Fire
Concrete provides the best fire resistance of any building material. It does not burn, it cannot be 'set on fire' like other materials in a building and it does not emit any toxic fumes, smoke or drip molten particles when exposed to fire. Concrete and its mineral constituents enjoy the highest fire resistance classification (class A1) under EN 13501-1.
This excellent fire performance is due in the main to concrete's constituent materials (i.e. cement and aggregates) which, when chemically combined, form a material that is essentially inert and has poor thermal conductivity. It is this slow rate of heat transfer that enables concrete structures to perform well in a fire. Concrete also acts as an effective fire shield between adjacent spaces. In an intense fire, concrete can spall. Spalling occurs when entrapped air expands causing causing pieces of the concrete to break off. Measures, such as the introduction of polyester fibers to the concrete mix, can reduce or eradicate the incidence of spalling. The performance of reinforced or prestressed concrete elements (columns, beams, floors etc.) in a fire is largely dependant on the performance of the reinforcing bars or strands. Steel reinforcing counteracts high tensile stress in concrete elements. However, steel looses its high tensile properties at relatively low temperatures (350°C to 400°C). The fire performance of reinforced and prestressed concrete elements therefore, is closely related to the ‘depth of cover’ of the concrete (i.e. the distance from the steel reinforcing to the surface of the element).
Fire engineering and whole building performance
Moving on from the physical characteristics of concrete as a fire-resistant material, it is important to place this information in the context of whole building fire performance and design.
For any building or structure, regardless of its complexity, design for fire safety should address the following four principal objectives:
- to ensure stability of the load-bearing construction elements over a specific period of time
- to limit the generation and spread of fire and smoke
- to assist the evacuation of occupants and ensure the safety of rescue teams
- to facilitate the intervention of fire fighters and other rescue parties
Good practice in design for fire safety incorporates these aspects and more, in what is termed 'fire engineering' for large, complex structures that warrant additional design effort. Although prescribed data (such as dimensions for thickness and cover) may be used, the aim of fire engineered structures is to move away from the traditional methods and create a fire strategy dedicated to the project in hand, based for example on the building's design, how it will be used, fuel load and the probability of a fire occurring. For this reason, computer software is used to perform a probability analysis of the behavior of both fire and people.
From a whole building standpoint, concrete can satisfy the four principal objectives of fire safety through its inherent fire resistance and the utilisation of its structural continuity in fire engineered design.
Find out more
Follow the links below for more information.
- Further articles on 'Fire' are contained in Insist on a Concrete Home
- Comprehensive fire protection and safety with concrete Click here.
- Part B of the Irish Building & Fire Regulations Click here.
- Fire, World Trade Centre New York - NIST Report / Concrete Today, Dec 2006 Click here.
- Fire, Windsor Tower Madrid / Concrete Today, Nov 2005 Click here.
- Enniscorthy fire, Viking Wharf Developments / Concrete Today, Nov 2005 Click here.
- Fire destroys timber frame office under construction / Concrete Today, Nov 2005 Click here.
- Publication , Fire safety of concrete structures / Concrete Today, May 2005 Click here.
- The high cost of arson / Concrete Today, Nov 2005 Click here.
- Cardington (Precast) Fire Test - Pal Chana and Bill Price, BCA / Concrete Today, July 2003 Click here.
