Method of test for non-combustibility of building materials
1979 Edition

According to the standard, five cylindrical specimens must be prepared for each test. Each specimen should have a diameter of 45 mm with a permissible variation of ±9 mm, a height of 50 mm with a tolerance of ±3 mm, and a volume of approximately 80 cm³ with ±5 cm³ allowance. Specimens should represent the average characteristics of the material sample. For materials thinner than 50 mm, multiple horizontal layers are stacked and tightly bound with fine wire to minimize air gaps. In cases of thin composites, component thicknesses are adjusted to reach the required height, ensuring that the top and bottom surfaces are finished material faces. The specimen density must align with that of the original material. Before testing, specimens are conditioned by drying in a ventilated oven at 60 ± 5°C for at least 20 hours, then cooled in a desiccator containing a drying agent and weighed.

The furnace temperature is controlled by employing tight or separate coil windings at the ends of the furnace tube to create defined temperature zones, ensuring uniform heat distribution. A voltage stabilizer is used to keep the power input steady within ±1% of the calibration power level, which is critical for test accuracy. The furnace temperature must reach and maintain a steady state with fluctuations not exceeding ±10°C for a minimum of 10 minutes prior to specimen insertion. Automatic thermostatic controls are not utilized during testing. Temperature monitoring involves continuous recording of furnace and surface thermocouple data, with center thermocouple readings logged at intervals no greater than 5 seconds. Calibration tests are performed without the specimen holder to guarantee uniform temperature across the furnace walls.

The temperature measurements employ NiCr-Ni (Type K) thermocouples for both the furnace and specimen. Three thermocouples are used: one located in the furnace to monitor ambient conditions, one positioned at the specimen's center, and one attached to the specimen surface at mid-height opposite the furnace thermocouple. Sheathed thermocouples are used for wall temperature measurements via a scanning device, capable of withstanding temperatures in the range of 750 to 850°C. Alternatively, an optical micropyrometer may be employed to measure wall temperatures, providing readings between approximately 815 and 865°C. Continuous recording instruments capture temperature variations throughout the test.

Sustained flaming is defined as the continuous presence of flames within the furnace lasting five seconds or longer during the test duration. During testing, observers monitor and record the duration of any sustained flaming events using thermocouple data and visual inspection. For each specimen, the maximum sustained flaming duration is noted. After completing five tests, the average flaming duration is calculated by summing the individual flaming times and dividing by five. Additionally, the mass loss of each specimen is determined post-test. These measurements assist in assessing the material's contribution to fire spread.

A material is classified as non-combustible if it meets several criteria during the test. It must not ignite or exhibit flaming at any point. The temperature rises recorded by furnace, surface, and center thermocouples must not exceed 50°C above the initial temperature. The duration of sustained flaming must be 20 seconds or less, and the specimen's mass loss should not exceed 50% of its original mass. These parameters ensure that the material does not actively contribute to fire development or propagation, making it suitable for use in fire-sensitive construction applications.