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by the NFCC


Utilities: Flooding

Hazard Knowledge

Water in buildings can compromise the safety of gas and electric supplies to both the building and appliances in the building, causing an increase in fire risk.

Electricity in buildings

Water is an excellent conductor of electricity, therefore there is a significant risk of electrocution if water has entered buildings. This may be caused by:

  • Touching or operating electrical installations or appliances while standing in water
  • Electrical installations or appliances being submerged in water, causing electrification of the water
  • Damaged electrical installations or appliances, causing electrification of the water

High-voltage electricity systems

Transmission system substations or overhead lines operate at significantly higher voltages (400kV or 275kV) than local distribution networks. Emergency services should keep away from transmission and distribution system substations and downed overhead line conductors that are affected by flooding until they receive notification from the owner or operator of the transmission system. In flood conditions it should be assumed that all high voltage equipment remains live.

For more information refer to Utilities and fuel – Electricity.

Most equipment in substations is designed to be unaffected by a degree of flooding, although there will be a safe operating flood-level limit. If water reaches this level, the network operator may have to switch off electricity supplies for safety reasons and to prevent damage to the equipment.

Personnel should assume that all equipment in substations presents a hazard, unless the distribution network operator or transmission operator confirms that it has been isolated. The environment around a flooded substation may contain hazards, such as hidden trenches.

Battery storage facilities

The presence of any renewable energy systems, such as turbines or photovoltaic (PV) systems, may indicate that the building or facility also has battery storage facilities.

For a building, battery storage could be located anywhere inside or outside; for a residential building, the garage is a common location. Although the installer should site the battery storage so that it cannot be affected by flooding, it should not be assumed that this advice has been followed or, if it has, that the flood has remained within predicted levels.

For a larger site, such as a solar farm, the location of the battery storage should have undergone a flood risk assessment at the planning stage. In an area that is subject to flooding, the battery storage may be housed in a structure that is raised from the ground. Similarly, it should not be assumed that a flood risk assessment was carried out, that advice from the assessment was followed or that the flood has remained within predicted levels.

Flooding of lithium-ion battery storage facilities may result in the risk of thermal runaway, an accelerating increase in temperature caused by chemical reactions, which could result in fire and the release of flammable and toxic gases and vapours. If this were to occur in an enclosed space, such as a garage, there would be an increased risk of an explosive atmosphere rapidly developing.


Most infrastructure has some dependence on electrical supply and although back-up systems may be available, they may also be affected by floodwater. For example, many hospital back-up generators are in basements that can be affected by flooding.

Gas and fuel oil

Gas appliances, such as boilers, may be unsafe to use if they or their vents or flues have been affected by floodwater. Floodwater can cause liquefied petroleum gas (LPG) or fuel oil bulk storage vessels and gas cylinders to move or detach from installation pipework.

Utility pipelines

Pipelines carrying gas, oil, water or sewage may be damaged by floodwater. For more information refer to Utilities and fuel – Pipeline failure.