Why Do EVs Catch Fire in India? Thermal Runaway, Causes and AIS-156

In short

• EV battery fires start with thermal runaway: one lithium-ion cell gets hot enough that its own chemical reactions make more heat than it can lose. Past about 80 °C reactions speed up, the protective film on the anode breaks down above about 90 °C, the separator melts between about 135 °C and 165 °C, and some cathodes release oxygen near 200 °C.
• The cell usually gets there through an internal short or abuse: a manufacturing defect, overcharging or charging too fast or too cold, a BMS or charger fault, heat, crash damage or water.
• After a run of electric scooter fires in early 2022, three makers recalled 6,656 scooters and the road transport ministry rewrote India's battery standards. AIS-156 Amendment 3 (two- and three-wheelers) and the matching AIS-038 (Rev 2) amendment (cars, buses, trucks) came into force in two phases, on 1 December 2022 and 31 March 2023.
• LFP cells start self-heating later and burn cooler than NMC cells, but no chemistry is fireproof. Safety comes from cell quality, the BMS, pack design that stops one failed cell from spreading, venting and testing.

Electric vehicles catch fire when a lithium-ion cell inside the battery pack goes into thermal runaway, a self-feeding loop in which heat speeds up chemical reactions that release still more heat, along with flammable gas. The trigger is almost always an internal short circuit or abuse of the cell: a manufacturing defect, overcharging, a battery management system (BMS) that misses a fault, too much heat, crash damage or water getting in. A pack catches fire when that one failing cell heats its neighbours and the gas it vents ignites.

India learnt this the hard way in 2022, when a string of electric scooter fires led to recalls, a government investigation and a rewrite of the national battery safety standards. This guide explains the physics with temperatures from peer-reviewed studies, the six root causes, what the official record says about the 2022 fires, what the amended AIS-156 and AIS-038 (Rev 2) standards now require, whether Indian heat is to blame, and what engineers do to stop a bad cell from becoming a burning vehicle.

What actually happens when an EV battery catches fire?

A lithium-ion cell is a sandwich: a graphite anode, a metal-oxide or phosphate cathode, a thin porous plastic separator that keeps them apart, and a liquid electrolyte of lithium salt in organic carbonate solvents. Every layer is stable in its normal operating window. Heat it far enough and each layer starts to break down in turn, and most of those breakdowns release heat.

Thermal runaway is what happens when an exothermic reaction goes out of control. Think of it like a campfire that starts collecting its own firewood: the hotter it gets, the faster the reactions run, and the faster they run, the hotter it gets. The review by Liu and colleagues in Science Advances (2018) lays out the sequence, and an accelerating-rate calorimetry study by Golubkov and colleagues (2014) measured where real cells cross the line.

The thermal runaway sequence, step by step

1. Above about 80 °C, reactions speed up. Side reactions between the electrodes and electrolyte, which are negligible at room temperature, become fast enough to warm the cell from the inside. This is where the positive feedback begins.
2. Above about 90 °C, the SEI breaks down. The solid electrolyte interphase (SEI) is a thin film that forms on the graphite anode during the first charges and protects it from the electrolyte. Its components are only metastable, and they decompose with heat, releasing flammable gases. With the film gone, fresh lithiated graphite reacts directly with the electrolyte, adding more heat.
3. From about 130 °C, the separator softens and melts. Separators are commonly made of polyethylene (PE, melting near 135 °C) and polypropylene (PP, near 165 °C). Commercial cells can use a three-layer PP/PE/PP "shutdown" separator: the PE layer melts first and closes its pores, stopping ion flow, while the PP layers hold the structure. If the separator shrinks or collapses, anode and cathode touch, and the resulting internal short dumps the cell's stored energy as heat in a small spot.
4. Around 200 °C, some cathodes release oxygen. A charged nickel oxide cathode (LiNiO₂) releases oxygen into the electrolyte around 200 °C, and lithium cobalt oxide can start to decompose from about 180 °C. That oxygen lets the electrolyte burn inside a sealed can.
5. The electrolyte vents and burns. The common carbonate electrolyte (a mix of ethylene carbonate and dimethyl carbonate) has a flash point of about 25 °C. Once pressure bursts the cell's vent, hot flammable vapour meets air and a spark or hot surface, and the cell becomes a torch.

Golubkov's team heated fully charged 18650 cells, the cylindrical format used in many scooter packs, until they failed. The NMC (nickel manganese cobalt oxide) cell started self-heating at 168 °C, went into rapid runaway at 223 °C and peaked at 678 °C. The LFP (lithium iron phosphate) cell started self-heating later, at 195 °C, never showed a sharp rapid-runaway transition, and peaked at 404 °C. Liu's review describes the whole event in three stages: overheating, then heat build-up and gas release, then combustion and explosion.

The engineering lesson is in the gaps between the rungs. A healthy cell in normal use sits far below 80 °C. The job of every safety layer, from the cell maker to the BMS to the pack designer, is to keep it there, and if one cell does run away, to stop it taking the next cell with it.

What are the main causes of EV battery fires?

Most real fires trace back to one of six starting points. They are not independent: an internal short is the most common final trigger, and the other five are ways of creating one or of heating a cell until it fails.

1. Manufacturing defects

Liu's review calls internal shorting the predominant reason for thermal runaway, and it is hard to control because it starts inside a sealed cell. A speck of metal debris, a burr on an electrode edge or a wrinkle in the separator can sit harmlessly for months, then wear through and short. The best-documented example is global: in August 2021 GM expanded its Chevrolet Bolt recall to every remaining 2019 and all 2020-2022 Bolts after finding that, in rare cases, the supplier's cells had two manufacturing defects at once, a torn anode tab and a folded separator, which raised the risk of fire. GM put the extra cost at about $1 billion. Defects like these are why standards now demand certified cells and traceability down to the cell batch.

2. Electrical abuse: overcharging, fast charging and cold charging

Overcharging means pushing a cell beyond its designed voltage. The cathode starts to decompose and release oxygen, and the electrolyte breaks down into heat and gas. Charging too fast, or at low temperature, causes a quieter problem: lithium arrives at the anode faster than it can slide into the graphite, so it plates out as metal. Over many cycles that metal can grow into needle-like dendrites that pierce the separator. An external short, such as a damaged cable or a tool across the terminals, forces a huge current through every cell at once.

This is why the charging profile matters. Lithium-ion cells are charged at constant current until they reach their voltage limit, then at constant voltage while the current tapers. The charger and BMS must agree on that limit and stop on time.

3. BMS and charger faults

The battery management system measures cell voltages, currents and temperatures, and opens the circuit when something goes out of limits. If a voltage sense wire is loose, a temperature sensor sits in the wrong place, the firmware thresholds are wrong, or a cheap charger ignores the BMS, a cell can be overcharged or overheated with no warning. A pack with several strings of cells in parallel adds another trap: if one string is weaker, current can circulate between strings even when the vehicle is parked. Our guide to how a battery management system works covers the functions in detail.

4. Heat and poor thermal design

Every cell makes heat when it charges and discharges, and the pack has to get rid of it. Densely packed cells with no air gap, no heat spreader and no path to the outside run hotter in the middle of the pack than at the edges. Add a hot day, sun on a parked vehicle and charging straight after a hard ride, and the margin to the cell's limits shrinks. Heat alone rarely ignites a healthy cell, as the next sections show, but it makes every other fault more likely.

5. Mechanical damage

A crash, a crushed pack or anything that penetrates a cell can short it internally on the spot. Damage can also be delayed: a dented cell may hold for weeks before the damaged layer gives way.

6. Water ingress

Water, and salt water in particular, conducts electricity. If it gets inside a pack it can bridge the terminals and set up a short circuit that heats the cells. After Hurricane Ian flooded Florida in 2022, research by the US road-safety regulator NHTSA, as reported by the Associated Press, found 3,000-5,000 electric vehicles flooded. Six hundred were written off, and 36 of those caught fire. That is 6% of the write-offs and roughly 1% of all flooded EVs. Fires can also start after the water has drained away. For India's monsoon-flooded streets this is why the amended standard tests the battery for full immersion.

What happened with the 2022 electric scooter fires in India?

In the first months of 2022, several electric scooters caught fire across India. When road transport minister Nitin Gadkari announced an expert committee on 21 April 2022, he noted that people had lost their lives and several had been injured in incidents over the previous two months.

Here is what the official record says, as later set out in replies to Parliament by the Ministry of Heavy Industries and in Press Information Bureau (PIB) releases:

• Who: fires were reported in electric two-wheelers made by Okinawa Autotech, Pure EV, Jitendra Electric Vehicles, Ola Electric and Boom Motors.
• Recalls: after repeated requests from the ministry, Okinawa recalled 3,215 vehicles on 16 April 2022, Pure EV 2,000 on 21 April and Ola Electric 1,441 on 23 April, a total of 6,656.
• Investigation: the road transport ministry (MoRTH) set up an investigating team of independent experts from DRDO, the Indian Institute of Science (IISc) Bengaluru and the Naval Science and Technological Laboratory (NSTL) Visakhapatnam to find the root cause and recommend remedies.
• Standards committee: a separate expert committee, chaired by the Director of the International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad, with members from DRDO's Centre for Fire, Explosive and Environment Safety (CFEES), IISc, NSTL and IIT Madras, was asked to recommend extra safety requirements for battery cells, the BMS, on-board chargers, pack design and thermal propagation.

What was reported but not published. The investigation reports themselves have not been made public. In May 2022 news outlets, citing people who had seen the DRDO fact-finding report, said it found serious defects in the batteries, including in battery pack and module design, and suggested that some makers may have used lower-grade materials to cut costs. Treat these as press reports, not official findings. What is on the record is the government's response: new rules.

What do the AIS-156 and AIS-038 (Rev 2) amendments require?

Automotive Industry Standards (AIS) are the technical standards that vehicles must meet for type approval under India's Central Motor Vehicles Rules. AIS-156 covers L-category electric vehicles (two-wheelers, three-wheelers and quadricycles). AIS-038 (Rev 2) covers M and N categories (passenger and goods vehicles with four or more wheels). Based on the committee's recommendations, MoRTH issued Amendment 2 to both standards on 29 August 2022, then Amendment 3, notified by S.O. 4567(E) on 28 September 2022. To give manufacturers time, Amendment 3 came in two phases: Phase 1 from 1 December 2022 and Phase 2 from 31 March 2023. A further notification, G.S.R. 888(E) of 19 December 2022, set the procedure for type approval and conformity of production of traction-battery components.

The table below lists what Amendment 3 to AIS-156 requires, clause by clause, and which phase each clause came in under, from the amendment text and MoRTH's phase list. AIS-038 (Rev 2) has a parallel set of clauses in its Annexure IX-K for cars, buses and trucks.

Requirement (AIS-156 Amendment 3)	Clause	Phase
BMS must be microprocessor or microcontroller based	6.1.2.1	1 (1 Dec 2022)
BMS verified for over-charge, over-discharge, over-temperature, over-current and short-circuit protection	6.1.2.3	1
Charger: voltage cut-off, soft start, pre-charge for deeply discharged packs, protection against 230 V AC ±10% supply variation, communication with the BMS	6.1.3 (except e)	1
Every cell put through at least one charge-discharge cycle at C/3, with records kept	8K-3	1
Enough cell-to-cell spacing for heat transfer and to isolate a cell in thermal runaway	8K-7	1
An extra safety fuse or circuit breaker besides the BMS	8K-8	1
Traceability of cells, BMS and charger by serial or batch number	8K-9	1
Cells protected during regenerative braking	8K-10	1
Battery pack tested at 100% charge for IPX7 water ingress (immersion), with no fire or explosion	6.1.1	2 (31 Mar 2023)
BMS meets electromagnetic compatibility (EMC) requirements	6.1.2.2	2
Charger earth-leakage detection	6.1.3 (e)	2
Thermal propagation test: a single cell driven into runaway must not cause fire or explosion of the pack; an audio-visual warning at least 5 minutes before any fire or explosion; a documented risk analysis (for example ISO 26262 or a DFMEA)	6.11, Annex 8J	2
Cell manufacturing month and year visible on cells or recorded, and printed on the pack	8K-1	2
Cells certified to IS 16893 Parts 2 and 3 by an accredited lab	8K-2	2
Pressure release vent on the pack	8K-4	2
At least 4 temperature sensors; above 60 °C an audio-visual alarm, and the BMS gradually cuts power to the motor	8K-5	2
Active paralleling circuits, or fuses or bond wires, to stop circulating currents between parallel strings	8K-6	2
BMS logs critical battery data for at least one month, locally or in the cloud	8K-11	2

The thermal propagation test is the heart of the change. The pack is charged to at least 95%, one cell (usually the one in the middle, where heat escapes worst) is heated with a block or film heater until it runs away or its surface passes 300 °C (heating should end within 30 minutes), and runaway is confirmed by a voltage drop or over-temperature together with a temperature rise of at least 1 °C per second. The pack passes if there is no external fire or explosion. In plain words: the standard no longer assumes cells never fail. It asks the pack to survive when one does.

Does India's heat make EV batteries catch fire?

Heat matters, but not in the way most headlines suggest. The India Meteorological Department declares a heatwave when the actual maximum air temperature reaches 45 °C (or the maximum is 4.5 °C or more above normal, at stations already at 40 °C or more in the plains). That is still about 35 °C below the roughly 80 °C at which a cell starts heating itself, and far below the 168-195 °C self-heating onset measured in Golubkov's full cells. Hot weather alone does not push a healthy, idle cell into runaway.

What heat does is eat the safety margin. A typical cell datasheet, such as LG's INR18650HG2, allows charging only between 0 °C and 50 °C cell surface temperature and discharging between −20 °C and 75 °C. A pack that starts a summer afternoon at 45 °C, gains heat from the sun and then from its own current is close to those limits, which is exactly why AIS-156 puts the alarm and power cut-back at 60 °C. Reaction rates also rise with temperature, so side reactions and ageing run faster in a hot pack. Heat turns a marginal cell, a weak weld or a poorly placed sensor into a real risk, and a pack designed and tested only for a cooler climate may have too little margin for an Indian summer.

The monsoon brings the second Indian-specific risk: water. Scooters are often ridden through flooded roads, and a pack whose seals fail can take in water. That is the reason the IPX7 immersion test is in Phase 2 of the amendment.

Are LFP batteries safer than NMC?

On cell chemistry alone, yes. In LFP every oxygen atom is tied up in strong covalent bonds with phosphorus, forming phosphate groups, so the cathode holds on to its oxygen far better than the layered oxides in NMC, and less oxygen is available to burn the electrolyte. Liu's review describes olivine LiFePO₄ as stable up to about 400 °C. In Golubkov's tests, the LFP cell started self-heating 27 °C later than the NMC cell (195 °C against 168 °C), peaked 274 °C cooler (404 °C against 678 °C) and released about a third as much gas (50 mmol against 149 mmol). The NMC cell also stored more energy (5.7 Wh against 3.5 Wh), which accounts for part of the gap.

LFP is not fireproof, though. An LFP cell still contains flammable electrolyte, still vents flammable gas when abused, and a pack of LFP cells can still burn if one cell's runaway spreads. Chemistry buys time and margin. Pack design decides whether the margin is used well. For the full comparison of energy density, cost, cycle life and which Indian EVs use which chemistry, see our LFP vs NMC battery guide.

How do engineers prevent EV battery fires?

Battery safety engineers work in layers, so that no single failure can lead to a fire. Each layer maps onto the fault chain above.

Choose and check the cells

• Buy cells certified to the relevant standard (IS 16893 Parts 2 and 3 in India), from suppliers with traceable lots.
• Screen incoming cells: capacity and internal-resistance checks, a formation or C/3 cycle, and rejection of outliers that may hide a defect.
• Pick the chemistry for the use case. LFP for maximum thermal margin and cost, NMC where energy per kilogram matters most, with the pack designed around the chemistry's runaway behaviour.

Design the BMS to catch faults early

• Monitor every series cell group's voltage, and enough temperature points to see the hottest cell, not just the pack average. AIS-156 sets a floor of four sensors; well-designed packs place them where thermal simulation shows the hot spots.
• Enforce voltage, current and temperature limits with redundant protection: a fuse or breaker that works even if the BMS firmware does not.
• Derate charging current when cells are cold or hot, and talk to the charger so it cannot overcharge.
• Log data. A month of BMS logs, as AIS-156 now requires, turns a mystery fire into a root-cause investigation.

Skill-Lync's battery technology for electric vehicles course covers cell modelling and BMS algorithms in MATLAB and Simulink.

Design the pack so one cell cannot take down the rest

• Space cells and add heat barriers between cells or modules so a cell in runaway cannot heat its neighbours past their own onset temperature.
• Fuse cells or strings individually (bond-wire fuses or active paralleling) so a shorted cell is cut off from its parallel neighbours.
• Give the pack a pressure release vent that sends hot gas away from the rider and away from other cells.
• Seal the enclosure for immersion and design the thermal path, by air, by conduction to the casing or by liquid cooling, so cells stay inside their datasheet window on the hottest day. Skill-Lync's battery thermal management course with Ansys Fluent teaches the CFD side of this, and our article on battery thermal management systems gives the overview.

Prove it by analysis and test

• Run a structured risk analysis (DFMEA, fault tree, or a functional-safety process such as ISO 26262), which AIS-156 now asks for as part of the thermal propagation clause.
• Test abuse cases deliberately: overcharge, external short, crush, immersion, and the single-cell thermal propagation test.
• Audit production, not just prototypes. Conformity-of-production checks exist because the cell in the thousandth pack has to match the one that passed type approval.

Designing a full pack, from cell selection through BMS, thermal system and validation, is the core of Skill-Lync's master's programme in electric vehicle design and development.

What can EV owners do to lower the risk?

• Charge with the charger supplied or approved by the vehicle maker. AIS-156 chargers must communicate with the BMS; a generic charger may not.
• Take warnings seriously. A battery temperature alarm or sudden loss of power on a compliant vehicle is the BMS doing its job: stop, get off and move away.
• After a crash, a hard hit to the battery area or a ride through deep water, have the pack inspected before charging it again. After floods, fires have started even once the water had drained away.
• Do not open, modify or "upgrade" a battery pack, and check whether your vehicle is covered by any recall.
• Where possible, charge in an open, ventilated spot, clear of flammable materials and not blocking an exit.

Frequently asked questions

At what temperature does a lithium-ion battery catch fire?

There is no single number. Self-heating can begin above about 80 °C, the anode's protective SEI film breaks down above about 90 °C, and separators melt at about 135-165 °C. In one heating test on fully charged 18650 cells, an NMC cell started self-heating at 168 °C and peaked at 678 °C, while an LFP cell started at 195 °C and peaked at 404 °C. Fire happens when vented electrolyte vapour, which has a flash point near 25 °C, meets air and an ignition source.

Why did so many electric scooters catch fire in India in 2022?

The official investigation reports were not published. The government's response, documented in PIB releases and replies to Parliament, was recalls by three makers (6,656 scooters) and new battery rules covering cells, the BMS, chargers, pack design and thermal propagation. Press reports in May 2022 said the DRDO investigation found serious defects in the batteries, including pack and module design, but that is reporting, not an official finding.

What is AIS-156 Amendment 3?

It is the 2022 amendment to India's safety standard for L-category electric vehicles (two-wheelers, three-wheelers and quadricycles). It added requirements for certified cells, BMS protections, charger functions, cell spacing, fuses, a pressure vent, at least four temperature sensors with a 60 °C alarm, data logging, IPX7 immersion testing and a single-cell thermal propagation test. It came in two phases, on 1 December 2022 and 31 March 2023. AIS-038 (Rev 2) carries matching requirements for cars, buses and trucks.

Can an EV battery catch fire when the vehicle is parked?

Yes. An internal short from a manufacturing defect, earlier damage or water ingress can develop with no current flowing, and current can circulate between parallel strings inside a poorly designed pack. That is why the amended standard requires protection against circulating currents and a warning at least five minutes before any thermal event can turn into fire.

Are electric vehicles more likely to catch fire than petrol vehicles?

We have not found a reliable, like-for-like Indian dataset that compares fire rates per vehicle or per kilometre, so we do not quote one. What is clear is that EV battery fires behave differently. They can start without a crash, from a hidden defect or water ingress, and sometimes after a delay, which is why the engineering focus is on preventing a single cell failure from spreading.

Sources and further reading

• Liu K, Liu Y, Lin D, Pei A, Cui Y. "Materials for lithium-ion battery safety". Science Advances 4, eaas9820, 22 June 2018 (open-access full text).
• Golubkov AW et al. "Thermal-runaway experiments on consumer Li-ion batteries with metal-oxide and olivin-type cathodes". RSC Advances 4, 3633, 2014.
• LG Chem. INR18650HG2 product specification, 13 October 2014.
• PIB, Ministry of Road Transport & Highways. "Additional safety requirements recommended in the existing battery safety standards with effect from 1st October 2022", 1 September 2022.
• PIB, Ministry of Road Transport & Highways. "Amendments to EV battery testing standards: AIS-156 and AIS-038 (Rev 2) to be implemented in two phases w.e.f 1st Dec, 2022 and 31st March, 2023", 27 September 2022.
• MoRTH / ARAI. Amendment 3 to AIS-156 (09/2022), copy hosted by ACMA.
• Ministry of Heavy Industries. Lok Sabha unstarred question 4559, "Incidents of fire in electric vehicles", answered 28 March 2023.
• Ministry of Heavy Industries. Lok Sabha unstarred question 4431, "Quality assurance in production of EVs", answered 28 March 2023.
• Ministry of Heavy Industries. Lok Sabha unstarred question 2076 (in Hindi), on recalls after EV fires, answered 20 December 2022.
• Ministry of Heavy Industries. Lok Sabha unstarred question 2032, "Fire incidents in electric vehicles", answered 1 August 2023.
• The Tribune. "Expert panel to probe EV mishaps", 22 April 2022.
• The Tribune (IANS). "Serious battery defects in EVs that caught fire: DRDO report", 23 May 2022.
• India Meteorological Department. FAQ on Heat Wave.
• General Motors. "General Motors to Recall Additional Bolt EVs", 20 August 2021.
• InsideEVs. "Why Hurricane Floods Can Cause EV Battery Fires", 30 September 2024 (citing NHTSA research via the Associated Press).