BS 476 Part 4: 1970 (1984) and BS 476 Part 11: 1982 are bench-scale fire tests. Previously, they have been referenced within Approved Document B (England, Wales and Northern Ireland) and Technical Handbook 2 – Fire (Scotland) to determine whether a product can be classified as non-combustible or of limited combustibility (England, Wales and Northern Ireland only) based on their reaction to fire. They were one of two routes to arrive at this classification, the other being through the Euroclass system.
However, the update to Approved Document B (England) in 2019 saw the removal of references to Part 4 and a focus placed on the Euroclass System. Part 11 is still referenced in the transposition table at the back of the document. The update to the Technical Handbook 2 – Fire (Scotland) saw the removal of references to both Part 4 and Part 11, again with the focus now being placed on the Euroclass System.
Below is an explanation of both bench-scale fire tests.
BS 476 Part 4 – Non-Combustibility Test for Materials
In this test, a small furnace is heated to 750°C and a cuboid product specimen is lowered into the centre on a holder. Three specimens are tested separately, each measuring 40 mm wide and deep, 50 mm tall and having a volume of 80 cm³.
Two temperature sensors (thermocouples) are used in the tests, one placed at the centre of the specimen, the other around the mid-point of the furnace tube.
The specimen is placed in the furnace for the 20 minute test duration and monitored both visually and through a continuous recorder attached to the temperature sensors.
To be classified as non-combustible, the samples must not:
- Cause temperatures at either of the thermocouples to rise by 50°C or more above the initial furnace temperature
- Flame continuously for 10 seconds or more
BS 476 Part 11 — Method for Assessing the Heat Emissions from Building Materials
The procedure for BS 476 Part 11 is very similar to that of Part 4 with a product sample placed at the centre of a furnace heated to 750°C. Five cylindrical samples are tested separately, each with a 45 mm diameter and a height of 50 mm. As with Part 4, temperature sensors are placed at the centre of the specimen and within the test chamber.
Once the specimen is placed within the chamber, the test is either run for 2 hours or until one of the following conditions is met:
- The specimen temperature falls below the temperature of the furnace and the temperature gradient on both thermocouples is negative and less than 5°C over a period of 10 mins
- In cases where the specimen’s temperature does not rise above that of the furnace, the test is run until the specimen’s temperature has passed its maximum and its temperature gradient is negative and less than 5°C over a period of 10 mins
Temperature rises at either of the thermocouples are calculated by subtracting the temperature measurement recorded on the sensors at the end of the test from the maximum temperature recorded during the test.
The specimen is also visually monitored throughout the test and any sustained flaming (longer than 5 seconds) is recorded. Flaming is then recorded by taking the mean duration of sustained flaming from the five samples.
Density and mass loss are also recorded but these values are not used within the Approved Documents and Technical Handbooks.
According to the national guidance set out in the building regulations, for individual products assessed under either of these tests to be considered non-combustible, or of limited combustibility, they should meet one of the following criteria:
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|Wales & Northern Ireland
- Non-combustible according to BS 476: Part 4: 1970 or detail the requirements
- The material does not flame or cause any rise in temperature on either the centre (specimen) or furnace thermocouples according to BS 476: Part 11: 1982 (1988)
- The material does not flame and the recorded rise in temperature on the furnace thermocouples is no greater than 20°C according to BS 476: Part 11: 1982 (1988) There are different requirements depending on material density. Check table A6 of ADB2 A7
- Any non-combustible material
It is important to note that in both tests, the tested specimens are both small (roughly the size of three matchboxes stacked on top of one another) and tested in isolation. As such, they cannot consider how the combination of materials and fixings within a final system may impact its real-life performance.
Testing standards such as BS 8414, LPS1181 or FM4880, which test the ‘in-application’ performance of a complete construction may therefore be considered to provide a more accurate assessment of the real-life reaction to fire performance of a system.
You can download the full testing standards from the British Standards Institution shop:
BS 476 Part 4: 1970 (1984), Fire tests on building materials and structures. Non-combustibility test for materials
BS 476 Part 11: 1982, Fire tests on building materials and structures. Method for assessing the heat emission from building materials