Automotive Interior Flammability Testing

Automotive interior flame retardancy testing mainly conducts scientific testing and analysis on horizontal burning testing, vertical burning testing, 45° angle burning testing, oxygen index determination, smoke density testing and heat release rate testing, 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

Horizontal burning testing: Mainly evaluates the burning rate and burning performance of the automotive interior materials in the horizontally placed state. During the testing, one end of the horizontally placed specimen is ignited with a specified flame, the flame spread distance and time are recorded, and the burning rate is calculated. This is the basic method for evaluating the flame spread resistance of the material, and is commonly used for the thin materials such as the textiles and plastic films.

Vertical burning testing: Emphatically evaluates the burning characteristics of the interior materials in the vertical state, including the afterflame time, afterglow time and damaged length. The specimen is vertically hung, the bottom is ignited with a flame, and the burning behaviour after the flame extinguishes is observed and recorded. This method is crucial for evaluating the components installed in the vertical direction such as the seat fabrics and headliner materials, and the requirements are stricter.

45° angle burning testing: Simulates the burning behaviour of the material in the inclined state, between the horizontal and vertical burning. The specimen is fixed at a 45° angle, the upper end is ignited with a specified flame, and the flame spread rate is determined. This method is applicable to evaluating the flame retardant performance of the inclined installed components such as the door trim panels and the side parts of the instrument panels.

Oxygen index determination: Determines the minimum oxygen concentration (OI value) required for the material to maintain stable combustion in the nitrogen-oxygen mixed gas. The higher the oxygen index, the more difficult the material is to burn. This is a quantitative method for evaluating the intrinsic flame retardant performance of the material, and has important guiding significance for the screening and development of the polymer interior materials such as the polypropylene, polyethylene and foamed plastics.

Smoke density testing: Evaluates the concentration of the smoke generated during the burning or thermal decomposition of the interior materials and the luminous flux loss. In a fire, the smoke is the main hazard causing suffocation and visibility reduction. By measuring the maximum smoke density and specific optical density of the material under the specific conditions, this testing provides the key data for the escape and rescue in the vehicle.

Heat release rate testing: Equipment such as a cone calorimeter is used to measure the parameters such as the heat release rate peak value and total heat release during the burning of the material under a specific radiant heat flux. The heat release rate is the core indicator for measuring the fire hazard, is directly related to the development speed of the fire, and is an important basis for evaluating the fire safety of the high-end interior materials.

Testing Scope

Seat system: Including the seat fabrics (fabrics, leather and artificial leather), filling foam (polyurethane foam) and frame protective panels. The seat is the interior component with the largest surface area and volume in the passenger compartment, and its flame retardant performance directly affects the fire development in the initial stage of the fire, and needs to meet the strict vertical burning and smoke toxicity requirements.

Instrument panel and auxiliary instrument panel: Usually composed of the composite materials such as polypropylene (PP), ABS, PVC skin and foaming layer. The burning rate and melt dripping behaviour of the whole and each component need to be evaluated, preventing the burning melt drips from igniting the other parts after heating.

Headliner and lining: Including the headliner fabric, substrate (usually the thermoplastic or thermosetting composite material) and sunroof sun visor. These components are located in the upper part of the passenger compartment, and the flame is easy to spread along them. The testing focus is on the horizontal burning performance, smoke density and whether a large amount of toxic gases is generated during burning.

Door trim panel and side wall: Including the decorative fabrics, plastic panels, armrests and map pockets. Their installation positions are close to the possible fire sources (such as the door circuits), and most of them are vertical or inclined surfaces, so the vertical burning and 45° angle burning testing are the main evaluation means.

Carpet and floor mat: Usually made of the textile fibres, rubber or thermoplastic elastomers. As the horizontally laid components, they mainly undergo the horizontal burning testing. Attention needs to be paid to their burning rate and whether melting and sticking occur, avoiding hindering the escape of the occupants.

Other interior components: Including the steering wheel wrapping materials, seat belts, sun visors, trunk linings, various decorative strips and wiring harness sheaths. Although these components are small, they may also become the fire sources or promote the fire spread, and their flame retardant performance needs to comply with the corresponding standard provisions.

Testing Methods

FMVSS 302 standard method: The US Federal Motor Vehicle Safety Standard, and the most widely applied automotive interior flame retardancy regulation in the world. The horizontal burning method is adopted, specifying that the specimen is exposed to a specified flame for 15 seconds, and the burning rate must not exceed 102 mm/min. This method is simple and low-cost, and is the benchmark of the regulations of various countries.

ISO 3795 standard method: The standard formulated by the International Organization for Standardization, basically equivalent to the technical content of FMVSS 302, and widely adopted by the EU, Japan, China and other countries. The horizontal burning testing is also adopted, with detailed provisions on the specimen preparation, conditioning, testing environment (temperature and humidity) and burning chamber specifications.

GB 8410 standard method: The Chinese national mandatory standard "Burning behaviour of interior materials of motor vehicles". The technical content is consistent with FMVSS 302 and ISO 3795, requiring the horizontal burning rate ≤100 mm/min. It is the mandatory testing item for the market access and conformity inspection of the domestic automotive products.

Vertical burning testing method (such as UL 94 V-0, V-1, V-2): Although UL 94 is mainly the standard for the plastic parts of the electrical equipment, its vertical burning classification (V-0, V-1 and V-2) is often used by the automotive industry as the internal technical requirement for the specific high-performance interior materials, to evaluate their stricter flame retardant grades.

Cone calorimeter method (ISO 5660-1): An advanced burning performance evaluation method. By applying a controllable radiant heat flux to simulate the real fire conditions, the key fire parameters such as the heat release rate, effective heat of combustion, mass loss rate, smoke production rate and CO/CO2 production rate can be precisely measured, and it is used for the material research and development and in-depth safety evaluation.

Smoke density chamber method (such as ASTM E662 and ISO 5659-2): In a closed test chamber, a flaming or non-flaming radiant heat source is applied to the specimen, and the specific optical density (Ds) and maximum smoke density are calculated by measuring the attenuation of the light beam passing through the smoke. This method is the approach for evaluating the smoke generation characteristics of the interior materials.

Testing Standards

Domestic Standards:

1. GB 8410, Burning behaviour of interior materials of motor vehicles

International Standards:

1. FMVSS 302, Flammability of interior materials — Passenger cars, multipurpose passenger vehicles, trucks and buses

2. ISO 3795, Road vehicles — Determination of burning behaviour of interior materials

3. ISO 5660-1, Reaction-to-fire tests — Heat release, smoke production and mass loss rate — Part 1: Heat release rate (cone calorimeter method)

4. ISO 5659-2, Plastics — Smoke generation — Part 2: Determination of optical density by a single-chamber test

5. ASTM E662, Standard test method for specific optical density of smoke generated by solid materials

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

Horizontal/vertical burning test chamber: The core equipment for executing the standard tests such as FMVSS 302, ISO 3795 and GB 8410. The chamber is made of the heat-resistant and corrosion-resistant materials, and is internally equipped with a specimen clamping device, standard Bunsen burner, adjustable flame height gauge, automatic or manual timer and backboard scale, used to precisely measure the flame spread distance.

Oxygen index tester: Used to measure the limiting oxygen index (LOI) of the material. The instrument is mainly composed of a transparent glass burning cylinder, specimen clamp, gas mixing and flow control system and igniter. By precisely adjusting the ratio of the oxygen and nitrogen, the critical oxygen concentration at which the material just maintains the stable combustion is determined.

Cone calorimeter: A large precision analytical instrument and the core tool of the fire science research. It is mainly composed of a radiation cone (providing the adjustable radiant heat flux), sample holder, exhaust system, oxygen analyser, laser smoke meter and data acquisition system. By measuring the oxygen consumption in the combustion exhaust gas, the series of parameters such as the heat release rate is calculated according to the oxygen consumption principle.

Smoke density test chamber: The dedicated equipment for determining the smoke production of the material during burning. The chamber is closed, and is internally equipped with an electrically heated or propane radiation cone heat source, vertical or horizontal specimen holder and photometer measurement system (including the light source and photoelectric receiver). The testing is carried out in the specific flaming or non-flaming mode, and the light transmittance change is recorded in real time.

Thermogravimetric-infrared combined instrument: A laboratory research equipment for analysing the thermal decomposition behaviour and gas products of the material. The TG part measures the mass loss of the material under the programmed temperature rise, and the FTIR part analyses the gas components (such as CO, CO2, hydrocarbons and HCN) generated by the decomposition in real time, providing data support for the flame retardant mechanism research and the development of the low-smoke and low-toxicity materials.

Environmental preconditioning chamber: To ensure the repeatability and comparability of the test results, the specimen must be conditioned under the standard temperature and humidity conditions (such as 23±2 °C and 50±5% RH) before the testing. The environmental preconditioning chamber can precisely control the temperature and humidity, and is the essential auxiliary equipment of the flame retardancy testing laboratory.