Fire Risks Posed by EVs to Buildings & Car Parks: A Comprehensive Analysis

As EVs and EV charging systems become integrated into urban infrastructure, they introduce additional structural, electrical, environmental and cybersecurity risks that require coordinated management. 

This article therefore provides a comprehensive analysis of the types of risks related to fire (with a focus on car parks), exploring the challenges and proposing some recommendations for enhancing safety in those buildings and car parks that are accommodating them.  

Statistical Probability of Fire Incidents

Research indicates that EVs are generally less prone to catching fire than their ICE counterparts. This lower fire incident rate is often attributed to the simpler mechanical design and fewer flammable fluids present in EVs. For example, a study in Sweden in 2022 revealed that EVs had a fire incidence of 0.004%, significantly lower than the 0.8% observed in gasoline and diesel vehicles. Other studies by the US National Transport Safety Board (NTSB) suggest that 1 in every thousand ICE vehicles will catch fire, compared to 1 in every 83,333 EVs. Further evidence is that despite EVs growing at significant rates, vehicle fires as a share of the total has remained mainly around 20% for most countries.

Despite the promising statistics for EVs, the unique nature of EV battery fires does require careful consideration as the impact, propagation and explosion risks can be far greater than those involving ICE vehicles. We also need to consider hybrid vehicles as several studies also show that hybrid vehicles present a greater risk than both ICE and BEVs. These having particular implications for enclosed areas where EVs are either parked or stored. For example:

Location of Fires: ICE vehicle fires often occur during operation, while EV fires tend to happen when parked and charging. This can lead to property damage, especially in car parks.

Cause of Fires: EV battery fires are primarily caused by faults in battery design, overheating, or collisions, which can trigger thermal runaway. For example, approximately 15% of EV battery fires have been found by studies to occur while connected to charging. Faulty components accounting for a large percentage of incidents.

Thermal Runaway: Thermal runaway is a significant concern for the fire prevention industry, as a damaged battery cell can overheat, causing a chain reaction that leads to more cell failures and potential explosions. Early warning signs include detectable heat, dashboard fault codes, popping noises, and dark vapours.

While the incidences of EV fires might be low, it is also essential to consider risks to battery overheating from the charging infrastructure itself, including compliance with electrical safety standards and full integration into building safety systems.

Unlike ICE vehicle fires, which predominantly occur during operation due to engine overheating or fuel leaks, EV fires appear to have a tendency to happen when the vehicles are parked and charging. This distinction is crucial, particularly for buildings and car parks, as parked vehicles (including ICE, EVs and Hybrids) within enclosed spaces can lead to significant property damage and pose risks to occupants if a fire takes hold.

While the causes of fires in ICE and to an extent Hybrids are more understood, there is less research or data on the causes of EV fires.

Research does, however, suggest that some of the primary causes of EV battery fires include faults in battery design, manufacturing defects, overheating during charging, and physical damage resulting from collisions. Incidents often involve the process of thermal runaway; a dangerous chain reaction within the battery.

Fires and safety risks can also be heightened by charging systems installed with non-compliant installations. Increasing the risks of electrical faults and electrocution for responders once a fire has initiated by failing to cut off the supply.

There have been some notable recent fires in car parks that have focussed public attention. While many of these have been found to be initiated by ICE or Hybrid vehicles, the additional complexity created by the coexistence of ICE, Hybrid, and EVs creates a potential for greater uncertainties in terms of their interactions once a fire is initiated and has then taken hold.

• Luton Airport Fire (2023): A fire started by a Diesel ICE in a parking structure destroyed over 1,300 cars and caused significant disruptions.
  • First report was from a member of the public.
  • 100 Firefighters and 15 Appliances
  • 3 Firefighters and 1 member of public hospitalised due to smoke inhalation
  • 27 arriving flights rerouted.
  • 30,000 passengers impacted.
  • £10m in insurance claims by motorists
  • Car park badly damaged and demolished – Built for £20m in 2019.
• High-Rise Residential Complex, Korea (2021): A BEV fire spread rapidly, damaging 90 vehicles and affecting 800 more, leading to infrastructure outages and parking restrictions. ​
• Stavanger Airport, Norway (2020): A fire affected around 300 vehicles in a confined parking area. ​
• Liverpool Echo Arena, UK (2017): A fire damaged approximately 1,400 vehicles. ​​

Fires in enclosed car parks (of whichever vehicle types) also pose higher risks of toxic gas accumulation, complicating evacuation, and suppression efforts for site operators and emergency services.

In understanding the specific risks of EV fires, it is important to understand some of the processes involved in this type of vehicle technology.

• Thermal Runaway: EV fires are driven by thermal runaway, a chain reaction in lithium-ion batteries causing rapid temperature-rise and fire spread. ​ This can occur immediately after a crash or even weeks later. ​
• Critical Detection Window: EV fires typically begin 20 to 25 minutes after thermal runaway begins, with temperatures exceeding 1000°C within 2 minutes of the fire starting. ​ Early detection within the first 20 to 25 minutes is therefore crucial to prevent escalation. ​
• Fire Intensity: Once started, EV fires reach higher peak heat release rates (PHRR) faster than ICE fires, with EVs hitting 4000 kW at 15 minutes compared to 19 minutes for newer ICE vehicles. ​
• Explosion Risks: Flammable gases released during EV fires can accumulate and lead to deflagration (explosions) in confined spaces such as car parks. ​ Smart gas venting systems can help mitigate this risk. ​
• Toxic Emissions: EV fires release hazardous gases and metals, posing significant health and environmental risks. ​These gases include hydrogen fluoride and hydrogen chloride, presenting severe health hazards in confined spaces.
• Extinguishing Challenges: EV fires are harder to extinguish due to the battery’s internal oxygen supply. ​ Specialised methods like large water volumes or submersion are required. ​
• Re-Ignition Risk: Damaged EV batteries can reignite hours or days after being extinguished, necessitating continuous monitoring. ​
• Emergency Responder Hazards: EV fires pose unique risks for responders, including toxic emissions, electrocution, silent vehicle movement, and projectiles from exploding battery cells. ​

Thermal runaway is a critical concern in EV battery fires. It occurs when a battery cell experiences a short circuit or overheating, leading to an uncontrolled increase in temperature. This can cause cell failures, the release of flammable gases, and potentially explosions. Early warning signs of thermal runaway include:

• Dashboard fault codes
• Heat emanating from the vehicle.
• Unusual popping noises emanating from the battery pack.
• The emission of dark vapours.

The escalation typically follows predictable stages: initial overload or damage compromises a cell, generating heat, releasing toxic gases, triggering further failures, and making suppression extremely difficult. Long-term monitoring is often required even after apparent extinguishment to make sure that the fire does not reappear.

It should also be noted that ISO 15118 (vehicle to charge-point communications) does also cater for vehicle battery temperature monitoring while charging and it is therefore important that this is implemented and resiliently connected to an EV charging management system with corresponding alerts and emergency actions. This should also ideally include the building and safety management system, to enable immediate alerts to be sent.

In terms of identifying fires, time is therefore of the essence, and it is likely that multiple approaches and network redundancy are required to ensure early detection. For example, measures that are central to the vehicle systems, the charging system and network, and external monitoring systems.

Understanding and mitigating thermal runaway is therefore an essential part of developing effective fire safety strategies.

To help understand the processes that are often involved in EV fires, a flowchart illustrating the process of thermal runaway in lithium-ion batteries is provided below:

Figure: Thermal Runaway Process Flow in Lithium-Ion Batteries

This diagram emphasises the sequential escalation from initial battery compromise to the challenges in fire suppression and the need for persistent monitoring.

Difficulties in Extinguishing Fires

EV battery fires present significant challenges to emergency responders due to the energy density and chemical composition of lithium-ion batteries. Unlike ICE vehicle fires that can be extinguished relatively quickly, EV battery fires can burn for extended periods, often lasting 4-5 hours on average. Traditional suppression techniques are less effective, as the battery’s internal oxygen supply sustains combustion, even when external flames are suppressed. Effective suppression methods often involve:

• Applying large volumes of water (potentially up to 10,000 litres or more) to cool the battery pack.
• Submerging the vehicle in a water-filled container to ensure thorough cooling.
• Elevating the vehicle to allow direct access to the battery pack for cooling.
  • For example, in the US, firefighters used 20,000 litres of water for over 2 hours and could only cool the battery after the vehicle was lifted, and water hosed directly towards the battery enclosure. The vehicle however reignited on the tow truck and again in the depot.

Toxic Emissions and Environmental Concerns

EV battery fires also release a cocktail of toxic and flammable vapours, including hydrogen fluoride and hydrochloric acid, posing both respiratory and explosion hazards. These emissions can contaminate the surrounding air and water, necessitating careful environmental management during and after fire incidents. Emergency responders must wear appropriate personal protective equipment (PPE) to mitigate the risks of chemical exposure.

Risk of Re-Ignition

A unique and alarming aspect of EV battery fires is the potential for re-ignition hours or even days after the initial fire has been extinguished. This phenomenon is attributed to previously damaged battery cells that can ignite after an initial fire has been suppressed. Therefore, continuous monitoring of damaged EVs is crucial to prevent secondary fire incidents.

New Hazards for Emergency Responders

EV battery fires introduce new risks and complexities for emergency responders, including:

• Silent, uncontrolled vehicle movement due to damaged electrical systems.
• Jet-like directional flames that can spread rapidly.
• The risk of projectiles being ejected from exploding battery cells.
• Chemical exposure from toxic emissions.
• Electrocution hazards from high-voltage systems.

Designers must also account for structural loading, especially where dense battery arrays or storage units may stress older car park infrastructure that may be subject to damage.

The level of compliance of charging equipment also significantly affects safety. For example, compliant AC systems use Residual Current Devices (RCDs), circuit breakers, and isolator switches within two meters of the unit to ensure automatic power cut-off during faults, enabling safe suppression by qualified responders. Non-compliant installations lack these features, posing severe electrocution risks for users and emergency responders under failure conditions.

Research indicates that a notable proportion of EV fires occur while the vehicles are connected to charging units or shortly after disconnection. These incidents can result in fires originating from the traction battery or electrical sources within the charging infrastructure. For example, some studies have revealed that over a third of reported incidents involve fires at charging units or soon after disconnecting. (Note that statistical research is subject to key variations and that while some studies highly state this as a correlating factor, others present it as less prevalent).

In properly functioning EVs connected to electrically compliant charging units, the battery management system (BMS) prevents overcharging.

Instead, charging-related fires often appear to stem from pre-existing vehicle damage, manufacturing defects, or external factors that are then exacerbated by resultant charging. Analysis of EV fire incidents reveals that the primary causes of charging-related fires appear to include:

• Vehicle damage from collisions.
• Submersion in floodwater, leading to short circuits and corrosion.
• Un-responded manufacturer recalls due to defects in battery design or charging systems.
• Exposure to external fires that compromise battery integrity.

Operating a fully connected and secure EV charging network and vehicle monitoring system is therefore a vital part of fire safety, preferably with additional measures for detecting and communicating the signs that thermal runaway is occurring on site and to centralised systems.

Operational best practices such as maintaining a lower State of Charge (e.g., below 50% for stored vehicles) can also help reduce the risk of initiating thermal runaway.

When planning EV charging systems or accommodating various vehicle types in car parks, it is important to understand how the new paradigm affects risk strategies, preventative measures and responses. For example:

Electrical Risks Mitigation

• Controlled charging strategies, grid integration, and dedicated circuits reduce voltage deviations and transformer overloads.
• Coordination with DSOs and TSOs is vital for large-scale deployments to balance energy needs.

Structural Risks

• Structural assessments are crucial, especially in older car parks retrofitted with charging stations that might increase the load (also understanding that EVs tend to be heavier than ICE vehicles due to the battery weight).
• Concentrated battery arrays that are there to supplement and supply EV charging equipment can also increase floor loads and may require reinforcement measures.

Environmental and Chemical Risks

• Battery fires release toxic substances and their containment is an important aspect of safety.
• Ventilation design and spill containment measures are therefore also essential to prevent build-up of gases and contamination of water supplies in the vicinity.

Cybersecurity Measures

• Smart charging systems require robust cybersecurity to prevent unauthorised access or manipulation that could cause overloads or disable safety systems.

Emergency Preparedness

• Regular drills, training for first responders, and clear incident management protocols can help improve readiness for EV fire scenarios.
• Inter-agency coordination is critical for effective response.

It is also important to understand that an effective and onsite strategy should alerts begin to be raised is put in place. It is key that users and employees are not put at risk in attempts to resolve or contain fires that might be emerging or taking hold.

Despite the dangers, comprehensive emergency response strategies are crucial for mitigating the risks of EV fires in buildings and car parks.

These strategies should include:

• Providing a real time, connected rapid detection system for thermal runaway in vehicles. For example, Gas detection systems and thermal imaging cameras are crucial for spotting BEV fires early:​
  • Thermal Imaging Cameras: These cameras detect temperature differences, enabling the identification of overheating batteries. They provide an opportunity to cool the battery or isolate the vehicle before thermal runaway occurs. However, they require direct visual contact to be effective.
  • Gas Detection Systems: Gas detection systems can identify gas emissions before combustion begins, providing an early warning of potential fire hazards. This allows for preventive measures such as venting gases or activating fire suppression systems. It is vital that these systems are connected to alarm systems to ensure rapid alert and response.
  • A comprehensive and compliant, fully networked and secure EV charging infrastructure that can communicate warning signs at a very early stage.
• Where appropriate, early detection enables proactive measures such as cooling the battery, isolating the vehicle, or activating fire suppression systems to prevent the progression to thermal runaway and subsequent fire.
• Again, where appropriate, early intervention can prevent the rapid spread of fire caused by radiant heat feedback and ceiling jets, which can ignite nearby combustibles and penetrate passenger compartments. Ensuring early detection and intervention also reduces the risk of re-ignition, which is common in BEV fires due to residual heat and chemical reactions within the battery cells.
• It is crucial to ensure that safety-first protocols and measures are in place to deal with thermal runaway once it is detected.
  • Ensuring on-site hydrants are readily accessible for fire suppression.
  • Maintaining clear access for fire appliances to reach affected vehicles.
  • Developing detailed incident response plans tailored to EV battery fires.
  • Implementing water runoff management systems to contain contaminated water.

Compliance with Standards

Adherence to relevant safety standards is essential for minimising the risks associated with EV charging infrastructure. For example, mandating the installation of isolator switches within two meters of charging units and the use of protective devices like Residual Current Devices (RCDs) and circuit breakers are generally recommended. These measures help prevent electrocution and ensure automatic disconnection in case of faults.

EV Safe Charging Systems

Safer charging systems are designed to enhance safety during EV charging. For example, safer charging system incorporates various features to monitor charging conditions, detect potential anomalies, and automatically disconnect the power supply if a fault is detected.

Emergency Responder Training

Specialised training for emergency responders is paramount for effectively managing EV battery fires. Firefighters and responders need to be equipped with the knowledge and skills to:

• Identify the specific risks associated with EV fires.
• Safely approach and assess the situation.
• Use appropriate suppression techniques, including the application of large volumes of water.
• Manage toxic emissions and prevent environmental contamination.
• Mitigate the risk of re-ignition.

For example, EV fire responder training programs offer structured training levels designed to enhance the knowledge and skills of emergency responders in managing EV incidents.

Figure: Illustration of typical time responses availability (for illustrative purposes only):

Enhanced Safety Measures in Car Parks

Buildings and car parks accommodating EVs should implement enhanced safety measures to minimise fire risks:

• Use fire-resistant construction materials to contain fires and prevent structural damage.
• Install adequate ventilation systems to disperse toxic fumes and prevent the build-up of flammable gases.
• Provide clear signage indicating the location of EV charging stations and emergency procedures.
• Implement fire detection and suppression systems specifically designed for EV battery fires: Early warning is critical, so systems such as heat detection cameras and gas warning systems that can detect problems are essential measures.

Further recommendations include adopting advanced Battery Management Systems (BMS) with real-time monitoring, ensuring full compliance with evolving national and European standards, and prioritising cybersecurity integration in smart charging networks.

Charging Infrastructure Compliance

Ensure that all EV charging units comply with relevant safety standards and regulations, including:

• Proper installation by qualified electricians.
• Regular inspections and maintenance.
• Use of certified charging equipment with built-in safety features.
• A fully connected and secure monitoring system of EV chargers and vehicle systems be in place.

Emergency Responder Preparedness

Provide specialised training and equipment for emergency responders to effectively manage EV battery fires, including:

• Access to large volumes of water for cooling and suppression.
• Appropriate PPE for protection against toxic emissions and electrocution hazards.
• Specialised tools for disconnecting high-voltage cables.

Public Awareness and Education

Increase public awareness about the risks and safety measures associated with EV fires through educational campaigns and informational materials can help mitigate or detect fires. This includes:

• Providing guidance on safe charging practices.
• Educating EV owners on the warning signs of battery issues.
• Promoting responsible EV ownership and maintenance.

Allow Battery to Burn Out (When Safe to Do So)

In certain situations, if the location and time permit, allowing the battery to burn out under controlled conditions may be the safest approach to minimise risks, while being mindful of potential reignition. This should only be considered when the fire is contained, and there is no immediate threat to life or property.

While electric vehicles offer numerous benefits, including reduced emissions and enhanced energy efficiency, the potential fire risks they (combined with ICE and Hybrid vehicles) pose to buildings and car parks must be assessed to protect the safety of users, property, and vehicle assets. This is as although the risk of fires caused by EVs is small, the consequential action of fires started by other vehicles where EVs are present can create new safety risks.:

• Comprehensive risk management must address not only fire hazards but also electrical, structural, environmental, and cyber risks.
• Understanding these risks and implementing appropriate mitigation strategies is essential for the safe integration of EVs into parking and storage infrastructure.
• By focusing on early detection methods, enhanced safety measures, compliance with standards, emergency responder preparedness, and public awareness, we can help minimise potential damage and ensure the safety of buildings, car parks, and their occupants.
• As this is an ongoing and emerging field, continuous research, regulatory updates, and stakeholder training are essential to ensure safe urban integration of electric mobility in major buildings.

Continuous research, development, and collaboration among automakers, regulatory agencies, and emergency responders are therefore crucial to staying ahead of the emerging challenges discussed and creating a safer future for electric mobility as we move forward.