What is a Thermal Insulation Material Smoldering Tester?

With the increasingly widespread application of building insulation materials, their fire resistance performance has become a core indicator concerning public safety. Smoldering, as a concealed form of fire without an open flame, is difficult to detect yet continuously releases heat, eventually igniting into an open flame, making it a key focus in fire risk assessment of building insulation systems. The smoldering tester for insulation materials, as an experimental device specifically designed for this phenomenon, provides a scientific basis for the quantitative assessment of material fire resistance performance by simulating the smoldering process in real fire scenarios.

Technical Background

Smoldering is a slow, flameless combustion phenomenon commonly found in porous media such as wood, paper, polyurethane foam, and some insulation materials. Its characteristics include slow combustion rate, uneven temperature distribution, and susceptibility to environmental factors, but it continuously releases toxic gases such as carbon monoxide and can abruptly ignite into an open flame when oxygen supply is sufficient. In building insulation systems, if the smoldering performance of materials is substandard, it may be ignited by electrical faults, unexploded or leftover fire sources during construction, or external ignition sources, eventually leading to a large-scale fire.

International fire safety standards impose strict requirements on this. For example, both British Standard BS 8414 and Chinese National Standard GB/T 29416-2012 clearly stipulate that building exterior wall insulation systems must pass a 24-hour smoldering test to verify the material's self-extinguishing ability under prolonged conditions without open flame. The US standard 16 CFR 1209.7 further refines the testing process, requiring materials to be ignited by a non-open flame source under specific density conditions, and monitoring their temperature changes and combustion products.

Principle

The core design concept of the smoldering tester for thermal insulation materials is to reproduce the smoldering conditions that materials may encounter in actual use. The equipment typically consists of the following modules:

Temperature Control System A programmable temperature controller is used to precisely control the furnace temperature according to a standard curve (such as Appendix C of GB/T 29416-2012). For example, one model can achieve a gradient temperature increase from room temperature to 600℃ within 24 hours, simulating the entire process of smoldering from initial slow oxidation to later heat accumulation. Thermocouples are placed inside the furnace and on the sample surface to collect temperature data in real time and generate curves, ensuring the traceability of test results.

Sample Fixation and Ignition Device The sample chamber is designed with an open structure, typically 20cm × 20cm × 10cm in size, to accommodate thermal insulation materials of different densities. Ignition methods are divided into two categories: one uses an electric heating wire or radiant plate to simulate an external heat source, and the other creates a localized high-temperature point inside the material by inserting an 8mm diameter metal rod (as described in 16 CFR 1209.7). The latter more closely resembles the internal smoldering caused by construction defects or electrical faults in real-world scenarios.

Environmental Simulation System: The test chamber is equipped with an airflow control device to adjust the airflow velocity (typically not exceeding 0.5 m/s) to simulate smoldering propagation under different ventilation conditions. Simultaneously, the chamber is encased in thermal insulation material to avoid external temperature interference and is equipped with a smoke extraction system to collect combustion products (such as CO and CO₂), providing data support for toxicity analysis.

Test Procedure

Taking GB/T 29416-2012 standard as an example, the complete test procedure includes the following steps:

Sample Preparation: Cut the insulation material to standard dimensions and fill it into the sample chamber according to the actual usage density. For loose filling materials (such as glass wool), repeated drop tests (height ≤ 7.6 cm) are required to ensure density uniformity.

Ignition and Monitoring: Insert a metal rod into the center of the sample and heat it to 300°C. After 10 minutes, remove the heat source and start the temperature recording system. During the test, the furnace temperature must be maintained within ±5°C of the set curve, while monitoring the sample surface temperature change. If the center temperature does not exceed the furnace temperature by 5°C within 24 hours, the material is considered合格 (qualified); if the temperature continues to rise or open flames appear, the material is considered不合格 (unqualified).

Data Analysis: Temperature-time curves are generated using software to analyze parameters such as smoldering wave propagation speed and heat release rate. For example, a study testing 14 common insulation materials found that glass wool exhibited varying smoldering tendencies due to differences in resin content: high-resin materials could self-extinguish at a height of 400mm and a temperature of 250°C, while low-resin materials experienced persistent smoldering due to localized heat accumulation.

Application Cases

Case 1: External Wall Insulation System Assessment

A high-rise residential project selected polystyrene foam board (EPS) as the external wall insulation material. During smoldering tests according to BS 8414 standard, it was found that the material's core temperature exceeded the furnace temperature by 10°C after 18 hours, and carbonization cracks appeared on the surface. Further analysis showed that the cracks allowed oxygen to penetrate, accelerating the smoldering reaction. Based on this, the project team replaced it with flame-retardant rock wool board, and after retesting, it passed certification, successfully avoiding potential fire risks.

Case 2: Screening of Loose Roofing Filler Materials

An industrial plant used glass wool as the roof insulation layer. According to 16 CFR 1209.7 standard, testers conducted smoldering resistance tests on three different densities of glass wool. The results showed that the material with a density of 16 kg/m³ maintained a temperature below 200°C within 12 hours after ignition, while the material with a density of 12 kg/m³, due to its high porosity, allowed for smooth oxygen flow, accelerating the smoldering wave propagation speed by 30%. Ultimately, the project selected the high-density material, significantly improving the fire resistance rating.

Technological Challenges and Development Trends

Although smoldering testers have formed a standardized system, their application still faces two major challenges:

Material complexity: The smoldering behavior of new composite insulation materials (such as graphite polystyrene boards and vacuum insulation panels) differs significantly from that of traditional materials, requiring the development of targeted test parameters.

Limitations in scenario simulation: Existing equipment mostly focuses on single-material testing, while the interaction between the insulation system and structural and decorative layers in actual buildings may alter the smoldering path. Future development requires the creation of multi-scale coupled testing platforms that integrate heat conduction and airflow dynamics models to improve prediction accuracy.

Regarding technological development trends, intelligentization and automation will become core directions. For example, some devices have incorporated AI image recognition technology, using high-speed cameras to capture changes in carbonization morphology during the smoldering process and combining this with temperature data to automatically identify the combustion stage. Furthermore, the development of portable testers will promote rapid on-site detection, providing real-time feedback for construction quality control.

As a key technological device in the field of building fire protection, the smoldering tester for insulation materials provides a scientific basis for material selection, system design, and construction specifications by quantitatively assessing the smoldering resistance of materials. With the improvement of standards and technological iterations, its application scope is expanding from laboratories to the entire industry chain, becoming an important tool for ensuring building safety and promoting green building development. In the future, with a deeper understanding of smoldering mechanisms and continuous innovation in testing technologies, this equipment will play an even greater role in building safer urban environments.