If you’ve been on a plane this summer the safety briefing may have been a bit different.

But did you even notice?

Among the usual information about seatbelts, lifebelts and the nearest exit – not forgetting of course that it might be behind you – many airlines are now stressing the importance of mobile phone safety.

Not the usual advice about putting it into flight mode but what to do if you lose your phone down your seat or the phone or any other personal electronic device such as a tablet or laptop overheats or even catches fire.

For this is happening more and more in a process called thermal runaway.

Hundreds of devices are taken on board every flight, all powered by rechargeable lithium ion batteries but there is always a possibility that poor quality or damaged batteries can overheat, causing the device to catch fire.

Thermal runaway is a rapid, uncontrolled chemical reaction within the battery that causes the internal temperature to rise. When one cell in a battery overheats it can produce enough heat - up to 900°C (1652°F) - to cause adjacent cells to overheat. This can cause a lithium battery fire to flare repeatedly.

According to the Federal Aviation Administration in the USA, between March 20, 1991, and May 2, 2018, there were 206 thermal runaway incidents involving lithium batteries either at airports or on board aircraft. 

Now passengers on several airlines are now warned that if they lose their phone down their seat they must not try to find it. This is because if the seat is moved the phone could become trapped in it and if that happened and the phone became crushed it could send it into thermal runaway caused by damage to the battery.

Passengers are now told to make sure they take their electronic devices into the cabin with them and NOT to put them in the aircraft hold.

This is because a fire in a laptop in the hold could be enough to bring a passenger plane down.

A shocking new government study in the USA has shown that carrying electronic devices in luggage in aircraft holds can, in rare circumstances, be exceptionally dangerous.

According to the American Journal of Transportation a single personal electronic device that overheats and catches fire in checked luggage on an airliner can overpower the aircraft’s fire suppression system, potentially creating a fire that could rage uncontrolled.

Safety experts had thought that single lithium battery fires would be knocked down by the flame-retardant gas used in passenger airliner cargo holds. But tests conducted by the United States Federal Aviation Administration found the suppression systems can’t extinguish a battery fire that combines with other highly flammable material, such as the gas in an aerosol can or cosmetics commonly carried by passengers in their luggage.

FAA tests found that the anti-fire halon gas installed in airline cargo areas wouldn’t extinguish a lithium battery fire, but it prevents the blaze from spreading to adjacent material such as cardboard or clothing.

However, aerosol cans exploded in tests even after being bathed in the halon gas, the FAA found.

Worryingly, the FAA said in a notice to airlines: “There is the potential for the resulting event to exceed the capabilities of the airplane to cope with it.”

That’s a somewhat wordy way of saying the plane could crash.

More than 50 airline companies across the world – including some of the biggest and best-known - now have a unique invention that contains lithium-ion battery fires on board passenger cabins in planes.

This means that well over 13,000 AvSax fire mitigation bags are on board aircraft in case of any emergency sparked by fires in passengers’ electronic devices.

The AvSax were invented and are manufactured by Huddersfield company Environmental Defence Systems Ltd which received the prestigious Queen’s Award for Innovation 2018 for the pioneering bag.

The bag has been used 27 times to deal with emergencies since the start of 2017.

Richard Nikolic from Environmental Defence Systems Ltd said: “The danger is that with so many poor quality and fake batteries around there is no doubt that incidents will continue to happen. The fact that AvSax have been deployed so many times shows there is a real need for this product. Any fire on board a plane is a frightening prospect but the AvSax has proved itself in action time and time again.”

How do AvSax work?

If an electronic device starts to seriously overheat or emit smoke the cabin crew will pour at least two litres of water into an AvSax. It is imperative to first knock down the flames from the device using an on board halon fire extinguisher, then transfer the device into AvSax before it reignites. Additional water is then required. The water activates the polymer gel inside the bag causing it to expand around the device. Should the device keep on venting then the AvSax is tough enough to absorb the energy.

The AvSax cools the batteries in the device, reducing the likelihood of the battery igniting but if it does go into thermal runaway it is all contained within the bag.

Amazingly, the water is absorbed into the internal lining of the bag so the device is dry when it is removed.