Is Structural Steel Fireproof? Fireproofing Steel Beams

The fire protection of steel structures is some of the best in the world of construction materials. Unlike timber, which is highly combustible without treatment, steel is a durable and non-combustible material with natural fire resistance. With these incredible attributes, there should be no need for fireproofing steel beams since steel is technically fireproof, right?

In practice, however, the practical design of a building can significantly impact fireproofing for steel beams and structures, regardless of their fire resistance.

Fireproofing steel beams, steel structures, and any other building, for that matter, is a part of passive fire design. This term refers to the use of building components intended to stop or impede the spread of fire and/or smoke to various areas of a structure or protect structural components from collapse.

In combination with active fire protection measures like sprinklers and fire alarms, passive fire protection, like fireproof coatings for steel structures, helps to facilitate escape in the event of a fire and avoid damage to adjacent buildings.

To achieve passive fire protection, builders can control the flammability of construction materials by using fire resistance-rated elements, like structural steel.

If you’re starting to build your own home, or want to learn more about how to preserve one of your most valuable assets, be sure to learn more about the fire protection of steel structures and how structural steel helps to improve a building’s passive fire protection.

Passive Fire Protection

According to Wikipedia, the main characteristics of passive fire protection systems are:

  1. Contain a fire to the compartment of fire origin
  2. Slow a fire from spreading from the fire’s origin
  3. Slow the heating of structural members
  4. Prevent the spread of fire through intentional openings, e.g. doors.
  5. Prevent the spread of fire through penetrations, e.g. gaps in the walls for plumbing and cables.

These five characteristics can be best summed up as follows:

Resistance to Fire: the ability of a fire-separating element (wall/ floors/ ceiling etc.) to limit fire spread.

Reaction to Fire: how much burning behaviour of material encourages rapid flame spread or smoke creation.

The primary objective of passive fire protection and design is to give building occupants ample time to leave and find safety while allowing firefighters enough time to put out the fire. Even a burnt building is better than one that has collapsed.

Classification of Fire Resistance

A building element’s fire resistance rating (FRR) is determined by its structural suitability, integrity, and insulation. Fire resistance is measured by the number of minutes each threshold is met when the element is exposed to the temperature, pressure, and applied load specified in the test procedure.

Structural adequacy is the ability to support a vertical axial (from above) load and only applies to load-bearing elements of a structure like walls, floors and columns.

Integrity is the ability to prevent the passage of flame and hot gases measured by the creation of a gap or ignition of a cotton pad on the non-fire (unexposed) face.

Thermal Insulation is the ability to limit the temperature rise on the non-fire (unexposed) face.

The fire resistance of an element of construction is a measure of its collapse, fire penetration and the transfer of excessive heat.

Properties of Steel that Affect its Fire Resistance

Because steel has a high melting point, around 1500°C, it can withstand high temperatures for a considerable time before melting. The properties of steel that impact fire resistance of steel include its thermal conductivity, melting point, and strength.

Steel will lose its ability to support weight at extreme temperatures (between 350°C and 750°C). However, depending on the load and forces in play, structural steel elements can fail at temperatures between 500°C and 600°C, making structural steel protection a necessity for maintaining the stability of a structure in the event of a fire.

Rating Fire Resistance

Fire resistance ratings must consider the following factors:

  1. Steel serial size: dimensions or designated profile of the material for calculating the total volume of steel.
  2. The number of exposed sides: how many exposed sides a structural element has will affect fire resistance. More exposed sides mean less fire resistance.
  3. Fire Resistance Level (FRL): national regulations for buildings and structures.
  4. Critical Temperature: temperature when structural components fail.

Is Structural Steel Fireproof?

Structural steel is not fireproof but can be fireproofed to some extent. Fireproofing steel beams involves applying a fireproofing material on the surface of the steel to insulate it from heat. Fireproofing material is applied to the surface of the steel beams to create a barrier between the steel and the fire, slowing down heat transfer and giving the steel beams more time to withstand the fire without melting. A fireproof coating for steel structures is a common method for fireproofing steel beams.

Improving Steel’s Fireproofing With Intumescent Paints

Although structural steel is non-combustible and resistant to fire, there is always room for improvement. One of the simplest and most effective ways to shield load-bearing structural components of buildings from fire is using intumescent coating, often known as intumescent paint. Intumescent paint is easily applied and does not modify the intrinsic properties of your building materials, making it ideal for the modern architectural design of both industrial and commercial buildings.

When exposed to heat, the intumescent coatings expand, increasing their volume and reducing density. This expansion creates a carbonaceous char (it burns) made of many tiny bubbles that serve as an insulating layer, shielding your materials from fire. For external or high-humidity applications, a top coat may need to be applied to protect against environmental degradation. Builders can also use top coats for decorative and aesthetic purposes.

How Effective is Fireproofing Steel Beams?

Fireproofing steel beams is an effective method for increasing fire resistance, but it is not a guarantee against fire damage. The effectiveness of fireproofing depends on several factors, including:

  • The thickness of the fireproofing material
  • The type of fireproofing material used
  • The temperature and duration of the fire

Structural Steel is Fire-Resistant

Buildings and structures that are constructed using structural steel are inherently fire-resistant. Structural steel framing is naturally durable and non-combustible, making steel a common building material where fire resistance is required.

With proper design and fabrication, steel framing can preserve its structural integrity in the event of a fire and exposure to prolonged elevated temperatures.