In addition to the fire resistant cables in the fire and emergency systems, another type of cables is required which transmit signals to the notification (Indicating) device Circuits such as alarm sounders, horns, strobes and other remote signaling equipment.
Fire alarm cables work under high temperature each to 105C to do it's function in energizing or send the signals to specific device and it is observed that the fire resistant cables work under extreme conditions, the main difference between fire alarm and fire resistance cables is that fire alarm cables doesn't require to maintain circuit integrity under fire conditions; it only turns on the alarm systems at the beginning of the fire.
Fire alarm cable is specified in the article 760 of the American national electric code "NEC" and haoguang electric appliance company is an UL certified as recognized manufacturer.
Low Smoke and Halogen free Cables
In all fire disasters, smoke, halogen and toxic fumes of traditional PVC sheathed cables are the main obstacles to safe evacuation of a building or an area. In addition to the fire resistance and flame retardant tests there are some tests to ensure maximum safe evacuation of people with no harmful effects.
Smoke Emission Tests: (IEC 61034, BS EN 61034)
This test is for determination of smoke density. A 1m length of cable is placed in a 3 m3 enclosures (lt is called 3 meter cube test) and exposed to a beam of light through a clear window. This light travels across the enclosure to a photocell connected to recording equipment in the window on the other end.
A minimum light transmission value greater than 60% is acceptable after a fire is generated. The higher the light transmittance, the less smoke emitted during a fire.
Acid Gas Emission Tests: (IEC 60754, BS EN 50267)
A corrosive halogen gases can be generated by burning PVC or chlorine containing material. HCL gas combines with the water in the eyes, mouth, throat, nose and lungs to form hydrochloric acid that has harmful effects and increasing potential fatalities by inhalation of carbon monoxide and oxygen depletion, additional dangers exist on all metallic materials and devices in the proximity of a fire.
IEC 60754-1, BE EN 50267 specifies a method in determining the amount of halogen acid gas other than the hydrofluoric acid evolved during combustion of compound based on halogenated polymers and compounds containing halogenated additives taken from cable constructions. Halogen includes Fluorine,Chlorine, Bromine, lodine and Astatine. If the hydrochloric acid yield is less than 5 mg/g, the cable specimen is categorized as LSZH.
IEC 60754-2 specifies a method in determining the degree of acidity of gases evolved during the combustion of materials taken from electric cables by measuring pH and conductivity. This standard requires the weighted pH value of not less than 4.3 when related to 1 liter of water, and the weighted value of conductivity should not exceed 10uS/mm.
