IS 1643:1988 is the Indian Standard (BIS) for fire safety of buildings (general): exposure hazard. This code establishes guidelines to prevent the spread of fire between adjacent buildings (exposure hazard), primarily focusing on radiant heat transfer and flying embers. It provides methods to determine safe separation distances based on the building's fire load, the dimensions of the radiating face, and the percentage of unprotected openings.
Code of practice for fire safety of buildings (general): Exposure hazard
BIM-relevant code. See the BIM Hub for ISO 19650, IFC, and LOD/LOIN frameworks used alongside it.
| Parameter | IS Value | International | Source |
|---|---|---|---|
| Hazard Classification System | Three categories: Low, Moderate, High based on occupancy and size. | Multiple Occupancy Groups (e.g., A-Assembly, S-Storage, R-Residential) and Construction Types. | IBC: 2024 |
| Separation Distance Measurement | Measured in plan between the external faces of opposing buildings. | Distance measured from the building face to the closest interior lot line, to the centerline of a street, or to an imaginary line between two buildings on the same lot. | IBC: 2024 |
| Basis for Requirements | Prescriptive tables based on hazard class and dimensions of the 'exposing rectangular face'. | Prescriptive tables based on fire separation distance, occupancy, and construction type, with performance-based options. | IBC: 2024 |
| Allowable Unprotected Openings (Example) | Not explicitly tabulated by distance; requires openings to be protected if wall is rated. | Permits up to 25% of wall area for unprotected openings at a fire separation distance of 15 to <20 feet (for Group F-1). | IBC: 2024 (Table 705.8) |
| Exterior Wall Fire Rating (Example) | A separating wall must have 4-hour fire resistance for High Hazard if separation is not met. | An exterior wall for a Group S-1 occupancy at 5 to <10 feet separation distance requires a 2-hour fire-resistance rating. | IBC: 2024 (Table 705.5) |
| Assumed Heat Radiation Flux (High Hazard) | Implicitly based on 167 kW/m² (4 cal/cm²/s) for high hazard occupancies (Appendix A). | Provides calculation methods or guide values (e.g., 80 kW/m² for light hazard, with higher values for more severe fires) for fire engineering analysis. | NFPA 80A:2022 |