Fundamentals
Why does structural steel need fire protection?
Steel is noncombustible, but increasing temperature reduces its stiffness and load-bearing capacity. Fire protection slows the heating rate so the member can maintain structural stability for the required fire-resistance period.
Load-bearing capacity
The ability to maintain mechanical and structural function during fire.
Integrity
Prevention of flame and hot-gas passage through a separating element.
Insulation
Limiting temperature rise on the unexposed surface during testing.
Reaction to fire describes how a material contributes to ignition and flame spread; fire resistance describes how long a member or assembly maintains its required function during fire.
System selection
Common passive protection systems for steel
Sprayed mineral coating
A thick, lightweight cementitious or gypsum-based layer that limits heat transfer. Adhesion, density and thickness control are critical.
Intumescent coating
It expands under heat and forms an insulating char. It must not be directly covered by other materials and requires space to expand.
Boards or protective enclosure
The member is enclosed by approved boards or a membrane assembly. Continuity, fixings, joints and details govern performance.
Coating type or thickness must not be selected from generic experience; it must come from the product technical assessment and design tables for the actual section, required fire-resistance period and service conditions.
Design and documentation
From required fire rating to an approved product
Certificate and assessment report
Factory-produced steel fire protection must have a valid technical assessment appropriate to its type; Code 112 refers to EN 13381 and the legal technical-certification authority.
Complete member protection
Columns, primary beams and related members require continuous protection; column protection continues from structural floor to the structural soffit above and includes its connections.
No services embedded in protection
Pipes, wiring, ducts or building services must not be embedded within the protection required for an independently protected structural member.
Multidiscipline coordination
Suspended ceilings, MEP supports, structural connections, impact guards, anticorrosion paint and future maintenance must be coordinated before application.
Substrate
Surface preparation and primer compatibility
The surface is free of oil, grease, dust, contamination, loose rust and unsound paint.
The anticorrosion system is explicitly compatible with the fire protection assessment.
An intermediate primer or bonding agent is used only where technically approved.
A mock-up and adhesion test are completed on the actual project substrate before full application.
Wet cementitious coatings create an alkaline environment. Alkali-sensitive anticorrosion paints, including some alkyd systems, can be damaged; mechanical mesh does not eliminate the need to verify chemical compatibility.
Adhesion and reinforcement
Minimum adhesion and when mechanical mesh is needed
Pre-application testing
Test adhesion to the actual project anticorrosion coating using a project mock-up.
Acceptable result?
If criteria and dimensional limits are met, application without mesh may be permitted.
Primer or mesh
Where adhesion is inadequate, use an approved bonding agent or mechanical retention system.
Minimum mass of continuous galvanized retention mesh where required.
Recommended stand-off distance of continuous mesh from the substrate.
Recommended maximum pin spacing in both directions.
Minimum impact-protection height above finished floor in exposed areas.
For buildings above 128 m, the code requires continuous galvanized retention mesh for sprayed mineral protection of steel beams and columns.
Quality control
Field inspection: adhesion, density and thickness
Adhesion testing
ASTM E736 commonly indicates internal cohesive strength, while EN 1015-12 with perimeter cutting can identify failure at the coating-substrate interface.
Dry-density control
Samples are dried for at least 24 hours at 43±6°C; measured dry density should remain within ±15% of the design dry density.
Thickness control
For each floor or approximately each 1000 m², at least one column, one primary beam and one secondary beam are checked, using two sections about 30 cm apart.
Thickness acceptance
The average thickness on each member must not be below design thickness. Local deficiency must also remain within the code limits of 6 mm and 25% of design thickness.
If a member fails, the deficient area is repaired and another randomly selected member of the same type is retested.
Quality-control records
Wrap-up
Application checklist and final quiz
Five-question quiz
0 / 51. What is the main purpose of fire protection on steel?
2. What is the minimum mineral-coating adhesion for a high-rise up to 128 m?
3. Can an intumescent coating be directly covered by another material?
4. Which properties are checked using ASTM E605?
5. What is required when a member fails the thickness check?
Source and scope
This course summarizes and rewrites the fire-protection-coating provisions in Chapters 8 and 11 of Iran Code 112, first revision. Actual design and application require the complete code, specialized Code 830, the product assessment report and project documents.