Fire has always been one of the most serious threats to human society. As buildings, transportation systems, textiles, electrical products, and polymer materials have become increasingly widespread, the demand for improved fire performance has continued to grow.
It is important to distinguish flame-retardant materials from completely non-combustible materials. The purpose of flame-retardant technology is to reduce the likelihood of ignition, slow the spread of flames, limit heat release, and provide more time for evacuation and firefighting.
From clay protective layers used in ancient buildings to modern intumescent systems, nanocomposites, and low-smoke, low-toxicity technologies, the development of fire-resistant materials has been a long process of continuous exploration.
1. Ancient Chinese Fireproofing Materials and Building Protection
China began exploring fire protection methods at a very early stage.
At the Dadiwan archaeological site in Qin'an, Gansu Province, dating back approximately 5,000 to 8,000 years, ancient builders placed layers of earth around wooden columns in large public buildings and applied protective cementitious materials to the surface of wooden structures. These practices may be regarded as early forms of architectural fire protection.
During the Spring and Autumn period, people had already recognized that removing smaller structures, coating larger buildings, and creating separation zones could help slow the spread of fire.
During the Spring and Autumn and Warring States periods, the Chinese philosopher Mozi proposed a number of fire prevention and firefighting measures. These included coating city gates and buildings with mud, making water-carrying tools from hemp cloth, using leather containers to hold water, and installing water storage facilities on defensive towers.
These measures reflected an early integrated approach that combined fire-resistant surface treatment, building design, and firefighting equipment.
By the Yuan Dynasty, the agricultural scientist Wang Zhen had provided a relatively systematic discussion of building fire protection in his work Nong Shu, or Book of Agriculture. He wrote:
Fire grows when it meets wood, is extinguished by water, and ends when it reaches earth.
Wang Zhen also documented a fire-resistant material made from ingredients such as crushed brick, clay, tung oil, charcoal powder, and lime, mixed with glutinous rice paste. The material provided surface coverage, thermal insulation, and protection, and may be regarded as an early Chinese composite fire-protective coating.
Although these historical practices did not yet constitute a modern flame-retardant chemical system, they already demonstrated several important principles: isolating combustible materials from air, reducing heat transfer, covering flammable substrates, and preventing direct flame exposure.
2. Early Western Exploration of Flame-Retardant Treatment
Records of flame-retardant treatment in the West can also be traced back to ancient times.
According to historical accounts from ancient Greece, wood was treated with alum-based solutions around 450 BCE to reduce its flammability. The Romans later improved the process by adding substances such as vinegar to the treatment solution, helping to enhance its durability and effectiveness.
By the first century BCE, flame-retardant methods had already been applied in military defense. Alum-based solutions were reportedly used to treat wooden fortifications, while coatings made from clay and fiber-reinforced materials were applied to protect wooden siege equipment against fire.
In 1638, the Italian stage designer and architect Nicola Sabbatini proposed adding clay and gypsum to coatings used on theater curtains to reduce their fire risk. This application shows how fire hazards in public buildings helped drive the early development of flame-retardant technologies.
In 1735, a British patent was issued for the treatment of wood and textiles using alum, borax, and ferrous sulfate. By the late eighteenth century, compounds such as ammonium sulfate were also being investigated as components of flame-retardant formulations.
3. The Formation of Modern Flame-Retardant Science
The nineteenth century marked an important transition from experience-based fireproofing practices to scientific research.
In 1821, French chemist J. L. Gay-Lussac was commissioned to investigate methods for reducing the flammability of theater curtains. He found that ammonium salts of sulfuric, hydrochloric, and phosphoric acids could improve the flame resistance of hemp and linen.
He also observed that combinations of ammonium chloride, phosphoric acid, and borax could further improve flame-retardant performance.
This work is widely regarded as an important starting point in the scientific study of flame-retardant fibers and formulations. Its underlying principle-the use of phosphorus- and nitrogen-containing compounds to promote dehydration and char formation-remains relevant to flame-retardant technology today.
Around 1859, compounds including ammonium phosphate, ammonium chloride, borax, ammonium sulfate, and stannate salts were further applied to textile flame-retardant treatment.
Through impregnation, coating, and the formation of inorganic protective layers on fiber surfaces, the combustion behavior of fabrics could be improved.
During this period, flame-retardant research gradually shifted from the use of individual substances toward composite formulations, chemical reactions, and surface-treatment technologies.
4. Industrial Development in the Twentieth Century
With the rapid growth of plastics, synthetic rubber, and synthetic fibers in the twentieth century, flame-retardant technology became an increasingly important part of the materials industry.
Many polymer materials are easy to ignite, burn rapidly, and release large amounts of heat. As a result, improving their fire performance became a major technical challenge.
In the early twentieth century, chlorinated rubber entered the research and industrialization stage. By around 1913, stannate salts and ammonium salts were being used for textile flame-retardant treatment.
In the 1930s, synergistic systems based on chlorinated paraffin and antimony oxide began to be used in flame-retardant materials. Halogenated compounds helped inhibit free-radical reactions in the flame, while antimony oxide enhanced their effectiveness.
These systems were widely used for many years in plastics, rubber, coatings, and textiles.
During the same period, inorganic fire-protective coatings based on water glass binders and mineral fillers began to appear. Researchers later developed coatings that expanded and formed a protective char layer under heat, laying the foundation for modern intumescent fire-protective coatings.
During the Second World War, demand for military tents and canvas materials with both flame resistance and water resistance further accelerated the development of flame-retardant coating systems based on chlorinated paraffin, antimony oxide, and binders.
5. The Development of Intumescent Flame-Retardant Systems
In the late 1940s, researchers began using the term "intumescence" to describe the expansion and foaming that occur when certain flame-retardant polymers are exposed to heat or fire.
Between approximately 1948 and 1950, the basic structure of intumescent flame-retardant systems became clearer, leading to the concepts of an acid source, a carbon source, and a blowing source.
· The acid source promotes dehydration and carbonization.
· The carbon source forms the framework of the protective char layer.
· The blowing source releases gases that expand the char into a porous structure.
When the material is exposed to flame or high temperature, the intumescent layer covers the substrate and limits the transfer of heat, oxygen, and combustible decomposition products. This slows the heating and burning of the underlying material.
In the 1970s, researchers further demonstrated that the formation of a stable char layer during polymer combustion could significantly improve flame-retardant performance.
The protective effect of char therefore became an important part of condensed-phase flame-retardant theory.
In 1989, G. Camino and other researchers published systematic studies of intumescent flame-retardant systems, helping to advance both their theoretical understanding and practical application.
6. The Shift Toward High-Performance Composite Systems
After the 1950s, reactive flame-retardant monomers and flame-retardant resins began to emerge.
Unlike additive flame retardants, reactive flame retardants can be chemically incorporated into the molecular structure of a polymer. This can improve durability and reduce the migration or loss of flame-retardant components during use.
From the 1960s onward, various aromatic halogenated flame retardants entered commercial use, and flame-retardant materials gradually moved into large-scale industrial production.
In the 1980s, the development of nanocomposite materials opened a new direction for flame-retardant research.
Some nanomaterials can improve thermal stability, promote the formation of protective layers, and reduce heat-release and mass-loss rates at relatively low loading levels.
Modern flame-retardant materials generally no longer rely on a single additive. Instead, they combine multiple mechanisms, including:
· inhibiting combustion chain reactions in the gas phase;
· promoting char formation in the condensed phase;
· reducing heat transfer through insulating layers;
· limiting the movement of oxygen and combustible gases with inorganic barriers;
· reducing smoke through smoke-suppressant systems;
· improving char structure and thermal stability with nanomaterials.
7. Regulations and Standards Drive Improvements in Fire Safety
In the second half of the twentieth century, plastics, synthetic rubber, and synthetic fibers became widely used in buildings, transportation, furniture, electrical products, and consumer goods.
At the same time, the fire risks associated with polymer materials received increasing attention.
From the 1960s onward, the United States, Europe, and other regions gradually introduced industry requirements, product standards, and safety regulations relating to material flammability.
Improving flame resistance therefore evolved from a voluntary action by manufacturers into a mandatory market-access requirement for certain products.
Today, flame-retardant and fire-resistance requirements apply to a wide range of industries, including:
· building and construction materials;
· textiles;
· furniture and mattresses;
· automobiles and rail transportation;
· aerospace;
· wires and cables;
· electrical and electronic equipment;
· new-energy battery systems.
Different applications require different levels and types of fire performance.
In addition to resistance to ignition, materials may need to be evaluated for flame spread, heat release, smoke production, toxicity, flaming droplets, circuit integrity, fire resistance, and long-term durability.
8. The Practical Value of Flame-Retardant Materials
The purpose of flame-retardant technology is not to guarantee that a material will never burn under any conditions.
Its value lies in controlling combustion behavior and reducing the likelihood that a fire will start, spread, or become more severe.
An effective flame-retardant design can delay ignition and flame spread, reduce the heat-release rate, limit material loss, and provide more time for evacuation, firefighting, and property protection.
As fire-safety requirements continue to develop, modern flame-retardant technologies are placing greater emphasis on balancing fire performance with smoke suppression, low toxicity, environmental compatibility, durability, and mechanical properties.
Flame-retardant performance must therefore be verified through standardized testing rather than judged solely by a material name, chemical composition, or supplier declaration.
