Code of practice for fire safety of buildings (general): Details of construction
1989 Edition

Per IS 1642, Clause 4.1 and Table 1, structural elements have specified minimum fire resistance durations depending on construction type and function. For instance, exterior load-bearing walls with fire separation under 3.7 m require up to 4 hours resistance in highest fire-resistive construction (Type 1), while lower types may need between 1 to 2 hours. Fire walls, fire doors, exit enclosures, and shafts have prescribed fire resistance typically ranging from 2 to 4 hours. These ratings cover stability, integrity, and insulation, validated by IS 3809 testing or approved calculations.

Separating walls per IS 1642 should extend at least 15 cm beyond roof eaves with the eaves cut back on both sides to prevent fire spread onto the roof. The wall must rise at least 60 cm above the roof surface, except for reinforced brick or concrete slab roofs where it should be bonded flush with the slab's top. Openings within 3 meters on either side must be sealed with fire-resisting doors rated at least 2 hours for walls with 4-hour fire resistance, or 1 hour otherwise. Openings are limited in size (maximum 5.6 m² area, 2 m width, 2.75 m height) and the wall must be continuous vertically through all stories, bonded to fire-resisting floors to ensure full fire separation.

IS 1642 permits Class 1 finish materials anywhere including staircases, corridors, and external facades. Class 2 materials are allowed except on walls and ceilings of staircases and corridors. Class 3 materials are restricted to living and bedrooms (excluding roof rooms) and must not be used on staircases, corridors, or facades. Permissible finishes include one layer of plasterboard at least 12.7 mm thick finished with gypsum or lightweight gypsum plaster, and layers of asbestos insulating boards with appropriate joint backing and mineral wool or glass fiber finishing. Buildings taller than 15 meters require interior finishes not exceeding Class 1 fire rating.

The standard mandates refuse chutes to be enclosed in non-combustible walls with at least 2 hours fire resistance, located away from staircases and exit routes. Inspection panels and doors must be tight-fitting with a minimum of 1 hour fire rating. Basement staircases require enclosures with at least 2 hours fire resistance and lobbies with 1 hour self-closing fire doors. Mechanical smoke extractors must provide 30 air changes per hour during fire, activate automatically or manually via detectors or sprinklers, interlock to shut off supply fans, and have alternate power supply. Ventilation ducts should be brick or reinforced concrete with fire dampers near electrical equipment. Usage restrictions apply to basements not equipped with sprinklers.

IS 1642 requires ventilation ducts to be metal as per IS 655:1963, with all penetrations through fire walls or floors sealed with materials matching the fire resistance rating. Insulation must be flame-retardant and non-heat-conductive (per IS 4355:1977). Escape routes should not be used as return air passages, and metallic ducts are preferred over false ceiling spaces. Buildings with floor areas over 750 m² must have fire walls and automatic fire dampers installed at fire separation walls, vertical shafts, floor penetrations, and supply/return duct inlets. These dampers must close automatically and shut down air handling fans upon fire detection. Large assembly spaces require smoke-sensitive controls to prevent smoke circulation before heat activation, ensuring compartmentalization and limiting fire/smoke spread.