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Underground structures

An underground structure can be defined as:

'A natural or manmade structure, where all or part is below ground level or covered, where people can resort to for work or pleasure. This includes underpasses or associated shafts.'

Although some non-fire and rescue service organisations may use other definitions to satisfy their own requirements, this definition is the most appropriate as a basis for fire and rescue service risk assessments and planning.

Fire and rescue services attend incidents involving a variety of underground structures, particularly in tunnels, where the danger to operational personnel and the public is significant.

This guidance deals with the hazards present in the subsurface environment, providing a number of control measures and links to other National Operational Guidance.

Manmade subsurface structures vary greatly in depth, surface area and design. These often have restricted access and egress, poor or no lighting, the potential for extreme temperatures and complex and extensive topography.

Some structures are modern and well documented, while others are very old and have few or no plans. Some may come under heritage designation or be tourist attractions in their own right, while others may have no official public access.

The subsurface environment includes:

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

Such environments can be under construction, operational, disused or abandoned.

Various types of incident may occur in tunnel and underground infrastructure:

  • Fire in infrastructure
  • Fire in vehicles
  • Collisions, including road traffic collisions or derailments
  • People trapped on or in vehicles or machinery
  • People lost or fallen into underground structure
  • Flooding/inundation
  • Hazardous materials (Hazmat)
  • Explosions
  • Collapse
  • Aggressive acts involving any of the above.


Tunnels include those used for road, rail, waterway and pedestrian travel or for transporting goods and services. These may be in full operational use or disused, new or historic, and of varying size and complexity.

In general, tunnels used for pedestrian access do not present many incidents for fire and rescue services, unlike tunnels used for transport infrastructure systems, such as road and rail. A number of incidents in the UK and worldwide have occurred in or around a tunnel where the resolution of the incident has been led by fire and rescue services. These have included collisions and fires in road tunnels, derailments, fires in rail tunnels and fires in boats in waterway tunnels.

Where tunnels have public access, fire and rescue services will normally have prior knowledge and understanding of the hazards presented. There may be pre-planned arrangements for attendance and the actions to be taken in the event of an incident.

Tunnels under construction or renovation

This guidance focuses on the construction and operational use of existing tunnels, but much of the information may be relevant to disused or decommissioned tunnels.

Tunnels under renovation, restoration or construction can present challenging and unusual hazards. Fire and rescue services should ensure that all reasonable arrangements are made to liaise with those operating the tunnel system, and should review Site-Specific Risk Information (SSRI) and response plans so that they reflect the current situation.

As construction nears completion, it will be necessary to re-evaluate information previously collated and to work with infrastructure managers, tunnel user representatives, regulators and other multi-agency partners to ensure that the final emergency plan is validated. Plan validation should take place before commissioning exercises and the official opening, through exercises using the access and systems that are in place.

Many aspects of the construction of an underground structure fall outside the knowledge and skills of fire and rescue service personnel. It is recommended that fire and rescue services liaise with experts to ensure that proposals fulfil statutory duties, legal requirements and specific construction standards and that the services required to support a fire and rescue service incident are established.

Sewers and associated underground assets

Fire and rescue services may be called on to attend incidents in sewers and associated underground assets operated by a number of sewage or wastewater undertakers. Refer to National Operational Guidance: Operations for further information about water and sewage services.

Some operations involving sewage systems will be subject to the Confined Space Regulations because they present one or more of the specified risks that define a confined space. These areas may present a number of other hazards, such as working at height and biological contamination.

Sewage or wastewater undertakers should have emergency procedures for their employees and subcontracted staff working in those environments. The assistance that fire and rescue services can provide will depend on the knowledge, training, skills and equipment of the individual services. It may be necessary to seek specialist assistance, such as urban search and rescue (USAR).

Operational mines

A mine is defined as:

'An excavation or system of excavations (including all excavations to which a common system of ventilation is provided) made for the purpose of, or in connection with, the extraction, wholly or substantially by means involving persons working below ground, of minerals (in their natural state or in solution or suspension); or mineral products.'

Depending on the type of incident at a mine, first responders may be limited in their ability to deal with the situation. It may be necessary to seek specialist assistance from teams skilled in rope rescue, confined space rescue, mine rescue or urban search and rescue.

Mines present various hazards, including:

  • Complex layout
  • Lengthy travel distances
  • Vertical shafts, some hundreds of metres deep
  • Totally dark environments
  • Traverses and climbs
  • Constricted and restricted passages and squeezes
  • Static and running water (sometimes completely submerging the passageways)
  • Mud and unstable rocks

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

Fire and rescue services may need to provide equipment and personnel to assist specialist organisations, rather than directly use fire and rescue personnel to enter and operate as the primary rescuers.

The British Geological Survey (BGS) continually monitors the location and nature of active onshore mineral workings in the UK and publishes this information in its Directory of Mines and Quarries. A number of mines are used for other purposes such as tourism and storage of documents, computer records, wine and cheese.

Under the Mines Regulations 2014, the mine operator needs to make suitable arrangements for the escape and rescue of persons from the mine; this may include using safe havens in the mine. Arrangements for rescue may include using companies that provide specialist rescue training, trained rescue staff at mines, cave rescue teams in locations such as tourist mines and, in some instances, fire and rescue services.

Although large-scale coal mining operations have ceased in the UK, there may be hazards to people, livestock, property and the environment from:

  • Collapse of mine entries and shallow coal mine workings (subsidence)
  • Emissions of mine gases
  • Incidents of spontaneous combustion
  • Discharge of water from abandoned coal mines

The Coal Authority manages the effects of past coal mining, including subsidence damage claims that are not the responsibility of licensed coal mine operators. It deals with mine water pollution and other mining legacy issues.

Fire and rescue services need to be aware that they may be called to some mining-related surface 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.

As large-scale incidents involving mine or mine surface hazards are infrequent, fire and rescue services should carry out joint exercises with the mine operator to acquire the skills and techniques required.

At all mine and mine surface incidents, it is important to consider the need to preserve the scene for investigation purposes. Fire and rescue services need to be aware that other organisations may have to carry out their own investigations. The police, British Transport Police, Office of Road and Rail, Rail Accident Investigation Branch, Coal Authority, Health and Safety Executive and utility companies, as well as local agencies, will all need to be considered when dealing with mine and mine surface-related incidents.

Caves and recreational underground environments

Depending on the type of incident at caves or recreational underground environments, first responders may be limited in their ability to deal with the situation. It may be necessary to seek specialist assistance from teams skilled in rope rescue, confined space rescue, cave rescue or urban search and rescue.

Attendance and intervention will often be led by attending cave rescue specialists, but there may be occasions when fire and rescue services have the ability and resources to intervene. For example, in the case of a person falling into a vertical entry point at the start of a cave system, the fire and rescue service personnel may have the rope rescue capability to immediately access and recover the casualty.

Abandoned mines and unfamiliar caves

Beneath the surface of the UK lie hundreds of miles of natural caves and abandoned but accessible mine workings and other tunnels. Each year, new caves or extensions to caves are discovered and old mines and passages in mines are rediscovered.

Almost all the caves and many of the disused mines occur in limestone areas, but all counties contain at least some disused mines that are accessed by people including recreational explorers, industrial historians and geologists.

Although the majority of those people have some knowledge and experience of these environments, it is an uncontrolled and unregulated pastime. As skills and understanding of the hazards vary widely, there is the potential for incidents to can become life-threatening.

Cave rescue

The British Cave Rescue Council (BCRC) is the body recognised by UK governments as providing the underground search and rescue service in caves and disused mines. It has a seat on the UK Search and Rescue Operators Group, where it meets regularly with other national search and rescue operators, including the Chief Fire Officers Association (CFOA).

The responsibility for inland rescue usually rests with the police under their general public order powers and responsibilities. However, if the police are unable to conduct searches or rescues in caves and disused mines, they will rely on the members of the BCRC.

BCRC members are also called on by the police to assist in animal rescues and occasionally to carry out other types of search to assist investigations.

The range of underground environments that may be accessed for recreational purposes is wide; some will have been formed by erosion within natural geological formations and others will have been created by mining or tunnelling operations. Many of the entry points to these sites will be in locations that are difficult to find and access and that may require approach by specialist vehicles or on foot over significant distances.

Fire and rescue services may need to provide equipment and personnel to assist specialist organisations, rather than directly use fire and rescue personnel to enter and operate as the primary rescuers.

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

Armed forces and civil protection underground structures

Many underground structures are part of, or have been developed by, military or civil protection organisations; some are still in operation while others have been decommissioned or sold on to private organisations. Some older sites have fallen into various states of disrepair or dereliction and others have since become accessible to members of the public.

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.

Some of those in use are fully occupied, while others are remote stations that are only visited occasionally. Some are only visited by staff to check or maintain equipment or to assess the security of the site. Other sites provide resilience and have only occasional use, but there are usually procedures in place to ensure the safety of those who visit.

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

The relevant Defence Fire Risk Management Organisation (DFRMO) may provide normal emergency response activities for all operational military establishments.

Structures may have been decommissioned and either sealed or handed to another organisation to maintain and run for other purposes. One use of such establishments is for historical education via 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.

Structures in private or commercial use will be required to maintain a safe system of work for any working staff or visiting public and, depending on the use and levels of commercial security and sensitivity, will include notification and collaboration with local fire and rescue services.

Fire and rescue services should work with the establishment's management to provide additional assistance if required, to establish a structured response plan and arrange regular joint exercises and familiarisation of sites to ensure all partners have a clear understanding of the extent and limitations of their role and responsibilities.

Critical national infrastructure

Some subsurface 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