When we stand at the highest point in the city center, overlooking the magnificent view of the entire city, skyscrapers rise one after another, outlining strong and powerful profiles; when we are in grand sports stadiums or airport terminals, we are amazed by their vast spaces and intricate structures. Supporting these modern buildings are their ‘skeletons’—steel structures.
However, while marveling at its strength and efficiency, an unavoidable safety issue also arises: the seemingly indestructible steel structure is actually very susceptible to fire.
01 Why are steel structures afraid of fire?
To understand why steel structures need fire protection, we first need to break a common misconception: steel is not afraid of burning, but of high temperatures.
Specifically, there are several key points:
Sudden drop in strength: Steel has high strength at room temperature, but its yield strength begins to decrease significantly when the temperature exceeds 350°C；When the temperature rises to 500°C, the strength of ordinary structural steel drops to about half of its room temperature strength；When the temperature reaches 600°C, its strength is basically lost, and it becomes as soft as noodles.
Distortion and deformation: In a fire, flame temperatures typically range between 800°C and 1200°C, far exceeding the critical strength loss temperature of steel.Steel beams and columns that have lost their strength can no longer support their designed loads, which can cause the entire building structure to twist, deform, or even collapse in a short period of time. This type of collapse is sudden, with almost no warning, posing a devastating threat to the lives and property of people.In 1996, during a fire experiment in Cardington, UK, a steel-structured building without fire protection suffered severe deformation just 20 minutes after the fire started, fully demonstrating this point.
Rapid heat conduction: Steel is an excellent conductor of heat. High temperatures generated by a local fire can quickly transfer through steel components to other connected areas, even those not on fire, causing the temperature of the entire structural system to rise and thereby expanding the scope of damage.
Therefore, unprotected steel structures typically have a fire resistance limit of only about 15 minutes. This is far from enough time for people to evacuate safely and for firefighters to carry out rescue operations. Therefore, putting a ‘fireproof armor’ on steel structures is not an option; it is a mandatory life safety measure.
02 China’s ‘Fireproof Armor’ Technology System for Steel Structures
In the face of the threat of intense fire, Chinese construction technology professionals and fireproof material companies have developed, through decades of research and practice, a set of mature, efficient, and diversified fire protection technologies for steel structures. These technologies act like custom-made “armor” for steel structures, enabling them to maintain sufficient strength and stability during a fire, buying precious time for evacuation and firefighting.
Currently, ‘fireproof armor’ is mainly divided into four categories: fireproof coatings, fireproof board wrapping, concrete/mortar wrapping, and water-cooling methods.
First Armor: Fireproof Coating
Fireproof coatings are the most widely used and economical method for fire protection of steel structures. They are applied to the surface of steel structures by spraying or brushing, forming a protective film that serves both decorative and fire-resistant purposes. They are mainly divided into two categories:
• Thick fireproof coatings ( Insulated type): This type of coating is applied in a thick layer, usually reaching several centimeters or even more. It is mainly composed of inorganic insulating materials and binders, with the coating itself having a very low thermal conductivity. In a fire, it relies on its thickness and low thermal conductivity to effectively block heat transfer to the steel substrate, delaying the temperature rise of the steel. Its fire resistance limit can reach over 3 hours, making it widely used in industrial plants with high fire resistance requirements, load-bearing columns of high-rise buildings, and similar applications.
• Thin/ultra-thin fireproof coatings (expansive type): These coatings contain key components such as blowing agents, charring agents, and catalysts. The coating is very thin, usually within a few millimeters, and has good decorative appearance.When a fire occurs, the coating rapidly expands dozens or even hundreds of times, forming a dense, sturdy layer of carbonized foam that insulates against heat.This layer of foam acts like a ‘thermal barrier,’ isolating the steel from the flames, while its porous structure also effectively inhibits heat transfer.Thin coatings, known for their aesthetic appeal and lightweight properties, are widely used in public buildings such as gymnasiums, exhibition halls, airports, and commercial complexes where appearance and space are important.
Second Layer of Armor: Fireproof Board Wrapping Method
Fireproof board wrapping technology involves using boards with excellent fire-resistant properties to encase steel structures with the help of studs, adhesives, or fasteners, forming a sealed fire protection layer. Commonly used materials include fireproof gypsum board, calcium silicate board, vermiculite board, and mineral wool board.
These panels themselves have excellent non-combustibility and a low thermal conductivity, so their fire resistance is stable and reliable. They are easy to control in terms of construction quality and are not affected by seasonal weather conditions.At the same time, some fireproof panels also serve decorative, soundproofing, and insulation functions. They are widely used in office buildings, hotels, and other places that have high requirements for interior aesthetics and durability. Super high-rise buildings in Beijing, such as the CITIC Tower, have extensively used this technology.
Third Layer of Armor: Concrete/Mortar Encapsulation Method
This is a traditional and highly effective fire protection method, which involves encasing steel structures in concrete, mortar, or wire mesh mortar.
This method is relatively low-cost, has a high fire-resistance limit, is strong and durable, and offers excellent fireproof and impact-resistant performance. However, its drawbacks are also obvious: it has the greatest self-weight, a long construction period, and takes up more building space.
Fourth Armor: Water Cooling Method
This is a very clever ‘active’ protection system, which can be seen as building a ‘blood circulation cooling system’ inside the steel structure.
A water-filled cooling system is one in which the hollow sections of steel columns or beams are filled with water.In the event of a fire, the heated water circulates naturally, carrying away the heat and releasing it through preset cooling devices, thereby keeping the temperature of the steel structure below the critical point.This method has extremely high protective efficiency and can achieve both prevention and treatment. However, the system is complex, very costly, and requires high maintenance, so it is mostly used in experimental buildings with special requirements or in supertall landmark structures.
03 Innovation and the Future
With the development of intelligent technology in China and the deepening implementation of the ‘dual carbon’ strategy, China’s steel structure fire protection technology is continuously advancing towards being more efficient, smarter, and more environmentally friendly.
New Material Research and Development: Research institutions and companies are working on developing high-performance nano-composite fireproof coatings and water-based environmentally friendly fireproof coatings, aiming to achieve thinner coatings, better fire resistance, and lower VOC emissions.
Intelligent Design and Construction: By using BIM technology, precise modeling and simulation analysis of fire protection for steel structures can be carried out during the design stage, optimizing coating schemes and avoiding conflicts with other pipelines. During construction, the use of automated technologies such as robotic spraying also greatly improves construction efficiency and coating uniformity.
Performance-Based Fire Protection Design: This is an advanced design concept based on the overall safety performance of a building. Instead of sticking to traditional prescriptive codes, it uses computer simulations of fire scenarios and structural responses to tailor the most economical and reasonable fire protection solutions for specific buildings, making the ‘fireproof armor’ more scientific and precise.
Conclusion
The rise of steel structure buildings reflects the remarkable achievements of modern engineering technology. Behind these achievements, however, lies layer upon layer of ‘fireproof armor’ that safeguards them. It may not be glamorous, but it plays a role in critical moments that appearances alone cannot replace.
As members of China’s construction sector, we deeply understand that safety is the lifeline of a building, a social responsibility, and the highest respect for life. Choosing compliant, high-quality, and reliable fire protection solutions for steel structures is not only adherence to national standards but also a solemn commitment to users and to society.