A recent WTW seminar audience in London heard how bus manufacturers and operators are electrifying fleets and implementing safety measures.

There are currently around 2500 fully electric buses operating in the UK. With transportation estimated to account for about 25% of global greenhouse gas emissions, the UK bus sector has, to a large extent, been the 'green' standard bearer for other domestic transportation modes, despite only representing 3% of total sector emissions.

For now, electrification of bus fleets is clearly the way of the future as far as UK bus operators are concerned, not least in respect of playing their part in slowing or halting global warming.

Yet the UK is in the early stages of a journey and, as the UK bus sector continues its transformation, one issue in particular has regularly resurfaced from a risk management perspective – a perception among many insurers that battery-operated electric vehicles (BEVs) are more susceptible to high temperature events that damage either vehicles, depots, or both, and put the travelling public at risk. This is despite only four of the last 120 reported bus fires being linked to BEVs.

Separating hype from reality

Such concerns have undoubtedly been fuelled by the fire that destroyed six buses and caused some minor damage to Metroline's Potters Bar depot in Hertfordshire in May 2022, when in fact this event was due to human error.

Against this background of potential confusion about what the genuine risks may be – and potential reticence on the part of insurers to cover BEV risks – we at WTW felt it was time to bring manufacturers, operators and insurers together to separate fact from rumour and to find out exactly what steps the bus industry is taking to minimise any specific BEV risks.

The fire risks associated with BEVs potentially affect two principal areas of bus operations:

  • Loss of vehicles
  • Loss of depots and charging infrastructure

Vehicle considerations

Currently there are two alternative battery cell chemistries used in battery power packs; these being Lithium Iron Phosphate (LFP) batteries and Nickel Manganese Cobalt (NMC).

Research has identified battery packs utilising LFP cells as less susceptible to thermal runaway events than other types.

The bottom line is that manufacturers were able to articulate the steps they are taking to reduce the likelihood of a fire on a BEV occurring. These include the use of comprehensive battery monitoring systems and telematics to continually monitor that battery cells are operating within defined parameters, allowing early identification of events that could result in a thermal runaway event and allowing immediate actions to be taken to avoid or contain a vehicle fire.

Depot and charging infrastructure considerations

The depot and storage requirements for a BEV fleet are, of course, very different from those of diesel vehicles. For a start, the need for charging infrastructure and sufficient space and clearance for BEVs to access charging points safely reduces depot capacity by 10% to 15% based on experience to date. Ultimately it is likely this space will be recovered as diesel refuelling facilities become obsolete.

Another core consideration is whether to adopt DC or AC charging, or a mixture. Based on feedback from the seminar, there is a clear movement towards DC exclusively because if sufficient energy is available vehicles can be charged quicker as there is no reliance on a vehicle based system to convert the supply from AC to DC - thereby limiting charge capacity.

Many operators are not helped in adapting for BEVs as many depots are traditionally constructed, irregularly shaped buildings. Nonetheless, operators are united behind the emerging core principles of modern depot design that incorporate factors such as efficient and safe location of infrastructure, reducing tripping hazards, improved lighting, use of software based bus throughput and charging schedules, walkway locations, people safety, and the siting of shutdown switches.

Procedurally, operators are also extremely conscious of putting safety first. Charging intensity and monitoring, effective power isolation and verification when maintenance is taking place, data gathering and monitoring, and enhanced vehicle fire safety checks have all become routine parts of BEV operation.

Training is also a very high priority. That not only includes the technicians who are responsible for maintenance and charging - where operators are typically insisting they are trained to at least the same level as the manufacturers' staff. Operators confirm all depot staff receive training on revised access and emergency procedures where BEVs are present. Furthermore, several companies say they offer driver training and incentivisation programmes to encourage safer driving and awareness of the different driving styles required for an electric battery vehicle.

Ian Foster, Director of Engineering Strategy for Metroline, highlighted another area where operators are enhancing BEV safety understanding in the wake of the Potters Bar fire. That is the potential impact of BEV fire bi-products on the surrounding environment, such as chemical concentrations in water courses after attendance by the fire brigade. Effective drainage isolation is key to prevent contamination and environmental issues.

Summing up his views of what operators can do and are doing to manage fire risk, Ralph Roberts, Chief Executive Officer of McGills Bus Services, outlined a four-part doctrine that they follow.

  • Evaluate the whole supplier package (chemistry, packaging, battery management system strategy, research and development history, number of units, mileage)
  • Train staff; invest in diagnostics; build the relationship with the manufacturer
  • Monitor, evaluate, repeat
  • Do not rest on laurels

How can the insurance market help?

A risk assessment perspective: Andrew Millinship – Transport Risk Management Executive, WTW

For now, the number of insurers underwriting bus industry risks remains limited. However, with the steady growth in the expected numbers of BEVs on UK roads, the excellent enhanced risk management manufacturers and operators have implemented and the range of impacted classes, including property, there should be opportunities in the years ahead for insurers that are willing to take a closer look under the bonnet of the sector.

WTW comparative assessment of fire risk in diesel and electric buses

Risk Scenario Likelihood
(1 - 5)
(1 - 5)
Risk Scenario Unexpected ignition of an ICE powered bus in a depot at night resulting in a major incident 2 2 4
Unexpected ignition of a BEV in a depot at night resulting in a major incident 1 4 4

Figure 1: WTW comparative assessment of fire risk in diesel and electric buses (For illustrative purposes only)

Any risk materialising is a balance between likelihood and severity as shown in Figure 2. And while the severity of an incident if it occurs involving BEVs could be greater because a thermal event could take longer to bring under control, our assessment, based on the historical information and the work the industry is undertaking to continue to understand and mitigate the risks is that the likelihood of a BEV being the source of a fire in a depot is lower than a conventional diesel-powered bus.

"It's evident that the UK bus industry is actively collaborating to manage BEV fire risk, reducing the likelihood of an incident occurring."

Anthony Monaghan | GB Transportation Leader, WTW

It's evident that the UK bus industry is actively collaborating to manage BEV fire risk, reducing the likelihood of an incident occurring.

Andrew Millinship highlighted in his presentation the ongoing work WTW is undertaking to support its clients and articulate risk back to the insurance market, by undertaking risk exposure assessments

These assessments involve a detailed review of implementation, installations, and the way data is being used to identify, manage, and control risk.

This collaboration reinforces what we heard throughout the seminar by ensuring effective risk management remains paramount as clients transition into this new technology.

And it was clear from what we heard that manufacturers and operators are already collaborating, not only with the design of vehicles to meet requirements but also battery technology and safety.

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