Are Petrol & Diesel cars in a car park more flammable than electric cars ?

Discussion are taking place around the UK and Europe on the safety of electric cars and fire risks.

Charging, is one of the greatest risks, as high currents are being used in confined spaces.

Poor press reporting on BEV battery fires has fuelled the debate in a negative way.

The examples quoted were not caused by lithium ion batteries in cars, 

Many views by fire brigades are based on lithium ion batteries in general and not specifically for electric cars. 

Authorities and the public are reacting poorly and there is a risk of the negative press resulting in a slower uptake of electric vehicles.

Different risks are listed below in the event of fire in an EV

Scenarios:

Release of toxic substances (electrolyte, hydrogen fluoride, lithium oxide)

Minor explosions (explosion gas)

Flames

Risk of electrocution

Pollution of the environment by polluted extinguishing water

The risks have been identified and analysed by several studies

General conclusions: there are no greater risk involved by a BEV car in the event of a fire compared to an ICE car.

Energy comparison between BEV and an ICE

A study looked at the energy content of a electric car, and to those of a comparable petrol or diesel car.

this discovered that when the petrol or diesel tank is filled to 13%, it has the same amount of energy as a comparable electric car with a fully 100% charged battery.

 Audi e-Tron 55Audi Q7 55 TFSI e quattro
Kerb weight2,499 kg2,425 kg
battery7 kg/kwh 
fuel 10 kWh/liter
Energy content95 kWh750 kWh(total)
Thermal energy content1.71 GJ3GJ
Weight battery or fuel655 kg75 kg
Net weight1,834 kg2,335 kg

From the known fires recently in parking garages 

Main findings: Lacking extinguishing systems

•  Dedicated extinguishing systems (sprinkler and water mist) would probably have reduced the potential for fire spreading to other cars, making it easier for fire and rescue crew to strike the fire down

•  The parking garage had no such, and there is also imminent danger that a fire could spread from one storey to another through drainage gutters (relevant for fuel from ICE cars, not BEVs)

•  The case was the same in 2017, when a fire in a similar multi-storey parking garage in Liverpool, UK, damaged 1,400 cars.

Main findings: No evidence of thermal runaway

•  According to the Rogaland fire and rescue service (RBR) evaluation report no significant differences in fire intensity or duration were observed, regardless of different involved drivetrains

•  There is no evidence that thermal runaway occurred in any of the parked BEVs

•  It is unclear if any battery packs were totally damaged by the fire, but it is undisputed that the contribution to the inferno was limited or none

Main findings: Little BEV related water pollution

•  Water analyses conducted by COWI consultants, of selected metals relevant for batteries in electric vehicles, did not show any lithium, and only low concentrations of cobalt

•  This indicates that batteries in electric vehicles did not contribute to pollution of nearby water resources

•  Observations during the fire indicate that electric vehicles did not contribute to the fire development beyond what is expected from conventional vehicles

If a BEV fire includes the battery pack…

•  If the battery pack is not involved in the fire, as it is in most cases well protected within the casing, a fire can be extinguished just like in any other car

•  If or when the battery pack is involved, a thermal runaway is hard to stop

•  This may occur in a process accelerated by increased temperature (in a fire), in turn releasing energy that further increases temperature

•  The fire course is different than when ICE cars are involved

If a BEV fire includes the battery pack…

•  If the battery pack is not involved in the fire, as it is in most cases well protected within the casing, a fire can be extinguished just like in any other car

•  If or when the battery pack is involved, a thermal runaway is hard to stop

•  This may occur in a process accelerated by increased temperature (in a fire), in turn releasing energy that further increases temperature

•  The fire course is different than when ICE cars are involved

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