Batteries in an electrical device caused a fire in a giant passenger plane flying over Canada. 

The Lufthansa Airbus A380 carrying 500 passengers to Houston in the USA was around 260 miles north of Montreal when the crew was alerted to heavy electrical smoke and fire beneath seat 10C. 

The Transportation Safety Board of Canada says a passenger power bank – a battery-powered portable device for providing electrical supply – was the source and was "stuck in the seat mechanism."

Three fire extinguishers were used by the cabin crew to smother the fire. No emergency was declared and the aircraft has since been returned to service following seat repair.

The fire happened on August 2. There have been other incidents when mobile phones caught up in airplane seats have been crushed, causing their batteries to catch fire.

Special fire-retardant bags called AvSax specifically designed to deal with fires in electronic devices are now on board several major US carriers.

The AvSax is used when lithium-ion batteries in mobile phones or other electronic devices catch fire.

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.

In short, the AvSax cools the batteries in the device, reducing the likelihood of the battery catching fire but if it does go into what is known as thermal runaway it is all contained within the bag.