Halogen-Free Cable
Increasingly used in public and government buildings and where
there is sensitive electronic equipment (i.e. Hospitals, Supermarkets,
Airports, Control Rooms & Computer Suites) these cables are designed for
increased safety in the case of a fire:
- Reduction in hazardous fumes which can cause injury when inhaled
- Reduction in corrosive chemicals which can cause damage to electronics
Historically, most cables used in installations have been
insulated with PVC or similar materials. In fires, these insulation
materials release chlorine gas. Chlorine is a poisonous gas and a danger
to people. In addition it forms hydrochloric acid when coming into
contact with water. Hydrochloric acid (HCL) can have devastating effects
on adjacent equipment.
To overcome the problems associated with the release of chlorine
gas, halogen-free cables are used. Typically a halogen free cable is made
of polypropylene, which does not produce a dangerous gas or acid in fire
conditions.
What are halogens?
Halogens are non-metallic elements found in the periodic table.
The five halogens are fluorine, chlorine, bromine, iodine, & astatine. A
common material that contains halogens in the chemical structure is PVC. Halogens
make cable jackets and insulation highly flame retardant. Some naturally
non-halogenated materials have halogen added because of the flame retardant
properties. When burned, halogens emit a thick toxic smoke and become
corrosive. These characteristics can cause damage to equipment and pose a
safety concern.
Why consider halogen-free
cable?
Over the last few years, halogen-free wire and cabling products
have seen an increase in popularity. Halogen-free cables are used in
consideration of issues including fire safety, fire damage prevention, and the
environment. Halogen-free cables help eliminate the use of environmentally
sensitive materials.
What does LSZH mean?
LSZH stands for low smoke zero halogen. The compounds in the
cable insulation and jacket have no fluorine, chlorine, bromine, iodine, or
astatine. This means that the cable emits little to no toxic halogens and
minimal smoke when in contact with fire. These are important safety precautions
and they often appear together in wire and cable specifications. LSZH wire and
cable is also called: low smoke non halogen (LSNH), low smoke halogen free
(LSHF), and low smoke zero (0) halogen (LS0H).
In what applications can
halogen-free cable be used?
Halogen-free cable is intended for use in applications in which
insulation with low toxicity, low smoke generation, and low corrosiveness is
needed. Examples include rapid transit, industrial, shipboard, and commercial
fields where human safety and protection of equipment is a concern.
Does the NEC allow low-smoke
halogen-free cable in all applications?
The NEC (National Electrical Code) doesn't prohibit halogen-free
cable or wire installation in any application. The NEC does require low smoke
cables for plenum spaces.
Is there a difference
between low smoke and zero halogen?
Low smoke and zero halogen are not equivalent. Low smoke cable
emits a thinner and clearer smoke when burning. This feature makes evacuation
and firefighting efforts much easier and safer. A cable may be low smoke and
still contain toxic halogens. Zero halogen means that the cable does not
contain fluorine, chlorine, bromine, iodine or astatine. Zero halogen cable may
still emit a thick smoke when burned. Both properties are not always needed for
all cables. Check specifications to be sure that the cable meets both
requirements if necessary for your application.
Are there any disadvantages
to using low smoke zero halogen cables?
Low smoke zero halogen cables provide a lot of great safety
advantages, but there is a bit of an electrical and mechanical trade-off. In
order to be low smoke zero halogen, the cable jacket must incorporate a high
percentage of filler material. This increase in filler material could make the
jacket less chemical and water resistant and could provide poorer mechanical and
electrical properties than a non-LSZH counterpart. LSZH jackets are also more
likely to experience jacket cracking during installation, so special lubricants
may be necessary to avoid damage. This is especially true in cold environments.
Because of the limited flexibility of LSZH, it is not recommended in robotic or
continuous flex applications. As a result, LSZH cable is commonly chosen for
applications where fire safety is more of a concern than the cable’s specific
electrical and mechanical properties. Advances in compound materials and
processing have decreased some of these issues.
Can LSZH pass a flame test?
Yes. LSZH may pass a standard flame test. To determine how an
LSZH cable will react in a fire, the following five criteria are considered:
·
How easily the cable will catch fire
·
How quickly the fire will spread along the cable
·
How much smoke is produced upon combustion
·
How toxic are the byproducts
·
How corrosive are the byproducts
Some test standards
related to this type of cable are Plenum rated, LS rated, S1 rated, and ASTM
D5424.
What should be considered
when choosing LSZH?
When choosing LSZH products, factors such as the environment and
price should be considered. An environmental factor such as the temperature of
the installation could reduce the flexibility of the cable. Will the
application be in an open area or confined? Will other flammable material be
present? Low smoke zero halogen cable also tends to be higher in cost. Consult
an expert from Allied Wire and Cable to find the best fit for your application.
Cables intended to fulfil this type of function are often
labelled as one of the following:
LSZH - Low Smoke Zero Halogen
LSOH - Low Smoke Zero Halogen
LSF - Low Smoke and Fume
OHLS - Zero Halogen Low Smoke
Both LSZH and LSF are used to limit smoke, fumes and halogen
given off in fire conditions.
Halogen & Smoke
Emission, Corrosively & Toxicity Standards
IEC 60754-1 / BS6425-1 - emission of halogen
IEC 60754-2 - corrosivity
IEC 61034-1 / ASTM E662 - emission of smoke
ISO4589-2 / BS2863 - oxygen index LOI
ISO4589-3 / BS2782.1 - temperature index TI