WCA November 2019

Behaviour of cables in a fire By Nagi Ahmed Abdulmagid, section technical manager, Alfanar Cables Company, Saudi Arabia

After the King’s Cross fire on 18 th November 1987, it became mandatory to use LSHF materials on all London Underground cables. These LS0H cables, which emit non-toxic levels of halogen and low levels of smoke when exposed to fire, are now recommended for use in all highly populated enclosed public areas. LSHF properties are particularly important where smoke and toxic fumes may cause a threat to life. What are halogens? Halogens are non-metallic elements found in the periodic table. The five halogens are fluorine, chlorine, bromine, iodine and 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.

There is confusion about the terminology for halogen-free cable because of a lack of an agreed term. The most frequent identifications are found below:

Terminology

Abbreviation meaning

LS0H

Low Smoke, Zero Halogen Low Smoke, Zero Halogen

LSZH

LSHF LSNH NHFR HFFR FRZH

Low Smoke, Halogen Free Low Smoke, Non-Halogen Non-Halogen, Flame Retardant Halogen Free, Flame Retardant Fire Retardant, Zero Halogen

Zero halogen and low smoke Zero halogen and low smoke do not have the same meaning and cannot be used interchangeably. Zero halogen describes the amount of halogens used to make the compound. These cables may still emit a thick smoke when burned. Low smoke describes the amount of smoke that a compound emits when burned. The cables emit a thin and clear smoke when burning, which makes evacuation and fire fighting much easier and safer. Very often the end user is interested in cables containing both properties. Halogen-free materials Halogen-free cable does not contain any of the chemical elements defined as a halogen. Materials used in wire and cable are divided into two categories: one category for

Alkali metals Transition metals

Halogens Noble gases

Halogen-free cables and their application Halogen-free cables and wires are applicable in delicate areas, for example: • Railway and subway stations and cars, buses and bus stations, aeroplanes and airports, and other mass transit facilities • Any public underground or poorly ventilated location • Public entertainment and sports facilities • Apartment buildings and hotels • Hospitals • Computer/data centres

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Wire & Cable ASIA – November/December 2019