Understanding the fire-resistance of building materials

A successful passive fire protection strategy involves reviewing construction materials for their ability to inhibit the passage of flames. This ensures the right levels of protection for a building in the event of a fire, in line with stringent building and construction regulations.

Multiple factors are considered when choosing the right fire-resistant material, from its load-bearing capabilities and thermal conductivity to its tendency towards decay. In this article, we will be reviewing the specific fire resisting properties of common building materials.

Brick and Mortar

An individual brick offers high levels of heat resistance, with the ability to withstand a maximum temperature of 1200°C. A commonly-cited reason as to why bricks have such a high fire-resistance rating is because they are usually made in a fire kiln.

Brick walls, however, are often held together with mortar, which is less effective as a fire-resistant material. Mortar is a component material in masonry construction and is used to fill the gaps in between the blocks and bricks that come together to create walls.

Most mortar is fire resistant to some extent, as the materials that make it (usually a mix of clay, cement, lime, and sand) are resistant to fire and heat. However, a drastic increase in temperature can cause mortar to crack and expand. Despite this, brick has endured as the most popular fire-resistant material for buildings, being widely used for external walls and other common building elements.

Stone

Stone suffers under the effects of fire and is prone to disintegration when suddenly cooled. Based on the specific type of stone, the exothermic reactions can vary greatly. For example, granite explodes when exposed to heat – and therefore requires extensive risk management when used as a construction material. While excessive heat often causes limestone to crumble, sandstone’s unique composition (formed of small mineral particles and rock fragments) means it can usually withstand moderate fire conditions and is less likely to crack and break apart like other stone materials.

Timber

While wood is known as a common conductor of heat, timber that is used in heavy construction can be reasonably fire-resistant. The fire resistance levels of building materials will often differ following the addition of surface chemicals such as ammonium phosphate, sulphate, and zinc chloride. Timber can also be painted to provide an extra layer of fire protection. This reminds us that it is important to distinguish between raw materials and structural materials (that have often been treated as part of the design and construction process).

Fire-retardant materials should not be confused with fire-resistant materials. Fire-retardant materials are designed to burn much more slowly, in comparison to some of their more flammable counterparts such as plywood and fibreboard.

Steel

Steel is well known for its enduring structural integrity and high tensile strength. Steel buildings are resistant to degradation, withstanding the adverse effects of termites, rust and rot. However, steel is not so able to hold out against the temperatures of fire. When exposed to fire for too long, steel beams will sag and the columns will buckle, causing the structure to collapse. Temperatures above 600°C can induce the stress of mild steel, and at 1400°C, steel will melt completely.

For this reason, fire protection is a crucial factor in the design of steel structures. Site owners and project managers should consult with fire protection experts from the outset. These experts can then recommend measures such as intumescent paint to improve the fire resistance rating of structural steel. This paint forms a carbonaceous layer when subjected to extreme temperatures, offering an additional layer of protection to steel beams. To find out more, consult our guide to structural steel fireproofing.

Concrete

How concrete behaves under high temperatures depends upon its composition of materials. This is to say that the quality of both cement and aggregates used will affect the fire resistance of building elements. Usually, reinforced concrete will tolerate temperatures of up to 1000°C for about sixty minutes before it begins to lose its strength. We cover this subject in more detail in our guide to the fire resistance of concrete structures.

Glass

Much like stone, glass will crack and shatter when it is exposed to heat and then left to then cool down again. Therefore, for safety reasons site teams will commonly use reinforced, toughened and laminated glasses. These glasses, especially those that feature steel wire, are far more fire-resistant than ordinary glass.

Cast iron

Cast iron is not frequently used as a common building material. This is because of its behaviour under high temperatures. When exposed to heat and then suddenly cooled, cast iron will shatter into pieces. Because of this, it will often be covered with brickwork or another more stable fire-resistant material, such as concrete.

Fire-resistant materials are treated to reinforce them against extreme temperatures. However, these materials cannot be 100% fire-resistant; fireproofing is a method that works to massively reduce their susceptibility to fire. Ultimately there is not a single material that cannot be destroyed by the effects of heat. It is for this reason that passive fire protection is so important.

Choosing the right materials is only a small part of protecting buildings against fire. If you’re interested in finding out more, we recommend you start with our article on structural measures to prevent the spread of fire.

Leading experts in passive fire protection

CLM Fireproofing are the UK’s leading specialists in designing and implementing passive fire protection systems, helping our clients remain fully compliant with regulatory requirements and industry practice.

Our team can easily navigate the unique and complex requirements of specific sectors. We are highly experienced at providing passive fire protection and fire stopping solutions within the construction industry. We also offer training and Continued Professional Development (CPD) for project managers and site teams, as part of our commitment to raising standards for passive fire protection.

Interested in finding out more about our comprehensive range of services, including compartmentation and spray-applied fireproofing? Contact CLM Fireproofing today by phone or submit a contact form today.