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IS 3809:1979 is the Indian Standard (BIS) for fire resistance test for structures. This standard lays down the testing method for determining the fire resistance of structural elements such as walls, columns, floors, and beams. It defines the standard temperature-time curve, the loading required during the test, and the exact criteria for structural failure based on stability, integrity, and insulation.
! Failure in a fire test is determined by three criteria: Stability (structural collapse), Integrity (passage of flames or hot gases), and Insulation (excessive temperature rise on the unexposed face).
! Structural elements must be tested while bearing their full characteristic design load to accurately simulate real-world stress under fire conditions.
ISO 834-1:1999ISO (International Organization for Standardization)
HighCurrent
Fire-resistance tests — Elements of building construction — Part 1: General requirements
Defines general procedures and requirements for fire resistance testing, forming the basis for many national standards.
EN 1363-1:2020CEN (European Committee for Standardization), Europe
HighCurrent
Fire resistance tests - Part 1: General Requirements
The current harmonized European standard for general fire resistance test principles, derived from ISO 834.
BS 476-20:1987BSI (British Standards Institution), United Kingdom
HighCurrent
Fire tests on building materials and structures. Method for determination of the fire resistance of elements of construction (general principles)
IS 3809 was originally based on earlier versions of BS 476; this part covers the same general principles.
ASTM E119-20ASTM International, United States
MediumCurrent
Standard Test Methods for Fire Tests of Building Construction and Materials
The primary US standard for fire resistance testing with a similar scope but some key differences in procedure and furnace control.
Key Differences
≠IS 3809:1979 specifies furnace pressure vaguely as 'a pressure slightly above that of the atmosphere', whereas modern standards like EN 1363-1 specify a precise pressure gradient and location for the neutral pressure plane.
≠Modern international standards (e.g., EN 1363-1) include integrity failure criteria based on gap gauges (6 mm and 25 mm), which are not specified in IS 3809, which relies solely on the cotton pad test and visual observation of flame passage.
≠The Indian standard is a 1979 document (reaffirmed without major technical updates), while international counterparts like ISO, EN, and ASTM are regularly revised to incorporate new research, measurement techniques, and alternative fire curves (e.g., hydrocarbon, slow heating).
≠European standards are supported by an extensive framework of Extended Application (EXAP) standards (EN 15254 series) that provide rules for extrapolating test results. IS 3809 lacks a similar formal and comprehensive framework.
Key Similarities
≈The standard time-temperature curve specified in IS 3809 is functionally identical to the cellulosic fire curve used in ISO 834-1 and other international standards, ensuring a comparable thermal exposure.
≈All standards are based on the same three primary performance criteria for failure: Stability (Loadbearing Capacity), Integrity (resistance to flame/hot gas passage), and Insulation (limiting temperature rise on the unexposed face).
≈The fundamental test methodology is consistent: a full-size or representative sample of a building element is installed in a furnace and exposed to fire on one side while its performance is monitored.
≈The criteria for Insulation failure are nearly identical across the standards, defined by an average temperature rise of 140°C or a maximum single-point temperature rise of 180°C on the unexposed surface.
Parameter Comparison
Parameter
IS Value
International
Source
Time-Temperature Curve Formula
T = 345 log10(8t + 1) + 20
T = 345 log10(8t + 1) + 20 (where t is in minutes, T in °C)
ISO 834-1:1999
Insulation Failure: Average Temp Rise
Shall not exceed 140°C above the initial temperature.
Shall not exceed 140°C above the initial average temperature.
EN 1363-1:2020
Insulation Failure: Maximum Temp Rise
Shall not exceed 180°C at any point above the initial temperature.
Shall not exceed 180°C at any point above the initial average temperature.
EN 1363-1:2020
Furnace Pressure Control
A pressure slightly above that of the atmosphere shall be maintained.
A positive pressure shall be established such that it is 8.5 Pa at 1m below the ceiling (for vertical elements).
ISO 834-1:1999
Integrity Failure: Cotton Pad Test
Ignition or glowing of a cotton wool pad held for 30 seconds over a fissure.
Ignition of a cotton pad within 30 seconds when applied to an opening.
EN 1363-1:2020
Integrity Failure: Gap Gauges
Not specified.
Failure if a 6 mm gauge can pass through, or a 25 mm gauge can pass through and move.
EN 1363-1:2020
Thermocouple for Unexposed Face
Type K or J thermocouples covered by a 12mm asbestos pad.
Plate thermocouples, with specific design, covered by an inorganic pad of specified density and thermal properties.
ISO 834-1:1999
⚠ Verify details from original standards before use
Key Values6
Quick Reference Values
Average temperature rise limit on unexposed face140 °C
Maximum temperature rise limit at any single point on unexposed face180 °C
Standard furnace temperature at 30 minutes842 °C
Standard furnace temperature at 60 minutes925 °C
Standard furnace temperature at 120 minutes1049 °C
Standard furnace temperature at 240 minutes1153 °C
Key Formulas
T - T0 = 345 log10(8t + 1) — Standard temperature-time relationship where t is time in minutes
What are the three main criteria for determining fire resistance failure?+
Failure is determined by loss of Stability (load-bearing capacity), Integrity (crack formation allowing flames through), or Insulation (temperature on the safe side exceeding limits).
What is the acceptable temperature rise on the unexposed side of a wall or floor?+
The temperature rise on the unexposed face should not exceed an average of 140°C or a maximum of 180°C at any single point.
Does a column have an insulation or integrity criteria in fire testing?+
No, for fully exposed load-bearing columns and beams, only the 'Stability' criterion (ability to carry the test load without collapsing) applies.