Fire Safety Defined
The National Building Code of Canada1 (NBCC) defines fire safety under Objective OS12 as "an objective of this code is to limit the probability that as a result of the design or construction of the building, a person in or adjacent to a building will be exposed to an unacceptable risk of ingury due to fire."
In simpler terms, fire safety is the reduction of the potential for harm to life as a result of fire in buildings. Although the potential for being killed or injured in a fire cannot be completely eliminated, fire safety in a building can be achieved through proven building design features intended to minimise the risk of harm to people from fire to the greatest extent possible.
Designing a building to ensure minimal risk or to meet a prescribed level of safety from fire is more complex than just the simple consideration of what building materials will be used in construction of the building. 3,4,5,6. Many factors must be considered including the use of the building, the number of occupants, how easily they can exit the building in case of a fire and how a fire can be contained.
The NBCC only regulates those elements which are part of the building construction. The building contents found in any building are typically not regulated by the NBCC but in some cases are regulated by the National Fire Code of Canada3. The classification of buildings or parts of buildings according to their intended use accounts for:
- the quantity and type of combustible materials likely to be present (potential fire load)
- the number of persons likely to be exposed to the threat of fire
- the area of the building
- the height of the building
This classification is the starting point in determining which fire safety requirements apply to a particular building.
- the type of building construction
- the level of fire protection
- the degree of structural protection against fire spread between parts of a building that are used for different purposes
Even materials that do not sustain fire do not guarantee the safety of a structure. Steel, for instance, quickly loses its strength when heated and its yield point decreases significantly as it absorbs heat, endangering the stability of the structure (Graph 1). An unprotected, conventional steel joist system will fail in less than 10 minutes under standard laboratory fire exposure test methods, while a conventional wood joist floor system can last up to 15 minutes.
Even reinforced concrete is not immune to fire. Though concrete structures have rarely collapsed, concrete will spall under elevated temperatures, exposing the steel reinforcement and weakening structural members.
Graph 1: Steel loses strength at elevated temperatures
It is generally recognized then, that there is really no such thing as a fireproof building. Fires can occur in any type of structure. The severity of a fire, however, is contingent on the ability of a construction to:
- confine the fire
- limit its effects on the supporting structure
- control the spread of smoke and gases
To varying degrees, any type of construction can be designed as a system, that is, a combination of construction assemblies, to limit the effects of fire. This allows occupants sufficient time to escape the building and for firefighters to safely reach the seat of the fire.
Occupant safety also depends on other parameters such as detection and exit paths, and the use of automatic fire suppression systems such as sprinklers. These concepts form the basis of the NBCC.
- 1. National Building Code of Canada, NRCC No. 38726, National Research Council, Ottawa, ON, 1995.
- 2. Objective-Based Codes: A Consultation on the Proposed Objectives, Structure and Cycle of the National Building Code, National Research Council, Ottawa, ON, 2000.
- 3. National Fire Code of Canada, NRCC No. 38727, National Research Council of Canada, Ottawa, ON, 1995.
- Fitzgerald, Robert W., Fundamentals of Fire Safe Building Design, Fire Protection Handbook, National Fire Protection Association, Quincy, MA, 1997.
- Watts, J.M. (Jr); Systems Concepts For Building Fire Safety, Fire Protection Handbook, National Fire Protection Association, Quincy, MA, 1997.
- Rowe, W.D.; Assessing the Risk of Fire Systemically ASTM STP 762, Fire Risk Assessment, American Society for Testing and Materials, West Conshohocken, PA, 1982.