NT 5: LSOH Cables
Fire-retardant and halogen-free cables
|Espacios públicos cerrados|
All over the world, countries are increasingly using halogen-free materials for electrical installations in underground train tunnels, mines, big stores, small shops, cinemas, theatres, supermarkets and other high-risk or busy locations in order to eventually evacuate visitors and ease the work of firefighters in the event of fire.
According to experience, the heat produced by a burning cable is absorbed by adjacent cables, which consequently ignite and produce heat. Under these circumstances, the bunch of cables gains temperature and the flames spread all over the place.
There are tests which measure a cable's capacity to prevent flame propagation. The most exhaustive and worldwide renowned tests are described under IEC 60332-3. The tests simulate the ordinary scenario of a burning cable tray: conductors are vertically arranged and exposed to a flame of 70000 BTU/hour at approximately 750ºC for 20 minutes. Plastics melt completely and the fire starts to spread along the cables. After the flame has been moved away from the cable, the fire must self-extinguish. The cable can be considered to comply with flame- retardancy requirements when the fire had not spread vertically beyond 2.5 metres from the bottom of the burner to the top. Our products have passed these tests successfully. Clearly, fire-retardancy does not guarantee the safe evacuation of the location at risk. In fact, thermoplastics such as PVC are fire-retardant but release large amounts of black smoke which eventually impair sight when trying to find a way out of the fire; besides, the gases they produce are poisonous and may induce fainting. Halogen-free flame-retardant materials have been developed to avoid these situations, as they generate no toxic or corrosive gases and emit no dark smoke during combustion. Materials specially developed to address these problems are called LSZH (Low Smoke Zero Halogen) or HFFR (Halogen-Free, Flame-Retardant). To measure material effectiveness and define material property compliance with the relevant specifications, the products are tested to different standards as follows:
- Generation of toxic and non-corrosive gases is tested to IEC 60754-1/2
- Absence of smoke is tested to IEC 61034 or ASTM E662
- Toxicity is tested to the Italian standard CEI 20-37 or to NES 713.
These products present the following advantages:
a. They are not flammable
b. They release transparent smoke which does not impair vision
c. Humans exposed for 20 minutes to cable combustion gases are not prone to irreversible health conditions.