All these gadgets are in everyday use and look innocent enough … but pack them on a plane in the hold luggage and they could cause a terrible disaster.

People routinely carry them on board planes … and although the advice by some airlines is to remove all batteries if they are in the hold, few airlines have any clear guidance even though the Civil Aviation Authority accepts there is a problem with lithium-ion batteries.

The CAA states: “If you're taking loose lithium batteries of any kind on your flight, you can have only two and they must be individually wrapped in either the original retail packaging or taped over to prevent any shorted circuits. You must take these with you in your cabin baggage: they must not be stored in your hold baggage under any circumstances.

“If your batteries are already in devices such as your camera, you can either take them with you in your cabin baggage on board or pack them in your checked luggage.”

The stark reason is that they are all powered by lithium-ion batteries and if they overheat or became faulty then they could catch fire in a devastating process that is called thermal runaway. This burns at an exceptionally high temperature and if it reaches aerosol cans and other explosive or flammable items such as nail polish or other cosmetics the fire could quickly spread through the hold.

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 commonly carried by passengers.

The 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.

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

In short, the fire would be enough to cause the plane to crash.

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. 

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.

Yet despite these warnings there is no clear policy on what items should be in checked baggage and what must be carried into the cabin.

The FAA hasn’t imposed any new restrictions on what passengers may pack in checked bags. Last year, in a notice to airlines, it said they should conduct a safety study to determine what more they should do to limit the risks of battery fires in cargo areas.

But United Airlines in the USA has just updated its policy, stating: “Effective July 9, 2018, lithium batteries that are installed in any checked or carry-on baggage must be removed by the customer. Once removed, these batteries can be transported on board. Smart bags that do not have a removable battery cannot travel on any United or United Express flights.”

American Airlines state: “Please remove batteries from devices in your checked bags and put them in your carry-on in separate plastic bags.”

It seems that more airlines are moving towards asking passengers to carry all personal electronic devices in their hand luggage so if there is a problem it can be swiftly tackled by the cabin crew.

More than 50 airline companies worldwide – including some of the biggest – now carry AvSax fire mitigation bags on board. These were used in 27 times in 2017.

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, even if the battery explodes.

AvSax managing director Richard Bailey said: “AvSax is the result of many years of development, drawing on experience from the production of an alternative sandbag we invented called a BlastSax designed for the military to reduce the impact of fragmentation generated by small improvised explosive devices.

“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.”