Smartphones are top of a list of ‘undesirable’ items to be taken on board planes due to their fire risk.

The dubious title of the "least wanted dangerous good" to be brought on flights has been given to the phones by The Australian Civil Aviation Safety Authority (CASA).

Portable batteries and spare lithium ion batteries (similar to those powering laptops and drones) were placed second on CASA's list.

These lithium-ion powered electronics were considered a greater flight risk than compressed oxygen, power tools with engines, gas cylinders, paint, fireworks, lighters and matches.

Data obtained by Australian consumer organisation Choice has revealed that batteries powering everyday electronics overheated, caused smoke or caught fire on Australian aeroplanes in 118 instances over the last five years.

These are Australian statistics and do not include those that happen on foreign airplanes, including the case where a headphone battery exploded, leaving a woman's face, hands and clothing burned.

A report by the US Federal Aviation Administration (FAA) states that lithium-ion batteries are "capable of ignition and subsequent explosion due to overheating.”

Batteries that overheat can lead to thermal runaway, a chemical reaction that results in the repeated flaring and releasing of chemical electrolyte.

One of the main dangers happens when the phones slip out of someone’s pockets and end up caught down the side of the seat.

When the seat is then moved the phone can get crushed in its mechanism which may cause it to catch fire.

Shane Carmody, director of aviation safety at CASA, said: "An increasing number of passengers accidentally crush their phone in the reclining mechanism of their aircraft seat.

"This can result in the damaged smartphone battery going into thermal runaway, possibly igniting a fire."

Such was the case on a Qantas flight travelling between US cities in June 2016 when what appeared to be a late-generation iPhone fell between and was crushed by the mechanics of a first-class seat.

The Australian Transport Safety Bureau (ATSB) report said: “The crushed phone immediately began hissing and emitting smoke. Moments later it ignited.

"When the cabin crew members carrying fire extinguishers arrived at seat 3A they observed an orange glow emanating from the seat.

"A crew member discharged a fire extinguisher into the seat, extinguishing the glow."

A crew member was assigned to watch the seat for the remainder of the flight, ready with a fire extinguisher.

But the report continues: "About 10 to 15 minutes after the incident this crew member identified further heat coming from the crushed personal electronic device. They again discharged the fire extinguisher, eliminating the heat."

So far this year the Federal Aviation Administration in the USA has reported at least 18 incidents involving lithium-ion batteries on airplanes and in airports compared to 31 incidents in the whole of 2016. That compares with 16 incidents in 2015, nine in 2014, and eight in 2013. 

This has led to major airlines such as Delta Air Lines turning to new anti-fire devices such as AvSax which are carried on all Delta planes.

The AvSax is a special fire-retardant bag used when lithium-ion batteries catch fire and has been deployed on planes several times already this year.

Simply pour at least two litres of water into an AvSax and then drop the burning device into the bag. 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 force.