A steel structure warehouse caught fire. After fire crews fought for several hours, two large steel beams lost their strength and fell from a height. Such cases have drawn attention to fire protection for steel structures.

Since China's reform and opening up, with a substantial increase in steel production, steel structure construction has developed rapidly. However, there are two misconceptions regarding fire protection and fireproof coatings for steel structures: first, that steel structures are strong and resistant to fire, so prevention is neglected; second, that once a steel structure is coated with fireproof coating, it is completely safe and will not catch fire. In reality, fireproof coating only delays the fire's effect, allowing time for personnel evacuation, firefighting, and preventing collapse—it does not make the structure fireproof or indestructible.

Steel is a temperature-sensitive material; its strength and deformation change dramatically as temperature rises. For common building steel, at about 500°C, its strength drops to 40%–50%; at 600°C, its load-bearing capacity is almost completely lost. Without fireproof coating (bare steel), the fire resistance rating of a steel structure is only 10–20 minutes. Once a fire occurs, the building collapses rapidly, causing catastrophic accidents and heavy losses of life and property. Therefore, fire protection measures must be taken for steel structures, enabling timely evacuation, reducing fire damage to the steel, and allowing effective firefighting within the fire resistance limit (1–2 hours) to avoid partial or total collapse leading to casualties and property losses.

Fire protection for steel structure engineering is of paramount importance. Design and fabrication must comply with relevant standards, such as GB14907-2000 "Fireproof Coatings for Steel Structures", GB50205-2001 "Code for Acceptance of Construction Quality of Steel Structures", GB50016-2005 "Code for Fire Protection Design of Buildings", GB50045-95 "Code for Fire Protection Design of Tall Civil Buildings", CECS24-90 "Technical Code for Application of Fireproof Coatings for Steel Structures", DG/TJ08-008-2000 "Technical Code for Fire Protection of Building Steel Structures", and others.

The supplier of fireproof coating for steel structures must possess the following necessary documents: a valid inspection report issued by the National Center for Quality Supervision and Testing of Fire Building Materials; a valid product type approval certificate issued by the China Fire Protection Products Conformity Assessment Center of the Ministry of Public Security; a professional contracting qualification certificate for fire protection engineering issued by the certification authority of the Ministry of Construction of the People's Republic of China; and a work safety permit issued by the local construction administrative department.

Rules for selecting fireproof coatings for steel structures: For high-rise and multi‑story steel structures requiring permanent fire protection, where the specified fire resistance limit is more than 1.5 hours, non‑intumescent fireproof coatings may be selected. For indoor exposed steel structures, light roof steel structures, and steel structures with decorative requirements, where the specified fire resistance limit is less than 1.5 hours, ultra‑thin or thin‑type intumescent fireproof coatings may be selected. For outdoor steel structures, fireproof coatings suitable for outdoor use must be selected; such coatings should have been tested in outdoor pilot projects for at least one year with no significant changes in coating performance. For steel structure projects requiring a fire resistance limit of more than 1.5 hours or those used outdoors, thin‑type fireproof coatings should not be used.

For ultra‑thin and thin‑type fireproof coatings, the expansion and foaming of the coating when exposed to fire can be inspected on site. The flame of a blowtorch should just touch the coating surface, applied perpendicularly for 15 minutes. Observe the foaming state: for ultra‑thin coatings, the foam thickness should be more than 10 times the coating thickness; for thin coatings, the foam thickness should be 5 times the coating thickness.

Fireproof coatings for steel structures are classified into three types by thickness: ultra‑thin fireproof coating (coating thickness ≤ 3 mm), thin‑type fireproof coating (3 mm < thickness ≤ 7 mm), and thick‑type fireproof coating (7 mm < thickness ≤ 45 mm).

Types of Fireproof Coatings and Common Selection Mistakes

Fireproof coatings are widely used in national defense and military engineering. Applying fireproof coating to steel structural members can increase their fire resistance from 15 minutes to up to 2 hours (depending on coating thickness). When ordinary cable trays are coated, the coating foams and chars in a fire, providing thermal insulation and greatly reducing the temperature rise inside the tray. Refractory cable trays with a double‑layer structure can operate for 0.5–1.5 hours in a fire, with internal temperature not exceeding 140°C, protecting ordinary wires and cables laid inside and allowing continued operation. Applying fireproof coatings to wood structural members greatly improves their fire resistance; with a 1 mm thick coating, the fire resistance limit can reach 30 minutes. Flammable materials such as flooring and carpet, after treatment with flame‑retardant impregnating liquids, have their flammability reduced and gain fire resistance. Coating cables with fireproof coating enhances their fire resistance.

Because fireproof coatings offer the excellent fire protection described above, they are welcomed by users and widely applied in many projects. However, many users are not familiar with the performance of fireproof coatings, leading to problems in their use. Therefore, based on actual situations encountered in projects, the following is introduced:

1. Applying wood‑structure fireproof coating to steel structures

At present, there are few manufacturers of fireproof coatings for steel structures in China. Products not labeled specifically for steel structures cannot be used on steel structures.

Because wood‑structure and steel‑structure fireproof coatings are indistinguishable by the naked eye, when selecting fire‑resistant products such as refractory cable trays, users must know which brand of fireproof coating the manufacturer uses. If a steel structure is coated with a wood‑structure fireproof coating, adhesion is greatly reduced, and it is prone to peeling off after one or two years. When a steel structure is coated with a steel‑structure fireproof coating, its service life is at least five years or more.

2. Using toxic fireproof coatings

Some domestic manufacturers produce fireproof coatings that decompose and release toxic gases when exposed to fire. If such coatings are used on fire‑resistant electrical products, toxic gases will be released in a fire. For example, the obsolete G60 perchloroethylene fireproof coating decomposes to release toxic chlorine gas and should not be selected.

3. Failing to distinguish between solvent‑based and water‑based fireproof coatings

There are two types of fireproof coatings for steel structures: solvent‑based and water‑based. In terms of adhesion, solvent‑based coatings are superior to water‑based ones. Therefore, for outdoor steel structures, solvent‑based fireproof coatings should be used. For indoor steel structures, either solvent‑based or water‑based coatings may be used.

4. Mistaking collapse‑delay measures for fire‑resistant electrical products

Applying fireproof coating to steel structure products can prolong their fire resistance. Some manufacturers coat ordinary cable trays with fireproof coating and market them as "non‑combustible" or "fire‑resistant" cable trays for laying ordinary wires and cables. This is wrong: in a fire, they cannot protect ordinary wires and cables to continue functioning. For a genuine fire‑resistant cable tray, the manufacturer must provide test reports on parameters such as temperature, burn time, and internal temperature range. Users can select fire‑resistant cable trays according to the requirements of their specific application.