What is the standard for flame retardant testing?

In today's society, where fires are frequent, flame retardancy testing, as a core means of assessing material safety performance, has become a crucial basis for product compliance in fields such as construction, transportation, and electronics. A multi-tiered testing system has been established globally, centered on international, regional, and industry standards, covering the entire chain of assessments from basic flammability performance to complex scenario simulations. 

International Standard System

1. UL Standard: The Authoritative Benchmark in Plastics and Electronics

UL 94. "Tests for the Flammability of Plastic Components for Equipment and Electrical Appliances," is the most widely used global standard for flame retardancy in plastics. It classifies flame retardancy levels into 12 grades: HB, V-0. V-1. V-2. 5VA, and 5VB. Taking the V-0 grade as an example, it requires that in a vertical burning test, after two 10-second flame applications, the afterflame time does not exceed 10 seconds, and no burning droplets ignite the absorbent cotton below. This standard sets strict requirements for parameters such as sample size (125mm × 13mm), flame height (20mm), and testing environment (23℃ ± 2℃, 50% ± 5% RH).

2. ISO Standard: A Model of Global Technical Collaboration

ISO 4589-2. "Determination of flammability of plastics—Oxygen Index Method," quantifies flame retardancy by measuring the minimum oxygen concentration (LOI) required to sustain combustion in an oxygen-nitrogen mixture. For example, materials with an LOI > 26% are considered flame retardant, while those with an LOI > 35% achieve a high flame retardancy rating. This standard is directly referenced by 37 countries, and its sample pretreatment temperature range has been extended to 70℃ to accommodate testing needs under different climatic conditions.

3. IEC Standard: A Safety Line in the Electrical and Electronic Fields

IEC 60695-11-10. "50W Horizontal and Vertical Flame Test Method," specifies the flammability test procedure for electrical and electronic products under a 50W flame (125mm height). 5VA grade materials must exhibit no flame spread to the marked line after 60 seconds of burning, and the burning time of dripping material must not exceed 60 seconds. This is suitable for high-risk equipment such as high-voltage switchgear.

Regional Standards

1. EU EN Standards: Dual Constraints of Environmental Protection and Safety

EN 13501. "Classification of Building Materials by Combustion Performance," classifies materials into seven grades: A1 (non-combustible), A2 (non-combustible), B (combustible), etc., and adds smoke toxicity classifications (S1-S3). For example, A1 grade materials must pass the EN ISO 1182 non-combustibility test, and the total heat release (THR) must be ≤2 MJ/m². EN 45545-2. "Fire Protection Standard for Railway Vehicles," specifically addresses rail transit scenarios, stipulating that seat fabrics must meet HL3 requirements (damaged length ≤150mm, afterflame time ≤5 seconds).

2. Chinese GB Standards: Balancing Localization and Internationalization

GB 8624-2012. "Classification of Burning Performance of Building Materials and Products," classifies materials into seven grades: A1. A2. B, C, D, E, and F. Grade A non-combustible materials must pass GB/T 5464. "Non-combustibility Test." For textiles, GB/T 5455-2014. "Vertical Burning Method," stipulates that Grade B1 decorative fabrics must meet the requirements of a damaged length ≤150mm, afterflame time ≤5 seconds, and smoldering time ≤15 seconds. The revised GB/T 17591-2025. "Flame-Retardant Fabrics," to be released in 2025. adds a Thermal Protection Performance Value (TPP) assessment, promoting the industry's transformation towards high-performance materials.

Industry-Specific Standards

1. Construction Sector: Comprehensive Protection from Components to Systems

ASTM E119. "Fire Resistance Testing of Building Components," simulates fire temperature rise curves to assess the fire resistance limits of components such as walls and floors. For example, the 1-hour fire resistance limit requires the temperature on the unexposed surface not to exceed 538°C, with no flame penetration. For fire-retardant coatings, GB 14907-2018. "Fire-retardant Coatings for Steel Structures," stipulates that thick coatings must be verified through a large-panel burning method to determine their expansion ratio (≥10 times) and carbon layer density (≤0.5 g/cm³).

2. Transportation Sector: Safety Challenges in Dynamic Scenarios

FMVSS 302. "Fire Testing of Automotive Interior Materials," requires materials to have a burning rate not exceeding 102 mm/min in a 45° inclined burning test. For the aviation sector, FAR 25.853. "Fire Testing of Aircraft Materials," stipulates that seat cushions must pass a vertical burning test (damage length ≤203 mm) and an oil burning test (burning time ≤15 seconds). The revised GB/T 32086-2025 standard for automotive interior trim, revised in 2025. adds a smoke density rating assessment, requiring a light transmittance reduction of no more than 50%.

3. Electronics: The Dual Pressure of Miniaturization and High Power

IEC 60695-10-2. "Glow Wire Test," simulates overheating scenarios for electronic components, stipulating that after a 650°C glow wire is applied for 30 seconds, the material must self-extinguish within 30 seconds without any burning drips. For lithium batteries, GB 38031-2020. "Safety Requirements for Power Batteries for Electric Vehicles," stipulates that battery packs must pass an external fire test (70 seconds of direct combustion and 60 seconds of indirect combustion) to ensure no explosion or fire.

Technological Development Trends

1. Intelligent Testing Equipment

A cone calorimeter integrating infrared thermal imaging and AI image recognition can monitor the combustion temperature field distribution in real time and automatically calculate parameters such as heat release rate (HRR) and smoke density (SDI). For example, a new testing system uses deep learning algorithms to reduce the measurement error of damaged length from ±2mm to ±0.5mm.

2. Multi-dimensional Evaluation System

Combining parameters such as heat release rate, smoke toxicity index (TIC), and combustion drippings, a comprehensive flame retardancy rating is constructed. For example, EN 45545-2 uses a three-dimensional evaluation of "combustion performance + smoke toxicity + drippings," requiring rail transit materials to simultaneously meet HL3 combustion rating, S2 smoke toxicity rating, and D0 no-drip rating requirements.

3. Dynamic Scenario Simulation

Developing a composite testing device combining radiant heat sources and forced ventilation to simulate the heat radiation and airflow conditions in a real fire. For example, a tunnel combustion test instrument evaluates the expansion performance of fire-retardant coatings in tunnel fires by adjusting the radiant heat flux (50kW/m²) and ventilation velocity (0.5m/s).

From UL94 plastic grading to EN 45545 rail-specific standards, from static combustion tests to dynamic scenario simulations, the flame retardant testing standard system is evolving towards refinement, scenario-based approaches, and intelligence. Faced with the continuous emergence of new materials, processes, and scenarios, standard-setting bodies need to accelerate the updating of testing methods, while enterprises need to establish flame retardant performance databases and correlate test data with production process parameters to achieve a leap from passive compliance to proactive safety. Only in this way can we build the last line of defense for human life and property in today's increasingly complex fire threat environment.