Lithium-ion fire protection refers to the entirety of technical,
organizational, and structural measures for the prevention, containment, and suppression
of fires caused by lithium-ion rechargeable batteries and batteries. The trigger is typically
thermal runaway – a self-amplifying
exothermic reaction in the cell, caused by mechanical damage, overcharging,
deep discharge, short circuit, or manufacturing defects.
Why lithium-ion rechargeable batteries require special protective measures
Unlike conventional fires, a lithium-ion fire cannot be smothered by
depriving it of oxygen: In the final phase of thermal runaway, the
cathode releases chemically bound oxygen, allowing the reaction to continue
independently of the ambient air. Characteristic features are high temperatures, the release
of flammable and toxic gases, and the risk of re-ignition hours after the
supposed extinguishing. Protective concepts therefore focus on
cooling, containment, and encapsulation, not on conventional extinguishing.
Phases of thermal runaway
The decomposition process of a cell goes through characteristic, time-compressed phases:
Decomposition of the SEI protective layer – begins at approx. 80–120 °C; first slight gases.
Electrolyte decomposition and evaporation – pressure build-up, swelling of the cell, release of flammable gases via the safety valve (venting).
Separator melting – internal short circuit, abrupt conversion of stored energy into heat.
Cathode decomposition – release of bound oxygen; the fire continues to burn autonomously.
If the runaway spreads to neighboring cells in a pack, this is referred to as
thermal propagation – a chain reaction of consecutive cell fires.
Fire dynamics by cell chemistry
Onset and maximum temperatures depend largely on the cathode chemistry. This is
crucial for the design of fire protection concepts:
Cell chemistry
Onset temperature
Maximum temperature
Gas quantity (18650 cell)
LCO / NMC (cobalt or nickel-manganese-cobalt)
149–170 °C
up to approx. 853 °C (± 24 °C)
approx. 150–270 mmol
LFP (lithium iron phosphate)
approx. 195 °C (± 8 °C)
approx. 404 °C (± 23 °C)
approx. 50 mmol
Important for LFP: The thermally more stable LFP cells burn less frequently
with an open flame. As a result, escaping, highly concentrated gases can accumulate unburned
in the room or cabinet – with an increased risk of a delayed gas explosion
(smoke gas ignition / backdraft) when opened. Open flames, on the other hand, immediately
consume the gases and thus reduce the explosion risk.
Toxic and explosive venting gases
The gas mixture released during runaway is both explosive and highly toxic:
Gas
Property / Hazard
Measured peak concentration
Carbon monoxide (CO)
highly toxic, blocks oxygen uptake in the blood
up to 10,000 ppm
Carbon dioxide (CO₂) / Hydrogen (H₂)
H₂ highly flammable, main cause of secondary explosions
CO/CO₂/H₂ together approx. 80% of the gas mass
Hydrogen fluoride (HF)
extremely toxic, highly corrosive (hydrofluoric acid), attacks the respiratory tract, electronics, and building structure
up to 500 ppm
Methane (CH₄) / Ethene (C₂H₄)
flammable, increase the explosion potential
up to 2,000 ppm each
In poorly ventilated rooms, safety cabinets must therefore be connected via an exhaust air connection to a
technical exhaust system, preferably explosion-protected.
Protection concepts
Passive fire protection
Fire-resistant storage and charging cabinets, containers, and fire containment blankets,
thermal insulation of the shelves, tightly closing joints to reduce oxygen, as well as
defined fire compartments.
Active fire protection
Detection and automated extinguishing systems, telemetric early warning (smoke/temperature
sensors, VdS-compliant alarm forwarding), as well as suitable fire extinguishers.
Emergency and recovery measures
Containers and procedures for the safe collection, quarantine, and cooling of damaged
or thermally conspicuous rechargeable batteries.
Effectiveness of extinguishing agents
Oxygen-displacing extinguishing agents (CO₂, powder, foam) have hardly any effect on the cell-internal
reaction, since the oxygen comes from the cathode itself. The most effective approach is
massive, sustained cooling in order to keep neighboring cells below the critical
onset temperature (e.g. below 150 °C) and stop propagation. Water is considered
the extinguishing agent of choice by fire brigades in major fires due to its high heat absorption capacity.
In preventive operation, the state of the art relies on fire containment without extinguishing agents:
controlled burn-out in thermally insulated, gas-tight closing cabinets as well as
fire containment blankets made of heat-resistant special fabric (e.g. fiberglass or silicate) for manual intervention.
Normative and regulatory principles
VDMA 24994:2024-08 – test requirements for storage/charging cabinets; tests fire from inside and outside including real thermal runaway test (type class I); current state of the art.
DIN EN 14470-1 – fire-resistant cabinets (type 90); protection only from outside to inside.
VdS 3103 – loss prevention for the storage of lithium batteries.
ADR (Class 9, Code 9A) / UN 38.3 – dangerous goods and testing regulations for transport.
DGUV Information 205-041 – fire protection when handling lithium-ion batteries.
Note: Regulations are continuously updated. The currently valid version is authoritative in each case.
Differentiation
Lithium-ion fire protection must not be equated with general operational fire protection:
Standard extinguishing concepts (e.g. CO₂ flooding) are only effective to a limited extent. The focus is
on controlling thermal runaway, not on storage organization alone.
Frequently asked questions
What is the greatest danger in a lithium-ion fire?
Thermal runaway with high temperatures, toxic and explosive gases, and the
risk of re-ignition – even hours after the first extinguishing attempt.
Why is a normal fire extinguisher not sufficient?
Because the cathode internally releases oxygen and the fire cannot be smothered
by depriving it of oxygen. Cooling is the main effective measure.
What temperatures occur during thermal runaway?
Depending on the cell chemistry: NMC/LCO cells up to approx. 853 °C, LFP cells approx. 404 °C. The onset temperature
is 149–170 °C for NMC/LCO and approx. 195 °C for LFP.
Which gases are released?
Primarily CO, CO₂, hydrogen, hydrogen fluoride (HF), as well as methane and ethene. HF is extremely
toxic and corrosive; hydrogen is the main cause of secondary explosions.
Are LFP cells safer than NMC cells?
Yes, they are thermally more stable, but they often vent without flames – which increases the risk of a
delayed gas explosion (backdraft) due to the accumulation of unburned gases.
