Fire does not normally start in two different places in a building at the same time but may propagate through riser ducts or shafts. At the initial state, fire poses a danger only in the part of the building in which it starts. Thus, an important principle in the design of fire safety is to contain the fire within a compartment and to extinguish it while preventing fire and smoke from spreading to other parts of the building.
The primary danger associated with fire in its early stage is not flame but smoke and noxious gases produced by the fire. A person can withstand a smoky situation for only about 3 minutes after which he will faint or die. Smoke also obscures the way to escape routes and exits and impede movement. Because of the danger posed by smoke and fumes, fire safety design must limit the spread of smoke and fumes especially through concealed spaces in buildings.
Basic Principles of Design
- In the event of fire, the occupants of any part of a building must be able to escape safely without reliance on external assistance or rescue by the fire service and without having to manipulate appliance or apparatus.
- The design of means of egress should consider the form of the building, the activities inside the building, the likelihood of fire and the potential of fire spread through the building. Building regulation stipulates differing requirements for different purpose groups of buildings and differing requirements for sprinklered and non-sprinklered buildings.
- There should be alternative means of egress in most situation as there is always the possibility of an escape being impassable by fire or smoke. Single staircase (with no alternative means of egress) and dead ends are allowed under certain conditions where fire risk is low because of the small size and low height of the building and the small number of persons accommodated within it.
- The provision of an appropriate warning and fire extinguishing systems should be an essential element in the overall strategy for safety.
In addition to safety and egress of occupants, practical and safe access to the building by fire fighters and rescue personnel and equipment to stage rescue, fire containment and extinguishment has to be provided.
An escape should lead to a place of safety. The ultimate place of safety is the open air outside the building, clear from the effects of the fire. In large complexes where this is not possible, it should be possible to reach a place or reasonable safety such as a protected staircase or a protected corridor from where people can travel in relative safety to a final exit. For this to be possible, protected staircase and protected corridor must not contain combustible materials and are designed to keep out flame, smoke and gases. The maximum permissible distance of an unprotected escape route is worked out by the period a person exposed to fire and smoke can reasonably by expected to endure when escaping a fire.