Why steel needs protection
Structural steel loses about half its strength at around 550°C. In a fire, unprotected steel can reach this in minutes, so many buildings need the steel frame protected for a set time.
Fire resistance periods
The required period - typically 30, 60, 90 or 120 minutes - comes from Approved Document B (Fire Safety) and the building's fire strategy. It depends on the use and height of the building. In houses, steel beams are often protected by the plasterboard ceiling or boxing-in rather than a coating.
The main methods
- Intumescent coatings - thin paint films that swell into an insulating char when heated. Neat, and keep the steel shape visible. Applied in a factory or on site
- Boards - fire-rated boards fixed around the steel, often used where the steel is hidden
- Sprayed coatings - cement or mineral based sprays for hidden steel in larger buildings
- Concrete encasement - less common today
Section factor
Thin, light sections heat up faster than heavy ones. The section factor (the heated perimeter divided by the cross-section area, often written Hp/A) tells the specialist how thick the protection must be. Lighter sections and 4-sided exposure need thicker coatings.
How it is specified
The fire engineer or designer sets the period and the members to protect. A specialist then calculates the thickness for each section using a tested product. Intumescent coatings must be compatible with the primer and any topcoat, and are best applied by a third-party certificated contractor.
How we handle it
We arrange intumescent coatings through specialist applicators and coordinate them with our fabrication programme, so the steel arrives protected and ready to fit. Use our coating area calculator to estimate the area to be protected.
General guidance only. Fire protection must be specified by a competent designer for your building.