How Does Fire Affect Structural Steel?

The versatility, strength and sustainability of structural steel has ensured its phenomenal market share over the past two decades. Architects enjoy the freedom it affords them, and building owners appreciate both its aesthetic possibilities and the relative ease of construction where steel is used.

Less widely understood, however is the way in which fire affects the integrity of structural steel. Knowing how a building component behaves in the extreme temperatures caused by fire, provides an important insight into the kinds of fire protection required to protect it. In this blog, we consider effective passive fire protection solutions for structural steel.


How Fire Affects Structural Steel

The physical and material properties of structural steel are changed by the high temperatures that occur in a fire event. These include a reduction in strength and stiffness, as well as thermal elongation. Once the temperatures reach 600°F steel loses 50% of its strength and begins to buckle and deform.

Most fires will quickly reach the temperature required to buckle steel, at which point the integrity of the building is at risk. Passive fire protection offers the most effective way to increase the fire resistance of steel and lower the risk of building collapse.

Structural Steel Fire Protection

Structural steel is now a staple of the construction industry, and as a result there are a number of ways in which its fire resistance can be increased. Below are the most common solutions:

1. Intumescent Paint

This is a reactive paint which is sprayed on to the steel to increase its fire resistance. In the event of high temperatures caused by fire, the paint swell to form a carbonaceous char which acts as thermal insulation to the steel. Whilst intumescent paint won’t stop the impact of rising temperatures completely, it will delay the time it takes for those critical temperatures to be reached.

2. Cementitious Coating

A non-reactive coating made of gypsum or cement. Instead of responding to high temperatures, these materials, with their high melting point, delay the transfer of heat from the fire to the steel. Cementitious coating needs to be between 10-20mm thick, and it is normally applied in multiple layers.

How Do You Choose Between Them?

Both intumescent paint and cementitious coating do a similar job, but each one offers unique merits which need to be taken into consideration:

Intumescent Paint

  • Visually Appealing. When intumescent paint is sprayed onto structural steel it looks stunning as well as providing fire protection.
  • Flexible. Intumescent paint is not only effective with steel; it can also be used on wood, concrete, plasterboard, brick, stone, and chipboard.

Cementitious Coating

  • Good for Non-Standard Structures. Cementitious coating is easy to use for difficult angles, or for covering non-standard shapes, structures, or objects.
  • Cost Effective. The materials used in cementitious coating are cheap, so the major cost involved is labour (especially where multiple layers are needed).
  • Thermal and Acoustic Benefits. Cementitious coatings don’t look great, but they provide the additional benefits of thermal and acoustic insulation as a by-product.

Working With Wallace Fire Protection

Wallace Fire Protection is an established UK contractor providing passive fire protection design and installation. We’re one of 6 UK companies licensed and approved Promat DURASTEEL® installer, and we regularly work in high-risk environments providing blast resistant walls and ceilings, high impact walls, and fire barriers.


Would you like to know more about Wallace passive fire protection design and installation for buildings using structural steel? Call our specialist team today on 01908 109045