Hazard Fires in basements
Knowledge and understanding
|Fires in basements||
Understand all associated hazard knowledge
Any floor that is more than 1.2m below ground level may be classed as a basement. Basements are also defined as areas requiring an upward means of escape.
A shallow basement can be described as having its lowest floor not more than 10m below the normal firefighting access level.
A deep basement can be described as having its lowest floor more than 10m below the firefighting access level.
Basements may not be clearly visible to the fire and rescue service on arrival. The access route from outside the building or from within the building may not be clear and there may be a lack of natural light. Access routes may also be the smoke egress route.
Fires in buildings with basements present a range of logistical and physical challenges. Incidents within these buildings can present an extremely hazardous environment for firefighters.
Incidents, especially in deep basements, may be constrained by the finite capacity of personnel and equipment. Additional time and resources may be required to implement safe systems of work for operations at below ground levels.
Sectorisation for fires in buildings with basements may require special consideration – refer to the National Operational Guidance: Foundation for incident command for further information about sectorisation including the use of lobby sectors.
Fire behaviour in basements is unpredictable and they may behave in a similar way to highly insulated buildings; the highly insulated space may allow for more intense and rapid fire growth.
There is likely to be a lack of ventilation within the basement, however some ventilation may be provided by means of pavement lights and doors. There is a risk of rapid fire development or backdraft during opening of such vents during firefighting operations.
When accessing a fire compartment from above, responders may be required to descend through hot fire gases. This ‘heat layer’ will usually be the hottest section of a compartment fire and may increase internal body temperature of responders, affect the integrity of firefighting lines and damage PPE.
Because vision may be obscured and thermal imaging may be ineffective, it will not always be possible to identify the depth of the hot fire gas layer.
The additional exposure to heat may increase or expedite the effects of physiological stress. See, National Operational Guidance- Operations: Physiological stress
Where there is, a basement consisting of more than one storey, only the storey directly below the ground floor is required to be of fire resisting construction
Access may be limited, although there may be external access routes into the basement horizontally, in addition to vertical access inside the building.
It is likely that each basement level will be separated by a line of fire-resisting construction up to and including separation from the ground level storey.
Considerations are similar as those for shallow basements; however, there may be firefighting facilities present such as:
- Firefighting shaft containing wet falling mains
- Foam inlets
- Firefighting lifts and firefighting stairs to provide access to every basement level
- Firefighting shafts with a pressure differential system
- Natural or mechanical ventilation shafts