UL Standards & Engagement collects thermal runaway incident data through the 热失控事件计划 (TRIP) and surveys airline passengers to better understand the risks and realities of thermal runaway in aviation. This report offers the second annual look at those findings.
What is the Risk?
Rechargeable devices—such as phones, laptops, tablets, and power banks—are essential to modern air travel. But as lithium-ion batteries become more widely used in these and other consumer products, the risk of safety hazards continues to grow.
These risks become more complicated at 40,000 feet.
If damaged, improperly charged, poorly manufactured, or counterfeit, lithium-ion batteries can enter a process called thermal runaway, which occurs when the batteries overheat, posing serious risks that include fire or even explosion. Lithium-ion battery fires burn with intense speed and heat, which can potentially cause significant and widespread damage within seconds. They can also be more challenging to extinguish compared to fires involving other materials.
KEY TAKEAWAYS
Hover over each stat below to learn more about the report findings.
Thermal Runaway Incident Rates and Trends
In 2024, an average of two flights per week experienced a thermal runaway incident. While there was a slight dip in the total number of reported passenger flight incidents compared to 2023, the marginal drop still makes the 2024 incident total the second highest since 2019 by 11 incidents.
18% of passenger flights that experience an on-board incident result in a diverted landing, return to the gate, emergency evacuation, or unplanned deplaning.
What Do Passengers Know About Lithium-Ion Batteries?
Half (50%) of Americans admit to knowing nothing about lithium-ion batteries. Further, 3 in 5 consumers (60%) are unaware that lithium-ion batteries power many of the products they routinely use.
When exposed to information about thermal runaway and the potential safety risks, travelers showed greater concern about the safety of other passengers’ devices compared to theirs: 52% of respondents say they are concerned about the devices belonging to other passengers overheating; 47% are concerned about their own.
The Leading Devices Behind Thermal Runaway Incidents
Nearly all airline passengers (96%) typically bring at least one rechargeable product containing lithium-ion batteries on board. The average traveler brings four devices — most commonly smartphones (81%), laptops (40%), wireless headphones (38%), and tablets (35%). Twenty-nine percent bring a portable charger or power bank with them. Vapes, while carried by only 10% of passengers, were still the leading cause of thermal runaway incidents, responsible for 28% of the reported total.
Packing Practices Reveal Troubling Behavior
Lithium-ion battery-powered devices should never be packed in checked baggage. Keeping these products at arm’s reach in the cabin provides better ability to handle thermal runaway incidents before they become a bigger threat.
However, approximately 2 in 5 (38%) passengers admit to putting lithium-ion powered products in their checked luggage. Vapes or e-cigarettes are put in checked luggage 31% of the time, and in the overhead bin 18% of the time. Portable chargers are in checked luggage 27% of the time and in the overhead compartment 29% of the time.
In cases where full compartments and plane sizes require gate-checked luggage, 30% of passengers say they were not asked about lithium-ion batteries in their luggage. The ability to repack or rearrange at the gate is also limited, which may lead passengers to leave potentially dangerous items in gate-checked bags.
Impact on Passenger Confidence
Major thermal runaway incident (i.e., device catching The unfortunate upward trend of thermal runaway incidents may lead to eroding passenger confidence. Passengers surveyed said that a major thermal runaway incident (i.e., device catching fire) would lead 46% to avoid traveling with an airline and 28% to never fly that airline again. Moderate incidents (i.e., visible smoke from a device) would cause 47% to avoid the airline with 18% saying they would not fly the airline again. Even minor incidents (i.e., a device overheating) would lead 33% of travelers to avoid the airline and 14% to never fly it again.
Despite the strong pull to avoid or stop flying an airline in the wake of a thermal runaway incident, many travelers still underestimate the threat their devices pose on airplanes and engage in behaviors that run counter to best practices.
Passengers & Cabin Crew Views on Safety
Do You Know What’s Allowed in Your Luggage?
We asked real passengers about their packing habits and their answers may surprise you. Most passengers have no idea they’re breaking a safety rule that could delay flight — or worse.
He Was Reluctant to Hand It Over — But We Couldn’t Risk a Fire in the Sky
A crew member recalls the tense exchange when a passenger hesitated to give up his overheating device mid-flight.
This Common In-Flight Mistake Can Be a Fire Risk
A flight attendant explains why retrieving a lost phone yourself isn’t just inconvenient — it can be dangerous. Most passengers have no idea.
One Laptop, One Big Flight Delay
A cabin crew member recalls how one passenger’s forgotten laptop in a checked bag caused a major delay— highlighting a safety rule too many travelers overlook.
Do You Know What’s Allowed in Your Luggage?
He Was Reluctant to Hand It Over — But We Couldn’t Risk a Fire in the Sky
This Common In-Flight Mistake Can Be a Fire Risk
One Laptop, One Big Flight Delay
Where and When Incidents Happen
TRIP data covers the continuum of air travel — from when passengers walk into the airport to baggage claim pickup at the end of their journey. In 2024, The vast majority (89%) of incidents were reported on the aircraft, with the remaining 11% involving checked baggage and items carried by passengers. The incidents happening on the aircraft ticked up slightly from 87% in 2023 data. Unfortunately, in 77% of incidents, no presumed cause of the event is provided in the reports submitted by flight crews.
More than half (52%) of incidents occurred during the cruising phase. Another 15% of incidents occurred during critical phases of flight (takeoff, climb, descent, final approach, and landing). During these phases, the risk is inherently higher: pilots are engaged and passengers cannot evacuate.
EXPLORE
Hover over the flight journey to see where 和 when incidents are occurring.
11%
of incidents occured off the aircraft, between the airport and baggage claim pickup.
89%
of incidents from 2024 were reported on the aircraft.
15%
of incidents occurred during critical phases of flight (takeoff, climb, descent, final approach, and landing).
52%
of incidents occurred during the cruising phases.
CASE STUDY:
What Should Be Learned in the Aftermath of the Air Busan Fire?
A recent spate of thermal runaway incidents is making the issue more visible to the traveling public. An Air France plane bound for the Caribbean was recently forced to turn around mid-flight after a passenger dropped a phone. A Hawaiian Air flight was forced to make an emergency landing in Japan. In May, a Southwest flight was forced to return to the gate in El Paso after a passenger’s phone caught fire.
One of aviation’s scariest battery fire incidents in recent years occurred in January when a suspected power bank — the kind that 29% of U.S. flyers are traveling with — went into thermal runaway, causing catastrophic damage to an Air Busan plane in South Korea.
The power bank was compressed in the overhead bin and caught fire. Fortunately for the 169 passengers and seven crew members on board, the plane was still awaiting takeoff when the flames tore through the aircraft and everyone was able to escape. The plane was a total loss.
The incident earned the attention and scrutiny of the aviation community and international media. As the news turned to coverage of the steps airlines in Asia are taking to help prevent another incident such as the one on Air Busan, a clear trend emerged: all the enforcement action was aimed at power banks. While no airlines have banned passengers from bringing power banks, aside from batteries greater than 100-160 watt-hours, most have cracked down on what is allowed during flight.
This product-specific action, however, is too narrow of a lens. It was the product’s power source — a lithium-ion battery — that was the cause of the fire.
The aftermath of the damage to the Air Busan flight is visually alarming. It is also a warning not to wait to make changes that will improve safety in the air.
Reversing the Trend
With more lithium-ion battery-powered devices carried on board by passengers — and the number of travelers having returned to pre-pandemic levels — the corresponding increase in thermal runaway incidents is unsurprising. Unsurprising does not mean acceptable.
- Passenger education: ULSE surveys show an alarming lack of awareness and concerning behavior among U.S. airline passengers. Clear, repeated, and contextualized education on the issue will help passengers contribute to reducing the risk.
- Cabin crew training: According to ULSE interviews and surveys with aviation professionals, all cabin crew are trained to respond to thermal runaway incidents on board an airplane. Training that is linked to available equipment, that is regularly evaluated and revised, and that replicates common, real-world scenarios will improve training that cabin crew receive.
- Standards for aircraft and baggage handling: To help mitigate potentially catastrophic incidents, ULSE publishes standards that address the risks and hazards of thermal runaway. These standards include UL 5800, Battery Fire Containment Products; UL 5840, Electrical Systems of Battery Powered Aviation Ground Support Equipment; and the forthcoming UL 5810, Active Fire Protection for Air Cargo Containers.
Download the full report to see more details about thermal runaway in aviation incidents in 2024, as well as learn how partnerships across industry, government, and other stakeholder can bolster collective efforts and help drive impactful change.
Ready to Learn More?
Learn About The
热失控事件计划
UL Standards & Engagement leads the 热失控事件计划 (TRIP), a voluntary reporting system designed for the aviation industry to better understand the extent of the problem and prepare for — or, ideally, prevent — future incidents.
Participants from 37 passenger and cargo airlines provide detailed information on incidents within their operation. The information is anonymized and shared with aviation industry and safety organizations, offering insights to improve the safe transport and usage of lithium-ion battery-powered goods. The TRIP database operates as a surveillance tool, designed to capture data on the frequency, characteristics, and consequences of lithium-ion battery thermal runaway incidents in passenger and cargo operations.
The Federal Aviation Administration also collect thermal runaway incident data. FAA data is taken from mandatory federal reporting, while TRIP includes additional reports from every stage of the travel process by factoring in incidents in the terminal, bag checking, security checkpoints, and leaving baggage claim.