Understanding electric vehicle fires
Fire Protection and Safety in Tunnels
6-8 September 2016, Stavanger, Norway
Francesco Colella, PhD
Energy storage All technology is driven by stored energy
• Common forms of energy storage: – Potential energy (height)
– Thermal energy (combustion)
– Electrochemical (batteries)
Any system storing energy has a risk (hazard) associated with sudden and unanticipated release of the stored energy
Stored water (hydraulic): Flooding, erosion
Energy storage hazards
Energy storage hazards
Thermal runaway
• Fires
– All sizes and shapes of Li-ion cells and batteries
• Explosions
– Predominantly in larger cells and batteries
• Human exposure to failure debris
Energy storage hazards & electric vehicles
• Characterization of electric vehicle fires requires understanding battery fire dynamics:
– Difficult to extrapolate between different families because there is not a “standard” cell
– Electrolyte is flammable
Electric vehicles fires
Small format cells 0–10 Wh (0–3 Ah)
Large format cells ~100 Wh (~30 Ah)
EV battery module (10–20 cells)
~2000 Wh (~600 Ah)
Hybrid vehicle pack ~500 Wh (~135 Ah)
Plug-in EV pack (multiple modules)
~20,000 Wh (~5500 Ah)
High performance EV pack (multiple modules)
~85,000 Wh (20000 Ah)
Large Transport & Grid Storage Packs
>100 kWh
Not to scale
Hybrid vehicle pack = ~100 x cell phone cells
EV battery module = >200 x cell phone cells
Energy storage hazards – Li-Ion batteries
What is the fuel?
What is the heat release rate?
Suppression strategies?
Understanding electric vehicles fires
Small Scale
Battery Testing
Small Scale
Battery Testing
• Cause thermal runaway failures in small format cells
• Collect and analyze gases released
• Cell tested: – 2.1 Ah (7.7 Wh) li-ion pouch cell
– Negative: Graphite
– Positive: LiCoO2
– State of charge during tests: Charged to 50%, 100%.
– Cells were unconstrained during the tests
Electric vehicles fires – vented gases
Goal: Measure the composition and quantity of gas released during a thermal event in a Li-ion cell
Cell Test Chamber
Gas
Collection
Canister
Electric vehicles fires – vented gases
• Total volume of gas released:
– 0.8 L at 50% SOC, 0.1 L/Wh (litres per Watt-hour) at STP
– 2.5 L at 100% SOC, 0.32 L/Wh
Fuel source
Amount of fuel involved
Electric vehicles fires – vented gases
Gas50% SOC
(%vol)100% SOC
(%vol)150% SOC
(%vol)
Roth et al.*(%vol)
Test 1/Test 2
Carbon Dioxide 32 30 20.9 61.4/75.8
Carbon Monoxide 3.61 22.9 24.5 15.1/6.4
Hydrogen 30 27.7 29.7 5.1/5.9
Total Hydrocarbons 34 19.3 24 7.4/1.9
• Battery vent gases are more energetic than pure hydrocarbons
• Flammability range of vent gases is wider than pure hydrocarbons
Electric vehicles fires – vented gases
Electric vehicles fires – HRR
INCOMING
SUPPLY
fuelm
Conical Heater
LOAD CELLCONTROL VOLUME
HOOD
EXHAUST
GASES
LASER
EXTINCTION
PITOT
TUBE
SAMPLE
PUMP
THERMOCOUPLE
FILTERING AND
CONDENSING
O2
CO/CO2
ANALYZER
am
em
EXHAUST FAN
SOOT VOLUME
FRACTIONFLOW RATE
MASS LOSS
PARAMAGNETIC
ANALYSER
INFRARED
TECHNOLOGY
Traditional calorimetry techniques (i.e. O2
consumption and CO2) need to be modified
to account for:
• Complex chemistry
• Self generated oxygen from active material
decomposition
Kapton Tape, 0.24%
Label, 0.47% Outer Packaging, 4.30%
Separator, 6.40%
Al Cathode (LiCoO2 coated), 42.40%
Cathode Tab, 0.87%
Cu Anode (Graphite coated), 34.90%
Anode Tab, 0.93% Electrolyte, 9.49%
Pouch cell composition:
– Large amount of inorganic material
Electric vehicles Fires – HRR
Material Net Heat of Combustion (kJ/g)
Douglas Fir 19.6
PMMA (clear plastic) 25
50% SOC li-ion cell 28.1
Acetone 30.8
Gasoline 44.1
Electric vehicles fires – HRR
Small Scale
Battery Testing
HRR testing
EV Battery Pack
HRR testing - EV battery pack
• Free burn.
• 400kW propane for ignition.
• HRR measured using O2 consumption
• Instrumented with TCs and heat flux gauges
• Max HRR 700 kW
• The thermal runaway occurred in stages.
• Visible flaming ceased after 1.5 h.
• 3 hours after extinction, external temperature were as high as 150˚C.
• HF not detected.
HRR testing - EV battery pack
Small Scale
Battery Testing
Full Scale Suppression
Testing
• 400kW propane for ignition.
• Instrumented with TCs, heat flux gauges, and voltage measurements.
• Suppression efforts – Water flow 125 gpm
– 4 Firefighters
– 2 on hose line, 2 support
– Restricted forcible entry with tools
Full scale suppression testing
Top View
3 suppression tests (1 w/ interior components)
Full scale suppression testing – Battery “A”
1 minute
Battery Only Battery w/ interiors
Full scale suppression testing – Battery “A”
2 minutes
Battery Only Battery w/ interiors
Full scale suppression testing – Battery “A”
4 minutes
Battery Only Battery w/ interiors
Full scale suppression testing – Battery “A”
8 minutes (burners off)
Battery Only Battery w/ interiors
Full scale suppression testing – Battery “A”
9 minutes (suppression starts)
Battery Only Battery w/ interiors
Full scale suppression testing – Battery “A”
12 minutes
Battery Only Battery w/ interiors
Full scale suppression testing – Battery “A”
25 minutes
Battery Only Battery w/ interiors
Full scale suppression testing – Battery “A”
Test Suppression Time (min)
Total Water Flow (gal)
Comments
A1 2.2 275 Battery Only
A2 3.5 442 Battery Only
A3 9.8 1060 Battery + Interior
Components
– No projectiles
– Popping heard/Arcing observed
– Off-gassing preceded re-ignition events
– No significant current measured at nozzle
– Re-ignition 22 hours after test
Full scale suppression testing – Battery “A”
Top View
3 suppression tests (1 w/ interior components)
Full scale suppression testing – Battery “B”
Test Suppression Time (min)
Total Water Flow (gal)
Comments
B1 14.03 1754 Battery Only
B2 21.37 2639 Battery Only
B3 9.32 1165 Battery + Interior
Components
– No projectiles
– Popping heard/Arcing observed
– Off-gassing preceded re-ignition events
– No significant current measured at nozzle
Full scale suppression testing – Battery “B”
Unable to extinguish the fire - concentrated efforts on cooling the metal
There was “tremendous heat”
Floorboard makes fire harder to extinguish
These fires were worse than a conventional vehicle fire,
harder to extinguish
EV fire behaves differently from traditional fire
Firefighter response: key quotes
Conclusions (1)
The complete evaluation of EV fire hazards requires a multi-step analysis involving small and large scale testing.
• Vent gas composition and flammability.
• Battery and battery module HRR.
• Effectiveness of suppression agents and suppression time.
Conclusions (2)
Full scale suppression tests:
• Water alone suppressed the EV fires.
• Water requirements depend on battery pack sizes and layout.
• Water flows increased over traditional ICE.
• First responders should be prepared for extended periods of suppression operations and monitoring during overhaul operations due to potential battery re-ignition.