Passive fire protection

Unprotected structural steel reaches its critical temperature within minutes of flashover. Passive fire protection delays that, and the required period — 60, 90, 120 minutes — comes from the fire strategy for the building or plant.

Thickness is calculated per member

The protection thickness is not a single figure for a project. It is calculated for each section from its section factor (Hp/A — the ratio of heated perimeter to cross-sectional area), the required fire resistance period, the critical temperature and whether the member is a beam or a column. A heavy column needs less protection than a slender beam for the same rating, and specifying one thickness across a whole frame either wastes material or leaves members under-protected.

Systems

Intumescent coating

A thin film that expands to many times its applied thickness when heated, forming an insulating char. Specified where the steel is visible and appearance matters, and where weight or space is constrained. Applied as a primer, basecoat and decorative topcoat, with dry film thickness measured against the calculated requirement for each member.

Spray-applied cementitious fireproofing

Cementitious or gypsum-based material sprayed to a substantial thickness. Commercial, medium and high-density grades cover concealed, semi-exposed and external or industrial applications respectively. More economic than intumescent at higher fire ratings and in concealed locations.

Board systems

Rigid board encasement where a clean rectilinear finish is wanted or where site conditions make spray application impractical.

Execution controls

• Section factor schedule prepared and the thickness calculated for every member
• Compatible primer verified against the fireproofing manufacturer’s approval
• Dry film thickness measured and recorded per member, not per area
• Adhesion and density testing on spray-applied systems
• Mesh reinforcement where the system or thickness requires it
• Damage inspection and making good after following trades

Also covered

• Fire-rated service penetration sealing
• Fire-rated joint and linear gap sealing
• Protection to structural steel, decks and approved substrates

Standards we work to

• BS 476-20
• BS 476-21
• EN 13381-8
• EN 13381-4
• ASTM E119
• ASTM E84
• EN 1993-1-2