Fire safety in buildings is one of the basic requirements for construction products in the EU Construction Products Regulation, CPR.
Fire safety in buildings primarily concerns personal safety, but also includes the protection of material values. Data from fire accidents indicates that smoke and toxic gases cause the majority of deaths. Smoke and toxic gases kill long before the temperature has risen or flames have developed. Consequently, the main design requirement from a personal safety perspective is that buildings are constructed and configured to ensure that people can get to safety and the emergency services have the capacity to respond in the event of a fire.
There are three components that lead to the development of fire in a building: oxygen, combustible material (fuel) and energy (heat). Usually there is access to both combustible material and oxygen. The third factor, energy, could result from the careless use of a flame, a spark or a cigarette etc. In order to prevent a combustion process, at least one of the three component parts of the fire triangle need to be eliminated.
If the fire emits heat energy faster than it can be expelled from the room exposed to the fire, the temperature in the room will rise rapidly. A flashover occurs when enough heat energy has accumulated. The fire then moves from the growth stage to becoming a fully developed fire. When this occurs, the fire spreads to all combustible surfaces in the area and flames leave the room through the openings. At this stage there will be no survivors in the room.
The most important factor from a flashover perspective is to check the heat release of the materials.
Fire development phase
In a fire development phase it is possible to distinguish three different stages
In the first stage of the fire (ignition) we see that the properties of the material play a very important role. Materials with good fire resistance properties provide no fuel for the fire and give people more time to leave the room. The smoke-generating properties of the materials must also be considered; toxic gases and poor visibility can kill before the fire is fully developed. Products with good fire properties emit no toxic gases or smoke.
In fire second stage (flame stage) the fire resistance of surrounding structures plays an important role in preventing the spread of fire. This stage lasts as long as there are combustible materials present.
The third stage (cooling stage) occurs when all the combustible materials have been burned up.
From ignition to fully developed fire
A typical house fire can start with a smouldering fire that might smoulder for hours before it flares up. After ignition, the temperature rises rapidly. When the smoke gas temperature reaches about 500 – 600 ⁰C the heat radiation is so high that all combustible surfaces in the room ignite causing a flashover. In modern homes, it normally takes 3-5 minutes from ignition (development of flames and smoke) to flashover, unless the fire dies due to lack of oxygen. After the flashover has turned into a fully-developed fire, the temperature can rise to 1,000 to 1,200 ⁰C.
The picture on the left shows a fire development phase over time and temperature and how various materials are affected.
If a building burns, this can cause considerable damage to property and death. Fire damage constitutes about half of all overall insurance payments. Water damage accounts for about 30 % and burglary 20 % of annual compensation payments. Both buildings and fixtures contribute to the spread of fire. Having effective fire protection significantly reduces the risk of fire. (Source: https://www.fkl.fi/materiaalipankki/esitysaineistot/Dokumentit/Vahinkotietoja_2013.ppt)
Fire protection in a building is divided into passive and active fire protection.
Passive fire protection is usually built into the structure itself ensuring the building can withstand fire for the stipulated time. The purpose is to protect the structure and the people occupying the building in case of fire by:
- Restricting or preventing internal and external fire and smoke spread.
- Maintaining the stability of the building.
- Ensuring a means of escape for those occupying the building.
The following components are considered as passive fire protection measures:
- safe distance from the fire to other buildings in the same property or neighbouring properties
- external surfaces on walls and ceilings that restrict the spread of fire
- division into fire safety units (fire compartments and fire cells) and fire partitioning structural elements
- internal surfaces on walls, floors and roofs that restrict the spread of fire
- penetrations in fire partitioning structural elements (fire doors and penetrations for installations, etc.)
- load-bearing structural elements
The choice of a building material and how the material is used to provide the required level of passive fire protection depends on two factors – how the material reacts in a fire and/or its fire resistance.
Active fire protection measures are characterised by them being activated by fire or by individuals. Depending on the use of a structural element, there may be different requirements for fire safety installations. Fire safety installations must be installed, inspected and maintained to ensure their reliability throughout the entire life of the building. Active fire protection usually provides alerts in the event of a fire to other fire protection measures, to people in the building and/or the emergency services.
Examples of active fire protection measures:
- automatic fire alarms
- evacuation alarms
- smoke alarms
- automatic extinguishing systems
- smoke ventilation
- door closers
- ventilation fire protection (dampers)