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Vehicle in water

Hazard Knowledge

Vehicles in water may be encountered by personnel during rescues from vehicles that have entered a body of water, or vehicles that have become partially submerged by rising flood water or tides. In low levels of water vehicles may be entirely safe but personnel should be aware that as water levels rise, previously stable cars may become buoyant. Vehicles, even larger vehicles like buses, can begin to float in low levels of water.

Even with every window open a car entering a body of water may initially float away from the point of entry. The electrical systems and powered windows may still work for a time, even if a vehicle is full of water. Once a vehicle is full of water other factors will influence how it behaves, including the underlying surface, water current and the weight and distribution of passengers or load.

During periods of inundation, uncontrolled flows of water can pick up vehicles and propel them at speed on to or into hazardous areas, including electrical installations, deeper water, areas where members of the public are trapped or where rescuers are working.

Depending on ground conditions, a partially buoyant vehicle may pivot around its heaviest point. Eventually, vehicles are likely to move to a position where its heaviest part is pointed into the flow. Although a vehicle may appear stable in this position no vehicle in water should be considered safe until secured as changes in flow, ground conditions, changes in load position in a car or release by an object such as a branch or rock holding a vehicle in position may cause sudden movement.

A vehicle’s orientation to the flow will affect its movement. If the vehicle is side-on to the current on a solid river bed in flowing water, a vehicle roll is almost inevitable. Even in slow currents a vehicle may be rolled a considerable distance. If a vehicle lands on its wheels on a soft river bottom each tyre will create an eddy. This may scoop out mud and sand causing the vehicle to settle onto its chassis.

If a vehicle comes to rest or becomes wedged against an obstacle, an eddy may present a seemingly safe area to work from. However, the obstacle or object may suddenly move due to its compromised stability causing the vehicle to rotate, roll or move whilst rescue operations are being attempted. Even seemingly stable vehicles may need to be secured.

Redistribution or removal of the load from a vehicle may cause it to flip or move suddenly. Responders should be aware of this risk and should avoid removing weight from a vehicle before stabilising and securing it. Movement of casualties within a buoyant vehicle may cause unexpected vehicle movements.

Any attempt to gain access to a vehicle or any sudden movement of the vehicle may trigger a vehicle’s supplementary restraint systems (SRS). These systems may present a direct hazard to personnel and any movement of the vehicle created by activation of the device may affect the vehicle’s stability.

Water conditions will dictate the best direction to approach an unsecured vehicle in water. Depending on the hydrology, flow of water around a vehicle, ground conditions and depth, a car may move or roll which will endanger personnel approaching from downstream. In flowing water, currents will pass under and around the vehicle creating a strainer or siphon-like effect. Creating openings on the upstream side may be difficult and affect the stability of the vehicle

Each situation will need to be carefully assessed to identify the appropriate approach angle and method.

When evacuating or rescuing people consider the effect of pets and other animals. Controlling the movement and behaviour of animals during rescue attempts may not be possible and their movement may affect the stability of the vehicle. Animals may be distressed by the incident and require additional restraint to prevent them posing a hazard to rescuers.

For guidance on extricating animals from vehicles see National Operational Guidance: Incidents involving animals