Hazard Fires in tall buildings
Knowledge and understanding
|Fires in tall buildings||
Understand all associated hazard knowledge
The definition of tall buildings used in regulations varies by location. However, fire and rescue services, and other agencies, may adopt different terms for tall buildings based on their risk management planning and local procedure.
Common terms used to categorise tall buildings include:
- Medium-rise buildings - sometimes referred to as buildings over 18m, or buildings with 5 storeys or more
- High-rise buildings – sometimes referred to as buildings over 30m, or buildings with 8 storeys or more
- Supertall buildings – any building over 300m
Tall buildings may be residential, commercial or mixed use. The use of the building and its occupancy type will affect the evacuation strategy.
External firefighting or rescue operations may not be possible because of the height, position or design of floors. Appliances, ladders, lines and hose will be of limited use externally on the upper storeys of tall buildings. Therefore, additional firefighting facilities should be provided within the building. For more information on facilities for firefighters in tall buildings see:
- Supplementary information: Greater than 18m and less than 30m
- Supplementary information: Greater than 30m
Although hazards present at tall buildings are not unique, the risk or consequences of hazards may be increased due to physical and logistical restrictions. These enhanced hazards can be separated into the following categories.
The position of the fire floor may be difficult to identify externally. Floors may be labelled or referred to differently in each building. The accuracy of floor counts or assessment of building heights may be affected if the ground level varies around the building. The design or layout of the building may give a false indication of the number of storeys.
Unusual floor layouts, such as mezzanines or scissor flats, may make identification of access points harder, and may increase travel distances.
It may not be possible to gain accurate situational awareness using only the information available from ground level. For example, weather conditions at height may be different from the conditions at ground level. Key information, such as the effectiveness of compartmentation and internal conditions, may not be visible from the ground.
The information received from the fire control room, building occupants, or other sources, may contradict an incident commander’s situational awareness.
The ‘stack effect’ may cause smoke to travel in an unexpected manner, indicating a fire floor below the actual origin of the fire. See hazard Uncontrolled ventilation for more information.
Due to the distances involved, and attenuation caused by the structure, there may be communication dead zones that prevent radio transmissions being sent or received.
The weather conditions, especially those at height, should be taken into account when considering potential fire development and spread. The speed of wind generally increases with the height of the building and the lack of shelter from surrounding properties. This, along with the design of the building and its surroundings, may affect fire development and ventilation, sometimes in an unpredicted way.
The ability to control or mitigate ventilation may also be affected by:
- Building management systems, such as heating, ventilation and air conditioning (HVAC)
- The behaviour of people
- The need to access the affected floor, breaching protected staircases and creating ventilation pathways
- Windows that are sealed or designed to restrict the size of opening
- Windows or external wall panels failing
See hazard, Uncontrolled ventilation for more information.
Tall buildings may have fire engineering solutions designed to increase the available evacuation time or suppress fire development. Personnel may be unfamiliar with fire engineering solutions, which can be affected by operational activity. See hazard Fires in buildings with complex fire engineering.
External firefighting may be limited for tall buildings as it may not be possible to direct firefighting media to the seat of the fire if at height, or because of cladding or façade assemblies. For information see hazard External firespread.
The building's use and occupancy type will affect its evacuation strategy. In residential premises a ‘stay put’ policy, as detailed in the Local Government Association’s Fire safety in purpose-built blocks of flats may be considered appropriate, based on the levels of fire resistance for compartment walls
The use of occupant evacuation or escape strategies that are based on ‘stay put’ or ‘defend in place’ policies should be kept under review throughout the incident.
Commercial properties may also implement 'stay put' or similar strategies depending upon the occupancy type.
Identifying the evacuation strategy and establishing if it is being followed is important when determining operational plans. Personnel should be aware that the evacuation strategy may not be being followed and all available sources of information should be used to identify whether evacuation has occurred and to what extent.
Evacuation of the building may be affected by:
- The evacuation strategy
- Occupancy type
- Travel distance
- Development of the incident
- Restricted evacuation routes
This may result in people still being inside the building when the fire and rescue service arrives. For more information, see Hazard People.
Insufficient media to extinguish or control the fire
The potential misuse of firefighting facilities may make them unsuitable for use. See hazard Failure or inappropriate use of fixed installations. This can include firefighting lifts, rising mains and ventilation systems.
Rising mains and other firefighting facilities may have been tampered with, damaged, or poorly maintained. Firefighting facilities may not be present in older buildings.
Pressure at the branch will be reduced as height increases. The condition of a rising main will also affect the available pressure and flow rate. Where a single rising main is being used to supply multiple jets, opening branches will reduce the working pressure of other jets. The jets attached to the rising main at the highest point will be most affected.
Long travel distances for personnel, restricted access, congestion and the presence of people evacuating the building, particularly where only a single staircase is available for use, may delay the arrival of necessary resources.
Increased travel distances and arduous conditions will affect the physiological conditions of personnel, particularly those carrying equipment, including breathing apparatus (BA) sets. This may mean personnel cannot be deployed immediately after reaching a staging area or bridgehead. This should be considered when developing tactical plans. See hazard, Physiological stress for further information.
Limited space in protected areas will affect operations by:
- Restricting access and egress
- Reducing space for staging areas
- Requiring staging areas to be positioned further away, increasing travel distances
The reduction of space available to lay out hose, and the requirement to change direction or traverse floors, may cause kinking of hose or reduce available pressures, even when working from fixed installations.
Due to the restricted space or lack of ventilation, smoke and fire gases are more likely to reduce visibility throughout a compartment, corridors and shafts.
Working in restricted spaces and reduced visibility may increase the risk of cable entanglement. See hazard Cables.
Due to the complexity and size of some tall buildings, co-ordinating searches may be difficult. For further information, see hazard Lack of co-ordinated search.