Minimising fire risk for Zero Emission Buses

Fire occurs in all types of vehicles but an electric vehicle fire, particularly one with a large battery, can be a tricky thing to manage. For one, unlike petrol or diesel, an electric battery fire can take a long time to extinguish. The other is that with any new technology, there can be a perception that it is less safe than the old technology.

Joe Paveley, WSP’s Technical Director for Fire Engineering says that while there is little data available on Zero Emission Buses, the preliminary findings seem to show that they do not catch fire at a higher rate than petrol or diesel buses.

“Electric buses are already on the roads in Australia and in many places around the world. Any vehicle has fire risks and the job of manufacturers, fleet operators and infrastructure managers is to minimise that risk as much as practicable.

“There is a lot of research now taking place to assess the risk of battery electric vehicles - one is the design of batteries themselves and how they can improve performance and fire safety.

“Excluding certain battery types as they're more fire prone than others is the first step. We don’t build battery electric buses in Australia so we are at the mercy of what overseas manufacturers are doing, but when sourcing activities are occurring, going with a reputable manufacturer who can show fire safety standards is a must.

“You also want a battery monitoring system that allows for real-time monitoring so drivers and fleet managers can see if there are issues before the battery ignites.”

Andrew Ah Toy, WSP’s Senior Principal – Infrastructure Investment Decisions says the real-time monitoring, particularly when charging is crucial to fire safety.

“If there is a fault or damage to the battery and thermal runaway occurs, the battery can ignite and start to burn itself and the surrounding materials. Vehicle batteries contain a large amount of chemical energy, so unlike a diesel or compressed natural gas fire, even if you extinguish the fire, it can reignite again from the residual energy in the battery.

“There’s a lot of specification and design requirements that can be implemented before a vehicle goes out on the road. Getting batteries that are designed for public transport use, installing fire suppression linings and systems, providing onboard cut-off switches for drivers, and mandating monitoring systems are some interventions that reduce the risk of fire.

“For one practical specification in New South Wales, fire suppression linings in diesel vehicles were fitted around the engine bay, for example. Similar types of fire protection, installed at higher risk areas of Battery Electric Buses, would be a sensible risk mitigation approach.”

Minimising risk with infrastructure changes

Bus depots will need extensive fire safety plans to include overnight charging and maintenance needs. Utilities like power and water will also need to be considered. As buses will likely be charging overnight into the early hours of the morning, where staffing levels at the depots will be very low, monitoring the charging fleet for faults or ignition events will be crucial.

“In terms of raw energy, when a large depot is charging buses, it is often using a whole suburb’s amount of power,” Andrew says.

“If there is a battery electric fire, operators and emergency responders need a large volume of constant water flow to put it out and keep the fire supressed, so it is likely there will need to be multiple high flow hydrants installed on depot sites.”

Depots, particularly in our metropolitan regions, are also notoriously cramped with buses parked close together, says Joe.

“One consideration that can mitigate the fire spread risk is to install firewalls in the depot, so if there is a fire, it won’t spread quickly. If there is a bus that has a suspected battery fault or has had a collision and needs to be checked – it can be parked in a special secure area away from the other buses, significantly reducing the risk of lateral fire spread between buses. Of course, installation of fire walls can impact bus operations and will add a cost to design and construct, so that needs to be taken into account based on the inherent risk of fire.”

Another potential consideration in a depot’s fire safety plan is installing automatic fire detection via thermal cameras, this can be valuable when charging overnight. Additionally, software that monitors each vehicle charging onsite and technology that identifies both faults and stops overcharging the batteries would also reduce fire risk.

“It’s not just the depot infrastructure that needs to be taken into account, but also local infrastructure while conducting services on the road. If a bus is travelling in a tunnel, is the tunnel designed to withstand a battery electric fire? When you add a new technology like electric vehicles to the mix, suddenly you have to look at the entire transport network and urban design,” Joe says.

Working with emergency services so they know what to do in case of a bus fire is also part of the transition strategy.

“Knowing the location of the battery on the bus is critical for emergency services and can give back crucial seconds into suppressing the fire,” adds Andrew. “For instance, some batteries are roof mounted whereas others are located beneath the floor or at the back of the bus. Also, ensuring the emergency services team knows where the hydrants are at the depot, and being aware of the location of cut-off switches, are all important factors in having an aligned safety plan.”.

While most of fire safety is predicting the worst-case scenario, it isn’t all doom and gloom. Like all risk and safety assessments, it should be approached with clear understanding of the risks and the systems and processes to reduce risk to an appropriate level.

“It’s about being prepared and having a robust processes and systems,” Joe concludes. “We are here to help mitigate as many of the risks as possible.”

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