This is what happens when a power bank explodes on a plane

First, the battery pack started to swell. Looking through the window into the laboratory, I could see the device bulging within its black plastic casing. A heat sensor showed the internal temperature climbing above 120C. Then the pack began to melt.

Suddenly, white plumes of toxic vapour escaped the battery and vented at speed. Moments later, it ignited. Fire jets blew with force in all directions, like a miniature flame-thrower. The temperature leapt to above 650C.

"It is a one-in-a-million event," whispered Simon Jones of Warwick Manufacturing Group, conducting this lithium battery device experiment for The Telegraph.

"But then, when you consider how many air passengers there are…" He didn't finish the thought.

There can be as many as a million people in the air at any one time, carrying an average of four lithium-powered devices each. Every year, there are more than nine billion air passengers globally. This "one-in-a-million" inferno, raging before us, is anything but a fringe concern. It is indeed today's single biggest threat to aviation safety .

Inside the 'abuse chamber'

Stepping inside the laboratory before the first experiment, I could smell the ghosts of half a century of toxic fires and saw the scars of burns on the walls. Technically, this is not called a laboratory. It is, more suitably, known as an "abuse chamber". The one next door had its doors blown off not too long ago.

Our aim was to see what happens when a battery pack's systems fail in different scenarios. To achieve this, the team at Warwick Manufacturing Group (WMG), based at the Warwick University campus, removed the circuit board from a standard 20Wh battery pack and inserted a heat pad. This simulates what happens when a lithium battery overheats.

In our first experiment, we witnessed the process of a battery pack entering "thermal runaway". Once this chain reaction begins, the hot chemicals within a lithium battery release a highly flammable white vapour cloud. If ignited, the whole battery can self-destruct within seconds.

Lithium battery fires are of great concern in electric cars , e-scooters and e-bikes. But in a way, this smaller eruption is even more concerning. All I could think, while looking through the glass watching this everyday electrical item spewing flames, was what would happen if it occurred in an overhead locker on a plane.

In our next test, we placed an identical overheating battery charging pack inside a fire-suppression bag, manufactured by Firechief. Airlines stock these special bags, which look a bit like oversized wash bags, because a lithium fire is self oxygenating and cannot easily be smothered by sand or water. At best, it must be contained.

After reaching 140C, the battery pack vented fumes which escaped the cracks of the zip. We saw the bag violently inflate, twice, as each half of the battery pack exploded, but the fire was contained and we saw no flames. This is the bag functioning as intended. If it was airtight, it would likely explode from the pressure of 100 litres of vapour.

I was not fully reassured, however. This toxic cocktail, if inhaled, can cause permanent lung damage – it's a "witch's brew" of chemicals, in the words of lithium-ion safety expert, Paul Christensen. Even from our position of safety, behind sealed doors, we were advised to step back into the fresh air just in case any vapour should leak out. You cannot take such a safe step outdoors if you're in the confines of an aircraft cabin.

Finally, we placed an overheating pack within a backpack filled with typical holiday clothes, books and electronics (all either used or damaged).

Seconds passed, then minutes. The bag failed to go up in flames, despite the battery recording temperatures above 300C. This was surprising, given the polyester bikini and charged-up laptop within the bag. We packed up our filming kit and left. However, when the WMG scientists went to check the abuse chamber hours later, they found the bag in the throes of a roaring inferno: the very sort of delayed reaction that could bring down a plane.

The plane that went up in flames

Airlines know about the risk of lithium batteries. At the point of check-in, passengers are now asked to remove all rechargeable battery packs from their hold luggage. Many airlines, including Emirates and Cathay Pacific, ban the use of portable battery packs during flights, or ask passengers to keep them close by.

This is because once lithium batteries are punctured or overheated, they don't just sizzle and smoke. As shown in our experiments, they can cause what professor Hannah Fry , host of The Rest is Science podcast, describes as "a slow-motion explosion that gets let off the leash." In a worst-case scenario it is better to have the malfunctioning item at arm's reach, so cabin crew can attempt to deal with the blaze.

This is not a hypothetical risk. In 2024, there were 123 instances of lithium devices overheating or malfunctioning on aircraft departing or arriving in the UK. In 2025, that number nearly doubled to 206.

One of the most troubling events took place in January 2025. A faulty portable battery pack on an Airbus A321, scheduled to fly from Gimhae, South Korea, to Hong Kong , went up in flames. Mercifully, the blaze occurred when the plane was preparing for departure.

All 170 passengers and six crew evacuated safely, although the plane was destroyed and three people sustained minor injuries. The photographs taken afterwards show the top of the fuselage blackened and torn open by the blaze.

Faulty battery packs are not the only concern. Just this week, a laptop caught fire on an American Airlines flight in a suspected thermal runaway event. The plane landed safely at Dallas Fort Worth International Airport in Texas, where one passenger received medical attention after the incident.

"There's a good track record of this being dealt with correctly," says Simon Jones of WMG.

"What really frightens me is if this happens in someone's luggage or in an overhead locker, perhaps at night when people are sleeping, and people are not aware of what's happening until the power bank has already set fire to something else.

"Then you could have quite a major fire in an overhead locker, which would be difficult to deal with.

"The very worst-case scenario is if that vapour forms a cloud and is ignited. You can then get an over-pressure incident, which would look like an explosion, which you really don't want in an aircraft."

'We must educate the public'

While airlines know the risk, many passengers do not. The Civil Aviation Authority (CAA) says over a third (36 per cent) of travellers are unaware of the dangers of packing batteries in checked baggage, even though 49 per cent fly with a power bank. This suggests hundreds of batteries could be incorrectly packed on a single flight.

The problem is going nowhere. Airlines continue to impose stricter rules but, ultimately, the responsibility falls on passengers to ensure they are carrying electronics safely. This includes not cramming a lithium device in the bottom of a bag, where it could become damaged.

"We must educate the public not to do stupid things with batteries," says lithium-ion safety expert Paul Christensen. "It's trivial little things; check your batteries for visible signs of damage, do they get very hot? Have you purchased with a reputable company? Are they swollen?"

As we left my backpack in the abuse chamber, smouldering through the night, I wondered what pilots make of this threat. Unlike the decision-makers at airlines, the battery-testing scientists and national aviation authorities, they are the ones spending the most time in the air. And indeed, they are the ones who must respond if a lithium device goes up in flames at 35,000ft.

"This is something that has worried me in-flight," says Brian Smith, a pilot with decades of experience flying both commercial and cargo aircraft.

"An uncontained fire in an aircraft will spread very quickly indeed. While the cabin crew have training procedures and equipment they can use to isolate a single device, the worry is that a device on fire in the baggage area or cargo hold will spread, which cannot be extinguished.

"If that's the case, pilots have a maximum of 15 to 20 minutes to put the aircraft on the ground before critical control systems are destroyed by fire, meaning the possible loss of the aircraft. It may even mean ditching it in the sea, or putting it down on rough terrain."

If the visuals of my blazing backpack don't give passengers pause to check the state of their lithium-powered devices before a flight, perhaps this mental image of an aircraft – marooned above an ocean, engulfed in flames, with only 15 minutes to land – will.

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