Fire protection for steel structures
which system fits?

Fire protection for a steel structure has one clearly defined goal: keep the steel temperature below a critical limit for a specified duration. Above that limit steel loses its load-bearing capacity, and the member fails.

The required duration is expressed as a fire-resistance class in minutes — R30, R60, R90, R120, R180 or R240. Which class applies in a given project follows from building type, use, and the relevant building code.

• Goal: hold steel temperature below the critical limit
• Classes: R30 / R60 / R90 / R120 / R180 / R240 minutes
• Driven by: building type, use, building code
• Evidence: a tested system with a valid approval

Four systems have established themselves for protecting load-bearing steel members. Each has its own strengths — there is no single “right” system, only the one that best matches geometry, aesthetic demands and the site conditions.

Fibre-reinforced calcium-silicate or calcium-sulphate boards are produced in the factory under controlled conditions. That delivers tight tolerances and consistent quality — something that is not easily reproduced on a construction site.

• Single-layer cladding is sufficient for most applications
• Direct installation without metal rails or complex supporting systems
• Minimal drying times — no waiting for the next trade
• Easier quality inspection because installation is straightforward
• Lower weight and transport volume
• Cut, screw and staple — year-round, with no temperature or humidity limits

Intumescent coatings are applied like paint and remain practically invisible under normal conditions. When exposed to heat they react chemically, expand to roughly 50× their original volume and form an insulating carbon foam that keeps the steel temperature under control.

• Steel geometry stays visible — ideal where architecture shows the steel
• Customisable in colour and finish
• Works even on complex members and connection nodes
• Application only under controlled conditions (temperature, humidity, substrate)
• Multiple coats with proper drying time between them
• Expansion space must stay free — no covering with rigid materials

Sprays are powder systems of cement- or gypsum-based binders with fillers and fibres. They are mixed on site and applied by machine — which lets them adapt to almost any geometry.

• Highly adaptable to complex beams, columns and connection nodes
• Acceptable as a plaster-like finish when executed properly
• Covers critical connection points cleanly
• Requires on-site mixing equipment and masking of surrounding elements
• Controlled drying conditions required
• Extensive thickness verification for handover — every position must hit the minimum thickness

Membrane systems take an alternative approach: they form a continuous protective surface and are particularly useful for complex ceiling geometries or composite (steel-concrete) structures — where cladding each profile individually would be uneconomic or geometrically impractical.

Instead of wrapping every steel member, the protection is suspended as a plane beneath — a clean solution in ceilings.

The performance of a fire-protection system for steel structures is demonstrated against harmonised European standards in a fire test. Three central references:

• EN 13381-1 — testing of membrane and ceiling protection systems
• EN 13381-2 — testing of vertical fire-protection systems for load-bearing members
• EN 1365-2 — fire resistance of load-bearing elements: floors and roofs

The choice is rarely free — it follows three drivers: the required fire-resistance class, architectural aesthetic demands and the site conditions. A handful of rules of thumb for an initial read:

• Want visible steel? → intumescent coating
• Complex, cluttered geometry? → spray or coating
• Fast, weather-independent installation required? → boards
• Large ceiling areas with many individual profiles? → consider membrane
• High fire-resistance class (R120 / R180 / R240)? → dimension thickness and system together