There has been a shift in recent years to using
newly developed compounds that emit less harmful gases, particularly
halogens. The term "Low-Smoke Zero Halogen" describes two distinct
properties of a compound. The term "low- smoke" describes the
amount of smoke that a compound emits when burned, while "zero-halogen"
describes the number of halogens used to make the compound. A product can be
low-smoke but not zero-halogen or be zero-halogen but not low-smoke.
However, these terms have typically been used together because the end-user
is interested in cables with both properties.
Increasingly used in public and government buildings and where there is
sensitive electronic equipment (i.e. Hospitals, Supermarkets, Airports,
Control Rooms & Computer Suites)
Low Smoke, Zero Halogen cables are
designed for increased safety in the case of a fire, providing :
- Reduction in hazardous fumes which can cause injury when inhaled
- Reduction in corrosive chemicals which can cause damage to
electronics
The European market is demanding that cables used in LANs, WANs, etc. meet
LSZH specifications. 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 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.
Cables intended to fulfil this type of function are often referred to 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, however, the challenge for buyers is there are no specific
standards for LSF cables In the event of a fire, both types will emit very
low levels of smoke. LSF cable will emit toxic gases while LSZH will limit
the emission of these (typically under 0.5% hydrogen chloride emission). In
addition to being toxic, hydrogen chloride is corrosive to equipment. The
use of LSZH cables protects both people and limits the amount of equipment
damage during a fire situation.
LSF is often a modified PCV with hydrogen chloride additives and while
performing better than PVC will give off more smoke and fumes than LSZH.
Hydrogen chloride emissions of LSF cable may reach up to 18% Compared with
normal PVC cables and LSF, Low Smoke Zero Halogen cables have better
fire-retardant properties, low toxic and corrosive gas emissions, and low
smoke emission.