Protective Clothing Radiant Heat Transmission Testing

Protective clothing radiant heat transfer testing mainly conducts scientific testing and analysis on radiant heat flux blocking rate testing, fabric thermal conductivity coefficient determination, TPP testing, residual heat flux evaluation after exposure, and material thermal stability and charring behaviour analysis, objectively assessing the product quality grade and issuing a detailed test report, providing a basis for manufacturers' quality control and downstream users' product acceptance.

Testing Items

Radiant heat flux blocking rate testing: This item aims to evaluate the blocking ability of the protective clothing material and its combination system against a specific radiant heat flux. During the test, the material sample is exposed to a standardized radiant heat source, and by measuring the temperature rise or heat flux change on the back side of the sample, its blocking percentage is calculated. This is the core indicator for measuring the protective performance of protective clothing in high-temperature radiation environments (such as metallurgy and fire rescue).

Fabric thermal conductivity coefficient determination: This item is used to determine the thermal conductivity coefficient of a single-layer fabric or composite fabric of protective clothing. Through a stable heat source and precise temperature sensors, the amount of heat passing through the material of a unit area per unit time under a unit temperature gradient is measured. This coefficient directly reflects the heat transfer characteristics of the material itself, and is an important parameter for evaluating the basic thermal insulation performance of protective clothing.

TPP (Thermal Protective Performance) value testing: The TPP test is a comprehensive evaluation method, simulating the protective performance of protective clothing when simultaneously subjected to radiant heat and convective heat (such as flame). By exposing the specimen to a specific heat flux, the time required to cause a second-degree burn on human skin is measured, and the TPP value is calculated. This value is the key data widely recognized internationally for evaluating thermal protective performance.

Residual heat flux evaluation after exposure: This item focuses on the transfer of the heat accumulated inside the protective clothing to the simulated skin after the clothing has undergone radiant heat exposure. The test simulates the sustained heating risk to the human body after leaving the heat source, measures the temperature decay curve and residual heat flux on the back side of the material, and evaluates its potential secondary burn risk.

Material thermal stability and charring behaviour analysis: This analysis aims to observe the physical and chemical changes of the protective clothing material under sustained radiant heat. By recording the phenomena such as shrinkage, melting, charring and cracking of the material and the time and temperature at which they occur, the structural integrity of the material under extreme conditions is evaluated, providing a basis for material selection and design improvement.

Testing Scope

Firefighter firefighting protective clothing: This type of protective clothing is the main object of the radiant heat transfer test, and needs to be tested strictly in accordance with standards such as NFPA 1971 and EN 469. The testing scope covers the combination system of the outer shell, waterproof and breathable layer and thermal liner of the clothing, evaluating its overall protective performance under complex thermal environments such as simulated building fires.

Industrial high-temperature protective clothing: Suitable for the protective clothing of workers in industries such as metallurgy, casting and glass manufacturing. The testing focus is on evaluating the ability of the clothing to isolate high-intensity and sustained industrial radiant heat (such as the accompanying radiation of molten metal splashes), ensuring its effective protection time in specific industrial environments.

Welding protective clothing and aprons: Aimed at the strong arc light radiation and flying sparks generated by operations such as arc welding and gas welding. Testing not only evaluates the blocking of the fabric against radiant heat, but also needs to test its resistance to molten metal dripping, ensuring that the material will not melt through or burn violently when in contact with high-temperature splashes.

Emergency response and military protective equipment: Including protective clothing for handling dangerous chemical leaks, explosions and other emergencies, as well as some military special clothing. Testing needs to simulate instantaneous high-intensity radiant heat impacts such as explosion flashes and high-temperature heat waves, evaluating the instantaneous heat blocking ability and flame retardancy of the clothing.

R&D of new thermal insulation materials and fabrics: At the material R&D stage, the radiant heat transfer test is a key link for verifying the thermal insulation performance of new materials (such as aerogel composite materials, phase change material coated fabrics and multilayer nanofibre membranes). It provides quantitative data support for material proportioning and structural design through testing.

Testing Methods

Radiant heat source method (such as ISO 6942): This method uses electric heating quartz tubes or carbon arc lamps as the radiant heat source to generate a stable radiant heat flow. The specimen is vertically placed at a specific distance in front of the heat source, and the transmitted heat flux is measured by a copper calorimeter installed on the back side of the specimen. This method is mainly used to determine the blocking performance of the material against radiant heat, and is an internationally common standard test method.

Thermal protective performance tester method (such as ASTM F2700/F2700M): This instrument integrates a radiant heat source and a convective (flame) heat source, and can simulate mixed heat exposure scenarios. The specimen is placed on a specimen holder with a sensor module, exposed to a set total heat flux, and the temperature rise curve of the skin simulator is recorded by the sensor, thereby calculating the time required to cause a second-degree burn and the TPP value.

Overall thermal resistance test method for protective clothing: This method uses a thermal manikin to simulate the real wearing state, placing the manikin in a controllable radiant heat environment. Through temperature sensors all over the manikin, the temperature distribution and heat flow on the inner and outer surfaces of the clothing under a stable radiant heat field are measured, thereby evaluating the overall thermal protective performance of the clothing and possible hot spot areas.

Cone calorimeter method (such as ISO 5660-1): Although mainly used for combustion performance testing, the cone calorimeter can provide a precisely controllable radiant heat flow through its radiation heating cone, while measuring parameters such as the heat release rate and mass loss of the material. It can be used to study the ignition time, combustion behaviour of protective clothing materials under radiant heat and their influence on the thermal protective performance.

Transient plane heat source method: This is a precise method for determining the thermal conductivity coefficient (thermal conductivity) of the material itself. A thin-sheet probe is clamped between two layers of the fabric sample to be tested. The probe itself serves as both the heat source and the temperature sensor. By recording the transient temperature rise data, the thermal diffusivity and thermal conductivity of the material are directly calculated.

Testing Standards

Domestic Standards:

1. GB 18401-2010, National general safety technical code for textile products

2. GB/T 3920-2024, Textiles — Tests for colour fastness — Colour fastness to rubbing

3. GB/T 3921-2008, Textiles — Tests for colour fastness — Colour fastness to washing with soap or soap and soda

4. GB/T 3922-2013, Textiles — Tests for colour fastness — Colour fastness to perspiration

International Standards:

1. ISO 13934-1, Textiles — Tensile properties of fabrics — Part 1: Determination of maximum force and elongation at maximum force using the strip method

2. ISO 105, Textiles — Tests for colour fastness

Note: The applicable standard can be selected according to the product use and customer trade requirements; standards agreed in the contract take precedence over general standards.

Testing Instruments and Equipment

Radiant heat protective performance tester (RPP tester): This equipment is the core instrument for implementing standards such as ISO 6942, mainly composed of a radiant heat source (usually silicon carbide rods or quartz tubes arranged in an array), a specimen holder, a movable shielding device, and a copper calorimeter or skin simulation sensor on the back side. Its temperature control precision and heat flux density uniformity are the key to ensuring the accuracy of the test results.

Thermal protective performance (TPP/TPP+) test system: An advanced TPP test system usually includes a main burner (for convective heat), a radiant heat panel, a movable specimen holder and a precision data acquisition unit. The system can precisely control the ratio of the two heat sources and the total heat flux, record the sensor temperature rise in real time, and automatically calculate the TPP value and related parameters.

Copper calorimeter: This is the standard sensor for measuring the radiant heat flux. Its core is a pure copper sheet with a known mass and specific heat capacity, with a thermocouple attached to the back. By measuring the temperature rise rate of the copper sheet per unit time, the heat flux acting on its surface (unit: kW/m²) can be precisely calculated.

Skin simulation sensor: A sensor used to simulate the response of human skin tissue to thermal stimuli. It is usually composed of an insulating substrate, a heating film and multiple precision thermocouples, and can simulate the thermal inertia of the skin. In accordance with burn prediction models such as the Stoll curve, it evaluates and predicts in real time the degree and time of skin burns caused by contact with heat sources.

Infrared thermal imager: In the thermal testing of protective clothing, the infrared thermal imager is used as an auxiliary observation device for non-contact measurement of the temperature field distribution on the surface of the protective clothing sample or thermal manikin. It can intuitively display the heat transfer path, hot spot positions and the uneven changes of the material after heating, providing visual evidence for analysing the shortcomings of the protective performance.