)