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by the NFCC


Below ground structures

Hazard Knowledge

A below ground structure is either partially or fully under the ground, or under another type of covering, such as concrete. Incidents in these types of structures may present significant hazards for emergency responders and the public.

Below ground structures vary greatly in depth, surface area and design, often presenting hazards such as:

  • Restricted access and egress
  • Reduced visibility
  • Extreme temperatures
  • Complex and extensive layouts

Some structures are modern and well-documented. However, older buildings may be lacking in plans; they may also, either due to their design or adaptation, not conform to current building standards. Some may come under heritage designation or be tourist attractions, while others may have no official public access.

Below ground structures include:

  • Pedestrian areas
  • Waterways
  • Road, rail or pedestrian tunnels
  • Utility provision
  • Car parks
  • Mines
  • Bunkers and underground storage facilities
  • Military installations
  • Basements
  • Cellars
  • Catacombs
  • Vaults
  • Cold stores

Such environments can be under construction, operational, disused or abandoned. Various types of incidents, either accidental or deliberate, may occur in below ground structures, including:

  • Fire in structure
  • Fire in vehicles
  • Vehicle collisions, including road or rail vehicles
  • Derailments
  • People trapped by or in vehicles or machinery
  • People lost or fallen into below ground structure
  • Flooding or inundation
  • Hazardous materials
  • Explosions
  • Collapse


Tunnels include those used for road, rail, waterway and pedestrian travel or for transporting goods and services, and will be of varying size and complexity.

Tunnels used for pedestrian access do not present many incidents for fire and rescue services. However, tunnels that form part of the transport infrastructure systems, including road and rail, more frequently require the assistance of the fire and rescue service. Incidents include vehicle collisions and fires in road tunnels, rail vehicle derailments and fires in rail tunnels, and fires on board vessels in waterway tunnels.

Hazards of working in tunnels include:

  • Disorientation, due to:
    • Repetition of features
    • Lack of wayfinder indicators, such as signage or landmarks
  • Reduced visibility
  • Restricted communication
  • Extended access, egress and evacuation distances
  • High temperatures

For further information on rail tunnel incidents refer to Transport – Rail-related incidents in tunnels.

Operational mines

Mines present various hazards, including:

The incident may also be affected by the impact of adverse weather conditions on the environment below ground.

For further information refer to Industry supplementary information: Mines and quarries

Fire and rescue services may be called to mining-related incidents, such as partial collapse of a building or a person or animal falling into old mine workings. There may be oxygen-deficient atmospheres or gases that are toxic or explosive. Areas around the original collapse may be unstable and subject to collapse.


The UK has an extensive system of natural caves, coastal and inland, with new caves or extensions to caves always being discovered. Caving, also known as potholing, is the recreational exploration of caves and potholes. Depending on the ability and experience of people participating in this activity, the caves may be well-known to them or previously unexplored. Caves may also be explored for scientific or historical research.

There are also incidents when people accidentally fall into caves, for example due to unstable ground or the cave entrance being obscured.

The incident may also be affected by the impact of the weather on the environment below ground; cave systems may flood rapidly and with little warning.

Abandoned mines

Some parts of the UK have extensive disused mining systems, some of which are accessible to the public. The exploration of abandoned mines is sometimes arranged as an activity through caving clubs. Although people may have some knowledge and experience of these environments, it is an uncontrolled, unregulated and dangerous activity.

There are also incidents when people accidentally fall into abandoned mines or mineshafts, due to unstable ground or where the mine entrance or mineshaft are obscured.

 Armed forces and civil protection below ground structures

The use of structures that are under military control is wide-ranging; they are not usually accessible by the general public or emergency services, as they are subject to security protocols.

Below ground armed forces or civilian protection structures have various uses including munition storage, command and control, equipment testing or accommodation. They may have several below ground levels or be on one level with a single entrance and exit. They may have ventilation and heating systems, be fully self-contained, and have pedestrian or vehicle access.

Decommissioned below ground structures may either be sealed up, or ownership transferred to another organisation to maintain and run for other purposes. One use may be that of historical education, in the form of a museum or historical society, such as the underground tunnels and command facilities at Dover. Others may be sold to private companies for a variety of purposes, such as document storage or housing of remote electronic equipment.

Critical national infrastructure

Some below ground environments may be used as a conduit for critical national infrastructure. An incident adjacent to these systems could have a potentially significant effect on the maintenance of essential services. Consideration should be given to the impact on:

  • National transport networks, with local, national and international dependencies, principally involving road and rail use
  • Telecommunications and power systems
  • Water treatment systems
  • Storage of significant items and use by industries
  • Potential for widespread flooding resulting from the inundation of tunnels
  • Tunnels being put to more than one use, for example a transport tunnel used to carry telecommunications cables, thereby compounding the community impact of a significant incident

For further information refer to the Centre for the Protection of the National Infrastructure: Critical National Infrastructure.