A burning issue

The Office for Zero Emission Vehicles has published guidance on electric vehicle fires in covered car parks

battery cells which leads to the decomposition of battery elements and can lead to the onset of fire within the battery.

The review reveals that there are both similarities and differences between EV and internal combustion engine vehicle (ICEV) fires. Some of the different risks associated with EVs include:

• reignition as fires which involve a vehicle battery can reignite hours or days after the initial fire burned in a process called thermal runaway

• compressed gas venting causing jet flaming or vapour cloud explosions –compressed gases can vent from a battery and if ignited can result in flash fires or directional jet flames, alternatively compressed gases can vent from a battery, and if accumulating in a confined space at the right mixture could result in a vapour cloud explosion (VCE).

Suppressing a fire involving the battery requires different firefighting techniques and equipment and can take longer and in some instances may not be feasible until all flammable material has burned. The battery material and smoke produced when involving the battery can be more toxic, which contaminates firefighting water run-off.

Designing mitigation measures

The interim guidance document reviews the hazards that could lead to a fire within an EV parked in a covered car park; and, within an EV whilst charging within a covered car park. For each hazard, mitigation measures are considered which could reduce the likelihood of a fire occurring involving an EV.

The document considers what mitigation measures could be introduced to minimise the impact of a fire on the occupants, the fire service, the car park structure, other vehicles, adjacent buildings, and the environment.

Mitigation measures are ranked using the ERIC (eliminate, reduce, isolate, control) hierarchy.

Planning for an EV future

Arup’s review states that available empirical evidence to date suggests that fires in EVs are less likely to occur than in hybrid vehicles and petrol or diesel vehicles. However, this will need to be monitored as fire risk may increase as cars age, and as EVs become more affordable to a wider range of drivers.

The guide provides two case studies, one for existing basement car parks where EV chargepoints were installed, and a new multi-storey car park that is future-proofed for 100% chargepoint coverage.

The guidance acknowledges different measures to mitigate an EV fire:

• mitigation relating to electrical, mechanical and thermal abuse

• increased preventative methods such as crash protection for chargepoints; thermal monitoring cameras; and watersuppression methods

• consideration for spacing

• consideration for ventilation.

The document advises that car park owners and operators should carry out a fire risk assessment to determine whether the introduction of EVs or chargepoints into their car park creates new or additional hazards and whether any of the mitigation measures discussed within this document could be implemented.