GB/T 14402-2026Reaction to fire tests for building materials and products - Determination of the heat of combustion (English PDF)

5.1 General Rules

The test device (oxygen bomb calorimeter) is shown in Figure 1.See 5.2 for detailed description.

Other equipment shall comply with the provisions of 5.3 ~ 5.8.

Figure 1 -- Oxygen Bomb Calorimeter

5.2 Oxygen Bomb Calorimeter

5.2.1 Calorimetric bomb

The calorimetric bomb shall meet the following conditions.

a) Volume of (300 ± 50) mL;

b) Mass not exceeding 3.25 kg;

c) Bomb bucket thickness not less than 1/10 of the bomb bucket’s inner diameter.

The calorimetric bomb cover is used to accommodate the crucible and electronic ignition device.

The calorimetric bomb cover and all sealing devices shall be able to withstand an internal pressure of at least 21 MPa.

NOTE. the calorimetric bomb described above can withstand the maximum pressure generated by the combustion of 1 g of coal under an initial oxygen pressure not exceeding 3 MPa (by the gauge method). The device has been verified to meet safety standards and does not require additional weight to improve safety.

The inner wall of the bomb bucket shall be corrosion-resistant, especially when testing materials like sulfur, and shall be able to withstand pitting and intergranular corrosion caused by acidic substances produced during combustion.

5.2.2 Outer cylinder of calorimeter

The outer cylinder of the calorimeter shall be a double-walled container with an insulated cover.

The outer cylinder shall be filled with water, and the gap between it and the inner cylinder shall be at least 10 mm. The inner cylinder shall be secured with an insulating material having the smallest possible contact area, preferably using a three-point support system.

For the adiabatic calorimetry system, the heater and temperature measurement system shall be integrated and installed inside the cylinder to ensure that the water temperature in the outer and inner cylinders is the same.

For the isothermal calorimetry system, the water temperature in the outer cylinder shall be kept constant and corrected in accordance with 9.2.

5.2.3 Inner cylinder of calorimeter

The inner cylinder of the calorimeter shall be made of a polished metal container, ensuring that the calorimetric bomb can be completely submerged in water (see 8.3.8).

5.2.4 Stirrer

A stirrer driven by a uniform-speed motor or a magnetic stirrer with equivalent performance shall be used. To prevent heat conduction within the calorimeter, insulating sheets shall be installed at the contact points between the stirring shaft, the outer cylinder cover and the outer cylinder.

5.2.5 Temperature measurement device

The temperature measurement device has a resolution of 0.005 K. When using a mercury thermometer, the division value shall be at least accurate to 0.01 K, ensuring the reading is within 0.005 K. In addition, the thermometer shall be gently tapped with a mechanical vibrator to ensure that the mercury column does not stick.

5.2.6 Crucible

The crucible shall be made of metal (such as platinum, nickel alloy, and stainless steel) or quartz.

The bottom of the crucible shall be flat, with a diameter of 25 mm (excluding the maximum size at the top) and a height of 14 mm to 19 mm. Recommended crucible wall thicknesses are as follows.

a) For metal crucibles, 1.0 mm;

b) For quartz crucibles, 1.5 mm.

NOTE. it has been proven that crucibles of several different shapes can meet the requirements.

5.3 Timer

The timer is used to record time, accurate to the second, with an accuracy of 1 s/h.

5.4 Power Supply

The voltage of the ignition circuit shall not exceed 20 V.

NOTE. adding an ammeter to the circuit can monitor the melting status of the ignition wire.

Installing a circuit breaker in the power supply circuit can improve equipment safety.

5.5 Pressure Gauge and Needle Valve

The pressure gauge and needle valve are installed on the oxygen supply circuit to display the pressure of the calorimetric bomb during oxygen filling, accurate to 0.1 MPa.

5.6 Balance

The balances are as follows.

a) Analytical balance, accuracy 0.1 mg;

b) Ordinary balance, accuracy 0.1 g.

5.7 “Cigarette” Preparation Device

As shown in Figure 2, the “cigarette” preparation device consists of a mold and a metal mandrel.

Avoid using aluminum as the material for the mandrel.

WARNING. oxygen produced by the electrolytic process contains trace amounts of hydrogen and is not suitable for this test.

6.3 Benzoic Acid Tablets or Powder

It shall be analytically pure. Benzoic acid with a stated heat of combustion is used as a

“calorimeter standard substance”.

6.4 Combustion Aid

Use a combustible material with a known heat of combustion as a combustion aid, for example, paraffin oil.

6.5 Cigarette Paper

Cigarette paper shall be pre-coated, with a minimum size of 55 mm × 50 mm.

NOTE. use commercially available 55 mm × 100 mm cigarettes, cut along the center line into two equal pieces.

6.6 Cotton Thread

Cotton thread is made of white cotton fibers.

6.7 Ignition Wire

The ignition wire shall be made of pure iron wire with a diameter of 0.1 mm, for example, piano wire. Other metal wires (for example, platinum, nickel or chromium) can also be used if they can melt when powered on and their heat of combustion is known. When using a metal crucible, the ignition wire shall not touch the crucible; it should be wrapped with cotton thread for insulation.

NOTE. some fully automatic or semi-automatic oxygen bomb calorimeters use permanent ignition wires with disposable crucibles. Refer to the device instruction manual for specific details.

7.1 General Rules

Each component of the product (including substantial and non-substantial components) shall be separately tested. If a non-homogeneous product cannot be separated into independent components, the client shall separately provide each component. If the components of a non- homogeneous product can be separated, each component shall be completely peeled off to ensure that no other components remain in the component under test.

Some substantial components have a surface layer during manufacturing. If the surface layer cannot be peeled off, the sample shall be taken from the middle of the core layer to avoid residue of the surface layer, adhesive and other non-substantial components.

If two or more adjacent layers of non-substantial components meet the definition of substantial component when combined together, then, each layer of non-substantial components shall be separately tested, and the results of the separate tests shall be combined together as the substantial component for evaluation. The gross heat of combustion is calculated by weighting the proportion of the heat of combustion of each layer of components (see Appendix D).

WARNING. this test device is prohibited from being used to test products containing metallic components, as overheating and/or overpressure may cause the calorimetric bomb to explode, threatening the personal safety of test personnel.

7.2 Specimen Preparation

7.2.1 Overview

Along the thickness direction of a certain component of a homogeneous or non-homogeneous product, select at least five different locations to prepare the specimen. When the component under test is the substantial component of a homogeneous or non-homogeneous product, the specimen shall not be less than 50 g; if the component is a non-substantial component, the specimen shall not be less than 10 g.

7.2.2 Loose filler material

Select at least 50 g of specimen from the product.

7.2.3 Aqueous product

Apply the aqueous product to a glass plate, allow it to dry, and then, scrape it off the glass plate surface. The dried specimen shall not be less than 10 g.

The specimen shall be dried or cured in accordance with the product instructions, and the drying or curing method shall be described in the test report.

7.2.4 Thin film product

The specimen shall not be less than 10 g. Whether tested using the cigarette method (see 7.10) or the crucible method, the thin film material shall be cut into small fragments. When using the crucible method, it is advisable to add 0.5 g of paraffin oil to the specimen surface as a combustion aid to prevent the thin film material from being blown out of the crucible by the airflow during combustion.

7.3 Surface Density Determination

The surface density of each component of the product shall be determined on a specimen with a minimum area of 250 mm × 250 mm, with an accuracy of ±0.5%.

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