Sep 13, 2026Applications & Projects
Fire Protection for Steel Structures: Pipe and Coating Options
Why unprotected steel fails in a fire, and the main protection options: cladding, water-filled members, shielding and fire-resistive coatings.
Quick answer: Steel is non-combustible, but it loses strength quickly in a fire. Most unprotected steel structures lose load-carrying capacity between 450 C and 650 C, giving roughly 15 minutes of fire resistance. Fire protection therefore uses cladding, water filling, shielding or fire-resistive coatings to slow heat transfer and keep the structure within the fire endurance required by the design specification.
Why Unprotected Steel Fails in a Fire
Steel is a non-combustible building material that is shock and bending resistant. In practice it increases a building load capacity and supports architectural design, and it avoids the brittleness that limits concrete and other materials in bending and tension. That is why steel is favoured by the construction industry and appears in single-storey buildings, multi-storey buildings, skyscrapers, factories, warehouses and waiting rooms.
However, steel has an unavoidable weakness in fire: its mechanical properties, including yield point, tensile strength and elastic modulus, fall sharply as temperature rises. Steel structures usually lose their load-carrying capacity at temperatures between 450 C and 650 C, causing large deformations that bend steel columns and beams until they can no longer be used. An unprotected steel structure typically has a fire resistance limit of only about 15 minutes, and that time also depends on how quickly the member absorbs heat.
What Fire Protection Is Trying to Achieve
Fireproofing is applied to raise the fire endurance of a steel structure to the limit required by the design specification. The principle is the same whichever method is used: block the flame and heat from reaching the steel directly, reduce the speed of heat transfer, and delay both the temperature rise and the point at which strength starts to fall. The method is then chosen to suit the member, the exposure and the required endurance.
Option 1: Concrete and Sprayed Mineral Cladding
The outer layer approach adds a protective layer to the outer surface of the steel structure, either cast in place or sprayed. Cast-in-place solid concrete cladding is usually reinforced with steel mesh or steel to limit shrinkage cracks and to ensure the strength of the outer casing. Spraying applies mortar to the steel surface at the construction site to form a protective layer; the mortar can be lime cement or gypsum, sometimes mixed with perlite.
Prefabricated cladding is another route. Panels or boards made from perlite or gypsum, or lightweight concrete, can be fixed to the steel structure with adhesive, nails or bolts. The advantage is that the layer thickness and finish can be controlled off site, while the disadvantage is the added weight and the space the cladding consumes.
Option 2: Water-Filled Members
Filling a hollow steel structure with water is the most effective protection against fire. Water keeps the steel at a lower temperature because it circulates inside the member and absorbs heat from the material itself. The heated water can be recirculated after cooling, or cold water can be introduced from the pipeline to replace it. Firefighting pipe systems are the natural feed for this approach, which is why water-filled columns and hollow sections are attractive where the structure is already hollow and can be sealed reliably.
Option 3: Shielding and Blocking
Shielding places the steel structure inside a wall or ceiling of refractory material, or hides the member in the space between two walls. Fireproofing is then achieved by adding a little refractory material or by increasing the surrounding build-up. This is the most economical method, because the architecture itself provides most of the separation, but it only works where the member can be concealed.
Option 4: Fire-Resistive and Intumescent Coatings
Fire-resistive coating protection offers good fire and heat insulation performance, and construction is not restricted by the geometric shape of the steel structure. It generally needs no auxiliary facilities, the coating is light in weight, and it can have a decorative effect, which makes it a modern advanced fire protection measure. Because it follows the member profile, it is often used where exposed steelwork must remain visible.
Choosing the Right Fire Protection
High-rise steel structures are increasing, especially super high-rise buildings, where steel is used widely. In a fire in a tall building the blaze will not be extinguished in a short time, so protection has to be designed in from the start and combined with an emergency plan to reduce casualties and property damage. Selection should weigh the required fire endurance, whether the member is hollow and can be water filled, whether cladding weight is acceptable, and whether the steelwork will remain exposed.
Unprotected structural steel typically holds its load for only about 15 minutes in a fire, so the required fire endurance - not the coating thickness alone - should drive the protection design.
FAQ
At what temperature does steel lose its strength?
Steel structures usually lose load-carrying capacity between 450 C and 650 C. Above that range, deformation becomes large enough to bend columns and beams beyond use.
How long can unprotected steel resist a fire?
The fire resistance limit of an unprotected steel structure is typically about 15 minutes, and the exact time depends on how quickly the member absorbs heat. That is why fireproofing is required to reach the design endurance.
Is water filling effective for steel columns?
Filling a hollow steel structure with water is the most effective protection against fire. The water circulates, absorbs heat and keeps the steel cooler, and it can be recirculated after cooling or replaced with cold water.
Are fire-resistive coatings suitable for complex shapes?
Yes. Coating protection is not restricted by the geometric shape of the steel structure, normally needs no auxiliary facilities, is light in weight and can be decorative, which suits members that stay visible.
Send your member sizes, exposure conditions and required fire endurance to our engineering team for a confirmed recommendation.
