Evaluating Fire-Resistant Cable and Ducting Standards: IS 7098 & NBC Guidelines

During a building fire, the electrical cabling and HVAC ventilation duct networks can either act as life-saving safety grids or dangerous conductors of fire and toxic smoke. Under high heat, standard PVC-insulated electrical wires burn rapidly, releasing highly corrosive hydrochloric acid gas and thick black smoke. This toxic smoke is the leading cause of fatalities in building fires. Similarly, uncompartmented HVAC ducts can act as horizontal chimneys, carrying toxic gases across fire barriers into safe escape corridors.

To prevent this, the National Building Code of India (NBC 2016) Part 4: Life Safety and Fire Protection, alongside Bureau of Indian Standards codes like IS 7098 (specification for XLPE insulated cables), enforces strict performance standards for electrical cabling and ducting. Every high-rise, industrial factory, and commercial space must use compliant, fire-rated materials and automatic dampers to secure containment barriers.

Technical Standards for Electrical Cables

Electrical wiring is classified into three performance tiers based on fire resistance and chemical emission profiles:

• Fire Retardant Low Smoke (FRLS): These standard PVC cables are treated with chemical additives to reduce flame spread and smoke density. However, when burned, they still release toxic acid gases, making them prohibited for critical emergency life safety systems.
• Low Smoke Zero Halogen (LSZH / ZHFR): Constructed without halogenated polymers, these cables burn with minimal, highly transparent white smoke and release zero toxic acid gases, preserving visibility in escape lobbies.
• Fire Survival (FS) Cables: Designed to maintain electrical continuity during a fire, FS cables feature a specialized mica tape wrap around the conductor under an LSZH jacket, allowing critical emergency equipment (pumps, lifts, alarms) to function at 950°C for up to 3 hours.

HVAC Ventilation Ducting and Fire Dampers

Ventilation systems must feature passive fire compartmentation barriers to prevent smoke spread through ducting channels. The core standards include:

1. Motorized Fire Dampers: Automated, motorized spring dampers must be installed inside exhaust ducts where they pass through fire walls. The damper features a fusible link that melts at 74°C, closing the blades to seal the duct.
2. Vertical Shaft Seals: Every cable tray and utility shaft passing vertically through building floors must be sealed at the floor level using high-density mineral rockwool and fire-stop mortar.
3. Heavy Sheet Metal: Ventilation ducts must be constructed of heavy-duty galvanized iron sheet metal (minimum 1.2 mm thick).

Frequently Asked Questions