IS 1646 : 1997Code of Practice for Fire Safety of Buildings (General) : Fire Fighting Equipment and its Maintenance

IS 1646 is the code of practice for fire safety of buildings (general): electrical installations — fire-safety provisions specifically related to electrical systems in buildings. While IS 732:1989 covers general electrical installation practice, IS 1646 focuses on the electrical aspects of preventing, detecting, and surviving fires.

Use IS 1646 when designing or auditing: - Multi-storey residential / commercial buildings (particularly > 15 m height per NBC 2016 Part 4) - Hospitals, hotels, schools, public assembly buildings - Industrial and warehouse premises - Buildings handling flammable materials (petroleum, paint, chemicals) - Server rooms, data centres, switchgear rooms - Any building requiring fire NOC from State Fire Service

IS 1646 + NBC 2016 Part 4 + IS 732:1989 + IS 3043:2018 together form the electrical-fire-safety framework. Statutory authorities (state fire service, local building bylaws, insurance) require compliance for occupancy + insurance certificates.

Key electrical fire-safety provisions covered: - Fire-resistant cables (FR / FR-LSH / LSZH grade selection) - Cable trays and conduit fire-stopping at floor / wall penetrations - Earth-leakage protection (RCD / RCBO mandatory in wet areas, public-use circuits) - Surge protection devices (SPD) - Emergency power and lighting systems - Smoke detectors and fire alarm panel - Power supply for fire-fighting equipment (jockey pump, main fire pump, hydrant) - Lift fire-rescue mode operation - Cable separation between primary and emergency systems

1. Fire-resistant cables: - FR (Flame Retardant) — does not propagate flame; basic fire-safety grade (per IS 10810 Part 53 — vertical wire flame test) - FRLS (Flame Retardant Low Smoke) — adds low smoke emission (IS 10810 Part 61); used in buildings with high occupancy - FR-LSH (Low Smoke Halogen-free) — Halogen content < 0.5 % (no toxic HCl gas in fire); for public buildings, hospitals, theatres - LSZH (Low Smoke Zero Halogen) / HFFR (Halogen-free flame-retardant) — strictest grade; for critical applications (data centres, metro, aircraft); per IS 17048:2018

2. Fire-stopping at penetrations: - Where cable trays / conduits pass through fire-rated walls / floors, the gap must be sealed with fire-stop material (intumescent putty, mortar, foam) to maintain fire compartment integrity - Fire-stop rating: matches the wall / floor rating (typically 1-2 hour fire resistance)

3. Cable separation: - Primary power cables separated from emergency power cables (different cable trays / conduits) - Separation prevents single-fire failure from disabling both systems - Critical for: emergency lighting, fire alarm, fire pump, lift rescue mode

4. Earth-leakage / RCD protection: - 30 mA RCD: bathrooms, swimming pools, outdoor sockets, schools, hospitals (life safety) - 100 mA RCD: sub-distribution boards (general) - 300 mA RCD: MDB upstream (fire safety against arc-fault leakage)

5. Surge protection devices (SPD): - Type 1 (lightning current protection) at building entry - Type 2 (surge protection) at sub-distribution boards - Type 3 (equipment-level) at sensitive electronic equipment - Particularly important in lightning-prone zones (per IS 2309)

6. Emergency lighting: - Battery / inverter-backed; auto-switch on mains failure - Minimum 30 lux at exit signage; 1 lux on escape route - Battery duration: minimum 90 minutes per NBC 2016 - Self-contained units OR central battery system

7. Fire alarm system: - Smoke / heat / multi-criteria detectors per IS 2189 - Manual call points at every floor exit - Fire alarm panel with battery backup - Sounders / strobes for evacuation alert - Voice evacuation system in larger buildings

8. Power supply for fire-fighting: - Dedicated feeder for fire pump (jockey pump + main pump + standby pump) - Auto-changeover from grid to DG within 10 seconds - Cable to fire pump: fire-resistant grade (FRLS minimum) - Power for firemen's lift, fire-rated lift control, fire fan in pressurised stairs

9. Lift fire-rescue mode: - All passenger lifts must descend to ground floor on fire alarm - Designated firemen's lift (in buildings > 15 m): independent power, fire-rated control, manual override at ground floor

10. Solar PV / EV charging integration: - Modern buildings with solar PV: PV-fire isolation switch (DC isolator near solar panel array) - EV charging stations: dedicated fire-rated cable, RCD + AFDD (arc-fault detection device)

Cable grade selection (per building type):

| Building type | Recommended cable grade | |---|---| | Residential single house | PVC FR (basic FR) | | Multi-storey apartment (≤ 15 m) | FR or FRLS | | High-rise residential (> 15 m) | FRLS or FR-LSH | | Commercial office | FR or FRLS | | Hospital, hotel, school, public assembly | FR-LSH (mandatory) | | Critical (data centre, metro, airport) | LSZH / HFFR (per IS 17048) | | Industrial premises | FRLS (general); special cables for hazardous areas |

RCD selection:

| Application | RCD trip current | Type | |---|---|---| | Bathroom / wet area | 30 mA | A or B | | Outdoor socket / garden | 30 mA | A or B | | General final circuit | 30 mA preferred (life safety) | A | | Sub-DB | 100 mA | A or B | | MDB upstream | 300 mA | A (fire protection) | | Three-phase machinery | 100-300 mA | B | | Solar PV (DC injection) | 30 mA | B (Type B handles DC) |

SPD selection: - Type 1 (10/350 µs lightning surge): 25 kA per pole minimum - Type 2 (8/20 µs switching surge): 40 kA per pole standard - Type 3 (equipment-level): per equipment manufacturer

Fire pump power supply: - Auto-changeover panel: switching time < 10 sec - DG capacity: ≥ 1.25 × jockey + main pump + 0.5 × standby pump motor rating - Cable to pump room: fire-rated, in dedicated route (not common cable tray with general-use cables)

Emergency lighting: - Average illuminance on escape route: ≥ 1 lux - At exit signage: ≥ 30 lux - Duration: ≥ 90 min (commercial), ≥ 180 min (hospital, hotel, public assembly) - Self-test capability (some units run self-test weekly to verify battery)

Cable separation distances: - Primary vs emergency cable: separate cable trays; minimum 300 mm separation OR fire barrier between - HV vs LV: separate cable trays; minimum 600 mm - Power vs telecom / data: separate cable trays; minimum 300 mm OR shielded cable

• NBC 2016 Part 4 — Fire and Life Safety (the umbrella fire code).
• IS 732:1989 — code of practice for electrical wiring installations (general).
• IS 3043:2018 — code of practice for earthing.
• IS 17048:2018 — Halogen-free, low smoke (HFFR) cables.
• IS 694:2010 — PVC insulated copper conductors (the general cable spec).
• IS 1554 Part 1:1988 — PVC insulated armoured cables.
• IS 7098 — XLPE insulated cables.
• IS 10810 — methods of test for cables (FR / FRLS / LSZH grade verification).
• IS 2189 — selection, installation and maintenance of fire alarm systems.
• IS 2309:1989 — lightning protection of buildings and allied structures.
• IS 12640 — RCCB / RCBO.
• IS 16121 — surge protection devices.
• IS 2190:2010 — first-aid fire extinguishers.
• IS 884:1985 — first-aid hose reel installations.
• IS 3844:1989 — internal fire hydrants.
• IS 9668:1990 — water supplies for fire fighting.
• IS 15105:2002 — sprinkler systems.
• IS 14665 — electrical installations: lifts.
• CEA Regulations 2010 — statutory framework for electrical safety.
• State Fire Service Acts and Rules — regulatory framework.
• Building Bylaws (Municipal) — local enforcement of fire safety provisions.

1. PVC general-purpose cable in public-assembly building. Burning PVC produces toxic HCl gas; survival in fire becomes hard. Use FR-LSH minimum for hospitals, schools, hotels, theatres. 2. No fire-stopping at penetrations. Cable trays through fire-rated wall = fire bypasses compartmentation; smoke + heat propagate. Fire-stop putty + barrier mandatory. 3. Fire pump cable shared with general cable tray. Single fire damages both; fire pump fails when most needed. Dedicated fire-rated route. 4. No 30 mA RCD in bathrooms. Electrocution risk; mandatory per CEA 2010 + IS 1646. Retrofit RCBO. 5. No emergency lighting / battery-backed. Power fails; occupants trapped in dark stairwell. Battery-backed emergency lights at every exit + escape route. 6. Lift not on fire-rescue mode. Occupants trapped in lift during fire. All passenger lifts must auto-descend on fire alarm. 7. Inadequate testing of fire alarm system. System works on day 1 but degrades; periodic test mandatory (monthly visual; annual functional). 8. No SPD on lightning-prone area. Lightning strike damages electronic equipment + can cause fire; SPD is cheap insurance. 9. Solar PV without DC isolator near array. Firefighters arriving find live DC even with grid off; cannot safely cut power. DC isolator near roof array; clearly labelled. 10. Old building electrical reuse without RCD retrofit. 30+ year old wiring without RCD = high earth-fault leakage = fire risk. Retrofit RCBO. 11. No periodic earth resistance test. Earth pit dries out over years; fault currents don't flow; RCD doesn't trip; fire risk. Annual earth resistance test mandatory. 12. Voltage drop > 3 % on long runs. Equipment runs hot, premature failure, fire risk. Calculate and verify drop. 13. No labelling on distribution boards. After 5 years, no one knows which breaker serves what; emergency response delayed. Mandatory labelling per IS 1646.

Building fire safety design cascade (electrical perspective):

1. Building category (NBC 2016 Part 4) — residential / institutional / commercial / industrial / hazardous; height + occupancy class. 2. Statutory requirements — state fire service NOC, building bylaw compliance, insurance requirements. 3. Electrical fire-safety design (this code, IS 1646): - Cable grade selection per building type - RCD / SPD layout - Fire-stop at all penetrations - Cable separation (primary vs emergency) 4. Active fire systems: - Fire alarm (IS 2189) - Sprinkler (IS 15105) - Hydrant (IS 884, IS 3844) 5. Power supply for fire-fighting equipment — DG, auto-changeover, dedicated cabling. 6. Emergency lighting + signage — battery / inverter backed, 90-180 min duration. 7. Lift fire-rescue mode + designated firemen's lift (in tall buildings). 8. Smoke management — pressurisation of stairs, fire fan, smoke vent. 9. Compartmentation integration — fire-rated wall + door + cable / pipe penetration sealing. 10. Construction phase — installation per design, inspection at every penetration, periodic update of as-built. 11. Commissioning — functional test of every system: alarm, sprinkler, hydrant, fire pump, emergency lighting, lift mode. 12. Operations + maintenance — quarterly inspection, annual functional test, repair of faults, periodic upgrade.

IS 1646 has been one of the foundational electrical fire-safety codes in India. Modern revisions and integration with NBC 2016 Part 4 keep it current; statutory enforcement by state fire services makes compliance practical mandatory for any major building.