Thermal Insulation Material Smoldering Tester，DB11/381-2016

With the widespread use of thermal insulation materials in building energy efficiency and industrial insulation, higher requirements have been placed on the thermal performance, combustion behavior, and safety of these materials. In particular, in building envelopes and equipment insulation systems, if thermal insulation materials ignite or undergo smoldering combustion, they can pose significant fire hazards. Therefore, monitoring and evaluating the smoldering behavior and fire risk of thermal insulation materials has become a key aspect of safety testing. To address this, specialized Thermal Insulation Material Smoldering Testers have been developed and adopted as essential tools in material laboratories and testing institutions. This article provides a comprehensive introduction to this equipment, covering testing background, principles, standard methods, experimental procedures, evaluation indicators, and application value, along with an in-depth discussion of the current technical system.

Smoldering Phenomena and Fire Risks of Thermal Insulation Materials

Smoldering combustion is a low-temperature, flameless, slow oxidation process. It typically occurs in highly porous, fibrous, or multi-structured materials. When heat accumulates but does not reach conditions sufficient for visible flames, slow oxidation reactions occur inside the material, generating heat and smoke. Unlike flaming combustion, smoldering is difficult to detect, can persist for long durations, and may propagate into deeper layers.

Thermal insulation materials such as cellulose-filled products, fiberglass, foamed plastics, and mineral wool often have porous structures in practical applications. Once internal temperatures reach a critical threshold, smoldering may occur and potentially transition to flaming combustion. This is particularly hazardous in building components, wall cavities, and insulation layers, as it can lead to material degradation, smoke accumulation, and deeper fire spread.

Research indicates that the ignition and propagation of smoldering in different insulation materials depend on complex interactions among heat sources, material structure, thermal conductivity, and oxygen availability. This necessitates finely designed test methods and equipment to accurately simulate smoldering behavior.

Consequently, testing and evaluating the smoldering characteristics, ignition tendency, sustained combustion behavior, and self-extinguishing ability of thermal insulation materials is not only an important part of performance assessment but also forms the basis for fire safety management and building code development.

Testing Background

Conventional combustion tests generally focus on whether a material burns with flames and the rate of flame spread. However, thermal insulation materials can smolder for extended periods without visible flames, releasing heat and smoke. Therefore, specialized testing equipment is required to simulate the reaction of materials under low-level heat sources and to collect data on thermal effects, mass changes, and flammability characteristics under controlled conditions.

Several international and regional standards provide procedures for evaluating smoldering behavior of insulation materials:

US 16 CFR 1209.7 specifies test procedures for thermal insulation smoldering, using defined sample containers, heat sources, and environmental conditions.

ASTM C739 provides detailed evaluation methods for the combustibility and smoldering resistance of certain thermal insulation products.

UK BS 5803-4 is used for testing roof insulation materials for thermal propagation and smoldering resistance.

Canadian CAN/ULC-S129-15 also includes methods for smoldering resistance evaluation.

These standards guide the design and operation of smoldering test equipment, ensuring objective assessment of a material’s smoldering resistance.

Testing Principles

Testing Objectives

The primary objectives of thermal insulation material smoldering testers are:

Assess material sensitivity to heat sources: Apply a defined heat source to the material and observe whether smoldering, sustained heating, or overheating occurs.

Evaluate combustion propagation during smoldering: Measure internal heat accumulation, weight loss, local temperature changes, and whether flaming or sustained heating occurs.

Provide quantitative indicators: Record data such as whether stable smoldering occurs, maximum mass loss rate, flame presence, and temperature curves.

Compare performance across materials or treatments: Compare multiple samples under identical test conditions to determine inherent smoldering resistance.

These objectives rely on scientifically controlled and stable test systems and standardized testing procedures.

Equipment Components and Basic Principles

Although detailed instrument structures are rarely publicly described, based on standard test methods, smoldering testers typically include the following core components:

1. Sample Test Chamber or Container

Samples are placed in a standardized container to ensure controlled test conditions. For example, US 16 CFR 1209.7 requires an open square box approximately 20 cm × 20 cm × 10 cm, made of stainless steel and ensuring air-tightness. The container rests on an insulating pad or equivalent material to control heat conduction.

This controlled environment allows heat and oxygen supply to meet the standard test requirements.

2. Heat Source or Heating Device

Smoldering tests require a localized heat source to simulate conditions that may induce smoldering, such as:

Electric heating wires, burners, or gas flames for high-temperature heat flux;

Hot plates or heaters for continuous heat input.

In some standards, the heat source is positioned under or beside the sample and maintained at specified temperatures or flame exposure durations. For instance, in the Canadian “basket method,” samples are inclined, heated from below with a flame for a defined period, and behavior is observed after flame removal.

3. Environmental Control System

Tests on automotive or building insulation often require defined temperature, humidity, and ventilation conditions for comparable data. Systems include:

Controllers for temperature and heat source output;

Temperature sensors inside the test chamber;

Adjustable ventilation to simulate different oxygen conditions during smoldering.

These systems ensure the test environment meets standard requirements and allows consistent, repeatable results.

4. Data Acquisition and Recording System

Modern testers include digital displays, temperature curve recording, and time control. They automatically record temperature changes, test duration, and other key indicators for post-test analysis.

Smoldering Test Methods and Evaluation Indicators

Although specific procedures vary by standard, core methods generally follow this logic:

Sample Preparation:

Thermal insulation samples are prepared according to standard requirements, including specified dimensions, density, and compaction. Samples should represent actual use conditions for valid results.

Test Conditions:

Set test conditions according to the standard, including heat source intensity, flame exposure duration, ambient temperature, and total test time. For example, some standards specify 5 minutes of flame exposure, followed by observation of smoldering behavior after heat removal.

Observation and Data Recording:

During the test, record whether the sample exhibits:

Visible smoldering heat or smoke;

Flame presence or propagation;

Mass loss during and after the test;

Temperature trends recorded by sensors.

Evaluation Criteria:

Common criteria include:

No flaming: No independent flames occur during or after the test;

Mass loss limits: Sample mass loss does not exceed standard thresholds (e.g., <15% in some standards);

Temperature trend: Temperature peaks during the test and gradually decreases, indicating no sustained smoldering.

These indicators allow researchers and testers to determine the safety performance of the material under heat exposure.

Relation to Other Combustion Performance Tests

Thermal insulation fire safety evaluation includes smoldering testing as well as other tests, such as flaming combustion, smoke release, and flame spread. Compared with these:

Flame spread tests (e.g., Steiner tunnel tests) focus on flaming conditions and flame propagation along material surfaces.

Ignition tests assess whether the material burns quickly or sustains combustion under direct flames.

Smoldering tests focus on low-temperature internal oxidation reactions, duration of heat release, and potential for self-sustained combustion.

Combining smoldering tests with other combustion tests provides a comprehensive picture of material fire behavior and risk.

Applications and Industry Value

Thermal insulation smoldering testers have important value in multiple industries:

1. Building Energy Efficiency and Envelope Safety:

In external walls, roofs, and internal insulation layers, smoldering can compromise thermal performance and pose smoke and fire hazards. Testing smoldering resistance is directly related to building fire rating and regulatory compliance.

2. Industrial Equipment and Pipeline Insulation:

Industrial equipment such as boilers, heat exchangers, chemical equipment, and pipelines often use insulation layers. Smoldering can cause insulation failure or escalate to equipment damage and safety incidents. Testing material behavior under such conditions is essential.

3. Product Development and Material Improvement:

Smoldering tests help developers understand how different formulations, structures, and flame-retardant treatments affect smoldering resistance, providing data to improve safety and performance.

4. Safety Certification and Standard Development:

Fire authorities and standard-setting bodies require smoldering performance testing for insulation materials to classify safety and regulate market access. Standardized testing and equipment verification ensure reliable evaluation.

Thermal insulation material smoldering testers are critical components of material performance evaluation and fire safety systems. By simulating slow internal oxidation under specific heat sources, these testers provide scientific assessment of material fire risk. Results reveal potential safety issues in practical applications and provide reliable data for researchers, engineers, and standard developers.

Integrating existing standards and test methods, smoldering testers offer strong technical support for building energy efficiency, industrial insulation material selection, product development, and fire safety regulation. Evaluating smoldering resistance in complex thermal insulation systems will continue to play a key role in materials science and safety engineering.