Unstable ground or surfaces
Unstable ground or surfaces can be hazardous as they may give way when downward pressure is applied. The ground or surface may be soft enough to allow people to sink, until movement becomes impossible. The ground or surface might have a layer of relatively firm ground covering softer material, but this may break through if sufficient pressure is applied.
Attempting to work on unstable ground or surfaces without the appropriate training, skills and equipment may result in serious injury to personnel.
Fire and rescue service vehicles may become trapped or stranded on unstable ground or surfaces. On sites that do not have designated hard standing or purpose-made vehicle routes, ground conditions can quickly deteriorate. For more information refer to Operations – Driving to incidents.
This hazard covers unstable ground or surfaces that could give way, break, collapse or allow people, equipment or vehicles to sink into or become stuck in. This includes:
- Steep slopes
- Rubble or debris, for example following a structural collapse
- Free-flowing solids, such as soil, sugar, grain or rice; if these are present in a confined space, refer to Height, structures and confined space – Confined space environment
Other related guidance includes:
- Height, structures and confined spaces – Fragile surfaces, such as roofs and structural elements
- Height, structures and confined spaces – Unstable or collapsed natural or built environments, such as trenches, excavations and pits
- Height, structures and confined spaces – Unstable or collapsed structure, such as the geological causes of instability or collapse
- Industry – Stacked materials, such as manufactured or waste materials, including landfill sites
If the incident on unstable ground or surfaces involves a casualty, refer to Search, rescue and casualty care – Casualty on unstable ground. If the incident on unstable ground involves an animal, refer to Incidents involving animals - Animal in water, on ice, or on unstable ground.
Ground or surfaces may become unstable due to:
- The effects of the incident, for example peat or waste burning away under the surface
- The introduction of water to the ground; this could be from:
- Operational activity, for example the application of large volumes of water to a soluble or semi-soluble substance, such as when carrying out a mud rescue
- Adverse weather
- Tidal water
- Thawing of an area where the ground or surface has been frozen
- Geological activity, for example erosion that has undermined the integrity of the ground
- Vibration from on-site machinery or on-site vehicles
- Severe impact
- Heavy loads close to an edge
- Partial or full structural collapse
There is frequently little or no indication of the transition between stable and unstable ground or surfaces. If there is evidence of structural collapse, this may indicate that the surrounding ground is unstable.
The following hazards and their associated control measures may also apply when working near unstable ground or surfaces:
- Operations – Working near water or other liquids
- Height, structures and confined spaces – Unguarded edges
Ice should never be considered safe to walk on. The thickness may vary depending on water depth, temperature and microclimates. It can be difficult to determine the depth and flow of water underneath the ice. People can fall through ice and travel a significant distance below the surface or become trapped beneath it, thereby requiring rescue from water.
It may be difficult to access the scene of operations through deep mud, as walking may become impossible without specialist equipment, such as mud shoes. The distance to the scene of operations can make the situation more difficult, as can working in reduced visibility. The mud may also be subject to tidal changes and quickly become submerged.
Unstable ground or surfaces may be due to geological movement. The cause may not be known and could be minor, but the history of the area may indicate a need to be aware of potential or further ground movement. For example, in areas of known mining, the movement may be caused by the collapse of old workings.
Knowledge and understanding
Understand all associated hazard knowledge
- Control measureSpecialist resource: Unstable surfaces and landslides
- Control measureSafe system of work: Unstable ground or surfaces